December 2002

Project Number: C&M/10/2001

Concrete and Masonry Research Group,

Faculty of Technology, Kingston University,

Penrhyn Road, Kingston-upon-Thames.

SURREY KT1 2EE

THE DEVELOPMENT OF SIMPLE ‘DEEMED TO SATISFY’ INSITU CONCRETE BASEMENTS FOR

DWELLINGS

FINAL REPORT

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ACKNOWLEDGEMENTS This project was commissioned by the Readymixed Concrete Bureau and carried out by a project team comprising Professor John Roberts (Kingston University), Dr Anton Fried (Kingston University), Alan Tovey (Tecnicom) and Tony Threlfall (Specialist Training Service). The project team would like to thank the Readymix Concrete Bureau for supporting this project and the following organisations for their advice and guidance provided through the project steering group: Readymixed Concrete Bureau Represented by John Hanna and Andrew Cotter British Cement Association Represented by Pal Chana Quarry Products Association Represented by Tom Harrison Basement Development Group Represented by Alan Tovey

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CONTENTS 1. Executive summary 3 2. Introduction 4

3. Analysis of unreinforced concrete walls (Uncracked section assumed) 5 4. Window openings. 6 5. Inclusions for the Approved document 7 6. The impact of soil pressures on domestic basements. 8 7. Analysis of vertically spanning unreinforced concrete basement walls 9 (Cracked section assumed) 8. Review of Existing information 10 9. Summary and Conclusions. 11 10. References 12 Appendix A Analysis of vertically spanning unreinforced concrete basement walls (un-cracked section assumed) 13 Appendix B Analysis of window openings in basements 16 Appendix C Inclusions for the approved document 19 Appendix D The impact of soil pressures on domestic basements 25 Appendix E Analysis of vertically spanning unreinforced concrete Basement walls (cracked section assumed) 28 Appendix F Review of existing information 34 Appendix G References 52

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1.0 EXECUTIVE SUMMARY

Tovey(1) in an assessment of potential basement usage in the U.K in 1999 notes that basements provide excellent ways of increasing the space of a house within the same footprint and are financially efficient in areas of high land costs. The study examines full and partial basements and concludes that greater savings occur with partial basements. Even in houses with basements in waterlogged ground the report is optimistic and suggests that the preliminary costings warrant further investigations. Many other papers (2,3,4,5,6,7,8,9) within the last 10 years stress the need for additional space in domestic properties in the U.K. Some studies (4,5,6,8,9,10) indicate the economic viability of including this space whilst others highlight the likely energy savings(6,8,9) and good sound properties of basements (8). Keyworth(11) examined the structure required and noted the minimal changes to the layout of a house which would be required when a basement is included. This view contrasts with that expressed in 1991(12) which indicated that basement design in the U.K. at that time was uneconomical unless reinforced masonry or reinforced concrete of some form was used. At present the Approved document “Basements for dwellings”(13) gives overall design guidance on basements for dwellings in England and Wales. This guidance allows the walls of basements to be constructed of reinforced masonry or reinforced concrete, the designs being in conformance with BS5628:Parts 1(14), 2(15) and 3(16) (masonry walls) and BS8110: Parts, 1(17) , 2(18) and 3(19) and BS 8007(20) (concrete walls). Both unreinforced concrete and unreinforced masonry have been excluded from this document. However, in 1999 guidance(21) on unreinforced masonry basements was produced for inclusion in the Approved Document “Basements for dwellings”. This, when included, would result in the anomalous position whereby the AD would give domestic basements in concrete designed to BS8110:Parts, 1, 2 and 3 and BS8007, with the consequent high levels of reinforcement, but masonry basements would be shown as both reinforced and unreinforced. The RCB has questioned the need for such high reinforcing levels in shallow domestic basements made of concrete and this project sets out to examine the feasibility of utilising unreinforced or lightly reinforced concrete in these situations. The investigation set out to determine: 1. An appropriate method of design. 2. Suitable waterproofing and/or crack control techniques. Analyses that utilised the tensile capacity of concrete produced acceptable wall thicknesses whereas stability methods of design which assumed a cracked section resulted in concrete sections which were too thick. Use of an uncracked design would mean no general concerns over waterproofing systems in the vertical direction but vertical cracking due to the effects of thermal contraction need to be considered. Designing for a cracked section would, as with masonry, require assessment of the expected crack widths which are likely to be greater that which would result from the thermal effects mentioned above. In addition, there would be significant gains to be made by rationalising the loading assumptions for shallow basement walls and by justifying the use of active rather than at rest pressures, but further research is required before this can be justified.

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2.0. INTRODUCTION There has been increased interest in including basements in domestic properties since 1990 in the U.K., in contrast to the eighty years prior to that when very few basements were built. Escalation of house and land prices in London and the South East of England has resulted in developers needing to capitalise on the available land space and including a basement below a house is now often economical. The need to build on brownfield sites means many of today’s housing developments are, of necessity, on poor ground often resulting in the need for deeper foundations where considerable amounts of excavation are required. In such circumstances the provision of a basement is likely to be particularly cost effective. In addition, basements result in energy savings both at the time of construction and in the long term. However, although basements were built under many domestic properties during Victorian times, techniques for producing low cost basements for modern housing are still in the development process. Although basements were not included in U.K properties for most of the twentieth century, in Europe and North America they have continued to be incorporated into new dwellings. Nowadays such space tends to be used for additional living (rather than storage) space and ways of making basements cheaper to construct warmer and drier have been developed. Until relatively recently, the use of basements in the UK was inhibited by the lack of comprehensive design guidance of the type now included in the Approved Document Basements for Dwellings(13) and Plain Masonry Basement Walls(21) . These documents provide excellent design guidance but the absence of an economic design procedure for plain concrete is a severe limitation because plain concrete walls would in many situations be a very cost effective solution. This programme of work was undertaken with the objective of producing a more effective method of design for plain or lightly reinforced concrete basement walls and was primarily funded through the Readymix Concrete Bureau. Details of the project team and steering group are provided in the Acknowledgements.

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3.0. ANALYSIS OF UNREINFORCED CONCRETE WALLS (UNCRACKED SECTION)

Initial investigations to determine an economic method of analysing unreinforced concrete basements examined a cracked model where the vertical load on the wall provides stability. The method is briefly introduced in section 6.0 and APPENDIX E gives the details. Obviously there is no allowance for the flexural capacity of the material in this technique although concrete has considerable flexural tensile strength when compared to masonry. Outcomes from applying this technique were disappointing. In response, a design technique that utilises the flexural strength of concrete was examined. Much thinner wall sections were possible than with the cracked analysis. Details of this technique are presented in APPENDIX A. Further, tables 3D.1 – 3D.3 derived using this technique are included in APPENDIX C. These relate the minimum wall thickness to the retained height of either granular or clay soils for walls of a particular height. In APPENDIX C walls of 2.5, 2.6 and 2.7m height are examined for axial loads ranging from 5.0 – 55.0 kN/m length. (A two storey domestic house would be under a vertical load of about 15kN/m). The following may be observed from the tables: § The effect of the axial load is not significant. Increasing the load from 5.0 – 55.0kN/m

results in a maximum decrease in wall thickness of 24mm with either soil types. § Wall thicknesses, based on clay soils (assumed rectangular pressure distribution) are

obviously greater than with granular soils (assumed triangular pressure distribution). § With walls bending flexurally, there is likely to be little deflection so “at rest pressures”

are assumed. This assumption results in higher pressures being exerted on walls than with the cracked method of analysis. Nevertheless wall thicknesses were reduced significantly.

§ In the analysis, wall thicknesses under 140mm were excluded, being considered impractical.

§ The properties used in assessing soil loads assumed a high quality granular material and a low quality clay.

4.0. WINDOW OPENINGS.

An economic method of basement design was possible when the tensile strength of the concrete was utilised. However, the effect of window openings still requires consideration. The approach adopted is indicated in APPENDIX B. Further, Tables 3D.4 – 3D.6 in APPENDIX C give the maximum height and length of openings for walls of a specific height with various retained heights of soil behind them, when this approach is adopted.

Deleted: Page Break

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5.0. INCLUSIONS FOR THE APPROVED DOCUMENT.

APPENDIX C in this document is a draft version of Appendix 3D - PLAIN IN-SITU CONCRETE RETAINING WALLS for inclusion in the Approved Document (13). The findings from this investigation indicate that an economic method of basement design was possible when the tensile strength of the concrete was utilised and that windows can be included provided they are sized in accordance with APPENDIX C. Information on the following is included in APPENDIX C: § Wall thickness § Concrete specification § Waterproofing system with no crack control. § Waterproofing system with crack control. § Window openings

6.0 THE IMPACT OF SOIL PRESSURES ON DOMESTIC BASEMENTS.

APPENDIX D examines the problems associated with soil loads on basements. Soil pressures at present are derived assuming deep soil cuts, which is clearly not the case with domestic basements. Consequently the discussion in APPENDIX D considers whether “Active”, “At rest” or indeed some other value of soil pressure should be utilised in shallow basement design because factors such as the interaction between the soil and the wall, the shear forces between the soil and the wall and arching effects within the soil may reduce soil pressures. The following aspects are considered: § The development of earth pressures § A review of earlier work § The required movement before active earth pressures develop. § Issues to be addressed

7.0 ANALYSIS OF VERTICALLY SPANNING UNREINFORCED CONCRETE BASEMENT WALLS (CRACKED SECTION ASSUMED)

Investigations to determine an appropriate design method for un-reinforced concrete basements commenced by assuming a horizontally cracked section as with un-reinforced masonry. One advantage of assuming a cracked section is that deflections may be assumed to be of a reasonably high magnitude. Consequently it may be appropriate to assume “active” earth pressures. Despite this relatively high wall thicknesses resulted. This method excludes any benefit which may accrue due to the tensile capacity of the concrete which can be up to

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10 times that experienced in masonry. Consequently significant improvements in wall thickness were achieved by utilising this property. The method is included as APPENDIX E. Included in Appendix E is information on a stepped section as well as a technique to check the effect of window openings with cracked sections. The method was superseded by that given in APPENDIX A.

8.0. REVIEW OF EXISTING INFORMATION.

An extensive review of existing information on basements is included in APPENDIX F. This review summarises the current state of the art on domestic basements with a particular focus on basements built with concrete. The following aspects are considered in the review. § Internal and external environments. § Design of basements. § Preventing water ingress § External drainage provision. § Improving the water resistance of existing basements. § Water and vapour resistance of residential basements. § Structural materials § Minimising reinforcement in basements. § Maintenance of basements § Construction of basements § Formwork systems for basements. § Repair to basements.

9.0 SUMMARY AND CONCLUSIONS 1. A method of design for unreinforced concrete basement walls, which utilises the tensile

strength of concrete has been developed. Allowances for window openings in the walls is included.

2. Appendix C which is produced for inclusion in an Approved Document gives details of wall thicknesses, construction materials and workmanship requirements.

3. Specific waterproofing details for these walls is not provided because existing guidance is adequate.

4. Discussion on whether to use “Active”, “At rest” or some other value of soil pressure is undertaken. Further research on soil loads is recommended as it is likely to produce additional economies.

5. Section 7 and Appendix E summarise a stability method of design for these walls but proved considerably less economical.

6. A review of domestic basement design and construction is included.

10.0 REFERENCES A list of sequentially numbered references is attached in APPENDIX G.

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APPENDIX A

ANALYSIS OF VERTICALLY SPANNING UNREINFORCED CONCRETE BASEMENT WALLS.

(Un-cracked section assumed)

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DESIGN PROCESS FOR UN-REINFORCED CONCRETE BASEMENT WALLS.

Introduction Design procedures have been developed for use in vertically spanning un-reinforced concrete or masonry basements (assuming a cracked section) as noted in APPENDIX E. Concrete will have no advantage over masonry in this instance. In order to obtain greater advantage from concrete, the following should be noted. 1. A more promising design approach would be to allow for the tensile strength of the

concrete as given in Eurocode 2(22) and then to analyse the wall as an uncracked member. 2. With two-way action there is little to be gained from a panel with an aspect ratio of 3 to 1.

If the panel is considered to be fixed up the edges and pinned along the top and base the maximum vertical bending moment coefficient for a full height triangular load is 0.059 for a simple vertical span, the comparable coefficient is 0.064). Coincidentally, for the two-way panel, the maximum horizontal bending moment coefficient at the vertical edges is also 0.064. A yield line analysis would be more advantageous for two-way action, but this could only be justified for a reinforced concrete wall. In any case for a plain concrete wall, the presence of vertical cracks would completely invalidate two-way action.

3. On the question of earth pressures, while the notion of active values can be argued for the cracked model, (i.e. as plain masonry), it is hard to see how it can be justified for the uncracked model. In this case the use of at-rest earth pressures in accordance with the current versions of BS8002(23) and BS8110(17 – 19) is more reasonable.

4. The following design approach is based on the approach as given in (1.) above which shows that a reasonable solution can be obtained with only slight benefits achieved from including the vertical loads. In the tables for inclusion in the Approved Document (Appendix C), allowance for vertical load is considered. In the following calculations, a high quality granular soil and a poor quality cohesive soil are both considered with full height loading and at-rest earth pressures.

5. With respect to uncontrolled vertical cracking, Eurocode 2: Part 1 provides a basis for estimating crack widths in clause 7.3.4. Here in paragraph (5), it is stated that ‘For walls subjected to early thermal contraction where the bottom of the wall is restrained by a previously cast base, the maximum final crack spacing may assumed to be 1.3 times the height of the wall’. This is compatible with an earlier statement in paragraph (3) of the code, ‘Where there is no bonded reinforcement within the tension zone, an upper bound to the crack width may be found by assuming a crack spacing equal to 1.3 times the height of the tension zone’. For a wall height of 2.7m, the maximum crack spacing becomes 3.5m and, by using the approach used in BS8007(20) , the maximum crack width due to early thermal effects may be estimated as:

mmsTw 5.035002510125.05.0 6max1max =××××== −α

In the above calculation, the value of T1 is based on 350kg/m3 Portland cement and the use of plywood or similar formwork, with a concrete placing temperature of 20oC. No allowance has been made for any further thermal effects due to changes of ambient temperature after construction.

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Plain concrete walls BS8002: 1994 (Clause 3.2.5) Consider a well drained good quality granular soil wit h f ’rep = 35o. f ’d = tan-1(tan f ’rep /1.2) = tan-1(tan 35o /1.2) = 30o Ka = (1 – Sin f ’d) /(1 + Sin f ’d) = 0.33, Ko = (1 – Sin f’d) = 0.50 BS8110-1: 1997 (Table 2.1) Design load for ULS: 1.2Ka = 0.4, 1.2 Ko = 0.6 Eurocode 2: Part 1 Section 1A. Plain and lightly reinforced concrete structures fctd = (a ct f ctk,0.05)?c = (0.8/1.5)f ctk,0.05 = 0.53f ctk,0.05 For fck = 25/30 (i.e. C30 concrete), f ctk,0.05 = 1.8 N/mm2, fctd = 0.96 N/mm2 Design Procedure 1. Assume standard values for K, γe and q.

(K = 0.4 0r 0.6, γe = 20 kN/m3, q = 5 kN/m2) 2. Calculate vo = (Kγehe

2/6H)(he + 3q/γe) (kN/m) 3. Calculate h1 = [(q/γe)2 + 2vo/Kγe] 0.5 – (q/γe) 4. Calculate m1 = [?o(H-he+h1) – (K?eh1

2/6)(h1 + 3q/?e)] 5. Calculate t = v(6m1/fd), where fd = fctd + pressure from weight of wall and ground floor. Considering the weight of wall at a depth of 1.5m, and the load from a beam and block floor (3 kN/m2, 6m span) on a 300mm thick wall, pressure = 24 x 1.5 + 3.0 x 3.0/0.3 = 66 kN/m2. It can be seen that pressure from weight of the wall and ground floor is of limited benefit and in the following calculation, fd is taken as fctd + 40 = 1000 kN/m2.

Example Consider H = he = 2.7 m, with K = 0.6. vo = (0.6x20x2.72/6x2.7)(2.7 + 3x5/20) = 18.63 kN/m h1 = [(5/20)2 + 2x18.63/0.6x20]0.5 - (5/20) = 1.53 m, (H – he + h1) = 1.53 m m1 = [18.63x1.53 – (0.6x20x1.532/6)(1.53+3x5/20] = 17.83 kNm/m t = v(6x17.83/1000) = 0.327m Note. Since m1 is directly proportional to K, with K = 0.4, t = 0.327v(0.4/0/6) = 0.267m

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APPENDIX B

ANALYSIS OF WINDOW OPENINGS IN BASEMENTS.

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WINDOWS IN BASEMENTS.

Consider a typical wall. For each he, a basic wall thickness tbasic can be found which is based on the position of the maximum moment Mmax. The exact location depends on he and Pw the axial load on top of the wall. Now consider a window located in the wall such that there is a 1.0m wide pier of concrete available to transfer the loads to the foundations either side of the window.

1.0m Lw

hw Window opening

45o

Mmax

h1

he

Pw/m

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Pw from over half the window is transferred to the 1.0m wide strip. i.e. The vertical load on the strip, if Lw is in metres is Pw(1 + Lw/2). At the bottom of the window this vertical strip disperses at 45o until it decreases to Pw/m at the level of maximum moment. For any part of the wall below this level, the window has no impact since the moments and vertical forces are the same as for a wall without openings. In a similar manner, the lateral loads could be considered to be increased over the depth of the window and then to gradually reduce to their original value at the level of maximum moment. The resulting moment over the window height is carried on a 1.0m length of wall. Calculations based on the above would result in the wall thickness at the level of maximum moment tbasic being acceptable (NB The original geometry was assumed to produce this outcome). A further analysis at the bottom of the window with enhanced vertical and lateral loads was then undertaken to give thw. Then if thw < tbasic the window is acceptable But if t hw > tbasic an iterative procedure was undertaken to determine the position of hw at which thw = tbasic. Results from this procedure can be seen in Appendix C. The above design procedure caters for the combined effects of lateral and vertical forces on the vertical spanning wall adjacent to the window but a further check needs to be made on the wall below the window spanning horizontally (assumed simply supported). This produced a thickness thw dependant on the retained height hew and the span Lw. This was found to be critical at large spans and Lw was limited so that the resulting thickness required was ≤ tbasic. Thus the window opening height and length was controlled to ensure that the required thickness did not exceed the basic wall thickness for a plain un-perforated wall. Because the wall under the window is unreinforced vertical cracking may occur, either within the length of the wall or at its supports, which could invalidate the assumption of a simple span. In order to cater for this reinforcement needs to be introduced at the window wall junction. This can be either a single bar just below the opening or spread over the lower wall height. The latter was adopted for this report but may be modified following discussion. An alternative would be to use nominal reinforcement as already given the AD - "Basements for dwellings", which would cater for the effects of cracking and enable the use of all waterproofing systems without the need to check crack size. This has been included for in the proposed Appendix 3D (see Appendix C of this report).

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APPENDIX C

INCLUSIONS FOR THE APPROVED DOCUMENT

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APPENDIX 3D – PLAIN IN-SITU CONCRETE RETAINING WALLS

3D.1 THE USE OF THIS APPENDIX 3D.1.1 A1 When using this appendix it should be noted that: (a) It must be used in conjunction with Section 3; (b) If wall thickness is to be determined according to paragraph 3D.2, all appropriate design conditions given in this appendix must be satisfied; (c) Walls should comply with the relevant requirements of BS 8110: Part 1: 1997, with the exception of the provisions given in paragraph 3B.3; (d) The guidance is based upon a characteristic strength of concrete of 35 N/mm2. 3D.2 THICKNESS OF WALLS 3D.2.1 A1 General w all thickness may be determined according to this appendix provided: (a) The conditions relating to the building of which the wall forms a part (paragraph 3.5), and (b) The conditions relating to the wall (Table 3.1 and paragraphs 3.6 to 3.11.) are met. 3D.2.2 A1 For external retaining walls, the thickness of wall should be not less than that required by Tables 3D.1, 3D.2 and 3D.3 (Other wall sizes may be determined by calculation (see 3.1.3) Table 3D.1 Minimum thickness for 2.7m high plain insitu concrete retaining wall

Minimum wall thickness (mm) Soil type Total dead load applied to retaining wall (kN/linear metre)

Retained height h

(m) 55 45 35 25 15 5Granular 2.7 301 306 311 315 320 325 2.6 291 296 300 305 310 315 2.5 281 285 290 295 300 305 2.3 259 263 268 273 278 282 2.1 236 240 245 249 254 259 1.9 211 216 220 225 230 235 1.7 186 191 195 200 205 209 1.5 161 165 169 174 179 184 1.3 135 139 143 148 152 157 1.1 Minimum wall thickness 140 mm Clay 2.7 352 356 361 366 371 376 2.6 340 345 349 354 359 364 2.5 328 333 337 342 347 352 2.3 303 307 312 317 322 327 2.1 276 280 285 290 295 300 1.9 248 252 257 262 267 271 1.7 219 223 228 233 237 242 1.5 189 193 198 203 207 212 1.3 159 163 168 172 177 182 1.1 129 133 137 142 146 151 0.9 Minimum wall thickness 140 mm

NOTE: With the introduction of this Appendix D, the current APPENDIX D to be renamed APPENDIX F {{ Items struck through or show in blue are changes previously submitted }}

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Table 3D.2 Minimum thickness for 2.6m high plain insitu concrete retaining wall

Minimum wall thickness (mm) Soil type Total dead load applied to retaining wall (kN/linear metre)

Retained height h

(m) 55 45 35 25 15 5Granular 2.6 284 289 294 298 303 308 2.5 274 279 284 288 293 298 2.3 254 258 263 268 272 277 2.1 231 236 241 245 250 255 1.9 208 212 217 222 227 231 1.7 184 188 193 197 202 207 1.5 159 163 167 172 177 182 1.3 133 137 142 146 151 156 1.1 Minimum wall thickness 140 mm Clay 2.6 332 337 342 346 351 356 2.5 321 325 330 335 340 345 2.3 297 301 306 311 316 321 2.1 271 276 280 285 290 295 1.9 244 248 253 258 263 268 1.7 216 220 225 230 234 239 1.5 187 191 196 200 205 210 1.3 157 162 166 171 175 180 1.1 127 132 136 140 145 150 0.9 Minimum wall thickness 140 mm Table 3D.3 Minimum thickness for 2.6m high plain insitu concrete retaining wall

Minimum wall thickness (mm) Soil type Total dead load applied to retaining wall (kN/linear metre)

Retained height h

55 45 35 25 15 5Granular 2.5 268 272 277 282 287 292 2.3 248 253 257 262 267 272 2.1 227 231 236 241 246 250 1.9 204 209 213 218 223 228 1.7 181 185 190 194 199 204 1.5 156 161 165 170 175 179 1.3 132 136 140 145 149 154 1.1 Minimum wall thickness 140 mm Clay 2.5 313 318 322 327 332 337 2.3 290 295 300 304 309 314 2.1 266 270 275 280 285 290 1.9 240 244 249 254 259 263 1.7 213 217 222 226 231 236 1.5 184 189 193 198 203 208 1.3 155 160 164 169 174 178 1.1 126 130 135 139 144 149 0.9 Minimum wall thickness 140 mm Note to tables 3D.1 to 3D.3: These tables assume simple vertical span and thinner walls may be possible where appropriate two way action can be justified and determined by appropriate calculations. 3D.2.3 A1 It will be appropriate,when using a wall sized in accordance with 3D.2.2, to allow for a base moment of 10Km/m when assessing foundations requirements in accordance with Appendix E

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3D.3 CONSTRUCTION MATERIALS AND WORKMANSHIP 3D.3.1 A1 The concrete in non-aggressive soil conditions should be not less than a RC35 to BS 5328: Part 2. In aggressive soil conditions the guidance in BS 5328: Part 1 should be followed. 3D.3.2 A1 The specified slump of the concrete should be sufficient to enable proper placing and compaction of the mix, and should generally be not less than 75 mm. 3D.3.3 A1 Where there is no reinforcement to control cracking a check should be made on the water proofing system that it can cope with the possible cracks that may develop in the plain concrete. 3D.3.4 GP BS8007 provides a method of assessment of crack spacing, which for a section not exceeding 2.7m high or greater than 300mm thick and a cement content not greater than 350kg/m3 indicates a crack size of 0.5mm. This may be appropriate for walls within the scope of this document but due consideration should be given to environmental conditions at the time of construction, mix proportions and type of formwork.

3D.3.5 A1 Assessment of crack width on the waterproofing system will generally not be necessary where minimum reinforcement in accordance with 3B.3.7, 3B.3.8, 3B.3.9 and 3B.3.11 is provided. Such reinforcement will only generally be required in a horizontal direction since the concrete will typically be free to move in the vertical plane. However, consideration should be given to the provision of vertical reinforcement where vertical restraint can occur.

3D.3.6 A1 Any reinforcement introduced for plain concrete walls in accordance with 3D.3.5 should comply with BS 4449.

3D.3.7 A1 The reinforcement as indicated in paragraph 3D.3.5 should be of carbon steel in buried concrete, concrete continually submerged in fresh water or external concrete. Where the concrete is exposed to sea water or flowing water with a pH less than or equal to 4.5, specialist advice should be obtained. 3D.3.8 A1 Any reinforcement used to control cracking should be adequately supported to maintain a cover of 40 mm both from the outside and inside faces of the in-situ concrete wall. This may require the introduction of vertical reinforcement which must also have adequate cover. The reinforcement used to control cracking should have the minimum cover. 3D.3.9 A1 The size and bar spacing of reinforcement to achieve the cross sectional areas in paragraphs 3B.3.5 to 3B.3.8 may be obtained from Table 3A.6. 3D.3.10 A1 The spacing of any reinforcement to control cracking should not exceed three times the wall thickness less 40mm or 750 mm. 3D.3.11 A1 Any window openings in a plain concrete wall (and where reinforced solely to control cracking) should be limited in accordance with Table 3D.4, 3D.5 or 3D.6. Intermediate sizes may be determined by linear interpolation. 3D.3.12.A1 Horizontal reinforcement should be positioned in accordance with figure 3D.1 or reinforcement in accordance with 3D.3.5 provided.

3D.3.13 A1 Openings larger than in Table 3D.1 (up to 3.0m) may be introduced where the wall under the opening is sized and reinforced in accordance with Appendix 3B or where shown otherwise adequate by appropriate calculations.

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Figure 3D.1 provision of reinforcement at openings

Table 3D.4 Maximum dimensions of window openings in a 2.7m high

plain insitu concrete retaining wall

Maximum height of opening below upper wall restraint (m) Length of opening (m)

Retained height h

(m) 0.6 0.9 1.2 1.5 1.8 2.12.7 0.63 0.55 0.49 0.42 0.27 0.122.6 0.64 0.56 0.50 0.45 0.36 0.212.5 0.65 0.57 0.51 0.46 0.42 0.302.3 0.69 0.61 0.54 0.49 0.45 0.422.1 0.73 0.65 0.59 0.54 0.49 0.461.9 0.79 0.70 0.64 0.58 0.53 0.501.7 0.85 0.76 0.69 0.63 0.58 0.541.5 0.92 0.82 0.74 0.68 0.63 0.581.3 0.99 0.89 0.80 0.74 0.68 0.631.1 1.07 0.96 0.87 0.80 0.74 0.69

Table 3D.5 Maximum dimensions of window openings in a 2.6m high plain insitu concrete retaining wall

Maximum height of opening below upper wall restraint (m) Length of opening (m)

Retained height h

(m) 0.6 0.9 1.2 1.5 1.8 2.12.6 0.60 0.53 0.47 0.38 0.23 0.082.5 0.62 0.54 0.48 0.43 0.32 0.172.3 0.65 0.57 0.51 0.46 0.42 0.342.1 0.68 0.61 0.55 0.50 0.46 0.431.9 0.74 0.66 0.59 0.54 0.50 0.471.7 0.80 0.71 0.65 0.59 0.54 0.511.5 0.87 0.77 0.70 0.64 0.59 0.551.3 0.94 0.84 0.76 0.70 0.65 0.601.1 1.01 0.91 0.83 0.76 0.70 0.66

w

H

Area of reinforcement=60 x H x W (mm2) per metre heightor reinforcement provided in accordance with 3D.3.5

Opening300mm

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Table 3D.6 Maximum dimensions of window openings in a 2.5m high plain insitu concrete retaining wall

Maximum height of opening below upper wall restraint (m) Length of opening (m)

Retained height h

(m) 0.6 0.9 1.2 1.5 1.8 2.12.5 0.58 0.51 0.45 0.34 0.19 0.042.3 0.60 0.53 0.47 0.43 0.36 0.212.1 0.64 0.56 0.51 0.46 0.43 0.381.9 0.69 0.61 0.55 0.50 0.47 0.431.7 0.75 0.67 0.60 0.55 0.51 0.471.5 0.81 0.73 0.66 0.60 0.56 0.521.3 0.88 0.79 0.71 0.66 0.61 0.571.1 0.96 0.86 0.78 0.72 0.66 0.62

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APPENDIX D

THE IMPACT OF SOIL PRESSURES ON DOMESTIC BASEMENTS

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SELECTION OF THE EARTH PRESSURE TO BE USED IN THE DESIGN OF SHALLOW BASEMENTS

The development of earth pressures. The Basement 2 document(12) indicates that the pressure exerted on a wall by the soil behind it is a function of: 1. The vertical effective stress 2. The soil type – soil parameters 3. The movement of the wall 4. The shearing resistance between the wall and the soil In addition to the earth pressures the pressure due to the ground water must also be considered. The pressures on the wall from the earth are related to the vertical effective stress by earth pressure coefficients. The value of these various coefficients varies with the amount of lateral wall movement/wall rotation. As the wall moves away, the earth pressure reduces to a minimal value, the active condition. If there is little movement then the pressures are termed “at rest”. As the wall moves into the soil the pressure increases to a maximum, the passive condition. For a typical dwelling basement the amount of lateral movement is difficult to assess. The walls themselves are likely to be relatively stiff and it is anticipated that they will be restrained at ground level by the floor slab. In the case of granular soils the possibility of lateral movement depends on the construction procedure particularly when the ground floor slab is placed and whether placing the slab effectively prevents movement of the top of the wall. In the case of clay soils it would be expected that in the short term no pressure would be exerted on the basement walls. With time the negative pore pressure induced by excavation will return to hydrostatic levels and the earth pressures on the walls will be governed by effective strength parameters. As the clay is self-supporting in the short term it is more likely that pressures will be closer to “at rest” if movement of the wall is less likely after it is propped by the ground slab. Results from earlier projects. ‘Plain Masonry Basement Walls’ Final Report – December 1999(21) (PII Project 39/03/4709 (cc1590)) and reference (24) concludes: “There would be significant gains to be made by rationalising the loading assumptions for shallow basement walls and by justifying the use of active rather than at rest pressures, but further work is required before this can be justified.” The Annex to Chapter 5 of the report ‘Comparison of Soil Loads Estimated - Basements 2 (1991, Reprint 1993) (12) with BS8002(23) indicates: “The two main issues which affect the pressure distribution on the back of the basement wall are:

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i. How much lateral movement will occur under working conditions and hence whether earth pressures should be based on “active”, “at rest” or towards “passive” conditions

ii. Where is the long term ground water table likely to be?” The conclusion as a result of the comparison is: “Overall BS8002(23) does not provide any better guidance than Basements 2(12) . Adopting the “at rest” solution is likely to be conservative.” Mann(25) and EC6(26) appear to use “active” pressures whereas the Approved Document(13) - “Basements for Dwellings” uses “at rest” pressures. Alternatively consideration could be given to the use of pressures in accordance with BS8002 but this is likely to give conservative results for shallow basements of the type that would be used in dwellings. How much movement is required before active pressures may be assumed? The current guidance from authors such as Coduto(27) gives a range of values for the movement that needs to take place for active pressure to be assumed depending upon the soil type. Thus for U.K conditions the following would be recommended: Dense sand/gravel 0.001h Loose sand/gravel 0.004h Stiff cohesive (clay) 0.01h Where h is the retained height of soil. The work of Terzaghi(28) indicated that even very small movements of the wall significantly changes the coefficient of lateral pressure. Clearly the situation is more complicated with masonry basement walls where the horizontal resultant load will occur between one third and one half of the way up the retained height of soil and the wall itself will be heavily stiffened by end returns, intersecting internal walls and the floor bearing on it. For a 2.4m high wall in dense sand/gravel a movement of about 3.0mm would be sufficient to assume the full active pressure situation whereas in clay a movement of around 24mm would seem to be required. Key points. 1. Given the conservative nature of the estimates of the pressure acting on shallow

basements (up to 3.0m deep) for dwellings it could be reasonable to base design on the use of “active” pressures.

2. If the above point is not acceptable it could be possible to produce construction details that would allow the wall to move or to simulate movement e.g. by the introduction of a compressible material that would allow the requisite movement.

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APPENDIX E

ANALYSIS OF VERTICALLY SPANNING UNREINFORCED CONCRETE BASEMENT WALLS.

(Cracked section assumed)

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DESIGN PROCESS FOR UN-REINFORCED CONCRETE BASEMENT WALLS ASSUMING A CRACKED SECTION .

Introduction Design procedures and examples have been developed for use in vertically spanning un-reinforced concrete or masonry basements as noted below. The design assumes a cracked section but allowances for imperfections in the expressions nmin and t min have been included. 1. A procedure for the exact calculation of no for solid walls (Figure 1 – Solid walls) has

been developed and examples comparing the exact and simplified methods are given. It can be seen that the exact method is advantageous and also imposes no restrictions on the proportions of the earth pressure diagram. Figure 1 - Solid wall, indicates the notation, load, moment, shear force, and axial load diagrams.

2. A second procedure (Figure 2 – Stepped wall) shows calculations for a stepped wall from which it can be seen that nmin will nearly always be more critical than no. In this procedure, there are two possible modes of failure, in which the middle hinge of the arch occurs either (a). at the step or (b). below the step as for a solid wall; (a) being the most likely. Two alternative design methods are shown; method B requiring a set of tables for standard walls of different thicknesses. The preparation of these tables has not yet been undertaken.

3. There are also some calculations for a wall below a window (Figure 3 – Window detail). In this case a propped cantilever detail is necessary, unless the wall can be designed to span horizontally. It can be seen that the sill member would need to be able to transfer the propping force onto strips of wall either side of the window. Further, there would need to be a shear connection between the sill and the wall below.

4. Soil pressures are considered in Section 6 and APPENDIX D.

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Exact calculation for solid walls

1. Assume standard values for K, γe and q. (K = 0.333, γe = 20 kN/m3, q = 5 kN/m2)

2. Specify values for H, he, t (m) and γw (kN/m3) 3. Calculate vo = (Kγehe

2/6H)(he + 3q/γe) (kN/m)

4. Calculate h1 = [(q/γe)2 + 2vo/Kγe] 0.5 – (q/γe)

5. Calculate no = (1.6/t) [vo(H – he + h1) – (Kγeh12/6)(h1 + 3q/γe)] - γwt(H – he + h1)

Example Consider H = 2.7 m, γw = 20 kN/m3. (a) he = 2.4 m, t = 0.3 m vo = (0.333x20x2.42/6x2.7)(2.4 + 3x5/20) = 7.47 kN/m h1 = [(5/20)2 + 2x7.47/0.333x20]0.5 - (5/20) = 1.27 m, (H – he + h1) = (0.3 + 1.46) = 1.57 m no = (1.6/0.3)[7.47x1.57 – (0.333x20x1.272/6)(1.27 + 3x5/20] – 20x0.3x1.57 = 33.8 kN/m Using the DIN1053: Part 2(29) equation (OK for q/γe = 5/20 = 0.25 ≤ 0.25)

no = t

Hhee

5.22

2γ - γwt(H - he/2) = 3.05.224.27.220 2

××× - 20x0.3(2.7 - 2.4/2) = 37.1 kN/m

(b) he = 1.2 m, t = 0.10 m vo = 1.16 kN/m, h1 = 0.39 m, (H – he + h1) = 1.89 m, no = 28.2 kN/m Using the DIN1053: Part 2 equation

no = 10.05.22

2.17.220 2

××× - 20x0.10(2.7 - 1.2/2) = 30.4 kN/m

Note. Taking 22.5 (rather than 22.56) in the DIN equation compares with taking 1.6 = 1/(5/8) as an approximation for 1/(0.666 – 0.04) in the equation given in step 5 for no.

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Stepped walls Consider the stepped detail as shown with H = 2.7 m, ho = (2.7 – he), and calculate values of nmin = (1.6hovo/ to - γwhoto) and no = (1.6/t)[vo(ho + h1) – (Kγeh1

2/6)(h1 + 3q/γe)] – γw(hoto + h1t) with t = to + 0.2 m.

nmin (kN/m) for value of to

no (kN/m) for value of t

he m

ho m

vo kN/m

h1 m

ho + h1 m

0.10 m

0.15 m

0.20 m

0.30 m

0.35 m

0.40 m

2.4 2.1 1.8 1.5 1.2

0.3 0.6 0.9 1.2 1.5

7.47 5.17 3.40 2.08 1.16

1.27 1.02 0.79 0.58 0.39

1.57 1.62 1.69 1.78 1.89

35.3 48.4 47.2 37.5 24.9

23.0 31.3 30.0 23.0 14.1

16.7 22.4 20.9 15.2 7.9

35.0 26.4 18.4 11.2 5.3

27.3 20.0 13.2 7.0 1.9

21.1 14.8 8.8 3.4

- 1.1

For structural adequacy, nmin ≤ superstructure dead load acting on inner leaf of wall, when backfill is placed, and no ≤ total superstructure dead load acting on wall. It can be readily seen that nmin is likely to be more critical than no in most cases. Design procedure for stepped walls

Method A

1. Determine minimum value of superstructure dead load acting on inner leaf, nmin, when backfill is placed (e.g. Table of typical superstructure loads).

2. Calculate value of tmin = [(nmi n/2γwho)2 + 1.6vo/γw]0.5 - (nmin/2γwho) or, for simplicity,

tmin = 1.6hovo/nmin, where vo = (Kγehe2/6H)(he + 3q/γe)

3. Select suitable values for to ≥ tmin and t ≥ to + (cavity + outer leaf).

4. Calculate value of no = (1.6/t)[vo(ho + h1) – (Kγeh1

2/6)(h1 + 3q/γe)] – γw(hoto + h1t), where h1 = [(q/γe)2 + 2vo/Kγe] 0.5 – (q/γe).

5. Check that no ≤ total superstructure dead load for both leaves, although this is unlikely

to be critical. Method B

1. Determine minimum values of superstructure dead loads, nmin and no, when backfill is placed (e.g. Table of typical superstructure loads).

2. Select suitable values of to and t from tables, similar to above, giving values of nmin

and no for specified values of H, he, ho, t and to.

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Design procedure for walls below windows.

Consider the window detail as shown and calculate, for the wall below the window sill, values of t = (3.4vs/γw)0.5 for cantilever, and t = [(1.6/ γw){vs – (Kγeh1/6)(h1 + 3q/γe)}]0.5 for propped cantilever, where vs = (Kγehe/6)(he + 3q/γe) and h1 = [(q/γe)2 + 2vs/Kγe] 0.5 – (q/γe).

Values of t (m)

he m

vs kN/m

h1 m

Free cantilever

Propped cantilever

1.8 1.5 1.2

5.1 3.8 2.6

1.01 0.84 0.67

0.93 0.80 0.67

0.50 0.43 0.35

For the wall to each side of the window, the procedure for the stepped wall will generally apply, with both nmin and vo multiplied by the same factor. The sill will need to be able to transfer the horizontal load vs kN/m onto the vertical strips each side of the opening. No allowance has been made for the weight of the sill and window, or for the possibility of the wall below the sill being able to span horizontally.

no

t/3

no t/3 t/3

t

H n1

no + nw

q

he

h1 ?e

K ?e he

Kq

m1 = (2/3)*n1t

vo = (K ?e he2/6H)( he + 3q/ ?e)

n1

no + nw v2 = (K ?e he/2)( he + 2q/ ?e) - vo

FIGURE 1 – SOLID WALLS (IDEALISATION FOR A VERTICALLY SPANNING SOLID WALL)

Note. * m1 reduced to 5/8n 1t to allow for imperfections

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vo

nmin

(n min + ?whoto)

t

no - nmin

to/6

ho

to/6

to

vo

FIGURE 2 – STEPPED WALL)

v2(1 + 2/b)

vo(1 + 2/b)

?whet

b b a

ho

he

K ?e he

Kq

t

?wh1t

h1

vs = (K?ehe/6)(he + 3q/?e)

nmin(1 + a/2b)

no(1 + a/2b) + nw

FIGURE 3 – WINDOW DETAIL

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APPENDIX F.

REVIEW OF EXISTING INFORMATION.

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CONTENTS. 1.0 INTRODUCTION. 2.0 REINFORCED CONCRETE DOMESTIC BASEMENTS. 3.0 INTERNAL AND EXTERNAL ENVIRONMENTS.

4.0 DESIGN OF BASEMENTS. 5.0 PREVENTING WATER INGRESS 6.0. EXTERNAL DRAINAGE PROVISION. 7.0 IMPROVING THE WATER RESISTANCE OF EXISTING BASEMENTS. 8.0 WATER AND VAPOUR RESISTANCE OF RESIDENTIAL BASEMENTS.

TYPE A. TYPE B. TYPE C.

9.0 MATERIALS. 10.0 STRUCTURAL MATERIALS

10.1 Concrete. 10.2 Masonry. 10.3 Tanking Material.

11.0 MINIMISING REINFORCEMENT IN BASEMENTS. 12.0 MAINTENANCE OF BASEMENTS 13.0 CONSTRUCTION OF BASEMENTS 14.0 FORMWORK SYSTEMS FOR BASEMENTS. 15.0 REPAIR TO BASEMENTS. 16.0 SUMMARY.

16.1 Constant thickness reinforced concrete walls. 16.2 Constant thickness unreinforced concrete walls with crack inducers. 16.3 Permanent Expanded Polystyrene Formwork. 16.4 Simple lightweight temporary formwork.

17.0 REFERENCES

1.0. INTRODUCTION. At present the Approved document “Basements for dwellings”(13) gives overall design guidance on basements for dwellings in the U.K. This guidance allows the walls of the basement to be constructed of reinforced masonry or reinforced concrete, the designs being in conformance with BS5628:Parts 1(14), 2(15) and 3(16) (masonry walls) and BS8110: Parts, 1(17), 2(18) and 3(19) and BS 8007(20) (concrete walls). Existing design guidance, when the Approved Document was published, on unreinforced masonry basement walls resulted in unacceptably thick sections being produced(12) despite the fact that most Victorian basements were unreinforced masonry and so this form of construction was excluded from the Approved Document. However, the guidance(21) produced in 1999 on this subject has resulted in material on unreinforced masonry for inclusion in an Approved Document being produced. At present Concrete basement walls still need to be in conformance with BS8110 and BS8007 which result in high proportions of reinforcing steel being included for structural and anti-crack reasons. The RCB has questioned the need for such high reinforcing levels in shallow domestic basements and this review sets out to examine the existing literature on the subject. Further, it will examine basement-waterproofing systems and attempt to balance this requirement with concrete quality. For example, if Type B construction is used, then the concrete needs to be of a good quality and in all likelihood reinforced, whereas if a Type A construction is adopted, good waterproofing may abrogate the need for high strength concrete. In addition to the structural requirements, the Approved Document (13) specifies many other design criteria, the most important being protection of the basement from water ingress. The document allows three forms of moisture control, Types A, B and C(30,31,32,33). The use of a particular form of water control in a domestic basement depends on the materials used to build the structure, the form of construction and the required internal environment to the basement. Using unreinforced concrete walls or walls with low percentages of reinforcement in them may influence the choice of water protection for these wall types but it is unlikely that the range of existing water protection techniques will need to be expanded. Tovey(1) in an assessment of potential basement usage in the U.K in 1999 notes that basements provide excellent ways of increasing the space of a house within the same footprint and are financially efficient in areas of high land costs. The study examines full and partial basements and concludes that greater savings occur with partial basements. Even in houses with basements in waterlogged ground the report is optimistic and suggests that the preliminary costings warrant further investigations. Many other papers (2,3,4,5,6,7,8,9) within the last 10 years stress the need for additional space in domestic properties in the U.K. Some studies (4,5,6,8,9,10) indicate the economic viability of including this space whilst others highlight the likely energy savings(6,8,9) and good sound properties of basements (8). Keyworth(11) examined the structure required and noted the changes to the layout of a house which would be required when a basement is included. This contrasts with the view in 1991(12) which indicated that basement design in the U.K. at that time was uneconomical unless reinforced masonry or concrete of some form was used. Further design guidance(34) specifically focused at reinforced concrete blockwork walls used in basement construction has been published. It examines in considerable detail, the need for design to conform to building regulations, waterproofing and its protection and the assessment of loads on basement wa lls. The relationship of the basement in terms of

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structural connectivity is examined and actual structural design is undertaken. Structural and construction details are provided. Provision of similar guidance which could be included in an Approved Document for concrete basement walls would place the two materials on a level playing field. Tovey and Keyworth(35) examined ten examples of basements below domestic properties. In all but one case the walls to the house were constructed using reinforced masonry and type A water protection was installed in all instances. The tenth basement was constructed using lightwight precast concrete panels. The thermal properties of basements are important and can result in considerable energy savings. One form of insulating basements is to use permanent expanded polystyrene (EPS). In response to this and to assist in simplifying the construction of domestic basements the review will also examine various forms of expanded polystyrene formwork. Other aspects of construction such as drainage will also be studied. 2.0 REINFORCED CONCRETE DOMESTIC BASEMENTS. It is impossible to separate out structural design of basements from the moisture protection and indeed constructional aspect. Consequently there will be some overlap in the various sections of this review. Many papers have been written on these subjects but an important source of information on basement design is CIRIA report No.139(30) . The report is not specifically on domestic basements but has a section dedicated to shallow basements and much of the other information is relevant to domestic basements. Much other information also exists. 3.0 INTERNAL AND EXTERNAL ENVIRONMENTS. Report 139 starts off by suggesting the required internal environment of the basement be determined as this will influence the type of construction required. Four grades of internal basement environment are defined which are summarised in Table 1. The report(30) offers further detailed guidance on the basement usage and performance level for each environmental grade. In domestic basements, however, only internal grades 2 and 3(13,31,33,35) would have applications.

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Grade of basement environment

Basement Usage Performance level

Grade 1 (Basic utility) Car parking, plant rooms (excluding electrical equipment workshops)

Some seepage and damp patches tolerated

Grade 2 (Better utility) Workshops and plant rooms requiring drier environments, retail storage

No water penetration but moisture vapour tolerated

Grade 3 (Habitable) Ventilated residential and working areas including restaurants and offices

Dry environment

Grade 4 (Special) Archives and stores requiring controlled environments

Totally dry environment

Table 1. Internal environments of basements (30) . The external environment to the basement is also very important as it affects the structural performance of the basement walls and how long they last. The report divides the external environment into five classifications (mild, moderate, severe, extreme or other) based on the likely hydrostatic pressure to be expected on the wall, the sulphate concentration surrounding the basement, the chloride concentration in the groundwater and the acidity of the surrounding ground. Advice on good practice when each of these environments is encountered is given and summarised in Table 2. Information from Tables 1 and 2 refer to deep basements but is also relevant to shallow domestic basements.

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Measures to be considered Classification of external environment

Hydrostatic pressure (m)

Sulphate concentration (g/l)

Chloride concentration (mg/l)

Acidic ground (pH)

Hydrostatic pressure Sulphate concentration Chloride concentration (reinforced concrete only

Acidic ground

Mild <1 <0.4 0-2000 Normal good practice applies Moderate >1, <5 0.4-3.0 2000-5000

>5.5 SRPC or combinations of PC plus pfa or ggbs SRPC mortar must be used in brickwork

Good quality PC or PC plus with either pfa or ggbs and a maximum free w/c ratio of 0.5

Normal good practice applies

Severe >5, <10 3.0-6.0 5000-10000 10000-20000

3.5 -5.5 SRPC or combinations of PC plus pfa or ggbs Tanking to be applied to brickwork

Low permeability PC plus either pfa or ggbs concrete with a maximum free w/c ratio of 0.45 Very low permeability PC plus either pfa or ggbs concrete with a maximum free w/c ratio of 0.40 Reinforcement may require additional protection

Advance classification of external environment by one class when groundwater is mobile.

Extreme >10 >6.0 >20000 (generally not applicable)

<3.5

Where hydrostatic pressure is greater than five times the thickness of concrete, advance classification of external environment by one class

As severe plus tanking As severe plus additional protection for the reinforcement

Advance other categories by one classification for static or mobile groundwater.

Other e.g. Contamination, gases etc. Where any of these features are found specialist advice must be sought

Table 2. Classification of external environment of basements(30).

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4.0 DESIGN OF BASEMENTS. CIRIA Report 139(30) considers the design of basements in considerable detail. The design procedure can be summarised as follows 1. Initially the purpose of the basement, the degree of quality assurance required during

construction and the internal environment are established. 2. The external environment is identified, factors likely to influence the design isolated,

standards and codes required are determined and existing defects established (if relevant) 3. Possible construction and drainage systems are identified and compared. 4. Heating, ventilation and pumping requirements are determined. 5. Detailed design undertaken. This includes establishing construction methods, and forms of

active and passive water control and ensuring the design will achieve the desired internal environment

6. Select appropriate materials 7. Are there any ancillary considerations 8. Confirm the design meets the client’s objectives and is buildable. The above checklist is for use with deep basements but a simplified version would be appropriate for shallow domestic basements, and improve design procedures. 5.0 PREVENTING WATER INGRESS CIRIA Report 139(30) considers construction methods and examples of passive precautions for preventing water ingress available to achieve the required grade of internal environment. Details for shallow basements are shown in Table 3. For shallow basements under external hydrostatic pressure, Grade 1 performance is unlikely to be required. For Grade 2 environments, Report 139(30) recommends that a monolithic concrete box with drained or tanked protection is likely to be necessary. Grade 3 habitable basements in masonry or plain or reinforced concrete require tanked or drained treatment in conjunction with a vapour barrier. Grade 4 environments are usually not required. For masonry or plain or reinforced concrete domestic basements with no external water pressure, Grade 1 accommodation is unlikely to be acceptable. Grade 2 type of internal environments will be achieved using any of the protection methods. Grade 3 may only be achieved by a combination of methods including some degree of vapour protection. Grade 4 environments are not usually required in domestic situations(30) . The BCA design guide(31) clarifies these requirements for domestic basements in the light of experience. The guide notes that Type A structures are not recommended in areas with an undrainable high water table. They may, however, be satisfactory when the water table is low. Conversely, a well built Type B structure carries a low risk of failure with the added advantage that if there is water ingress, repairs can be carried out from the inside. Combining this system with Type A or type C will enhance the effectiveness of the resistance to water ingress. If water tables are low this system is likely to be adequate on its own.

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Target internal environment/ examples of construction methods and passive precautions Grade 1 (basic utility)

Grade 2 (better utility)

Grade 3 (habitable) Grade 4 (special)

Limited environmental control (Low cost, low reliability)

Complete environmental control (High cost, high reliability)

Basement depth and construction materials

Some water penetration acceptable

Water penetration unacceptable

Increasing requirements for vapour control

Shallow (assumed no hydrostatic pressure, i.e. groundwater level below basement floor or drainage provided) likely to be residential Masonry, reinforced masonry, plain or reinforced pre-cast or in-situ) concrete or steel sheet piling.

Grade not usually acceptable for residential basements

Masonry or plain concrete plus tanking (Type A) or drained cavity (Type C) protection Reinforced concrete box (Type B) protection

Masonry or plain concrete plus tanking (Type A) protection and/or Type C protection Reinforced concrete box (Type B) plus tanking vapour barrier (Type A) or drained (Type C) protection

If grade required the methods and precautions for shallow basements with permanent hydrostatic pressure should be followed.

Shallow (with permanent hydrostatic pressure) Masonry, reinforced masonry, plain or reinforced pre-cast or in-situ) concrete or steel sheet piling.

Grade not usually acceptable for residential basements

Masonry, plain or reinforced concrete box construction plus tanking (Type A) or drained (Type C) protection. Reinforced concrete box (Type B) protection

Masonry or plain concrete plus tanking (vapour barrier (Type A) and drained (Type C) protection) Reinforced concrete box (TypeB) plus tanking (vapour barrier (Type A) or drained (Type C) protection)

Reinforced concrete box (Type B) plus tanking (vapour barrier (Type A) or drained (Type C) protection) Passive precautions alone are not likely to be sufficient

Table 3. Construction methods and examples of passive precautions available to achieve the required Grade of internal environments in shallow basements (30) . 6.0. EXTERNAL DRAINAGE PROVISION. CIRIA report 139(30) stresses the need to limit the water pressure on the wall to a basement. If feasible, drainage of water from the exterior of the walls should be provided. In this context, the long-term efficiency of the drainage system should be considered. Reference (36) considers some practical aspects of basement construction. The use of either heavy clay which is difficult to fully compact or soil with a high organic content which can subsequently decompose and leave voids in the backfill is not recommended. The voids in the backfill can subsequently fill with water which may cause sufficiently high pressures to crack walls. Settlement of poor quality backfill can also result in water accumulation behind basement walls so using high quality back fill is essential. Reference (36) recommends that the excavator slope the ground surface away from the basement to drain runoff away from the basement walls. Recommendations vary from slopes of 40 to 80mm per metre over distances from 1.5 to 3.0m from the wall. Further, using an adequate drainage system to ensure water is removed from behind the wall is also recommended. The authors recommend an adequate perforated horizontal

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drain at foundation level together with granular backfill to direct water to the drain which needs to be protected from fines ingress. The Author to reference (37) encourages the use of internal French drains to remove excess water from the basement. The drain is installed around the inside perimeter of the basement wall. The basic steps required are, to dig a trench prior to pouring the basement slab, install the perforated PVC pipe and surround it with appropriately graded material, install holding chambers with two pumps, a smaller one for economic and more regular use and a larger pump for more effective water removal, and finally to lay the discharge pipe and a means of disposing of the pumped water. Practical guidance on many aspects of the work is given. 7.0 IMPROVING THE WATER RESISTANCE OF EXISTING BASEMENTS. Report 139(30) examines a number of techniques for improving the water resistance of existing basements. However, this report is primarily concerned with newly built basements so this is not pursued. 8.0 WATER AND VAPOUR RESISTANCE OF RESIDENTIAL BASEMENTS. CIRIA report 139(30) contains a section which refers specifically to the waterproofing of residential basements. These structures are assumed to require an internal environment which corresponds to either Grade 2 or 3. The construction of shallow basements will depend on the prevailing conditions but are likely to be in reinforced or unreinforced masonry or reinforced concrete. The use the protection measures can be summarised as follows. TYPE A. Currently this method of waterproofing domestic basements is widely used. The tanking is best applied to the outer skin of the walls if possible as pressures then force it against the wall. Some protection of the membrane will be required whilst back filling to protect it against damage. The disadvantage of a tanking system is that if it is ruptured, it is very difficult to repair. TYPE B. It is possible to achieve an internal environment of Grade 3 with only Type B waterproofing. However, building regulations require a membrane to be included whenever a concrete floor is used, so including a barrier in the walls would not add to the cost significantly. When using type B water protection there may be some initial leakage but autogenous healing will reduce this with time. TYPE C. Cavity drainage is generally considered to be a secondary precaution but it can result in Grade 3 type environments being achieved. Nevertheless drained cavity protection is not widely used as a means of providing a particular internal environment to a basement. Reference (36) notes that water behind basement walls can penetrate into the living space via cracks caused by drying shrinkage or thermal cracking of concrete. The authors go on to recommend an adequate perforated horizontal drain at foundation level together with granular backfill to direct water to the drain. The drain needs to be protected from fines ingress.

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9.0 MATERIALS. Forming basements which are habitable requires the use of many different materials. CIRIA Report 139(30) recommends the following. 10.0 STRUCTURAL MATERIALS 10.1 Concrete. The specification for concrete to achieve a required degree of water resistance will be dependant on the passive precautions used and the external environment (particularly the hydrostatic pressure) to which the concrete is exposed. Reinforced concrete may be designed as both the structural and waterproofing element so with this form of construction in association with protection Types A, B or C , any internal environment can be created. When using Type A waterproofing the main requirement from the concrete is that the waterproofing material can bond to it, good mix design and workmanship being assumed in accordance with BS8110(17-19). With Type B and C waterproofing the concrete will need to be designed to BS8007(20) with its more stringent crack control requirements. Reference (36) notes high quality concrete and good site management is essential to ensure efficient delivery and good compaction of concrete. Lower water/cement ratios with slumps of about 50mm with concrete delivered from trucks via steep chutes to speed up delivery times and so improve quality are recommended. Reference (38) notes that concrete in foundation walls shrinks as it dries and contracts as it cools. Restraint to the concrete will result in tension forces which can result in cracking. The authors recommend reducing shrinkage by limiting the water in the mix and using aggregate that has low shrinkage characteristics. Using as large an aggregate as is feasible for the job will reduce the water required in the mix. High slump concrete must be avoided at all costs. Contraction of the concrete can be controlled by using contraction joints which can be formed by attaching a triangular cleat to both sides of the inside of the formwork to reduce the cross section by about 25%. Joints should be placed at 4.6 – 6.0m intervals and within 3.0 – 4.5m of corners. The authors of reference (38) recommend that in the absence of other guidance being available, basement walls may be constructed without reinforcement. The required wall thickness can be determined using ACI332R-84 “Guide to Residential Cast-in-Place Concrete Construction (39).” CIRIA report 139(30) identifies three features which determine the success of the concrete in reducing water ingress. 1. Firstly, macro defects need to be considered. These are thermal and flexural cracks, opening

joints, construction faults. Good site practice and design for early thermal and flexural cracking will largely eliminate these. BS 8007 limits crack widths to 0.2mm in severe or very severe environments, in order to limit water ingress into concrete. This is more stringent than the 0.3 mm required in BS8110 which relates to structural needs.

2. Secondly the report considers micro defects. These are cracks caused by different thermal movements of the constituents of the concrete or by tensile strain through concrete shrinkage.

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The main factors which designers can control in the micro cracking area are the curing of the concrete and selecting aggregates.

3. The third factor of importance is the intrinsic permeability of the cement paste. In terms of shallow basements this aspect is of considerable importance. The passage of water through concrete depends on the permeability of the cement paste and on the permeability of the aggregate. Most normal aggregates used in concrete are relatively impermeable so it is the cement paste which results in most moisture passing through the concrete. The water/cement ratio and content of cement in the paste are factors which affect this the most. Reducing the w/c ratio by using a plasticising agent can result in less permeable concrete. Curing is of paramount importance as it promotes a denser cement paste by prolonging its hydration. Further good curing reduces the likelihood of shrinkage cracking. Using ggbs and pfa as cement replacements also improve the impermeability of concrete and encourage autogenous healing of crac ks. Using plain unreinforced concrete in shallow basements is feasible but it can only be combined with Types A or C waterproofing systems.

CIRIA Report 91(40) examined a number of factors which influence early-age thermal cracking in concrete. The report considers the basic mechanism behind thermal cracking and then examines the variables which influence the temperature differences in concrete. How restraint, both internal and external affects the limits to the tensile strain capacity of concrete are also discussed. Studies on the significance and control of cracking then round off the report. Of greatest importance, however is the relationship,

a(Tp – Ta)KR > tensile strain capacity

where a = coefficient of thermal expansion of concrete Tp = Peak temperature Ta = mean ambient temperature R = restraint factor K = modification factor. If the left-hand side of the above inequality, is greater than the right hand side, cracking occurs. Each of the terms in the above equation will be considered Coefficient of thermal expansion (a). The possibility of affecting this factor in any significant way in normal structural concrete is limited. Peak temperature Tp. The peak temperature is affected mostly by the cement and binder content. Sulphate resisting cement has lower heat generation properties than Ordinary Portland cement which in turn has lower heat generating properties than Rapid Hardening Portland Cement. Additions of pfa and ggbs will probably, further lower the peak temperature of walls but by how much is still under investigation. The cement content and type of formwork also affect the peak temperature reached. In most crack calculat ions using the above equation the assumption that the thermal cracking results from the difference between Tp – Ta is usually made. This will only occur if the concrete is not insulated in any way, as indicated by the influence of various types of formwork. Using EPS formwork will provide insulation to the entire concrete mass (except the top surface) and although the peak temperature achieved may well be higher than if it were not used, the difference between Tp and Ta may reduce. The impact of this on early cracking still needs clarification.

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Mean ambient temperature Ta. This is seasonal and does affect the peak temperature. Higher ambient temperatures result in more rapid heat generation in concrete and higher peak temperatures, all other conditions being unchanged. In this project, a specified maximum placing temperature may be necessary. Restraint factor R. Guidance on both internal and external restraint is included. In the U.K. the Report suggests that internal restraint will not be a significant problem. External restraint though, when a wall is cast onto an existing base will exist. Further varying degrees of restraint will be caused horizontally when a box structure is cast onto a rigid base. In terms of shallow basements, the main problem is in the waterproofing. If Type B structures are being build then constraining cracking is very important, but it Types A or C are required then the problem of cracking need only be considered from a structural point of view. Clearly, reducing the peak temperature is the most effective way of reducing the restraint. Modification factor K. Full restraint of a wall by a base is only theoretically possible. Modification factors are introduced to enable practical solutions to be obtained. These are introduced to account for, the peak temperature being assumed to exist in the centre of the wall whereas it should be considered in the vicinity of the reinforcement, the assumption that the base remains at the mean ambient temperature, the premise that tensile stresses start developing immediately the concrete starts to cool and that the relative drying shrinkage between elements is the same. It is evident that there may be some scope for change within these factors. Emborg, Westman, Bernander(41) assessed the risk of thermal cracking in hardening concrete. In their investigation, thermal stresses and cracking risks were computed for two types of high strength and two more normal concretes. In general, the high strength concretes show higher cracking risks than the other concretes. However, the research also indicates that the mechanical properties of the young concrete affect the risk of cracking especially with thinner sections. The implication here is that if thin walls (150mm thick for example) are used stronger concrete may be acceptable with no extra risk to cracking. Anson and Rowlinson(42) studied the restraint to early age thermal movement in reinforced concrete walls. They compared their findings to those in CIRIA report 91. At the hottest part of the walls the temperature gradients were in agreement with predictions by the CIRIA report. However the research indicated that internal restraint exists around the perimeter of the walls and that the most critical time is when the peak temperature is reached. The work also indicates that bases are not totally dominant in restraining walls and will move and change temperature. Ogawa and Tomita(43) investigated crack control of reinforced concrete structures. They examined the effect of including a combination of an expanding admixture and a Shrinkage reducing admixture to concrete. Their findings indicate that cracking of walls is significantly reduced. Examination of actual walls after five years of exposure indicated that using the combined admixtures in external walls resulted in no harmful cracks. The cost of the concrete increases but whole life cost analysis would indicate if this combination of admixtures were feasible.

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Gheder and Fadhil(44), Rawi and Kheder(45) and Kheder(46) all examined the effect of base restraint on cracking in concrete but do not consider the effects of end restraint. The Authors suggest that base restraint results in a concentration of cracks in certain regions of the wall with some areas not undergoing any cracking at all. However, as basement walls have end restraint using the techniques may not be appropriate. Nevertheless the Authors note that un-reinforced walls with aspect ratios (L/H ) of between 1.0 and 2.0 tend to either not crack or undergo limited cracking. 10.2 Masonry. This project is primarily concerned with concrete basements so masonry basements will only be mentioned. These basements must be waterproofed using Type A or C waterproofing systems (30). 10.3 Tanking Material. Newly constructed domestic basements are normally waterproofed using some form of tanking, usually attached to the outside of the external basement wall(30). Membranes provide a physical barrier to the passage of water or water vapour but when applied to the inside of the structure they need a loading coat to resist the hydrostatic pressure. In forming domestic basements with no external hydrostatic pressure, Type A protection is usually adequate as it will enable internal environments of Grade 2 and 3. The success of the system depends on the site conditions and workmanship achieved during installation. The following materials are suitable as Type A protection. Mastic asphalt, bonded pre-formed sheet membranes, unbonded pre-formed sheet membranes, liquid membranes and water-resistant cementitious renders and polymer cement coatings. Reference (36) suggests the final defence against water ingress is the water proofing system employed. Types vary and include, spray applied polymers, elastometric sheets, bentonite filled panels and trowel applied cementitious systems. Whilst it is essential an appropriate waterproofing system be applied in particular circumstances, in all cases the excavation contractor will play a very important role in ensuring high quality. BCA Design Guide(31) on waterproofing summarises the entire design process with a particular emphasis on the waterproofing needed. The guide provides designers and clients with a procedure which covers the following aspects of basement design. 1. Basement usage. i.e. determining the internal environment. Design is specifically geared to

domestic basements and covers Grades 2 and 3. 2. The site environment needs to then be determined so the form of construction can be

determined. i.e. The external environment is determined 3. Form of construction. This will be determined by the site characteristics and the internal

environment required and refers specifically to the water protection design. Three options are given which should cover most eventualities. Type A construction which requires a separate waterproofing membrane, Type B construction which requires the waterproofing to be integral with the structure and Type C construction which utilises a cavity and associated drainage system to ensure water protection.

4. Characteristics of waterproofing system. Seven waterproofing systems are described and appropriate applications implied. In addition, information on ancillary aspects such as the use of waterstops and other sealing procedures is given.

5. Other design considerations such as thermal insulation, condensation, vapour control, chemical barriers, the flexibility of the waterproof membranes and their ability to accommodate movement are also considered.

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Selection procedures and other relevant information required to des ign water protection for basements is also given. The supporting BCA guide on site practice(32) offers complimentary guidance for site application of the various waterproofing systems. Tovey (33) offers general practical advice on waterproofing in this publication. 11.0 MINIMISING REINFORCEMENT IN BASEMENTS. It has been suggested(38) that constructing concrete basements without reinforcement is possible. However, Levi, Bosco, and Debernardi(47) recommend replacing evenly distributed bars with a series of well reinforced chords arranged parallel to the tensile stresses and spaced to keep the opening of cracks in intermediate sections where no or very little reinforcement is placed to a minimum. Such a solution would result in more economical walls (in terms of reinforcement content) than if minimum reinforcement is placed throughout the wall but the effort needed to ensure the optimum distribution is achieved will probably result in the wall being more expensive than if the minimum (but regular) reinforcement were employed. Another possibility is to include restraining chords made of prestressed concrete but embedded in the concrete of the wall. Two basic choices remain 1. Verifying that unreinforced concrete basements can be constructed but accepting the need for

high quality waterproofing (Type A or Type C) to be associated with the structure. 2. Constructing a high quality Type B conventional reinforced concrete structure and enhancing

the waterproofing with Type A or Type C construction. 12.0 MAINTENANCE OF BASEMENTS Whilst ensuring the basement is well constructed, ensuring proper maintenance is also important(36). This paper recommends leaving homeowners with an instruction sheet. Typical information should include: 1. Simple techniques to correct back fill settlement in the early years. 2. Keeping roof water away from the basement through appropriate guttering. If dispersed to

the ground water should be directed at least 1.5m from the walls. 3. Correct maintenance of sump pumps if appropriate. 4. The importance of watering dry cracked clay soil to prevent the ingress of water into the soil

and possible water pressures on the basement. 13.0 CONSTRUCTION OF BASEMENTS The authors of reference (38) note that soil settlement and heave are also causes of wall cracking. Advice from soil specialists to determine the settlement and/or heave characteristics of soils is recommended so the footing and walls can be adequately designed. Never building on made up ground and good detailing to prevent water flowing against the basement wall will help prevent the walls cracking.

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The authors note that wall cracks often occur at openings and where wall thickness alters. Placing a small area of reinforcing above doors and above and below windows reduces the likelihood of these cracks. They also recommend that in the absence of other guidance being available, basement walls may be constructed without reinforcement. The required wall thickness can be determined by using ACI332R-84 “Guide to Residential Cast-in-Place Concrete Construction(39).” Reference (38) also notes that excessive soil pressure causes cracking in unbraced concrete walls in excess of 7.3m long, although it is during backfilling that most cracking occurs. To eliminate cracking from soil pressure, the authors recommend using concrete which has strength in excess of 21N/mm2, delaying backfilling until the first floor deck is in place and anchored to the wall or by bracing the wall if back filling needs to be undertaken speedily. Heavy equipment must remain more than 2.5m from the wall and the backfill needs to be placed in thin layers and not compacted within 0.3 – 0.5m of the wall. Further, good quality well-drained soil is necessary in the backfill as this prevents water pressures building up behind the wall. Anderson (48) provides information and simple examples to check if basements conform to the elemental method of checking U-Values given in the Building Regulations. Basements 3(49) includes a report from the BRE which indicates that including basements in houses improves thermal performance. Martin(50) examines the construction procedure in forming a basement in very general terms. He describes the need to drain the soil around the basement walls, discusses fire requirements, ventilation problems and how to light a basement space. Tovey(33) offers general construction guidance in this publication. 14.0 FORMWORK SYSTEMS FOR BASEMENTS. In order to improve the cost effectiveness of basements, the formwork used to build the basement walls needs to be efficiently installed and removed. Alternatively, permanent formwork which improves the thermal properties of basement walls would make houses more energy efficient. Polystyrene formwork has been used on commercial buildings(51) with great success and in the year 2000 an underground house(52) was successfully constructed using the Permanent Insulted Formwork System (PIFS). Moss and Arora(53) studied expanded polystyrene permanent formwork systems for in-situ concrete construction in Germany and the U.K. The research described four forms of permanent formwork. Two methods use expanded polystyrene units which essentially comprise walls of polystyrene, linked together using metal ties. In the third system the links between the walls is achieved using polystyrene which is continuous with the walls. The fourth system uses high density expanded polystyrene panels which clip together to form the formwork. Moss and Arora note that all systems can be used in basement construction but with appropriate reinforcement and with suitable tanking which would need to be attached to the inner side of the external leaf of the expanded polystyrene formwork and would require further investigation. The main problem with any of these systems is the difficulty of compa cting concrete between the forms, and the

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impossibility of checking on the quality of workmanship. Examining the feasibility of using a high-density polystyrene system that clips together and can be reused would be worthwhile. With any system adopted the need to be able to provide external tanking must be possible. Arora, Moss and Chana (54) investigated energy efficient in-situ concrete housing using EPS permanent formwork. They summarise the findings given in reference 21 where four systems using EPS formwork are examined. The systems are recommended in general, but no mention of using them below ground is given. Design guidance is given on structural performance, fire safety, moisture (in walls above ground), sound movement, ventilation, energy savings, concrete mix design, concrete compaction and concrete curing. Moss(55) in 1997 examined the conformity with Building Regulations in England and Wales of expanded polystyrene (EPS) permanent formwork systems for in-situ Concrete Housing. The author assesses four EPS systems to determine if they conform to the Building Regulations and offers advice and guidance on the limitations of the systems and how to ensure they conform to the Building regulations. In the same year Arora, Moss and Chana (56) extended the investigation into energy efficient in-situ concrete housing using EPS permanent formwork by considering constructional and buildability considerations. They note that in terms of the construction of walls using EPS formwork, reinforced concrete walls should be designed in accordance with BS8110. However, as EPS formwork provides a good curing environment, the Authors state that cracking due to early age effects may not be a problem. They further state that this may obviate the need for the minimum reinforcement requirement for crack control purposes. They note, that walls without reinforcement may be constructed to BS8110(17-19) or ENV 1992-1-6(26) .However it is also clearly stated that basement walls will always require reinforcement. Another recommendation is that walls subject to water pressure be suitably tanked. However, there may be scope to investigate using lightly or unreinforced walls to basements when there is no water pressure. In all concrete walls it is deemed essential that good workmanship is undertaken during construction. Thompson(57) considers the appropriateness of building reinforced concrete walls with insulting concrete forms above ground. He discussed various types of walls that are possible which include flat, grid and post and beam systems. In all instances the wall is reinforced. Relatively high slump concrete is suggested and only modest compaction implied. To apply this system to a basement would require these weaknesses to be investigated. VanderWerf(58) offers tips for placing concrete into insulating wall forms. Van derWerf indicates many practical procedures which help when using insulating concrete forms. He recommends a relatively low slump concrete but if higher slumps are needed, the use of water reducing admixtures to maintain low w/c ratios but give higher slumps are recommended. High slumps need to be treated with caution as they can cause formwork blowouts. Van derWerf notes that when forming walls below ground level, concrete pumps are not essential. Provided the truck will not damage the basement excavation , concrete can be discharged from the truck chute. The Author recommends preventing the concrete falling the full wall depth by slowing the concrete fall with a shovel. Insulated forms provide an extremely good environment for concrete to cure in but if temperatures drop it is prudent to insulate the exposed top to the formwork. When the workers are relatively inexperienced placing a shallow (not exceeding

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1.0m) first lift will protect the lower parts of the formwork from excessive pressures. The next lift must be placed before the concrete has hardened to prevent cold joints forming. The order of placing concrete is emphasised. The wall space below windows should be initially filled. Then starting at corners and moving in one direction, place concrete around the form to a depth of 1.0m. Compaction should be undertaken by hammering timber blocks attached to the outside of the formwork or advice from the manufacturer should be obtained. Potential blowouts can usually be spotted by bulges in the formwork although this is more difficult with below groundwork. These areas should be supported with timbers. If a blowout occurs, then the formwork needs to be repaired and refilled at that location. 15.0 REPAIR TO BASEMENTS. This aspect of basements is not considered in this review. However, a number of papers exist on the subject, reference (59) being particularly relevant. 16.0 SUMMARY. The first meeting of the steering group advised the following be examined. 1. Constant thickness reinforced concrete walls. a. Constructing Type B Reinforced concrete basement walls designed according to BS8110

and BS8007 in regions with high water tables and then waterproofing them using Type A or Type C construction will ensure habitable interiors.

b. Constructing Type B Reinforced concrete basement walls designed according to BS8110 in regions with low water tables and then waterproofing them using Type A or Type C construction will ensure habitable interiors.

c. Reducing reinforcement proportions is feasible but requires irregular patterns. 2. Constant thickness unreinforced concrete walls with crack inducers. a. Constructing Type B unreinforced concrete walls will depend on how the thermal and

shrinkage cracking in the walls can be limited. The following factors affect the likelihood of cracks developing in early concrete. 1. Cement type and the effect of additives. 2. Formwork type and its effect on curing and thermal insulation 3. Ambient temperature. This aspect is unlikely to be important in the U.K. except in the

peak of summer. 4. The restraint of the base on which the walls are constructed. 5. The W/C ratio of the concrete. 6. Concrete curing

b. Ensuring concrete does not crack at unwanted locations can be achieved by using crack inducers and waterproofing across the crack using water stops.

c. Forming unreinforced concrete basement walls with crack inducers and with Type A or C or Type A and C construction in regions of low water tables should provide habitable basements if associated with an appropriate structural design procedure.

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d. In areas with high water tables, Type B construction with Types A or C or A and C should be utilised.

3. Permanent Expanded Polystyrene Formwork. a. Four systems of Permanent Expanded Polystyrene Formwork were examined, all of which

appeared feasible but with some disadvantages. The main problems of insulating formwork is that it is impossible to check the concrete quality during or after construction. Vibration of the concrete to compact it can weaken the formwork walls so using self compacting formwork is suggested. This latter suggestion would however, result in more porous, less waterproof concrete.

b. Improving the transverse lateral strength of the walls of the formwork with struts would alleviate this problem.

4. Simple lightweight temporary formwork. a. No simple system which have also been used in basements were noted.

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APPENDIX G

REFERENCES

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REFERENCES 1. Tovey, AK, “Basements 1 – Benefits, Viability and Costs”, British Cement Association,

Century House, Telford Avenue, Crowthorne, Berks., 1999. 2. ANON. “Guidance for House Builders on Basement Construction”, Quality Concrete,

July/August 1997 3. Tovey, AK, “Britain’s Basements come out from underground”, Concrete Quarterly,

Autumn 1997. 4. Tovey, AK. “Concrete basements – an idea whose time has come,” Concrete, May 2000 5. Clarke, M, “Maximising Space – the Use of Basements for Housing in Britain”, Science in

Parliament, Vol. 57, No. 3, Summer 2000 6. Tovey, AK , “Back to Basements”, Professional Builder, June 1995 7. Roberts, JJ and Tovey, AK, “Better Utilisation of Space in Housing”, Masonry International,

Vol. 5, No 3, 1992 8. Martin, S, “Cellar’s Market”, BCA Reprint 2/93, 1993 9. Tovey, AK and Keyworth, B, “Basements: land use and energy conservation – 1 Evaluation

with market and construction survey”, British Cement Association, Century House, Telford Avenue, Crowthorne, Berks, 1999.

10. Brinkley, M. “Big Cellar”, Building Homes, Feb 1998 11. Keyworth, B, “Basements 4 – House with Basement: Design Exercise”, British Cement

Association, Century House, Telford Avenue, Crowthorne, Berks. 1994 12. Roberts, JJ, “Basements 2 – A preliminary assessment of the design of basement walls”,

British Cement Association, Century House, Telford Avenue, Crowthorne, Berks. 1991. 13. The Building Regulations 1997, “Approved Document Basements for dwellings”, British

Cement Association, Century House, Telford Avenue, Crowthorne, Berks, 1997. 14. BRITISH STANDARDS INSTITUTION. BS 5628:Part 1. 1992. Code of practice for use

of masonry. Part 1: Structural use of unreinforced masonry, London. 1992 15. BRITISH STANDARDS INSTITUTION. BS 5628:Part 2. Code of practice for the use of

masonry. Structural use of reinforced and prestressed masonry, London. 2000 16. BRITISH STANDARDS INSTITUTION. BS 5628:Part 3. Code of practice for use of

masonry. Part 3: Materials and components, design and workmanship., London. 2001

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17. BRITISH STANDARDS INSTITUTION. BS 8110: Part 1: 1997. Structural use of concrete. Code of practice for design and construction , London. 1997.

18. BRITISH STANDARDS INSTITUTION. BS 8110:Part 2: 1985. Structural use of

concrete. Code of practice for special circumstances , London. 1985. 19. BRITISH STANDARDS INSTITUTION. BS 8110:Part 3. 1985. Structural use of concrete.

Design charts for singly reinforced beams, doubly reinforced beams and rectangular columns, London. 1985.

20. BRITISH STANDARDS INSTITUTION. BS 8007: 1987. Code of practice for design of

concrete structures for retaining aqueous liquids, London., 1987. 21. Roberts, JJ, Fried AN and Tovey, AK, “Plain masonry basement walls”, Kingston

University, Penrhyn Road, Kingston upon Thames, Surrey KT1 2EE, Feb 2000. 22. EC2 COMITE EUROPEAN DE NORMALISATION. Eurocode 2: Design of Concrete

Structures – Part 1: General rules and rules for buildings, ENV 1992-1-1, 1991. 23. BRITISH STANDARDS INSTITUTION. BS 8002: 1994. Code of practice for Earth

retaining structures, London. 1994 24. Roberts, JJ, Tovey, AK and Fried, AN. “Design of Plain Masonry Basement Walls”

Journal Institution of Structural Engineers, Volume 80, No. 11, ISSN 1466-5123, 5 June 2002.

25. MANN, W. “The loadbearing behaviour of bi-axially spanned masonry walls subjected

simultaneously to horizontal and vertical loading. 7th IBMAC, Melbourne, pp 1195 – 1204, 1985

26. EC6 COMITE EUROPEAN DE NORMALISATION. Eurocode 6: Design of Masonry

Structures – Part 1 – 1: General rules for buildings – Rules for reinforced and unreinforced masonry, ENV 1996-1-1, June 1995.

27. CODUTO, D. P. Geotechnical Engineering, Prentice Hall. New Jersy. 1999 28. TERZAGHI, K. Large retaining wall tests. Engineering News Record, Vol 112. 29. DIN1053:Part 2. Mauerwerk, 1984. 30. CIRIA Report 139, “Water resisting basements”, 1995 31. BCA Design Guide, “Basement waterproofing – Design guide”, British Cement

Association, Century House, Telford Avenue, Crowthorne, Berks, 1994 32. BCA Design Guide, “Basement waterproofing – site guide”, British Cement Association,

Century House, Telford Avenue, Crowthorne, Berks, 1994

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33. Tovey, AK, “Design issues in domestic basements: structure and water resistance”, Concrete, Volume 36, No. 3, March 2002

34. ANON., “Reinforced Concrete Masonry Basement Walls”, British Cement Association,

Century House, Telford Avenue, Crowthorne, Berks. 35. Tovey, AK and Keyworth, B, “Basements:land use and energy conservation – 2 House

basement case studies”, British Cement Association, Century House, Telford Avenue, Crowthorne, Berks, 1998.

36. ANON. “Preventing Wet Basements”, Concrete Technology Today, March 1996 37. ANON. “French Drains Help Keep Residential Basements Dry”, Based on the Book, “The

Wet Basement Manual” by AE Maurice, Published by The Aberdeen Group. Concrete Construction, June 1995

38. ANON. “How to control Basement wall cracks2, Concrete Technology Today, July 1995 39. ACI 332R-84. Guide to Residential Cast-in-Place Concrete Construction. 1984 40. Harrison, TA, “Early-age thermal crack control in concrete”, CIRIA Report 91,

Construction Industry Research and Information Association, Storey’s Gate, London SW1P 3AU, 1992

41. Emborg, M, Westman, G, Bernander, S, “Assessment of the Risk of thermal cracking in

hardening high strength concrete”, 1997 42. Anson, M and Rowlinson, PM, “Restraint to early age thermal movement in reinforced

concrete walls”, Cement and Concrete Association, Research Seminar, 30 June – 2 July, 1986

43. Ogawa, A, Tomita, R, “Crack control of reinforced concrete structures”, Concrete 2000,

Edited by Ravindra Dhir and Roderick Jones, Published by E & FN Spon. ISBN 0 419 18120 2. 2000.

44. Gheder, G, and Fadhil, S, “Strategic reinforcement for controlling volume-change cracking

in base retained concrete walls”, Materials and Structures/Materiaux et Construction, 1990, 23, 358-363

45. Rawi, RS and Kheder, GF, “Control of cracking due to volume change in base restrained

concrete members”, ACI Structural Journal, Vol. 87, No. 4, July/August 1990 46. Kheder, GF, “A New Look at the Control of Volume Change Cracking of Base Restrained

Concrete Walls”, ACI Structural Journal, Vol. 94, No. 3, May June 1997. 47. Levi, F, Bosco, C and Debernardi, PG, “Two aspects of the behaviour of slightly reinforced

structures”, Plain and Slightly reinforced concrete structures, 1990

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48. Anderson BR, “U-Values for Basements”, BRE information paper IP 14/94 August 1994 49. ANON., “Basements 3 – Thermal performance of dwellings with basements”, British

Cement Association, Century House, Telford Avenue, Crowthorne, Berks,1993. 50. Martin, S, “Realising that hidden asset”, BCA Reprint 3/93, 1993 51. ANON., “Expanded polystyrene shutters save time on fast track contracts”, Concrete Plant

and Production, February 1992 52. ANON. “Underground house is just the ticket”, Professional Builder, July/August 2000 53. Moss, RM and Arora, SK, “Expanded Polystyrene Permanent Formwork Systems for in-

situ concrete construction: Visits to sites in Germany and U.K.”, Building Research Establishment Note N77/97

54. Arora, S, Moss, R and Chana, P, “Energy efficient in-situ concrete housing using EPS

permanent formwork”, Building Research Establishment, Garston, Watford, Herts. 55. Moss, RM, “Expanded Polystyrene (EPS) Permanent Formwork Systems for in-situ

Concrete Housing: Conformity with Building Regulations in England and Wales”, Building Research Establishment Note N78/97, April 1997.

56. Arora, S, Moss, RM, Chana, P, “Energy efficient in -situ concrete housing using EPS

permanent formwork: Constructional and buildability considerations”, Building Research Establishment Client Report CR 197. May 1997.

57. Thompson, D, “Building with insulting concrete forms”, Portland Cement Association.

Concrete Technology Today. July 1988 58. VanderWerf, PA, “Tips for placing concrete into insulating wall forms”, Concrete

construction December 1996 59. Norton, WS, Bartley, RTB and McCoy, J, “Residential Basement Repair”, Concrete Repair

Digest, August/September 1994