Report: Phase 1 Engineering Geological Investigation: Erf ...

Report:

Phase 1 Engineering Geological Investigation:

Erf 502 Sandringham (City of Johannesburg, Gauteng)

Report to:

ConsulTauri Design (Pty) Ltd

Report by:

KHg Applied Geologists

Report No 118-018

Version 1.0

22 June 2018

Report 118-018: Engineering Geological Investigation: Erf 502 Sandringham

© 2018-06-22 KHg Applied Geologists Page i of 39

Client: ConsulTauri Design (Pty) Ltd

Att: Mr Rael Smith

Report Title: Phase 1 Engineering Geological Investigation: Erf 502 Sandringham (City of Johannesburg, Gauteng)

Reference Number: 118-018 ¨ Preliminary þ Draft ¨ Final

* A preliminary report is incomplete, and findings are provisional.

* A draft report is subject to change prior to finalisation on payment in full.

Author(s):

Matthys A. Dippenaar (PhD)

Pr.Sci.Nat. (400032/06)

Report Date: 22 June 2018

Important: The contents of this report is subject to (i) the provisions, terms and conditions

stipulated in §7 of this report and (ii) the terms and conditions of the appointment

for this work.

Moonlight Enviro (Pty) Ltd trading as KHg Applied Geologists

2008/021872/07 | Directors M. A. Dippenaar & M. D. Sole

+27 82 826 5468 | Postnet Suite 40 Private Bag X21 Queenswood 0121 South Africa | [email protected]


© 2018-06-22 KHg Applied Geologists Page ii of 39

Table of Contents

Page

1. INTRODUCTION ................................................................................................................ 1

1.1. Terms of Reference .................................................................................................................. 1

1.2. Scope ........................................................................................................................................ 1

1.3. Available Information ............................................................................................................... 1

2. SITE DESCRIPTION ............................................................................................................ 2

2.1. Locality and Prevailing Conditions ............................................................................................ 2

2.2. Regional Geology ...................................................................................................................... 2

2.3. Topography and Regional Hydrology ........................................................................................ 2

2.4. Vadose Zone Hydrology ............................................................................................................ 2

3. ENGINEERING GEOLOGICAL CHARACTERISATION ............................................................ 4

3.1. Soil Profile ................................................................................................................................ 4

3.2. Excavation Conditions .............................................................................................................. 4

3.3. Laboratory Results .................................................................................................................... 5

3.3.1. Foundation indicator test results .......................................................................................... 5

3.3.2. Soil corrosivity indicators ...................................................................................................... 5

3.4. Groundwater Conditions .......................................................................................................... 6

4. IMPACTS OF GEOTECHNICAL CONSTRAINTS .................................................................... 7

4.1. Problem Soil Behaviour and Volume Change............................................................................ 7

4.2. Water and Drainage ................................................................................................................. 8

4.3. Excavation and Stability ........................................................................................................... 8

5. SITE CHARACTERISATION AND FINDINGS ........................................................................ 9

5.1. Material Properties .................................................................................................................. 9

5.2. Impacts of Proposed Development ........................................................................................ 10

5.3. Foundation Recommendations and Solutions ........................................................................ 10

6. CONCLUSIONS AND RECOMMENDATIONS .................................................................... 11

6.1. Geology, Soil Profile, Topography and Excavatability ............................................................. 11

6.2. Material Properties ................................................................................................................ 11

6.3. Hydrology and Relief .............................................................................................................. 12

6.4. Founding Recommendations .................................................................................................. 12

7. REPORT PROVISIONS ..................................................................................................... 13

8. REFERENCES ................................................................................................................... 14

Appendices

Page

APPENDIX A. MAPS AND SITE PHOTOGRAPHS ........................................................................................ 15

APPENDIX B. SOIL PROFILES ................................................................................................................. 21

APPENDIX C. LABORATORY RESULTS ..................................................................................................... 26

APPENDIX D. SITE CLASS DESIGNATIONS ............................................................................................... 31


© 2018-06-22 KHg Applied Geologists Page iii of 39

Figures

Page

Figure 1. Locality of the study area (© GoogleEarth). .............................................................................. 16

Figure 2. Regional geology (© GoogleEarth). .......................................................................................... 16

Figure 3. W-E section (© GoogleEarth). ................................................................................................. 17

Figure 4. N-S section (© GoogleEarth). .................................................................................................. 17

Figure 5. Regional drainage (DWS; © GoogleEarth). ................................................................................ 18

Figure 6. Test pit positions (© GoogleEarth). .......................................................................................... 18

Figure 7. Test pit OW01. ...................................................................................................................... 19



Figure 10. Figure 10. Test pit OW04. .................................................................................................... 19

Figure 11. Geotechnical zoning and foundation recommendations. ........................................................ 20

Tables

Page

Table 1. Depths to base of different soil horizons in meters below surface. ................................................ 4

Table 2. Water and stability considerations. ........................................................................................... 5

Table 3. Foundation indicator test results. .............................................................................................. 5

Table 4. Field descriptors and laboratory test results influencing corrosivity. ............................................. 6

Table 5. Anticipated geological classification for urban development. ....................................................... 7

Table 6. Geotechnical considerations and classes by individual test pits..................................................... 7

Table 7. General influences of the corrosiveness of soils to steel and concrete. .......................................... 8

Table 8. Usability of site materials based on the Unified Soil Classification System (USCS). .......................... 9

Table 9. AASHO and Unified rating for sub-grade, sub-base and base (from Dyer, 1982). ............................. 9


© 2018-06-22 KHg Applied Geologists Page 1 of 39

1. INTRODUCTION

1.1. Terms of Reference

A Phase 1 Engineering Geological Investigation was requested by ConsulTauri Design (Pty) Ltd for the proposed development of

Erf 502 Sandringham (City of Johannesburg, Gauteng). The stand, covering a spatial extent of approximately 5 hectares, is

situated 2.20km west of the intersection of the N3 Highway and Linksfield Road (M16) in the City of Johannesburg (Gauteng).

The proposed development entails township establishment and all associated infrastructure.

1.2. Scope

The Phase 1 Engineering Geological Investigation comprise the following as per draft SANS 634:2012 (Geotechnical

Investigations for Housing Developments) and the GFSH-2 (Generic Specification for Housing Developments):

• Test pit excavation, soil profiling and sampling of key horizons for relevant laboratory analyses

• Evaluation of excavatability of site soils

• Assessment of geological, hydrological and geomorphological constraints potentially influencing the development

• Demarcation of site into zones with similar anticipated geological, hydrological and geomorphological constraints based

on results of field work phase

• Addressing of the potential geological concerns and appropriate foundation recommendations.

1.3. Available Information

The following were available at the time of the investigation:

• Relevant 1:250 000-scale Geological Sheets (© DME / CGS)

• Relevant 1:50 000-scale Topocadastral Sheets (© Government Printer)

• Site locality as supplied by Client

• Google Earth Imagery © 2013

• Catchment maps (www.dwa.gov.za 2010) and hydrogeological sheets (1996) (© DWA)

• Additional bibliography as noted in §8 (REFERENCES).



2. SITE DESCRIPTION

2.1. Locality and Prevailing Conditions

The site, Erf 502 Sandringham, is situated 2.20km west of the intersection of the N3 Highway and Linksfield Road (M16) in the

City of Johannesburg (Gauteng) (Figure 1). The site is presently undeveloped, although the site is being used informally for

parking. George Avenue, to the north, and Anne Street, to the west and south, confine the site. The property is situated next to

a business complex to the east, Yeshiwa College to the north and a residential area to the south.

The site, covering an area of approximately 5 hectares, is vegetated by grass and two old oak trees. Both the surface materials

and vegetation are likely highly disrupted due to historical anthropogenic activities.

2.2. Regional Geology

The regional geology is characterised by mafic and ultramafic rock of the Edenvale-Modderfontein Ultramafic Complex confined

by granitic rock of the Archaean Johannesburg Dome Granites (Figure 2). The stratigraphy comprises, from oldest to youngest,

the following:

• Archaean greenstone remnants of undifferentiated mafic and ultramafic plutonic and volcanic rocks (grey area - Zm) of

an age greater than 3340 Ma.

• Archaean Hornblende and biotite tonalite gneiss (peach area - Zh) that have a recorded age of 3200 ± 2 Ma.

The site is not underlain by soluble rock (e.g. dolomite) and no specialist investigations are required in this regard.

The area has a climatic Weinert N-value of less than 5, implying that chemical decomposition will likely predominate over physical

disintegration.

2.3. Topography and Regional Hydrology

The site slopes at roughly 6-8% to the south (Figure 3; Figure 4). Historical activities (such as agricultural practices, cut-to-fill

operations and previous development) may have disrupted the surface materials and resulted in some made materials being

present on the site.

The area under investigation falls within the A21C quaternary catchment of the Crocodile/ Marico (West) Water Management

Area (WMA3). Regional drainage is roughly towards the north via the Jukskei River to the Crocodile River (Figure 5). No defined

drainage feature are present on the site itself.

Precipitation is expected to flow as sheet flow or shallow interflow towards shallower slopes, natural depressions and drainage

features from where infiltration can occur. Seasonal perching of groundwater may cause seepage or wet profile conditions at

shallow depths, regardless of the extent of the 1:100-year flood lines.

2.4. Vadose Zone Hydrology

The vadose zone refers to the earth materials between the land surface and groundwater table. The influence of the vadose

zone on engineering development should not be discounted and, together with knowledge of the hydrogeology, can inform about

subsurface flow mechanisms and flow paths which may influence the proposed development. Additional to this, one should note



that disruption of the site materials will affect the properties of the vadose zone, and that subsurface hydrology will differ during

the complete project life cycle.

Depending on the residual weathering products, the texture of the transported materials, and the properties of imported fill

material, the surface soils may have highly variable permeability. This, together with (for instance) uncertainty of bedrock

properties, changes in land cover and regional groundwater levels, may result in localised zones of increased infiltration or runoff,

areas associated with water ponding on surface and/ or groundwater movement possibly mimicking surface topography. Note

should, therefore, be taken that local hydrology may be highly variable.



3. ENGINEERING GEOLOGICAL CHARACTERISATION

Four test pits were excavated by means of a Hidromek 102B (74kW) TLB on 1 June 2018 (Figure 6). Samples were retrieved and

submitted to Soilab (Pty) Ltd for a variety of tests to interpret material properties.

Photographs of the site and test pits taken during the field work phase are shown in Figure 7 to Figure 10 (APPENDIX A).

3.1. Soil Profile

Soil profiles are summarised in Table 1 and shown in APPENDIX B. All test pits terminated in moist, light grey brown, soft to firm,

clayey silt, lower residual greenstone. The upper residual green stone comprises of moist, reddish brown, medium dense,

shattered & pinholed, silty clayey fine sand. The general succession of materials above the residuum comprise, with the exception

of test pit OW01 and OW03, thin fine sandy topsoil, underlain by colluvium of varying thicknesses and a basal pebble marker.

Test pit OW1 has no topsoil due to surface erosion from cars using the site for parking and OW03 has a made ground horizon

from pervious developments.

Table 1. Depths to base of different soil horizons in meters below surface. TP TRANS MG PM RES DEPTH END

OW01 0.30 X 0.50 2.80 2.80 EoH Residuum

OW02 0.40 X 0.55 3.00 3.00 EoH Residuum

OW03 0.40 0.70 1.00 2.55 2.55 EoH Residuum

OW04 0.80 X 1.35 3.00 3.00 EoH Residuum

NOTES TRANS Transported: Colluvium; Hillwash; Topsoil; Alluvium

PM Pebble Marker

RES Residuum (corresponding to rock noted in END)

MG Made ground; Imported material

DEPTH End of hole depth

0.00 Horizon absent X Refusal prior to possible occurrence

END DoR - Depth of Refusal; EoH - Hole stopped, end of TLB reach or open excavation

Notes:

A pebble marker – although not always distinctly identifiable – commonly indicates the boundary between transported and

residual (in-situ formed) soils.

Made ground is used collectively for any disturbed (i.e. loosened, moved, stockpiled, compacted, etc.) natural or imported

material. Manmade materials are often associated with such made ground (i.e. building rubble, rubbish and waste, geotextiles,

steel, plastics, etc.). Fill and rubble are used specifically for material apparently imported for the purpose of construction, or

material remnant of historical demolished construction.

3.2. Excavation Conditions

Test pits were excavated by means of a Hidromek 102B (74kW) TLB. Excavation conditions are SOFT to depths exceeding 2.50 m

in accordance with SANS 1200D (1988) and SANS 634 (2009). Conditions become SOFT to FIRM in residual bedrock.

Residual soils are expected to be thick and no excavation problems in residuum are expected.

Influences of water and sidewall stability are summarised for the individual test pits in Table 2.



Table 2. Water and stability considerations. ID WETNESS (1) WATER SEEPAGE (2) STANDING WATER (3) STABILITY (4)

DEPTH DEPTH RATE DEPTH TIME (UN-)STABLE TIME

OW01 None none n/a none n/a Stable n/a




NOTES (1) Depth from which moisture content is very moist to wet

(2) Depth of seepage and estimation of seepage rate (slow, medium, fast, very fast)

(3) Depth of standing water in pit and time taken to fill to stated level (else immediate)

(4) Sidewalls stable or unstable and time since excavation until instability

No water seepage was encountered in any of the test pits. The influence of both possible sidewall instabilities and water seepage

should be anticipated for during and after construction, especially as wet or waterlogged materials may be more prone to

instability.

Discolouration (speckles, mottles and/ or patches) in most horizons suggest the likely presence of a localised perched water table.

These systems result from soils periodically reaching saturation from infiltrating water, shallow interflow or rising subsurface

waters.

3.3. Laboratory Results

3.3.1. Foundation indicator test results

The full laboratory results are shown in APPENDIX C. The results of three bulk, disturbed soil samples submitted for foundation

indicator testing are summarised in Table 3. The sampled horizons comprise the following:

• OW01 (0.50-1.24) – upper residual greenstone

• OW01 (1.24-2.80) – lower residual greenstone

• OW03 (1.00-1.45) – reworked residual greenstone.

Table 3. Foundation indicator test results. ID DEPTH GRADING/ HYDROMETER ATTERBERG LIMITS GM CLASSES HEAVE

%C %M %S %G LL PI LS TRB USC

OW01 0.50-1.24 29 24 36 11 36 16 7.0 0.76 A-6 CL Low

OW01 1.24-2.80 15 35 45 5 30 6 1.5 0.60 A-4 ML Low

OW03 1.00-1.45 25 19 44 12 34 13 7.0 1.01 A-6 SC Low

NOTES (1) Grading: Percentage clay (%C), silt (%M), sand (%M) and gravel (%G) by weight.

(2) Atterberg Limits: Liquid Limit (LL), Plasticity Index (PI), Linear Shrinkage (LS).

(3) Heave: Potential expansiveness (acc. Van Der Merwe).

All analysed samples grade essentially as sands with variable clay, silt and gravel that generally have poor to good compaction

characteristics. Soils are slightly to moderately plastic with low liquid limits and generally low anticipated heave according to Van

der Merwe’s method.

3.3.2. Soil corrosivity indicators

All samples were also analysed for pH and electrical conductivity (EC). These are shown together with parameters influencing

corrosivity of soils in Table 4.



Table 4. Field descriptors and laboratory test results influencing corrosivity. ID DEPTH MATERIAL MOISTURE %C pH EC (S/m) OTHER

OW01 0.50-1.24 Res greenstone Moist 29 5.43 0.0304 X



NOTES (1) Material as per soil profile description.

(2) Moisture as per soil profile description or natural moisture content.

(3) %C (percentage clay), pH and EC as per laboratory results.

3.4. Groundwater Conditions

The hydrogeological map series supply the following information pertaining to groundwater conditions at the site:

• Total dissolved solids (TDS) generally <300 mg/l

• Hydrochemical type (Ca,Mg) (HCO3)2

• Depth to groundwater level generally 20-30 m below ground surface

• Mean annual groundwater recharge 110 mm

• Electrical conductivity of groundwater <300 mS/m.

The ultramafic tocks will generally behave either as a solely fractured, or an intergranular and fractured aquifer system where

primary pore space stores water and fractures transmit water. Given the fine-grained weathered products and the properties of

the bedrock itself, the behaviour may not be as a proper aquifer, but possibly rather as an aquitard storing but not necessarily

transmitting significant amounts of water.

Assessment of groundwater conditions is, however, not included in the scope of this study.



4. IMPACTS OF GEOTECHNICAL CONSTRAINTS

The impact of the geotechnical constraints on housing developments may be evaluated according to Table 5 and APPENDIX D,

which is a summary of the general geotechnical constraints relevant to urban development (Partridge et al. 1993). The “class”

indicates the severity of the specific constraint for this site and – where multiple values are indicated – shows the variation over

the site. For non-residential developments, the system is applied as a sensible means of denoting geological constraints and

should not be viewed as a foundation design recommendation as the structure’s footprint and load will determine this. These

are discussed separately in this section.

Table 5. Anticipated geological classification for urban development. CONSTRAINT SITE CONDITIONS CLASS

A Collapsible soil Any collapsible horizon or consecutive horizons totalling depth of more

than 750 mm in thickness

2

B Seepage Permanent or perched water table more than 1.5 m below ground

surface

1

C Active soil Low soil heave potential predicted 1

D Highly compressible soil Moderate soil compressibility expected 2

E Erodability of soil Low 1

F Difficulty of excavation to 1.5m depth No difficulty expected n/a

G Undermined ground Not within scope of geotechnical investigation n/a

H Instability in areas of soluble rock Soluble rocks not identified during test pitting n/a

I Steep slopes Slopes between 6 and 12° 1

J Areas of unstable natural slopes Low risk 1

K Areas subject to seismic activity This area is not a known natural seismic active zone 1

L Areas subject to flooding Not within scope of geotechnical investigation n/a

NOTES: Class 1 – most favorable; 2 – intermediate; 3 – least favorable.

Geotechnical concerns and excavation conditions are summarised per individual soil profile in Table 6 according to APPENDIX D.

Thicknesses in the General Geotechnical Concerns column relate to thicknesses of materials subject to noted behaviour. Depths

in the Excavatability column refer to depth of TLB refusal (DoR), beyond which alternative means of excavation will be required.

When noted as EoH, excavation was ceased prior to TLB refusal.

Table 6. Geotechnical considerations and classes by individual test pits. TP GENERAL GEOTECHNICAL CONCERNS CLASS

OW01 Soils prone to collapse settlement given to the open structure C2-S2/ 2AC




4.1. Problem Soil Behaviour and Volume Change

Possible problem soil behaviour and volume change relate to A, C, D and E (settlement, collapse, expansiveness, compressibility

and dispersivity), as well as G and H (subsidence or sinkhole formation due to undermining or dolomitic land) as per Table 5.

Bulk of the site materials, given both its soil mass properties and thickness, are prone to collapse or consolidation settlement of

horizons greater than 1.00m in thickness. Due to the surface slope angle, cut and fill embankments may be needed for the

footing. Appropriate compaction of fill must be achieved to ensure no settlement of material after construction.

The absence of soluble rock at the site results in exclusion of the typical hazards posed by development on dolomitic land.

Undermined ground is not expected at the site; however, identification of mined-out areas falls outside the scope of this

investigation.



4.2. Water and Drainage

Possible seepage and water-related issues relate to B and L of Table 5. Additional to this are any possible contamination from

the site or influences of water and its chemistry on buried infrastructure.

No seepage or standing water was encountered in the test pits during the site investigation.

Significant changes in moisture content may contribute to the anticipated movement behaviour of the site soils. During

construction and after development, shallow perched water systems may develop due to stormwater management practices and

localised infiltration.

The influence of possible proximate surface drainages and their flood lines has not been accounted for in this investigation. Flood

line determination and wetland delineation, if applicable, do not fall within the scope of this investigation.

The complete development requires plumbing and drainage precautions. The installation of drains may prevent super-saturation

of the site soils and minimise differential movements on surface level.

Scaling and corrosion of buried infrastructure generally increases as shown in Table 7. Soil pH is mostly slightly acidic and EC is

fairly high, supporting evidence for moderate corrosivity. Given the presence of organic material in topsoil and the presence of

moist soil in winter, soils may be mildly corrosive to concrete and to a lesser extent to steel. Additional to this, chloride, suphate,

pH, organic matter and other contaminants also have significant influences on the corrosivity of materials.

Table 7. General influences of the corrosiveness of soils to steel and concrete. PARAMETER à INCREASING AGGRESIVENESS OR CORROSIVENESS OF SOILS à

EC (S/m) <0.0050:

Essentially non-

corrosive

<0.0100:

Mildly corrosive

<0.0200:

Moderately

corrosive

<0.0333:

Corrosive

<0.1000:

Highly corrosive

>0.1000:

Extremely

corrosive

Soil type Sand and gravel generally have lower EC:

Generally less corrosive

Clay generally has higher EC:

Generally more corrosive

Saturation <40% or 100%: Generally not

aggressive to mildly corrosive

60-85%: Maximum expected

corrosion rates

pH Soils with neutral pH are generally not very corrosive Very acidic or alkaline: corrosive to steel

Acidic (pH < 5.5): likely corrosive to concrete

4.3. Excavation and Stability

Excavation and stability issues relate to F, I, J and K (excavatability, slopes, seismicity) of Table 5 and is judged in combination

with other parameters influencing stability of cuttings, excavations, slopes and the like.

Excavation by means of TLB is possible to depths of 3.00m. Excavation conditions are medium dense becoming firm to soft in

residual material.

Excavation instabilities may be encountered, especially in waterlogged soils or in excavations left open for prolonged periods.

Deeper excavation conditions and fresh bedrock properties should be confirmed for excavation depths exceeding the depth of

investigation. This may include, for instance, cut to fill, basements and underground storage tanks.

Site slopes are fairly steep; minimal natural slope instabilities are anticipated; but cut and fill embankments may be needed for

founding platforms.

The site is not considered to be strongly affecting by natural seismicity.



5. SITE CHARACTERISATION AND FINDINGS

5.1. Material Properties

The site is underlain by Archaean greenstones of the Edenvale-Modderfontein Ultramafic Complex.

The usability of the on-site materials for construction purposes (based on the Unified classes) are shown in Table 8 and the

usability of the on-site material for sub-grade, sub-base and base layers (based on the AASHO and Unified Soil Classification

Systems) are shown in Table 9.

Table 8. Usability of site materials based on the Unified Soil Classification System (USCS). CLASS EMBANKMENT DRAINAGE COMPACTION COMPRESSIBILITY WORKABILITY

SC Reasonably stable Fair (impervious) Good to fair Slight to medium (low) Good

CL Good stability Impervious (Impervious) Good to fair Medium (medium) Poor

ML Poor Semipervious (Impervious) Good to poor Slight to medium

(medium) Fair

* All descriptors noted in brackets indicate conditions when compacted.

Table 9. AASHO and Unified rating for sub-grade, sub-base and base (from Dyer, 1982). SUB-GRADE SUB-BASE BASE

Very poor Poor Fair Medium Good Medium Good Medium Good Excellent

AASHTO SOIL CLASSIFICATION

A-1-b A-1-a

A-2-7 A-2-6 A-2-5 A-2-4

A-3

A-4

A-5

A-6

A-7-6 A-7-5

UNIFIED SOIL CLASSIFICATION

OH CH GM-u GM-d

MH OL GC

CL SW

ML SM-d

SC

SM-u GP

SP

Materials may serve to variable extent as different road pavement layers, although it will generally not be suitable for base

course. Some improvement may be required to optimise the use of onsite materials.

Excessive fines (clay and silt) may influence site material properties and affect the suitability for use as bedding and fill for

underground pipelines. On-site materials may require sieving (to required grading) and/ or chemical stabilisation for use as

bedding, fill or constructed fill areas.

The impact of historical agricultural, levelling and cut-and-fill operations and associated made ground should be considered as

such made materials will likely have different properties.



5.2. Impacts of Proposed Development

The proposed development will likely alter present conditions as investigated during complete project life cycle in the following

ways:

• Surface materials will be disturbed to an uncertain depth. The degree to which onsite materials are reworked and

mixed (disturbed, compacted, mixed, stabilised) will affect consolidation settlement and other possible volume

changes. Soil horizons will inevitably be disrupted, thereby also affecting the behaviour of the ground profile.

Compaction and improvement techniques employed should be conducted with diligence in this regard.

• Disruption of the shallow soil horizons will change this shallow interflow system, either resulting in deeper percolation

of water, changes in depth of the perched water table system, or surface ponding and runoff. Possible leaks in

underground pipes may contribute to this interflow system. Design of a shallow subsurface drainage system should

consider this as water may adversely affect infrastructure (foundations and pavements) after construction.

• Stormwater from the upslope property may influence site materials. Inadequate stormwater management may cause

a possible problem.

Surface runoff should be removed or allowed to infiltrate through permeable pavements so as to limit possible damage from

sealed surfaces. This can be exacerbated by facilities adding additional water to the development, e.g. rainwater, irrigation,

outside watering and washing facilities.

5.3. Foundation Recommendations and Solutions

The site is considered one site class designation zone based on the above constraints and the criteria as set out in the NHBRC

(1999) guideline document for single-story masonry buildings (Figure 11; APPENDIX D):

• Zone I: C2-S2/2AI – Soils prone to collapse settlement given to the open structure

The same solutions will apply to all zones and the site in its entirety can be considered class C2.

The classification and foundation recommendations are based on results from this investigation and for present conditions.

Laboratory test results are required to verify the recommendations.

For heavier structures, improved foundations should be considered. For any required filling and levelling, proper foundation

design will be required to minimise differential movement and to ensure suitable founding. Rippability of deeper materials may

require further investigation, depending on the depth of construction.



6. CONCLUSIONS AND RECOMMENDATIONS

The following pertains to the Phase 1 Engineering Geological (Geotechnical) Investigation for the proposed development of Erf

502 Sandringham (City of Johannesburg, Gauteng).

The site is considered suitable for the proposed residential development, although cognisance of geological constraints is

important to ensure minimal adverse impact on the development and to acknowledge additional costs incurred due to

engineering solution of these constraints.

All findings and recommendations are based solely on the data contained in this report and are subject to variation. Sampling

frequency is based on the appointed scope of works and terms of conditions of the accepted proposal. Findings need to be

confirmed during a Phase 2 Detailed Investigation, and/ or any other investigation required by the relevant authorities.

6.1. Geology, Soil Profile, Topography and Excavatability

• The site to be developed is underlain Archaean greenstone of the Edenvale-Modderfontein Ultramafic Complex.

• Bulk of the shallow site materials comprising transported materials and imported fill are classified as soft excavation.

• No shallow bedrock is expected in this area.

• Excavation stability should be confirmed during construction, especially given the possible induced influence of shallow

interflow or waterlogging on excavation stability, as well as the variability in material properties.

• The gradual gradient of the slope may cause the need for cut and fill embankments depending on type of proposed

development.

• Historical development, agricultural operations and/ or levelling practices may have disrupted surficial materials and

variations in soil properties should be accounted for. The likelihood of imported fill and building rubble should also be

accounted for in shallow horizons.

• The site is not underlain by soluble rock.

RECOMMENDED ACTIONS: TLB excavation should be possible to depths exceeding 2.50 m. Deeper excavation, notably into fresh

bedrock, may require more advanced techniques.

6.2. Material Properties

• Site soils are generally low plasticity sands with low potential expansiveness (according to Van der Merwe’s method),

although fines in the form of inactive clays and silts are abundant.

• Imported and poorly compacted fill have highly variable properties and should be investigated further if to be used. Fill

materials, as in OW03, may be present over portions of the site.

• Consolidation and/ or collapse settlement can be expected for the transported and upper residual soil horizons.

• Bulk of the site soils may require improvement to be used for specific road pavement layers or as bedding or fill.

Imported or improved material properties should fall within accepted limits for the proposed use.



RECOMMENDED ACTIONS: Site soils may require some compaction, stabilisation and/ or alternative improvement for shallow

foundations. Synthetic geotextiles may be required to minimise movement of site soils and to enhance drainage. The exact load

of the proposed structures will determine the specific improvement techniques.

6.3. Hydrology and Relief

• No water seepage was encountered in any of the test pits during investigation.

• Altering the soil profile commonly affects the subsurface seepage. Design should incorporate the likelihood of

enhanced shallow seepage and waterlogging due to localised infiltration, stormwater practices, etc.

• Flood line and wetland delineation, although not apparently influencing the site, are not determined as part of the

engineering geological investigation.

RECOMMENDED ACTIONS: Drainage precautions are required to minimise differential movements and erosion. If the site or a

portion thereof is situated within the 1:100-year flood lines, or have been delineated as a wetland, it is the prerogative of the

Civil Engineer or other suitably experienced specialist to overwrite the geotechnical recommendations for such portions.

Variation in material properties due to constructed fills (if applicable) will require special attention to drainage. Proper

stormwater management and subsurface drainage will be required to reduce the impacts of waterlogging and perched water

systems.

6.4. Founding Recommendations

• The site is considered one geotechnical zone. Major constraints include some consolidation settlement or compression

and gradual slopes.

• Water management (of waterlogged surface soils and possible perched water table systems) and excavation conditions

should be duly noted as additional constraints.

RECOMMENDED ACTIONS: Provisional foundation requirements for single-storey masonry structures are as per Figure 11 and

can be finalised based on the findings of the Phase 2 Detailed investigation.

A suitably qualified civil engineer should approve design of foundations. Any levelled land should be constructed as homogeneous

as possible to ensure minimal differential movements and to minimise adverse impacts on the shallow interflow.



7. REPORT PROVISIONS

All findings and recommendations are based solely on the data contained in this report and are subject to spatial and temporal

variation.

Good site drainage will be necessary as the occurrence of a perched water table is a reality. This may cause problems with

dampness in surface structures and with installation of services. The saturation of the soil profile will also need special site

drainage methods as this may lead to additional collapse settlements under load.

Areas of termite and other biotic activity are present and additional foundation modifications to prevent damage to single-storey

structures due to differential settlements may be necessary across these features. The biotic activity is generally limited to the

upper soil horizons.

The test pits were positioned to cover the accessible parts in order to zone the site. The pits were backfilled by the TLB or

excavator without proper compaction in layers. If structures are to be positioned over or across these pits proper compaction

must be executed to prevent differential settlements from taking place. The same will apply to development across existing

foundations, waste pits, root areas of removed medium to large trees and septic tanks.

The 1:100 year flood lines and the hydrogeological conditions are not within the scope of this investigation.

It is assumed that the development will be serviced by the usual municipal services and no recommendations are made on on-

site sanitation, waste disposal, and stormwater reticulation services.

It is recommended that a Phase 2 Engineering Geological Investigation be conducted prior to construction to confirm the results

contained in this report and for NHBRC enrolment of the site. This can be done during clearing of the site or when the

underground services are being installed.

Findings and recommendations contained in this report are subject to the representativeness of the excavations and/ or outcrops

inspected. Furthermore, although no doubt is placed over the quality of data obtained from other sources, the findings of this

report are also subject to the accuracy of the results received from laboratories and the reliability of maps, and data from the

Internet (including, for instance, the DWA National Groundwater Archive, Google Earth, old reports, geological and topocadastral

maps).

Additionally, refer to the Terms and Conditions of appointment as supplied by KHg Applied Geologists (trading as Moonlight

Enviro (Pty) Ltd) and/ or Moonlight Enviro (Pty) Ltd in the accepted cost proposal(s).



8. REFERENCES

• Bhattaria, J. (2013). Study on the corrosive nature of soil towards the buried-structures. Scientific World. 11(11):43-47.

• Brink, A. B. A. 1979. Engineering Geology of Southern Africa. Volume 1. Building Publications. Silverton.

• Dippenaar, M. A., Van Rooy, J. L., Breedt, N., Muravha, S. E., Mahlangu, S. and Mulders, J. A. (2014). Vadose Zone

Hydrology: Concepts and Techniques. Water Research Commission publication TT 584. Pretoria.

• DWAF [Department of Water Affairs and Forestry]. 1996. Electronic Maps of the Water Management Areas in South

Africa. Pretoria. (www.dwa.gov.za).

• DWAF [Department of Water Affairs and Forestry]. 1999. Drainage Regions of South Africa & Hydrogeological Map

Series. Pretoria.

• Jennings, J. E. B., Brink, A. B. A., Williams, A. A. B. 1973. Revised Guide to Soil Profiling for Civil Engineering Purposes in

Southern Africa. The Civil Engineer in SA. p3-12. January 1973.

• SABS [South African Bureau of Standards]. 1988. Standardized Specification for Civil Engineering Construction. DA:

Earthworks (Small Works). South African Bureau of Standards. SABS 1200 DA:1988 (as amended 1990).

• SAICE [South African Institute for Civil Engineers]. 1995. Code of Practice: Foundations and superstructures for single

storey residential buildings of masonry construction. Joint Structural Division, Johannesburg. First edition.

• SANS [South African National Standards]. 2009. Geotechnical Investigations for Township Development. South African

Bureau of Standards. Draft SANS 634:2012. Pretoria.

• SANS [South African National Standards]. 2009. Profiling, and Percussion and Core Borehole Logging in Southern Africa

for Engineering Purposes. South African Bureau of Standards. Draft SANS 633:2009. Pretoria.

• Stiff, J. et al. 1997. Guidelines for Urban Engineering Geological Investigations. South African Institute for Engineering

and Environmental Geologists and the South African Institution of Civil Engineers.

• Weinert, H. H. 1980. The Natural Road Construction Materials of Southern Africa. Academica. Cape Town.



APPENDIX A. MAPS AND SITE PHOTOGRAPHS



Figure 1. Locality of the study area (© GoogleEarth).

Figure 2. Regional geology (© GoogleEarth).



Figure 3. W-E section (© GoogleEarth).

Figure 4. N-S section (© GoogleEarth).



Figure 5. Regional drainage (DWS; © GoogleEarth).

Figure 6. Test pit positions (© GoogleEarth).



Figure 7. Test pit OW01. Figure 8. Test pit OW02.

Figure 9. Test pit OW03. Figure 10. Figure 10. Test pit OW04.



Zone I

C2-S2

Consolidation and

collapse

Stiffened strip

footings,

stiffened or

cellular raft

- Stiffened strip footings, stiffened or cellular raft with articulation joints or solid lightly

reinforced masonry.

- Bearing pressure not to exceed to 50kPa.

- Fabric pressure not to exceed to 50kPa.

- Site drainage and service/plumbing precautions.

Deep strip

foundations

- Normal construction with drainage requirements.

- Founding on a competent horizon below the problem horizon.

- Fabric reinforcements in floor slabs.

Compaction of

in-situ soils

below

individual

footings

- Remove in-situ material below foundations to a depth and width of 1.5 times the

foundation width or to a competent horizon and replace with material compacted o

93% MOD AASHTO density at –1% to +2% of optimum moisture content.

- Normal construction with lightly reinforced strip footings and light reinforcement in

masonry.

Piled or pier

foundations

- Reinforced concrete ground beams or solid slabs on piled or pier foundations.

- Ground slabs with fabric reinforcement.

- Good site drainage.

Soil raft

- Remove in-situ material below foundations to 1.0m beyond perimeter of building to a

depth of 1.5 times the widest foundation or to a competent horizon and replace

with material compacted to 93% MOD AASHTO density at -1% to +2% of optimum

moisture content.

- Normal construction with lightly reinforced strip footings and light reinforcement in

masonry

Figure 11. Geotechnical zoning and foundation recommendations.

ZONE I



APPENDIX B. SOIL PROFILES



APPENDIX C. LABORATORY RESULTS

Sample No. 1Soillab Sample No. S18-1192-01Depth (m) 0.50 - 1.24 PROJECT : OAKWOODPosition OW 01 JOB No. : S18-1192Material Description DARK REDDDISH DATE : 2018-06-11

BROWN

CLAYEYSAND

Relative density on < 2 mm (SANS 5844) 2.65Organic MaterialMoisture (%) / Dispersion (%)

SCREEN ANALYSIS (% PASSING) (SANS 3001:GR1)

63.0 mm 10050.0 mm 10037.5 mm 10028.0 mm 10020.0 mm 10014.0 mm 1005.0 mm 992.00 mm 890.425 mm 790.075 mm 56

HYDROMETER ANALYSIS (% PASSING) (SANS 3001:GR3)

49 µm 5329 µm 4812 µm 395 µm 292 µm 23

% Clay 29% Silt 24

% Sand 36% Gravel 11

ATTERBERG LIMITS (SANS 3001:GR10)

Liquid Limit 36Plasticity Index 16

Linear Shrinkage (%) 7.0Grading Modulus 0.76

Classification A-6 (6)Unified Classification CL

R54 revision 1

PARTICLE SIZE ANALYSIS

Chart Reference

Soillab is a SANAS accredited Testing Laboratory.

Engineering Materials LaboratoryT +27 12 813 4900 E [email protected]

Soillab Pretoriawww.soillab.co.za

0

20

40

60

80

100

Cum

ulat

ive

% p

assi

ng

0.005 0.01 0.02 0.06 0.1 0.2 0.5 1.0 2.0 5.0 10 50 100

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80PI

of w

hole

sam

ple

Clay fraction of whole sample

POTENTIAL EXPANSIVENESS

VERY HIGH

HIGH

MEDIUM

LOW

CLAY GRAVEL SILT SAND

0 0.2 0.4 0.6 0.8 1 1.2

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80 90 100

Plas

ticity

Inde

x

Liquid Limit

PLASTICITY CHART

0.002

HIDROMETER/1192-01 FI.xlsm

Sample No. 2Soillab Sample No. S18-1192-02Depth (m) 1.24 - 2.80 PROJECT : OAKWOODPosition OW 01 JOB No. : S18-1192Material Description LIGHT DATE : 2018-06-11

OLIVE

SILTYSAND





51 µm 5030 µm 4113 µm 296 µm 152 µm 8

% Clay 15% Silt 35

% Sand 45% Gravel 5




Classification A-4 (2)Unified Classification ML




R54 revision 1


Chart Reference

0

20

40

60

80

100

Cum

ulat

ive

% p

assi

ng

0.005 0.01 0.02 0.06 0.1 0.2 0.5 1.0 2.0 5.0 10 50 100

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80PI

of w

hole

sam

ple



VERY HIGH

HIGH

MEDIUM

LOW


0 0.2 0.4 0.6 0.8 1 1.2

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80 90 100

Plas

ticity

Inde

x

Liquid Limit

PLASTICITY CHART

0.002


Sample No. 3Soillab Sample No. S18-1192-03Depth (m) 1.45 - 2.55 PROJECT : OAKWOODPosition OW 03 JOB No. : S18-1192Material Description LIGHT DATE : 2018-06-11

RED

CLAYEYSAND





49 µm 4429 µm 3812 µm 335 µm 252 µm 23

% Clay 25% Silt 19

% Sand 44% Gravel 12




Classification A-6 (3)Unified Classification SC




R54 revision 1


Chart Reference

0

20

40

60

80

100

Cum

ulat

ive

% p

assi

ng

0.005 0.01 0.02 0.06 0.1 0.2 0.5 1.0 2.0 5.0 10 50 100

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80PI

of w

hole

sam

ple



VERY HIGH

HIGH

MEDIUM

LOW


0 0.2 0.4 0.6 0.8 1 1.2

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80 90 100

Plas

ticity

Inde

x

Liquid Limit

PLASTICITY CHART

0.002


R26 revision 2

Client:

Project:

Project No.:

Date:

Sample DepthNo (m)

S18-1192-01 0.50-1.24 5.43 0.0304

S18-1192-02 1.24-2.80 5.10 0.0302

S18-1192-03 1.45-2.55 6.90 0.0401

Note: Items marked with a star (*) is Not Accredited

Soillab is a SANAS accredited Testing Laboratory according to the Accreditation Scope

Comments:

OW 01

OW 01

OW 03

pHSamplePosition

Electrical Conductivity

S/m

pH & CONDUCTIVITY - TMH 1 A20 & A21T

2018/06/05

S18-1192

MOONLIGHT ENVIRO

OAKWOOD



APPENDIX D. SITE CLASS DESIGNATIONS



GEOTECHNICAL CONSTRAINTS IN URBAN DEVELOPMENT (SANS 634:2012) CONSTRAINT DESCRIPTOR

DESCRIPTION 1 (most favourable) 2 (intermediate) 3 (least favourable)

A Collapsible soil

Any collapsible horizon or

consecutive horizons totalling

depth of less than 750 mm in

thickness

Any collapsible horizon or

consecutive horizons totalling

depth of more than 750 mm in

thickness

n/a

B Seepage

Permanent or perched water

table more than 1.5 m below

ground surface

Permanent or perched water

table less than 1.5 m below

ground surface

Swamps and marshes

C Active soil Low soil-heave potential

anticipated

Moderate soil-heave potential

anticipated

High soil-heave potential

anticipated

D Highly

compressible soil

Low soil compressibility

anticipated

Moderate soil compressibility

anticipated

High soil compressibility

anticipated

E Erodibility of soil soil Intermediate High

F

Difficulty of

excavation to 1.5

m depth

Scattered or occasional

boulders less than 10% of total

volume

Rock or hardpan pedocretes

between 10% and 40% of total

volume

Rock or hardpan pedocretes

more than 40% of total

volume

G Undermined

ground

Undermining at a depth

greater than 200 m below

surface

Old undermined areas to a

depth of 200 m below surface

Mining within less than 200 m

of surface with total extraction

H Stability

(dolomite land) Possibly stable Potentially instable Known sinkholes and dolines

I Steep slopes 2-6 degrees < 2 degrees or 6-18 degrees > 18 degrees

J Unstable natural

slopes Low risk Intermediate risk High risk

K Seismic activity 10% probability of an event

less than 100 cm/s2 in 50 years

Mining-induced seismicity >

100 cm/s2 Natural seismicity > 100 cm/s2

L Flooding n/a Adjacent to known drainage or

channel with slope < 1%

Areas within drainage channel

or floodplain

RESIDENTIAL SITE CLASS DESIGNATIONS (SAICE, 1995)

TYPICAL FOUNDATION MATERIAL

CHARACTER OF FOUNDING MATERIAL

EXPECEDRANGE OF TOTAL SOIL

MOVEMENTS (mm)

ASSUMED DIFFERENTIAL

MOVEMENT (% OF TOTAL)

SITE CLASS

Rock (excluding mud rocks which

exhibit swelling to some depth) STABLE NEGLIGIBLE – R

Fine-grained soils with moderate

to very high plasticity (clays, silty

clays, clayey silts and sandy

clays)

EXPANSIVE SOILS

< 7.5

7.5 – 15

15 – 30

> 30

50%

50%

50%

50%

H

H1

H2

H3

Silty sands, sands, sandy and

gravelly soils

COMPRESSIBLE AND

POTENTIALLY COLLAPSIBLE

SOILS

< 5.0

5.0 – 10

> 10

75%

75%

75%

C

C1

C2

Fine-grained soils (clayey silts

and clayey sands of low

plasticity), sands, sandy and

gravelly soils

COMPRESSIBLE SOIL

< 10

10 – 20

> 20

50%

50%

50%

S

S1

S2

Contaminated soils

Controlled fill

Dolomitic areas

Land fill

Marshy areas

Mine waste fill

Mining subsidence

Reclaimed areas

Very soft silt / silty clays

Uncontrolled fill

VARIABLE VARIABLE – P



FOUNDATION DESIGN, BUILDING PROCEDURES AND PRECAUTIONARY MEASURES FOR SINGLE-STOREY RESIDENTIAL BUILDINGS FOUNDED ON EXPANSIVE SOIL HORIZONS (SAICE, 1995)

SITE CLASS

ESTIMATED TOTAL HEAVE

(mm) CONSTRUCTION TYPE FOUNDATION DESIGN AND BUILDING PROCEDURES

(Expected damage limited to Category 1)

H < 7.5 Normal

- Normal constructional (strip-footing or slab-on-the-ground

foundations).

- Site drainage and service/plumbing precautions recommended.

H1 7.5 – 15

Modified normal

- Lightly reinforced strip footings.

- Articulation joints at internal/external doors and openings.

- Light reinforcement in masonry.

- Site drainage and plumbing/service precautions.

Soil raft

- Remove all or part of expansive horizon to 1.0m beyond he

perimeter of the structure and replace with inert backfill,

compacted to 93% MOD AASHO density at –1% to +2% of

optimum moisture content.

- Normal construction with lightly reinforced strip footings and

light reinforcement in masonry if residual movements are <

7.mm, or construction type appropriate to residual

movements.


H2 15 – 30

Stiffened or cellular

raft

- Stiffened or cellular raft with articulation joints or lightly

reinforced masonry.


Piled construction

- Piled foundations with suspended floor slabs with or without

ground beams.

- Site drainage and plumbing/service precautions

Split construction

- Combination of reinforced brickwork/block work and full

movement joints.

- Suspended floors of fabric-reinforced ground slabs acting

independently from the structure.


Soil raft


light reinforcement in masonry if residual movements are < 7

mm, or construction type appropriate to residual movements.


H3 > 30

Stiffened or cellular

raft

- Stiffened or cellular raft with articulation joints or lightly

reinforced masonry.


Piled construction

- Piled foundations with suspended floor slabs with or without

ground beams.


Soil raft


light reinforcement in masonry if residual movements are < 7

mm, or construction type appropriate to residual movements.




FOUNDATION DESIGN, BUILDING PROCEDURES AND PRECAUTIONARY MEASURES FOR SINGLE-STOREY RESIDENTIAL BUILDINGS FOUNDED ON HORIZONS SUBJECT TO BOTH CONSOLIDATION AND COLLAPSE SETTLEMENT (SAICE, 1995)

SITE CLASS

ESTIMATED TOTAL

SETTLEMENT (mm)

CONSTRUCTION TYPE FOUNDATION DESIGN AND BUILDING PROCEDURES (Expected damage limited to Category 1)

C < 5 Normal


foundations).


C1 5 – 10

Modified normal

- Reinforced strip footings.

- Articulation joints at some internal/external doors.



- Foundation pressure not to exceed 50kPa.

Compaction of in-situ

soils below individual

footings

- Remove in-situ material below foundations to a depth and width

of 1.5 times the foundation width or to a competent horizon

and replace with material compacted o 93% MOD AASHTO

density at –1% to +2% of optimum moisture content.


light reinforcement in masonry.

Deep strip

foundations



Soil raft

- Remove in-situ material below foundations to 1.0m beyond

perimeter of building to a depth of 1.5 times the widest

foundation or to a competent horizon and replace with

material compacted o 93% MOD AASHTO density at –1% to

+2% of optimum moisture content.


light reinforcement in masonry

C2 > 10

Stiffened strip

footings, stiffened or

cellular raft

- Stiffened strip footings, stiffened or cellular raft with articulation

joints or solid lightly reinforced masonry.




Deep strip

foundations




Compaction of in-situ

soils below individual

footings

- Remove in-situ material below foundations to a depth and width

of 1.5 times the foundation width or to a competent horizon

and replace with material compacted o 93% MOD AASHTO

density at –1% to +2% of optimum moisture content.


light reinforcement in masonry.

Piled or pier

foundations

- Reinforced concrete ground beams or solid slabs on piled or pier

foundations.



Soil raft



foundation or to a competent horizon and replace with

material compacted to 93% MOD AASHTO density at -1% to

+2% of optimum moisture content.


light reinforcement in masonry



FOUNDATION DESIGN, BUILDING PROCEDURES AND PRECAUTIONARY MEASURES FOR SINGLE-STOREY RESIDENTIAL BUILDINGS FOUNDED ON HORIZONS SUBJECT TO CONSOLIDATION SETTLEMENT (SAICE, 1995)

SITE CLASS

ESTIMATED TOTAL

SETTLEMENT (mm)

CONSTRUCTION TYPE

FOUNDATION DESIGN AND BUILDING PROCEDURES (Expected damage limited to Category 1)

S 10 Normal


foundations).


S1 10 – 20

Modified normal

- Reinforced strip footings.

- Articulation joints at some internal/external doors.



- Foundation pressure not to exceed 50kPa.

Compaction of in-situ soils below

individual footings

- Remove in-situ material below foundations to a depth and width of

1.5 times the foundation width or to a competent horizon and

replace with material compacted to 93% MOD AASHTO density

at –1% to +2% of optimum moisture content.

- Normal construction with lightly reinforced strip footings and light

reinforcement in masonry.

Deep strip

foundations



Soil raft



foundation or to a competent horizon and replace with material

compacted o 93% MOD AASHTO density at –1% to +2% of



reinforcement in masonry

S2 > 20

Stiffened strip

footings, stiffened

or cellular raft

- Stiffened strip footings, stiffened or cellular raft with articulation

joints or solid lightly reinforced masonry.




Deep strip

foundations




Compaction of in-situ soils below

individual footings

- Remove in-situ material below foundations to a depth and width of

1.5 times the foundation width or to a competent horizon and

replace with material compacted o 93% MOD AASHTO density at

–1% to +2% of optimum moisture content.


reinforcement in masonry.

Piled or pier

foundations

- Reinforced concrete ground beams or solid slabs on piled or pier

foundations.



Soil raft



foundation or to a competent horizon and replace with material

compacted to 93% MOD AASHTO density at –1% to +2% of



reinforcement in masonry

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