Building Subsidence Associated With Cut-And-Cover Excavati…

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AIN SHAMS UNIVERSITY

FACULTY OF ENGINEERING

Vol. 37, No. 4, December 31, 2002

SCIENTIFIC BULLETIN

Received on : 10/10/2002

Accepted on : 24/12/2002

PP. : 55-71

Building Subsidence Associated with Cut-and-Cover

Excavations in Alluvial Soils

AHMED H. ABDEL-RAHMAN1 SAYED M. EL-SAYED

2

ABSTRACT

Assessment of building settlements associated with each stage of strutteddeep excavations has become an essential step in most of the projects. Reliable

prediction for the settlement comes by addressing all factors controlling its

development in a mathematical representation. Among these factors are the

subsurface soil condition, the foundation type and depth of the neighboringbuildings, the stages of excavation, and the overall stiffness of the retaining

system. This paper presents a case history in Egypt in which the settlements of

existing structures surrounding a deep excavation retained by strutted diaphragm

walls were monitored and the measured values were back-analyzed. The analysis

showed that building settlements during the different stages of deep excavationsare substantially influenced by the foundation depth of the proximate buildings

and its relation to the depth of excavation at any construction stage.

Key Words: Cut-and-cover; trenching, strutted excavation, settlement;

monitoring programs; piles, shallow foundations.

. . .

.

.1Assistant Professor, Civil Eng. Dept., Engineering Research Division, National Research Center of Egypt.2Assistant Professor, Structural Engineering Dept., Ain Shams University, Cairo, Egypt.


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1. INTRODUCTION

As a result of the urgent needs to improve the urban environment in Greater

Cairo, plans for environmental development call for relocating many services to

the underground space via engineered deep excavations. This approach has

increasingly become vital due to the scarcity of the ground space and the high costof lands. Cut-and-cover construction techniques employing diaphragm walls has

proved to be very successful in the construction of many underground projects inGreater Cairo such as basements, underground garages, tunnels, and subway

stations.

The geological formations encountered during the construction of deepexcavation projects in Egypt are typically alluvial soils with a shallow

groundwater table. These conditions are classified as problematic from the

geotechnical point of view, especially if the deep excavation is located near to

structurally sensitive buildings (El-Sohby and Mazen, 1985). Challenged with the

precarious geological conditions in Greater Cairo, geotechnical engineers are

often required to meet the restricted contractual provisions of the minimal loss of

support to existing foundations and limited deformations of buildings, streets, and

utilities surrounding the excavation.

Peck (1969b) provided the first comprehensive review of the factors that

control the deformations induced by deep excavations in alluvial soils. Although

his findings are now outdated, he explained that local subsurface conditions,

depth of excavation, and workmanship quality are the most distinguishing factors

affecting ground deformations near excavations.

Many researchers recommended settlement distributions associated withthe installation of diaphragm walls. Goldberg et al. (1976) reviewed 63 monitored

case histories of deep excavations in which they correlated the maximum

settlement to the soil type and the depth of excavation. Clough and O'Rourke

(1990) suggested settlement profiles in alluvial soils as shown in Fig. (1).

Recently, Bentler (1998) examined 17 case histories recorded from 1990 to 1998

and also provided recommendations for settlement troughs in alluvial soils. A

comparison between the recommended values of the maximum settlement with

respect to the maximum depth of excavation is given in Table (1).

Monitoring programs for deep excavations are not only used as a safetymeasure against distress of nearby buildings and buried utilities, but also can be

utilized to predict future performance of alike projects under similar geotechnicalformations (Peck, 1969a; El-Nahhas, 1992; Murray, 1990; Leca & Clough, 1994;

Thasnanipan et al., 1999). Settlements due to deep excavation projects in Greater

Cairo were monitored and reported by various researchers, e.g. El-Nahhas et al.

(1990) and Ahmed & Abd El-Salam, (1996). However, there is an escalating

necessity to address the building subsidence taken into considerations the

conditions of the nearby buildings. Attewell et al. (1986) reported that ground

deformations due to underground constructions could be influenced substantially


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by the configurations of the nearby buildings along with the subsurface soil

conditions.

The current research sheds a light on the effect of foundation type and its

depth on the settlements associated with deep excavations in alluvial soils. A case

history is presented where settlements of buildings with shallow and pilefoundations were monitored during a cut-and-cover excavation performed to

construct a basement of a multistory building in Giza, Egypt. The settlement wasmonitored during each stage of construction including diaphragm wall trenching,

and all steps of strutting and excavation until reaching the design level of

foundation. Back-analyses were performed on the monitored data to definesettlement troughs associated with strutted deep excavation in alluvial soil

conditions. The results are also compared with some of the widely used

settlement troughs.

2. SITE AND SUBSURFACE SOIL CONDITIONS

The project site is located in Dokki, Giza, Egypt away from the river Nile

by about 1.0 km. Giza is a part of the Greater Cairo area that extends along both

banks of the Nile south of the apex of the Delta. Generally, the geology of Giza is

characterized by tertiary sedimentary soils and rocks and quaternary soils, both

underlain by older basement rocks. The project area lies within the young alluvial

plain representing the lowland portion of the Nile Valley in the Greater Cairo area.

(Rushdi, 1989).

A geotechnical subsurface investigation program was performed including

the execution of 8 boreholes of 25m depth. The subsurface soil profile consistsgenerally from a top fill layer appeared from ground surface to a depth of 2.0 m,

followed by a silty sand layer up to a depth of 5.0 m. A layer of medium dense fine

to medium sand with some silt followed the silty sand layer to a depth of 11.0 m.

A dense to very dense graded sand layer followed the previous layer and extended

to the end of the boreholes at 25.0 m. The bottom sand layer occasionally

contained a percentage of fine gravel in the range of 5.0% to 15%. The results of

the SPT tests with depth are presented in Fig. (2). The groundwater is located at an

average depth of 2.00 m.

Five buildings, designated A, B, C, D and E, are located near to thediaphragm wall as shown in Fig. (3). Buildings (A), (B), and (C) are 12 to 14

stories, founded on piles of lengths ranging between 14.00 m and 16.00 m.Building (D) is a five story building and building (E) is a two-story building,

founded on shallow foundations at a depth of about 2.0 m to 3.0 m.

3. CONSTRUCTION SEQUENCE

A bottom-up construction method with two levels of temporary bracing

was adopted during excavation to construct the foundation and basement floors of

the multistory building. The contractor used a typical cast-in-situ diaphragm wallinstallation procedure using the mechanical grab bucket for excavation. The


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diaphragm wall was 21.0 m depth, and 0.60 m width. During the trenching phase,

the sides of the trench were stabilized by regulated and controlled bentonite

drilling fluid. The wall comprises 20 panels, as shown in Fig. (3), executed in the

sequence given in Table (2).

The natural groundwater level was required to be kept at its original leveloutside the excavation boundary to prevent any damage that might occur to

nearby buildings as a result of dewatering inside the excavation pit. Therefore, agrout plug, using cement and silica gel, was executed between levels (-18.00 m)

and (-21.00 m) after completion of all diaphragm wall panels. This is in order to

prevent bottom seepage towards the site, while dewatering from inside the pit.The subsequent phases of execution included the excavation of 9,100 cubic

meters of soil and the installation of lateral support for each panel to exclude the

use of walings. Most of the panels were supported using structural steel pipe struts

with outside diameters of 900 mm and a thickness of 9.0 mm. Some panels were

supported using tie-back anchors to provide sufficient space to move equipment

and soil from/to the pit. Fig. (4) demonstrates the different stages of construction.

A careful coordination between the mass excavation and installation of the

lateral bracing was accomplished to restrain the movements of the diaphragm

walls and safely maintain the sequence of activities. To achieve this goal, the site

was sectioned into 4 parts as shown in Fig. (3). Table (3) shows the synchronized

sequence of excavation performed for the four parts. Upon completion of the

excavation, at a depth of 10.8 m below ground surface, the concrete base mat was

constructed.

4. MONITORING PROGRAM

Developing of an instrumentation system begins with the definition of the

objectives of the program and proceeds through a comprehensive series of steps

that include all aspects of the required system (Dunnicliff, 1988). The program

concentrated on settlement measurements of the buildings surrounding the

excavation. This concept is compatible with the common criteria to assess

damage of buildings due to excavation, which are usually based on settlements

and differential settlements (Boscardin and Cording, 1989; Ou et al., 1993; Boone,

1997; Seok, 2001).Optical surveying methods, with accuracy of 0.1 mm, were used to monitor

the magnitude and rate of vertical deformations of 31 settlement points during theperiod from July 5, 2001 to March 24, 2002. The locations of the monitored points

were determined based on predicted behavior of the site to elude any geotechnical

and structural concerns. The layout of the instrumentation plan tend to provide

more monitoring data about building "A", as shown in Fig. (3), because the wall is

just 1.80 m from this building which means that its piles are closer to the

diaphragm wall boundary.


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5. OBSERVED SETTLEMENT

The compiled data were evaluated to assess building settlements associated

with the diaphragm wall installation and deep excavation for the basement.

Results of the monitored settlement versus time, starting from installation of the

diaphragm wall panels up to the excavation to the foundation level, are presentedin Fig. (5). Table (4) shows the total settlement of different points due to

diaphragm wall installation only (stage 1), and due to the complete site excavation(end to stage 4) along with the settlement increment between the two stages. The

following sections discuss the observed settlement during the installation of the

diaphragm wall and throughout the execution of the strutted deep excavation.

5.1 Settlement Due to Stage 1-Diaphragm Wall Installation

The plotted records indicate that buildings subsidence increased for all

points due to the trenching for the wall panels, which ended in mid of August

2001. A maximum settlement of 8.5 mm was recorded during trenching at the

location of point 15 (Building A on pile foundations), while a null settlement

was recorded at point 30 (Building C on pile foundations also). That could be

related to the fact that point 15 is located very close to the diaphragm wall, while

point 30 is located more than 40 m from the corner of the construction site. Points

20, 21, and 26 went through a minor upward movement of 0.6 mm between

August 2, 2001 and August 6, 2001, while no activities on site was going during

that period.

Figures 6 and 7 show plots of all settlement values with distances away

from the wall. It can be seen that points of the same distance from the wall haddiverse settlement values. That might be attributed to reasons related to the

sequence of panel construction of the wall, the change in the subsurface soil

conditions underneath each building, or due to each building stiffness and rigidity

(El-Sayed and Abdel-Rahman, 2002). But, generally the average settlements of

all buildings can be expressed with one envelope regardless of their foundation

type. That envelope was recommended by (Abdel-Rahman and El-Sayed, 2002)

to be with a maximum settlement equivalent to 0.045% of the diaphragm wall

trench depth, while its extent away from the wall reaches to twice the same trench

depth. Analysis of building settlement during the installation of the diaphragmwall of this project were reported and discussed in details by Abdel-Rahman and

El-Sayed (2002). The proposed distribution of the settlement trough wasexpressed by the following equation:

6

max2

2

=

d

xdSS trenchingtrenching .(1)

Where, trenchingS is the settlement at a distance x from the trench

boundary, trenchingSmax is the maximum settlement at the trench location, and d isthe trench depth.


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5.2 Settlement Due to Stages 2 to 4-Excavation Inside the Pit

During the excavation inside the pit, points (1) and (2) of building A,

founded on pile foundation, experienced only insignificant values of heave (0.5

mm max.). Some other points did not have any change in their settlements, e.g.points (27), (28), (29), and (30) of buildings B, and C founded on pile

foundations. However, buildings founded on shallow foundations suffered from

high additional settlements due to the execution of stages 2 to 4 (maximum

settlement increment of about 11.0 mm with an average increment at distance 3.2

m from the wall equal to 8.4 mm). Settlement of points on deep foundations

showed much less settlement increments (max. 4.7 mm with an average

increment at distance 2.5 m from the wall equal to 1.78 mm).

It is also worth noting that only points 18 and 19 of building B indicated

the maximum settlement values monitored for buildings on deep foundation (4.7mm), and generally didnt follow the pattern of behavior of the rest of their similar25 settlement points, as shown in Fig. (6-b). That is although building B is

located a bit away from the excavation boundary than building A. This pattern

could be related to the relatively short distance between the depth of its pile tip(14.0 m from ground surface, as reported or could be less when executed) and the

maximum depth of excavation inside the pit (10.80 m). Therefore, points (18) and

(19) located on building B were excluded in developing a settlement envelope

for buildings on pile foundations due to deep excavation as shown in Figure (6-b).

The settlement plots of buildings on pile foundation represents a case of deepexcavation of depth less than the pile foundation depth.

Generally, the settlement of buildings on deep foundation, during

executing stages 2 to 4, were much smaller than that occurred in stage 1

(diaphragm wall installation). On the contrary, buildings on shallow foundations

generally underwent considerable settlements with higher rates. This is because

the maximum depth of excavation was 11.5 m, which is much deeper than the

shallow foundation depth but shallower than the pile foundation depths of

buildings A, B, and C. In other words, the settlement gets generated withinfluencing values only when excavation occurs near to, or below the foundation

level of buildings. That argument could be supported by the fact that building B,

that is founded on pile foundation, showed a difference in behavior when the

excavation occurred near to its foundation level (pile tip).

6. ANALYSIS OF OBSERVATIONS

Fig. (6) and Fig. (7) show the spatial distribution of the settlement field for

building on deep foundations and on shallow foundations during the different

stages of construction.

The settlement envelope can be mathematically described by adding an

additional component (Spit excav) to the trenching settlement (Strenching); i.e.,


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excavpittrnchingtotal SSS += .(2)

The settlement component due to pit excavation only can be described by

the following equation:

=

2

2

max )(2exp HK

x

SS

excavpitexcavpit

.(3)

Where, excavpitS is the settlement at a distance x from the trench,

excavpitSmax is the maximum settlement at the wall location, K is a dimensionless

factor and H is the final depth of pit excavation. The anticipated distribution is

similar to that proposed by Peck (1969a) to describe the settlements associated

with shielded tunneling. Parameters of the previous equation were determined

using best fitting analysis on the measured values. The results of curve fitting are

summarized in Table (5).

Maximum settlements of 9.5 mm and 3.0 mm were extrapolated for thebuildings on pile foundations due to wall installation and pit excavation,respectively. This indicates that most of the settlement occurred during the

trenching stage (about 76%). The maximum settlements of buildings D and E,

on shallow foundations, were 9.5 mm and 12 mm due to wall installation and pit

excavation, respectively. On the contrary to pile-founded buildings, most of the

settlement (about 56%) is attributed to pit excavation.

The settlement component due to pit excavation can be expressed as 0.03%

H, and 0.11% H for the case of pile foundation and shallow foundation,

respectively. However, the maximum total settlement is about 0.20% and 0.12%

of the excavation depth for the cases of shallow, and pile foundations,

respectively.

It can be seen from Figs (6-b and 7-b) that the widths of the settlement

trough, in case of pit excavation, are about 41 m (3.8 H), and 24 m (2.2 H) for the

cases of pile foundations and shallow foundations, respectively. However, in bothcases, the final width of the settlement trough can be practically set to be 3.5 of the

pit excavation depth (~38.0 m) as shown in Figs (6-c and 7-c).

The maximum angular inclinations of settlements are 1/1600 and 1/700 for

deep foundations and shallow foundations, respectively. This points out that no

structural distress would occur as verified by the dilapidation survey.

7. SUMMARY AND CONCLUSION

The effect of the foundation type and depth on the settlement fields of

buildings surrounding deep excavations was studied based on analyses performed

on the results acquired from a case history carried out in alluvial soils. The

presented case history comprised inclusive settlement monitoring during the

different stages of construction including diaphragm wall trenching and pitexcavation. The compiled data demonstrates that wall construction stage

triggered most of the settlement occurred for pile-founded buildings while


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excavation stage produced most of the settlement for buildings on shallow

foundations.

Based on the analysis performed on the data, the extent of the settlement

troughs were found to reach up to a distance equivalent to 3.5 of the depth of

excavation in alluvial soils. The maximum settlement at a boundary of struttedexcavation was found to be in the range of 0.20% of the deep excavation depth.

That settlement is generated only if the depth of deep excavations goes enoughbelow the foundation depth of the proximate building. On the other hand, the

maximum settlement due to diaphragm wall trenching was estimated to be

equivalent to 0.045% of the diaphragm wall trench depth. The total settlementtrough generated due to cut-and-cover excavations utilizing diaphragm walls will

be the summation of both components; due to diaphragm wall trenching and due

to strutted deep excavation.

8. REFERENCES

1. Abdel-Rahman, A. H. and El-Sayed, S. M., 2002, "Settlement TroughAssociated with Diaphragm Wall Construction in Greater Cairo", the Journal

of the Egyptian Geotechnical Society.

2. Ahmed, A. A. and Abd El-Salam, N., 1996, "In-situ Performance of SubwayStations in Cairo", Seventh International Colloquium on Structural and

Geotechnical Engineering, Ain Shams University, Cairo, Egypt, Vol. 1, pp.

447-460

3. Attewell, P., Yeates, J. and Selby, A., 1986, "Soil Movements Induced byTunnelling and Their Effects on Pipielines and Structures", Blackie & SonsLtd., Glasgow.

4. Bentler, D. J., 1998, Finite Element Analysis of Deep Excavations, Ph.D.Thesis, Virginia Polytechnic Institute and State University, Blacksburg,

Virginia.

5. Boone, S.J., 1997, "Ground-Movement-Related Building Damage", Journal ofGeotechnical Engineering, ASCE, Vol. 122, No. 11, pp. 886-896.

6. Boscardin, M.D. and Cording, E.J., 1989, "Building Response toExcavation-induced Settlement", Journal of Geotechnical Engineering, ASCE,

Vol. 115, No. 1, pp. 1-21.7. Clough, G. and O'Rourke, T., 1990, "Construction Induced Movements of

Insitu Walls", Design and Performance of Earth Retaining Structures, ASCEGeotechnical Special Publications 25, pp. 439-470.

8. Dunnicliff, J., 1988, "Geotechnical Instrumentation for Monitoring FieldPerformance", John Wiley and Sons, Inc., New York.

9. El-Nahhas, F.M., 1992, "Construction Monitoring of Urban Tunnels andSubway Stations", Tunneling and Underground Space Technology, Pergamon

Press Ltd., Vol. 7, No. 4, pp. 425-439

10. El-Nahhas, F.M., Eisenstein, Z., and Shalaby, A., 1990, "In-situ Behaviour ofOrabi Subway Stations during Construction", Proc. of first Alexandria


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Conference on Structural and Geotechnical Engineering, Alexandria, Egypt,

Vol. 1, pp. 189-198

11. El-Sayed, S. M. and Abdel-Rahman, A. H., 2002," Spatial Stress-DeformationAnalysis for Installation of a Diaphragm Wall", the scientific bulletin of The

Faculty of Engineering, Ain Shams University.12. El-Sohby, M.A. and Mazen, O., 1985, Geology aspects in Cairo SubsurfaceDevelopment, Proc. of the eleventh ICSMFE, San Francisco, Vol. 3, pp.2401-2405.

13. Goldberg, D.T., Jaworski, W.E. and Gordon, M.D., 1976, "Lateral SupportSystems and Underpinning", Report FHWA-RD-75-128, Vol. 1, FederalHighway Administration, Washington D.C., p. 312

14. Leca, E. and Clough, G., 1994, "Construction and Instrumentation ofUnderground Excavations", XIII ICSMFE, New Delhi, India, pp. 303-309

15. Murray, R. T., 1990, "Rapporteur's paper", Geotechnical Instrumentation inPractice, Proceedings of the conference of geotechnical instrumentation in civil

engineering projects, Thomas Telford, London, England, pp. 75-85.

16. Ou, C.Y., Hsieh, P.G and Chiou, D.C., 1993, Characteristics of GroundSurface Settlement during Excavation, Canadian Geotechnical Journal, 30, pp.

758-767.

17. Peck, R. B., 1969a, State-of-the-art, "Deep Excavation and Tunneling in SoftGround", Proceedings of the Seventh International Conference on Soil

Mechanics and Foundation Engineering, Universidad Nacional Autonoma de

Mexico Instituto de Ingenira, Mexico City, Mexico, Vol. 3, pp. 225-290

18. Peck, R.B, 1969b, "Advantages and Limitations of the Observational Methodin Applied Soil Mechanics. Geotechnique, Vol. 19, No. 2, pp. 171-187.

19. Rushdi, S., 1989, "The Geology of Egypt", Balkema, Rotterdam.20. Seok, J.W., 2001, Settlement behavior of ground and structure adjacent to

excavation site, Ph.D. thesis, School of Civil, Urban and Geosystem

Engineering, Seoul National University, Seoul, Korea.

21. Skempton, A. W. and MacDonald, D. H., 1956, "The Allowable Settlements ofBuildings", Proc., Inst. of Civil Engrs., Part III, The Institution of Civil Engrs.,

London, pp. 727-768.

22. Thasnanipan, N., Maung, A. W., Tanseng, P. and Teparaksa, W., 1999,Behavior and Performance of Diaphragm Walls under Unbalanced Lateral

Loading along the Chao Phraya River, Field Measurements in Geomechanics,Leung, Tan & Phoon (eds), Balkema, Rotterdam, pp. 267-272


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Table (1) Estimated maximum settlement/depth of excavation adjusted to deep

excavations

Researcher(s)sands, gravels and very

stiff to hard clays

soft to stiff clays

Goldberg et al. (1976) 0.171% 1.22%

Clough and O'Rourke (1990) 0.30%

Bentler (1998) 0.22% 0.545%

Table (2): Progression of panel executions

PanelDate of

execution

Length

(m)Panel

Date of

execution

Length

(m)

1 June 6, 2001 5.90 11 June 24, 2001 2.70

2 August 13, 2001 5.90 12 June 25, 2001 6.133 June 9, 2001 6.54 13 June 26, 2001 6.72

4 June 18, 2001 6.54 14 July 2, 2001 5.86

5 June 20, 2001 6.13 15 June 28, 2001 6.54

6 June 11, 2001 6.72 16 July 4, 2001 6.13

7 June 16, 2001 5.86 17 July 7, 2001 6.54

8 June 23, 2001 6.13 18 July 8, 2001 2.70

9 June 21, 2001 6.13 19 July 11, 2001 6.72

10 June 10, 2001 6.13 20 July 10, 2001 6.72

Table (3): Progression of pit executions

Stages Stage (1) Stage (2) Stage (3) Stage (4) Stage (5)

Part (I)From Nov. 4,

2001 to Nov. 13,2001

From Nov. 18,2001 to Dec. 11,

2001

From Dec. 11,2001 to Jan. 10,

2002

Part (II)From Nov. 19,

2001 to Dec. 10,2001

From Dec. 12,2001 to Dec. 30,

2001

FromJan.2,2002 toJan. 9, 2002

Part (III)From Jan. 12,

2002 to Jan. 18,2002

From Jan. 19, toJan. 20, 2002

From Jan. 21,2002 to Feb. 3,

2002

Part (IV)

From June 6,2001 to

August 13,

2001

From

September 1,

2001 toOctober 15,

2001From Nov.20,

2001 to Nov. 23,2001

From Nov. 24,2001 to Dec. 10,

2001

From Dec. 20,2001 to Feb. 1,

2002


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Table (4) Settlement of different points

Point

settlement

due to

trenching

only (mm)

settlement

due to pit

excavation

only (mm)

Total

settlement

(mm)

Point

settlement

due to

trenching

only (mm)

settlement

due to pit

excavation

only (mm)

Total

settlement

(mm)

1 1.1 -0.4 0.7 17 8.6 2.4 112 0.7 -0.5 0.2 18 8 4.3 12.3

3 0.9 0.3 1.2 19 7.8 4.7 12.5

4 1.3 1.2 2.5 20 2.5 1.3 3.8

5 1.1 1.2 2.3 21 2 2.5 4.5

6 2 1.3 3.3 22 6 9.1 15.1

7 4 -0.2 3.8 23 6.8 11 17.8

8 5.3 0.5 5.8 24 0.5 0.7 1.2

9 5.3 0.7 6 25 6.5 7.4 13.9

10 6.5 2.2 8.7 26 5.8 6 11.811 3.4 1.1 4.5 27 1.1 0 1.1

12 7.5 0 7.5 28 0.3 0 0.3

13 8.5 0.7 9.2 29 0.4 0 0.4

14 8.6 1.4 10 30 0 0 0

15 8.6 1.4 10 31 0.4 2.4 2.8

16 8.4 1.9 10.3

Table (5) Parameters of the Pit excavation component

=

2

2

max )(2exp HK

x

SS

excavpitexcavpit

Buildings.

max

excpitS K Trough width

A, B & C

(on pile foundations)0.03% H 1.25 3.8 H

D & E

(on shallow foundations)0.11% H 0.75 2.2 H

Table (6) Comparison between measurements and different settlement criteria

Buildings

% Max. Final

settlement/ depth of

excavation

Final Trough

width/depth of

excavation

A, B & C

(on pile foundations)0.12 3.5

D & E

(on shallow foundations)0.20 3.5

Goldberg et al. (1976) 0.171 -

Clough and O'Rourke (1990) 0.30 2

Bentler (1998) 0.22 -


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Fig. (1): Normalized settlement profiles recommended for the estimation of

settlement adjacent to braced excavation (after Clough and O'Rourke, 1990)

0

5

10

15

20

25

30

35

40

0 5 10 15 20 25 30 35 40 45 50

SPT (NF/ft)

Depth(m)

FILL

SILT-SAND

FINE SAND,

SOME SILT

GRADED

SAND,

SOME

GRAVEL

VeryLoose

Loose

Medium Dense Dense to very dense

Fig. (2) Stratification and SPT data

0

0.5

1.0

0.50 1.0 1.5 2.0

v/vm

d/H

Settlement Envelope

vm

v

(a) Sands

0

0.5

1.0

0.50 1.0 1.5 2.0

v/vm

d/H

Settlement Envelopevm

v

(b) Stiff to Very Hard Clays

2.5 3.0

0

0.5

1.0

0.50 1.0 1.5 2.0

v/vm

d/H

Settlement Envelope

(c) Soft to Medium Clays

0.75


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Fig.(3) Layout of the site and the settlement monitoring system

Key


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Fig.(4) Stages of construction


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-10

-8

-6

-4

-2

0

1-6-01

1-7-01

1-8-01

1-9-01

1-10-01

1-11-01

1-12-01

1-1-02

1-2-02

1-3-02

1-4-02

DATE

Settlement(mm)

Point (1)

Point (7)

Point (12)

-10

-8

-6

-4

-2

0

1-6-01

1-7-01

1-8-01

1-9-01

1-10-01

1-11-01

1-12-01

1-1-02

1-2-02

1-3-02

1-4-02

DATE

Settlement(mm)

Point (2)

Point (8)

Point (13)

-12

-10

-8

-6

-4

-2

0

1-6-01

1-7-01

1-8-01

1-9-01

1-10-01

1-11-01

1-12-01

1-1-02

1-2-02

1-3-02

1-4-02

DATE

Settlement(mm)

Point (3)

Point (9)

Point (14)

-12

-10

-8

-6

-4

-2

0

1-6-01

1-7-01

1-8-01

1-9-01

1-10-01

1-11-01

1-12-01

1-1-02

1-2-02

1-3-02

1-4-02

DATE

Settlement(mm)

Point (4)

Point (10)

Point (15)

-12

-10

-8

-6

-4

-2

0

1-6-01

1-7-01

1-8-01

1-9-01

1-10-01

1-11-01

1-12-01

1-1-02

1-2-02

1-3-02

1-4-02

DATE

Settlement(mm)

Point (5)

Point (16)

-12

-10

-8

-6

-4

-2

0

1-6-01

1-7-01

1-8-01

1-9-01

1-10-01

1-11-01

1-12-01

1-1-02

1-2-02

1-3-02

1-4-02

DATE

Settlement(mm)

Point (6)

Point (11)

Point (17)

-14

-12

-10

-8

-6

-4

-2

0

1-6-01

1-7-01

1-8-01

1-9-01

1-10-01

1-11-01

1-12-01

1-1-02

1-2-02

1-3-02

1-4-02

DATE

Settlement(mm)

Point (27)

Point (18)

-12.5

-14

-12

-10

-8

-6

-4

-2

0

1-6-01

1-7-01

1-8-01

1-9-01

1-10-01

1-11-01

1-12-01

1-1-02

1-2-02

1-3-02

1-4-02

DATE

Settlement(mm

)

Point (28)

Point (19)

-10

-8

-6

-4

-2

0

1-6-01

1-7-01

1-8-01

1-9-01

1-10-01

1-11-01

1-12-01

1-1-02

1-2-02

1-3-02

1-4-02

DATE

Settlement(mm)

Point (30)

Point (21)

-10

-8

-6

-4

-2

0

1-6-01

1-7-01

1-8-01

1-9-01

1-10-01

1-11-01

1-12-01

1-1-02

1-2-02

1-3-02

1-4-02

DATE

Settlement(mm)

Point (29)

Point (20)

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

1-6-01

1-7-01

1-8-01

1-9-01

1-10-01

1-11-01

1-12-01

1-1-02

1-2-02

1-3-02

1-4-02

DATE

Settlement(mm)

Point (24)

Point (22)

Point (23)

-16

-14

-12

-10

-8

-6

-4

-2

0

1-6-01

1-7-01

1-8-01

1-9-01

1-10-01

1-11-01

1-12-01

1-1-02

1-2-02

1-3-02

1-4-02

DATE

Settlement(mm)

Point (31)

Point (26)

Point (25)

Fig. (5): Time-settlement relations for the monitored points


17/18

0

2

4

6

8

10

12

0 5 10 15 20 25 30 35 40 45 50 55 60

Distance (m)

Trenchingsettlement(mm)

0

1

2

3

4

5

6

0 5 10 15 20 25 30 35 40 45 50 55 60Distance (m)

Settlementduetopitexcavation(mm)

0

2

4

6

8

10

12

14

16

18

20

22

24

26

0 5 10 15 20 25 30 35 40 45 50 55 60

Distance (m)

Totalsettlement(mm)

Settlement after trenching

Envelope of settlement after trenching (after Abdel-Rahman & El-Sayed, 2002)

Settlement after pit excavation

Envelope for total settlment after excavation inside the site

Fig. (6): Settlement envelopes for buildings on pile

foundations A, B & C: (a) settlement due to trenching only

(b) settlement due to pit excavation only; (c) total settlement

(a)

(b)

(c)1600

1

Trenchingsettlement(mm

)

Settlementdueto

itexcavation(mm)

Totalsettleme

nt(mm)


18/18

0

2

4

6

8

10

12

0 5 10 15 20 25 30 35 40 45 50 55 60

Distance (m)

Trenchingsettlement(m

m)

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

0 5 10 15 20 25 30 35 40 45 50 55 60

Distance (m)

Settlementduetopitexcavation(mm)

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

0 5 10 15 20 25 30 35 40 45 50 55 60

Distance (m)

TotalSe

ttlement(mm)

Settlement after trenching

Envelope of settlement after trenching (after Abdel-Rahman & El-Sayed, 2002)

Settlement after excavation inside the site

Envelope for total settlment after excavation inside the site

Fig. (7): Settlement envelopes for buildings on shallow

foundations D & E: (a) settlement due to trenching only

(b) settlement due to pit excavation only; (c) total settlement

(a)

(b)

(c)760

1

Trenchingsettlement(mm)

Settle

mentdueto

itexcavation(mm)

Totalsettlemen(

mm)

Building Subsidence Associated With Cut-And-Cover Excavati…

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