STATE-OF-THE-ART REPORT: EFORMATIONS ASSOCIATED WITH DEEP EXCAVATION AND THEIR EFFECTS ON NEARBY...

Sayed Mohamed El-Sayed Ahmed

April, 2014

STATE-OF-THE-ART REPORT: DEFORMATIONS ASSOCIATED WITH DEEP EXCAVATION AND

THEIR EFFECTS ON NEARBY STRUCTURES

Ain Shams University

Faculty of Engineering

Structural Engineering Department

Geotechnical Engineering Group

SayedTypewritten TextCitation: Ahmed S.A. (2014) "State-of-the-Art Report: Deformations Associated with Deep Excavation and Their Effects on Nearby Structures," Ain Shams University, Faculty of Engineering, Structural Engineering Dept. DOI: 10.13140/RG.2.1.3966.9284.

2

CONTENTS 1. INTRODUCTION ................................................................................................................... 9

2. FACTORS AFFECTING EXCAVATION DEFORMATIONS ........................................... 14

2.1. Soil Type ........................................................................................................................ 15

2.2. Wall Stiffness and Excavation Stability ......................................................................... 15

2.3. Overconsolidation (OCR) and At-Rest Earth Pressure Coefficient (Ko) ....................... 22

2.4. Groundwater Conditions and Control Measures ............................................................ 23

2.5. Strut/Tie-back Prestressing ............................................................................................ 28

2.6. Construction Sequence ................................................................................................... 30

2.7. Wall Lateral Deformation Patterns ................................................................................ 32

2.7.1. Settlement pattern associated with the wall cantilever deformation mode ............. 35

2.7.2. Settlement pattern associated with the wall bulging deformation mode ................ 37

2.8. Time-Dependent Effects ................................................................................................ 39

2.9. Excavation Geometry and Three-Dimensional Effects .................................................. 39

2.9.1. Excavation dimensions and depth to firm layers .................................................... 39

2.9.2. Corner effect ........................................................................................................... 41

2.9.3. Parallel distribution ................................................................................................. 42

2.10. Wall Installation Effect ............................................................................................... 43

2.11. Building Stiffness and Weight .................................................................................... 49

2.12. Wall-Soil Interface ..................................................................................................... 51

2.13. Workmanship.............................................................................................................. 52

3. EMPIRICAL AND SEMI- EMPIRICAL METHODS ......................................................... 55

4. NUMERICAL MODELING ................................................................................................. 73

4.1. Beam-Column on Elastic Winkler Springs .................................................................... 73

4.2. The Finite Elements ....................................................................................................... 81

4.2.1. Constitutive soil modeling ...................................................................................... 83

4.2.2. Simulation of excavation and construction sequence ............................................. 84

4.2.3. Interface modeling. ................................................................................................. 86

4.2.4. Two-dimensional versus three-dimensional analyses ............................................. 87

4.2.5. Modeling of structures affected by excavations ..................................................... 87

5. ANALYTICAL APPROACH ............................................................................................... 88

6. ARTIFICIAL NEUTRAL NETWORKS (ANNS)................................................................ 90

7. PHYSICAL MODELING USING CENTRIFUGE .............................................................. 93

8. OBSERVATIONAL METHOD AND MONITORING ....................................................... 97

3

9. INSTRUMENTATION AND MONITORING..................................................................... 99

9.1. Deformation Instrumentations...................................................................................... 102

9.2. Stress Measurements .................................................................................................... 105

9.2.1. Piezometers ........................................................................................................... 105

9.2.2. Strain Gauges ........................................................................................................ 107

9.3. Real Time Monitoring .................................................................................................. 108

9.3.1. Robotic total stations (RTS).................................................................................. 108

9.3.2. Three-dimensional Laser scanning ....................................................................... 109

9.4. Trigger Levels for Monitoring ..................................................................................... 110

9.5. Monitoring Experience in Egyptian Deep Excavation Projects ................................... 111

10. BUILDING DAMAGE CRITERIA ................................................................................ 114

10.1. Superstructure Damage criteria ................................................................................ 114

10.1.1. The maximum angular distortion () criterion .................................................. 117

10.1.2. The maximum deflection ratio (/L) criterion .................................................. 118

10.1.3. The limiting tensile strain criterion ................................................................... 118

10.1.4. The crack width criterion .................................................................................. 126

10.1.5. The maximum settlement (Smax) maximum rotation (max) criterion ............. 128

10.1.6. The Damage Potential Index (DPI( criterion .................................................... 128

10.2. Assessment of the Induced Building Damage .......................................................... 129

10.2.1. Primary assessment ........................................................................................... 129

10.2.2. Second stage assessment ................................................................................... 130

10.2.3. Detailed assessment........................................................................................... 130

10.3. Features Affecting Structural Damage ..................................................................... 131

10.3.1. Ratio of the buildings Young modulus to its shear modulus (E/G) ................. 131

10.3.2. Grade beams ...................................................................................................... 133

10.3.3. Building-Soil Relative Stiffness ........................................................................ 133

10.4. Damage Assessment for Deep Foundations ............................................................. 136

10.5. Design Deep Excavations for Admissible Structural Deformations ........................ 140

11. SURVEY OF DAMAGE DUE TO INDUCED GROUND MOVEMENT .................... 141

12. RISK MANAGEMENT AND MITIGATIONS .............................................................. 143

13. SUMMARY OF THE PRESENTED WORKS ............................................................... 148

14. REFERENCES ................................................................................................................ 152

4

List of Figures FIGURE 1. GROUND AND BUILDING DEFORMATIONS INDUCED BY A DEEP EXCAVATION (HSIAO, 2007) ................................................ 9 FIGURE 2. FAILURE OF A BUILDING IN CHINA IN 2009 THAT WAS INITIATED BY A NEARBY DEEP EXCAVATION ....................................... 10 FIGURE 3. FAILURE OF A DEEP EXCAVATION ADJACENT TO NICOLL HIGHWAY, SINGAPORE (LEE, 2008) ............................................. 10 FIGURE 4. A MASONRY WALL SUFFERED FROM SEVERE CRACKING DUE TO GROUND DEFORMATIONS (VATOVEC ET AL., 2010) ............... 11 FIGURE 5. TYPICAL FORMATIONS IN THE GREATER CAIRO AREA (EL-SOHBY AND MAZEN, 1985) ...................................................... 12 FIGURE 6. EFFECT OF THE SOIL TYPE ON THE SETTLEMENTS INDUCED BY DEEP EXCAVATION (PECK, 1969A) ........................................ 15 FIGURE 7. EFFECT OF WALL STIFFNESS AND SOIL STABILITY NUMBER ON THE WALL DEFORMATIONS IN CLAYS (GOLDBERG ET AL., 1976) .. 16 FIGURE 8. EFFECT OF THE BASAL HEAVE STABILITY ON THE WALL DEFORMATIONS INDUCED BY DEEP EXCAVATIONS IN CLAYS (MANA &

CLOUGH, 1981) ..................................................................................................................................................... 16 FIGURE 9. EFFECT OF THE BASAL HEAVE STABILITY AND THE SYSTEM STIFFNESS ON THE WALL DEFORMATIONS INDUCED BY DEEP

EXCAVATIONS IN CLAYS (CLOUGH AT AL., 1989) ........................................................................................................... 17 FIGURE 10. NORMALIZED FIELD MEASUREMENTS OF THE LATERAL DEFORMATIONS AGAINST CLOUGH & OROURKES (1990) SYSTEM

STIFFNESS AND BASAL HEAVE FACTOR OF SAFETY FOR CASES WITH LOW FACTOR OF SAFETY (FOS3) (LONG, 2001) .................. 19 FIGURE 12. NORMALIZED FIELD MEASUREMENTS OF THE LATERAL DEFORMATIONS AGAINST CLOUGH & OROURKES (1990) SYSTEM

STIFFNESS AND BASAL HEAVE FACTOR OF SAFETY FOR SOFT CLAY (MOORMANN, 2004)......................................................... 20 FIGURE 13. NORMALIZED FIELD MEASUREMENTS OF THE LATERAL DEFORMATIONS AGAINST CLOUGH & OROURKES (1990) SYSTEM

STIFFNESS AND BASAL HEAVE FACTOR OF SAFETY FOR STIFF CLAY (MOORMANN, 2004) ........................................................ 20 FIGURE 14. NORMALIZED LATERAL WALL MOVEMENTS VS. RELATIVE STIFFNESS RATIO, R, FOR DEEP EXCAVATIONS IN COHESIVE SOILS

(ZAPATA-MEDINA, 2007). ....................................................................................................................................... 21 FIGURE 15. EFFECT OF THE FACTOR OF SAFETY ON THE SETTLEMENT TROUGH WIDTH (MANA AND CLOUGH, 1981) ............................ 22 FIGURE 16. CONTOURS OF STRESS LEVEL AT AN EXCAVATION DEPTH OF 13.26M: (A) KO=2; (B) KO=0.5 (POTTS & FOURIE, 1984) ....... 22 FIGURE 17. GROUNDWATER FLOW PATTERNS ENCOUNTERED IN DEEP EXCAVATIONS (CLOUGH & OROURKE, 1990) .......................... 23 FIGURE 18. INFLUENCE OF THE DEWATERING WORKS ON THE GROUND SETTLEMENT ..................................................... 24 FIGURE 19. GROUNDWATER CONTROL MEASURES FOR BRACED EXCAVATION (PULLER, 2003) ......................................................... 24 FIGURE 20. COLLAPSE OF CITY ARCHIVE BUILDING IN COLOGNE (GERMANY) DUE SOIL PIPING INDUCED BY DEWATERING (ROWSON, 2009)

........................................................................................................................................................................... 25 FIGURE 21. THE COLLAPSED CITY ARCHIVE BUILDING IN COLOGNE (GERMANY) (ROWSON, 2009) .................................................. 26 FIGURE 22. DAMAGE DUE TO SUBSIDENCE ALONG AN UNDERGROUND STATION OF THE NORTH-SOUTH TRAIN LINE IN AMSTERDAM (VAN

BAARS, 2011). ...................................................................................................................................................... 26 FIGURE 23. LEAKAGE AND DAMAGE AT THE BUILDING PIT IN MIDDELBURG, THE NETHERLAND (VAN BAARS, 2011) ............................ 27 FIGURE 24. FAILURE OF A DIAPHRAGM WALL IN THE INFINITY TOWER IN DUBAI IN 2007. THE CHRONOLOGICAL SEQUENCE OF EVENTS IS

(A) TO (D) .............................................................................................................................................................. 27 FIGURE 25. SCHEMES FOR GROUNDWATER CONTROL IN A DEEP EXCAVATION (EL-NAHHAS, 2006). ................................................. 28 FIGURE 26. THE EFFECT OF PRESTRESSING ON THE WALL DEFORMATIONS (CLOUGH, 1975) ............................................................ 29 FIGURE 27. THE EFFECT OF THE STRUT STIFFNESS ON THE MAXIMUM LATERAL DEFORMATION OF THE WALL AND THE MAXIMUM

SETTLEMENT (MANNA & CLOUGH, 1981) ................................................................................................................... 29 FIGURE 28. CONSTRUCTION PROCEDURE STEPS FOR THE GREATER CAIRO METRO - LINE 1 (EL-NAHHAS ET AL., 1988) ........................ 30 FIGURE 29. ROD EL-FARAG STATION (AHMED AND ABD EL-SALAM, 1996) ................................................................................ 31 FIGURE 30. SETTLEMENT PATTERNS ASSOCIATED WITH DIFFERENT WALL DEFORMATION MODES (GOLDBERG ET AL. 1976). .................. 32 FIGURE 31. MODES OF DEFORMATION OF THE WALL (CLOUGH AND OROURKE, 1990) ................................................................. 33 FIGURE 32. LATERAL AND VERTICAL DISPLACEMENT PATTERNS: CONCAVE ON LEFT, SPANDREL ON RIGHT (BOONE 2003; BOONE &

WESTLAND, 2005). ................................................................................................................................................ 33 FIGURE 33. THE RATIO BETWEEN THE MAXIMUM HORIZONTAL TO VERTICAL DISPLACEMENT AS A FUNCTION OF THE COEFFICIENT OF

DEFORMATIONS (OROURKE, 1981) .......................................................................................................................... 34 FIGURE 34. THE RATIO BETWEEN THE MAXIMUM HORIZONTAL TO VERTICAL DISPLACEMENT (MANA & CLOUGH 1981) ....................... 34 FIGURE 35. DEFORMATIONS PREDICTION FROM LATERAL WALL DEFLECTION VALUES PROPOSED BY AYE (2006): (A) SETTLEMENTS; (B)

LATERAL DEFORMATIONS .......................................................................................................................................... 35 FIGURE 36. SPANDREL-TYPE SETTLEMENT TROUGH (OU ET AL., 1993) ....................................................................................... 36

5

FIGURE 37. ASSUMED GAUSSIAN DISTRIBUTION FOR LATERAL AND VERTICAL GROUND DEFORMATIONS (LEE ET AL., 2007) ................... 36 FIGURE 38. CONCAVE SETTLEMENT PROFILE (HSIEH & OU, 1998) ............................................................................................. 37 FIGURE 39. RELATIONSHIP BETWEEN WALL MOVEMENT AND GROUND SETTLEMENTS FOR SOFT/LOOSE SOILS (KARLSRUD, 1997). .......... 37 FIGURE 40. VERTICAL AND HORIZONTAL GROUND MOVEMENT PATTERNS AS A FUNCTION OF THE EXCAVATION DEPTH (HE) AND THE

DISTANCE FROM THE WALL (D) (SCHUSTER ET AL. 2009) ................................................................................................ 38 FIGURE 41. SUBSURFACE SETTLEMENT DISTRIBUTION FOR CONCAVE SETTLEMENT PROFILES (AYE ET AL. 2006) ................................... 39 FIGURE 42. EFFECT OF THE EXCAVATION WIDTH ON THE MAXIMUM GROUND SETTLEMENT AND THE WALL DEFLECTION (MANA & CLOUGH,

1981) .................................................................................................................................................................. 40 FIGURE 43. EFFECT OF THE DEPTH TO FIRM LAYER ON THE MAXIMUM GROUND SETTLEMENT AND THE WALL DEFLECTION (MANA &

CLOUGH, 1981) ..................................................................................................................................................... 40 FIGURE 44. THE EFFECT OF THE HARD STRATUM ON THE COMPUTED WALL DEFLECTION (HSIAO, 2007) .......................................... 41 FIGURE 45. PLANE STRAIN RATIO (PSR) AS A FUNCTION OF THE ASPECT RATIO (B/L) AND DISTANCE FROM THE CORNER (D) (OU ET

AL., 1996) ............................................................................................................................................................ 41 FIGURE 46. THREE-DIMENSIONAL DISTRIBUTION OF SETTLEMENT AND LATERAL MOVEMENT AROUND FINITE DEEP EXCAVATION (FINNO &

ROBOSKI, 2005; ROBOSKI &FINNO, 2006) ................................................................................................................ 42 FIGURE 47. SETTLEMENT ASSOCIATED WITH TRENCHING IN HONG KONGS MTR (MORTON ET AL., 1980) ....................................... 43 FIGURE 48. MAXIMUM BUILDING SETTLEMENTS DUE TO SLURRY TRENCH EXCAVATION FOR DIAPHRAGM WALLS AS A FUNCTION OF

FOUNDATION DEPTH IN HONG KONGS MTR (COWLAND & THORLEY, 1984) .................................................................... 44 FIGURE 49. BUILDING SETTLEMENT DUE TO DIAPHRAGM WALL INSTALLATION IN HONG KONGS MTR (BUDGE-REID ET AL., 1984) ...... 44 FIGURE 50. SETTLEMENT DUE TO INSTALLATION OF A DIAPHRAGM WALL (CLOUGH AND OROURKE, 1990) ....................................... 45 FIGURE 51. LATERAL DEFORMATION ASSOCIATED WITH TRENCHING FOR SECANT PILES INSTALLED IN CHICAGO CLAY (FINNO ET AL.,

2002) .................................................................................................................................................................. 45 FIGURE 52. THE EFFECT OF SLURRY LEVEL VARIATION AND ITS HOLDING TIME ON THE LATERAL DEFORMATIONS ASSOCIATED WITH

TRENCHING (POH AND WONG, 1998) ........................................................................................................................ 46 FIGURE 53. VERTICAL DEFORMATIONS DUE TO DIAPHRAGM WALL INSTALLATION (GABA ET AL. 2003) .............................................. 47 FIGURE 54. INFLUENCE OF PANEL LENGTH ON LATERAL DISPLACEMENTS (GOURVENEC & POWRIE, 1999). ....................................... 47 FIGURE 55. THE SETTLEMENT ENVELOPES FOR SHALLOW AND DEEP FOUNDATION DUE TO TRENCHING TO A DEPTH OF 21M IN THE NILE

ALLUVIUMS IN THE GREATER CAIRO (ABDEL-RAHMAN & EL-SAYED, 2009). ...................................................................... 48 FIGURE 56. THE RELATIONSHIP BETWEEN THE LATERAL DEFORMATIONS AND THE MAXIMUM SETTLEMENT DUE TO TRENCHING IN THE NILE

ALLUVIUMS IN THE GREATER CAIRO (EL-SAYED & ABDEL-RAHMAN, 2002). ...................................................................... 49 FIGURE 57. BUILDINGS AND INTERFACES USED IN CENTRIFUGE TESTS (ELSHAFIE, 2008) ................................................................. 50 FIGURE 58. WALL DEFLECTIONS VARIATION WITH THE VARIATION OF THE WALL-SAND FRICTION (YU & GANG, 2008) ......................... 51 FIGURE 59. MAXIMUM SETTLEMENT VERSUS THE WALL-SAND INTERFACE FRICTION ANGLE (YU & GANG, 2008) ................................ 51 FIGURE 60. THE VARIATION OF THE RATIO BETWEEN THE MAXIMUM SETTLEMENT TO THE MAXIMUM WALL DEFLECTION VERSUS THE WALL-

SAND INTERFACE FRICTION ANGLE (YU & GANG, 2008) ................................................................................................. 52 FIGURE 61. DIFFERENT METHODS OF PLACING LAGGING (PECK, 1969A) ..................................................................................... 53 FIGURE 62. SUBGRADE REACTION MODEL FOR ANALYSIS OF WALLS SUPPORTING DEEP EXCAVATIONS (DELATTRE, 2001). ..................... 74 FIGURE 63. HORIZONTAL SUBGRADE MODULI, KH (AFTER PFISTER ET AL., 1982) .......................................................................... 75 FIGURE 64. IDEALIZED ELASTOPLASTIC EARTH RESPONSE-DEFLECTION CURVE WITH TWO SUBGRADE REACTIONS (DAWKINS 1994B) ........ 76 FIGURE 65. ELASTOPLASTIC SAND SUBGRADE DIAGRAM USING REFERENCE DEFLECTION METHOD (WEATHERBY ET AL., 1998) ............. 77 FIGURE 66. ELASTOPLASTIC CLAY SUBGRADE DIAGRAM USING REFERENCE DEFLECTION METHOD (WEATHERBY ET AL., 1998) .............. 77 FIGURE 67. GROUND ANCHOR T-Y CURVE (STROM AND EBELING, 2001) .................................................................................... 78 FIGURE 68. SHIFTED R-Y METHOD TO MODEL CONSTRUCTION STAGES (WEATHERBY ET AL, 1998) .................................................. 79 FIGURE 69. A SCHEMATIC SHOWING THE DISCRETIZATION OF DEEP EXCAVATION PROBLEM INTO A FINITE ELEMENT MESH ...................... 81 FIGURE 70. TYPICAL EXCAVATION SEQUENCE IN DEEP EXCAVATION SUPPORTED BY STRUTS (HASHASH & WHITTLE, 1996) .................... 82 FIGURE 71. INACCURATE EVALUATION OF THE DIFFERENTIAL SETTLEMENT AFFECTING BUILDINGS DUE TO THE UTILIZING OF

UNREPRESENTATIVE CONSTITUTIVE MODEL (KUNG, 2010) .............................................................................................. 83 FIGURE 72. VARIATION OF MODULUS WITH STRAIN LEVEL (OBRZUD, 2010)................................................................................ 84 FIGURE 73. STRESS REVERSAL APPROACH (GUTIERREZ ET AL., 2002) .......................................................................................... 85 FIGURE 74. INTERFACE STRESSES DURING EXCAVATION AND TENSIONING (STROM AND EBELING 2001) ........................................... 86 FIGURE 75. DISPLACEMENT FIELDS: (A) INCREMENTAL DISPLACEMENT FIELD FOR WIDE EXCAVATION; (B) INCREMENTAL DISPLACEMENT

FIELD FOR NARROW EXCAVATION; (C) PLASTIC DEFORMATION MECHANISM FOR CANTILEVER RETAINING WALLS IN UNDRAINED CONDITIONS. (OSMAN & BOLTON, 2007; LAM & BOLTON, 2011) .................................................................................. 88

6

FIGURE 76. ANN ELEMENTS (MAREN ET AL., 1990; FAUSETT, 1994; SHAHIN ET AL., 2001 & 2008) ............................................ 90 FIGURE 77.COMPARISON BETWEEN MEASURED GROUND DEFORMATIONS AND ANN PREDICTIONS (FAYED, 2002) ............................. 92 FIGURE 78. TEST SETUP UTILIZED BY LAEFER (2001) ............................................................................................................... 93 FIGURE 79. SOIL SURFACE SETTLEMENT OBTAINED BY LAEFER (2001) PLOTTED WITH RESPECT TO PECKS (1969A) ZONES.................... 93 FIGURE 80. CENTRIFUGE MODEL PACKAGE FOR EXCAVATIONS CUT AND PROPPED IN FLIGHT (LAM ET AL, 2011) ................................. 95 FIGURE 81. POTENTIAL BENEFITS OF THE OM ACCORDING TO CIRIA 185 (NICHOLSON AT AL., 1999) ............................................ 97 FIGURE 82. MEASURING POINT FOR MONITORING SURFACE SETTLEMENT .................................................................................. 102 FIGURE 83. INCLINOMETER MEASUREMENT OF DISPLACEMENT ................................................................................................ 103 FIGURE 84. ROD EXTENSOMETER ....................................................................................................................................... 103 FIGURE 85. MAGNETIC MULTIPLE POINT EXTENSOMETERS ....................................................................................................... 104 FIGURE 86. FEATURES OF DIFFERENT PIEZOMETERS (MURRAY, 1990) ...................................................................................... 106 FIGURE 87. DIFFERENT TYPES OF VIBRATING WIRE STRAIN GAUGES (EL-NAHHAS, 1980) .............................................................. 107 FIGURE 88. A REFLECTORLESS ROBOTIC TOTAL STATION (RRTS) MEASURING RSPS AND PRISMS (TAMAGNAN & BETH, 2012) .......... 108 FIGURE 89. OPERATING SCHEMATIC OF A TLS SCANNER (LATO, 2012) ..................................................................................... 109 FIGURE 90. SETTING TRIGGER LEVELS FOR A BUILDING SUBJECT TO SETTLEMENT FROM A DEEP EXCAVATION ..................................... 110 FIGURE 91. INSTRUMENTED SECTION AT ORABI STATION, CAIRO METRO LINE 1 (EL-NAHHAS, 2006) ........................................... 111 FIGURE 92. MEASURED PORE WATER PRESSURE BELOW THE DEEP EXCAVATIONS OF CAIRO METRO LINE 1 .................................... 112 FIGURE 93. LAYOUT THE MONITORING SETTLEMENT POINTS (ABDEL RAHMAN & EL-SAYED; 2002A, 2002B & 2003; EL-SAYED & ABDEL

RAHMAN, 2002; ABDEL RAHMAN & EL-SAYED, 2009) ............................................................................................... 112 FIGURE 94. THE MONITORING SYSTEM FOR AL-TAHRIR GARAGE (ABDEL-RAHMAN, 2007). .......................................................... 113 FIGURE 95. DEFINITION OF THE DEFORMATIONS AFFECTING THE BUILDING BASED ON BURLAND & WROTH (1974 & 1975) AND

BOSCARDIN & CORDING (1989) .............................................................................................................................. 115 FIGURE 96. DEFINITION OF SAGGING AND HOGGING DEFORMATION MODES (MODIFIED FROM FRANZIUS, 2003) .............................. 116 FIGURE 97. DAMAGE CRITERIA BASED ON ANGULAR DISTORTION (BJERRUM, 1963).................................................................... 118 FIGURE 98. DEEP BEAM MODEL (BURLAND AND WROTH, 1974 & 1975; BURLAND ET AL. 1977; BURLAND ET AL., 2001) .............. 119 FIGURE 99. THRESHOLD OF DAMAGE FOR SAGGING OF LOAD BEARING WALLS, E/G = 2.6 (BURLAND AND WROTH, 1974 & 1975) .... 123 FIGURE 100. THRESHOLD OF DAMAGE FOR HOGGING OF LOAD BEARING WALLS, E/G = 2.6 (BURLAND AND WROTH, 1974 & 1975) . 123 FIGURE 101. RELATIONSHIP OF DAMAGE TO ANGULAR DISTORTION AND HORIZONTAL EXTENSION STRAIN (BOSCARDIN &

CORDING, 1989) .................................................................................................................................................. 124 FIGURE 102. TENSILE STRAIN COMPONENTS DUE TO HORIZONTAL STRAIN, ANGULAR DISTORTION AND TILTING FOR WALL WITH L/H=1 &

E/G =2.6 (SON & CORDING, 2005) ........................................................................................................................ 125 FIGURE 103. DAMAGE ZONES WITH DIFFERENT CRITICAL TENSILE STRAINS (SON & CORDING, 2005) .............................................. 125 FIGURE 104. DAMAGE CRITERION ACCORDING TO BURLAND (1997). ...................................................................................... 126 FIGURE 105. BOONES (1996 & 2001) PROCEDURE TO ASSESS THE EXPECTED CRACK WIDTHS...................................................... 127 FIGURE 106. DAMAGE CRITERION ACCORDING TO CRACK WIDTHS (BOONE,1996). .................................................................... 127 FIGURE 107. THREE-PHASED DAMAGE ASSESSMENT FLOW CHART (BURLAND, 1995; MAIR ET AL., 1996; AND SON & CORDING, 2005)

......................................................................................................................................................................... 129 FIGURE 108. EFFECTS OF E/G AND NEUTRAL AXIS LOCATION FOR DEEP BEAM ANALYSIS (FINNO ET AL., 2005) ................................ 131 FIGURE 109. ESTIMATION AND OF THE EQUIVALENT WALL MODULII ......................................................................................... 132 FIGURE 110. EFFECT OF GRADE BEAMS FOR TWO-STORY AND THREE-BAY STRUCTURES ................................................................. 133 FIGURE 111. THE MODIFICATION FACTOR FOR THE DEFLECTION RATIO (GOH, 2010, GOH AND MAIR, 2011) .................................. 134 FIGURE 112. THE MODIFICATION FACTOR FOR THE HORIZONTAL STRAIN (GOH, 2010, GOH AND MAIR, 2011) ............................... 135 FIGURE 113. BASIC PROBLEM FOR THE PILE RESPONSE (POULOS & CHEN, 1997)....................................................................... 137 FIGURE 114. BASIC BENDING VERSUS DISTANCE FROM EXCAVATION FACE (POULOS & CHEN, 1997). ............................................ 137 FIGURE 115. BASIC MOVEMENT VERSUS DISTANCE FROM EXCAVATION FACE (POULOS & CHEN, 1997). ........................................ 137 FIGURE 116. CORRECTION FACTORS FOR BENDING MOMENT (POULOS & CHEN, 1997). ............................................................. 138 FIGURE 117. CORRECTION FACTORS FOR LATERAL PILE MOVEMENT (POULOS & CHEN, 1997). .................................................... 139 FIGURE 118. ITERATIVE DESIGNING OF EXCAVATION SUPPORT SYSTEMS FOR ADMISSIBLE DEFORMATIONS (ZAPATA-MEDINA, 2007) ... 140 FIGURE 119. CRACK PATTERNS ASSOCIATED WITH DIFFERENT MODES OF GROUND SETTLEMENTS ................................................... 141 FIGURE 120. CRACK PLOTTING ON BUILDING ELEVATION ........................................................................................................ 142 FIGURE 121. AL-TAHRIR GARAGE, ITS SURROUNDING STRUCTURES AND MONITORING SYSTEM (ABDEL-RAHMAN, 2007). .................. 145 FIGURE 121. PREDICTED LATERAL DISPLACEMENT OF THE DIAPHRAGM WALL WHILE ADVANCING THE CONSTRUCTION STAGES (ABDEL-

RAHMAN, 2007) .................................................................................................................................................. 146

7

LIST OF TABLES

TABLE 1: SUMMARY OF SOME OF THE ACKNOWLEDGED INTERNATIONAL EMPIRICAL AND SEMI-EMPIRICAL STUDIES .............................. 56 TABLE 2: SUMMARY OF SOME OF THE ACKNOWLEDGED NATIONAL EMPIRICAL AND SEMI-EMPIRICAL STUDIES ..................................... 70 TABLE 3. WEIGHTED VALUE OF DIFFERENT TYPES OF DEFORMATION MEASUREMENTS (NEGRO ET, 2009) ........................................ 101 TABLE 4. WEIGHTED VALUE OF DIFFERENT TYPES OF STRESS MEASUREMENTS (NEGRO ET, 2009) ................................................... 101 TABLE 3. EXPRESSION FOR THE LIMITING DEFLECTION RATIO (BURLAND & WROTH, 1974 & 1975; BURLAND ET AL., 1977) ............. 119 TABLE 4. DAMAGE CATEGORIES ACCORDING TO BURLAND ET AL. (1977) & BRE DIGEST 251 (1995) ........................................... 121 TABLE 5. RISK CATEGORIES ACCORDING TO RANKIN (1988) .................................................................................................... 128 TABLE 6. LEVELS OF BUILDING DAMAGE VERSUS DPI THRESHOLDS (SCHUSTER ET AL. 2009) ........................................................ 128 TABLE 7. EXAMPLES OF UNCERTAINTY IN THE GEOTECHNICAL WORKS (PATEL ET AL., 2007) .......................................................... 143 TABLE 8. CONTINGENCY PLANS FOR DEEP EXCAVATION (ABDEL-RAHMAN, 2007) ....................................................................... 147 TABLE 9. SUMMARY OF THE FINDINGS OF THE COMMON EMPIRICAL/SEMI-EMPIRICAL METHODS FOR AVERAGE WORKMANSHIP IN TERMS OF

THE EXCAVATION DEPTH (HE) OR THE TRENCH/PILE DEPTH (D) ....................................................................................... 149

8

The most fruitful research grows out of practical problems.

Ralph Peck

9

1. INTRODUCTION

There is a worldwide increasing demand to utilize the underground space in the developments of

the urban congested areas for different purposes such as transportation tunnels, underground

parking garages, basements and utilities. Such developments call for deep vertical excavations

and underground tunneling that are frequently close to existing structurally-sensitive buildings

and utilities. As deep excavations initiate lateral and vertical ground deformations due to the

stresses relaxation and bottom heave associated with the excavation process, the adjacent

buildings and buried utilities become kinematically loaded by the induced ground deformations

which depend in magnitude and direction on the building proximity to the excavations as

schematically demonstrated in Figure 1. It is well-acknowledged that the control of ground

movements and protection of adjacent or overlying structures is a major element in the design

and construction of deep excavations and tunneling in urban areas (Gill & Lukas, 1990; Son,

2003; Son & Cording, 2005 & 2007; Hsiao, 2007; Zapata-Medina, 2007; Lam, 2010 and others).

Figure 1. Ground and building deformations induced by a deep excavation (Hsiao, 2007)

To date, failures of structures or roadway adjacent to excavation occur despite the recent

advances made in assessing the stability of excavations and the effects of excavations on nearby

properties. Figure 2 shows a very recent example of a failure case history for a collapsed 13-floor

building by toppling in Minhang District of Shanghai, China. The failure, which happened in in

2009, was due to a nearby deep excavation which overloaded the piles of the collapsed building.

Chai et al. (2014) indicated that the failure was initiated by lateral overloading on the pile

foundation due to excavation near one side of the collapsed building and stockpiling the

excavation at another side of the building. The unbalanced excavation and fill on the sides of the

collapsed building induced lateral loads on piles were also accompanied by unforeseen soil

softening due to a rain event. This failure case history indicates the viral need for supporting

walls for deep excavations in urban areas even in soils that can sustain cuts to avoid affecting the

adjacent structures with the induced deformations. Commonly, a wall is required to support deep

excavations especially in urban areas to minimize the induced deformations. Therefore, the term

deep excavation herein is meant as a supported deep vertical excavation by means of a peripheral

wall. Deep excavations are also termed herein and in the literature as braced excavations (Puller,

2003).

10

Another very well-known recent failure is the failure of Nicoll Highway in Singapore, Figure 3,

which occurred due to insufficient site investigations, misinterpretation of the observations,

faults in design of the bracing system, and utilization of unsuitable method for wall strutting by

jet grouting (Whittle & Davies, 2006; Lee, 2008).

Figure 2. Failure of a building in China in 2009 that was initiated by a nearby deep excavation

Figure 3. Failure of a deep excavation adjacent to Nicoll Highway, Singapore (Lee, 2008)

11

Serviceability problems associated with the substantial foundation settlement and lateral

deformations induced by deep excavations are much more widespread than failures. Structure

may experience distresses such as cracking of structural or architectural elements, uneven floors,

or inoperable windows and doors due to the induced deformations. Figure 4 shows an example of

a cracked external wall due to a nearby excavation. The amount of the tolerable deformations

and the severity of excavation-related damage depend on the building type, configuration and

stiffness as well as the characteristics of excavation support, the ground geotechnical conditions

and the construction sequence. Both geotechnical and structural engineers are required to

collaborate in quantifying the amount of building settlement, assess the possible structural

damages and set up the counter measures and risk mitigations to avoid such damage (Boscardin

and Cording, 1989; Burland, 1995; Boone, 1996 & 2001; Boone et al., 1998 & 1999; Long,

2001; Finno and Bryson, 2002; Finno et al., 2002; Son, 2003; Son and Cording, 2005 & 2007;

and others).

Figure 4. A masonry wall suffered from severe cracking due to ground deformations (Vatovec et al., 2010)

It is acknowledged that the effect of deformations associated with deep excavation depends on

the geotechnical characteristics of the soils. The less strength and more compressible the soils

have, the more pronounced effects and deformations are anticipated. Awkwardly, most of the

deep excavations are in urban areas that have deltaic soils originating from rivers and oceans;

they comprise sediments such as silts, clay and sands under shallow groundwater table. Such

deltaic soils are often encountered in the most densely populated areas in the world. This fact

emphasizes the need to predict, control and mitigate the deformations resulting from deep

excavations (Peck, 1969a; El-Nahhas, 1992 & 2006; Boone, 1996 & 2001; Bolton, 2008; and

others).

12

Nationally, most of the developments that need deep excavations in Egypt are located in the

Greater Cairo area which is characterized by recent Nile alluviums with shallow groundwater

table. Geologically, the Nile developed its course in this area through the down faulting of the

limestone extending between the El-Muqattam cliff and the Pyramids plateau and deposited

recent alluviums of alternating layers of cemented silty sand, clayey sand and medium to coarse

sand underlain by very stiff plastic clay that rests on the limestone marine formations as

illustrated in Figure 5 (Said, 1981; El-Sohby & Mazen, 1985; El-Ramli, 1992; El-Nahhas, 2006;

and others).

Figure 5. Typical formations in the Greater Cairo area (El-Sohby and Mazen, 1985)

The geotechnical conditions of the Nile alluviums are considered problematic for deep

excavation particularly as the expected deformations impose risks on the adjacent structures and

utilities including possible loss of support to existing foundations and structurally distressing

buildings, pavements and utilities surrounding the excavation. Notwithstanding these

engineering challenges, there is an ever growing need for utilization of underground space in

Greater Cairo in the last decades due to the scarcity of the ground space and the high cost of

lands in this area (El-Nahhas et al., 1988 & 1990; El-Nahhas, 1992 & 2006; Abdel-Rahman,

1993; Abd El-Salam, 1995; Ahmed & Abd El-Salam, 1996; Ahmed et al., 2005; Abdel-Rahman,

2007; Abdel-Rahman & El-Sayed, 2009 and others).

Precise evaluation of the ground displacements induced by a deep excavation is not simple to be

achieved due to the uncertainties in soil properties, constitutive modeling, construction stages,

three-dimensional and time-dependent natures of the problem, and the need for incorporation of

human factors such as workmanship in the models. Notwithstanding that, reasonable assessments

can be reached if the diverse methods for analysis are carefully studied by an experienced

geotechnical engineer to reach a solid evaluation. Predicting the induced movements and

mitigating them by suitable means became more feasible with the development of observational

methods and the non-linear finite element analysis procedures and software since the early

1970s. (Peck, 1969b; Lambe, 1970; Clough & Duncan, 1969 & 1971; Duncan & Clough, 1971; Goldberg et al. 1976 ; ORourke et al., 1976; Boscardin et al., 1979).

13

Generally the methods to obtain the deformation field can be categorized into empirical/semi-

empirical methods, numerical methods, analytical methods, physical/centrifuge modeling, and

Artificial Neural Networks (ANNs). It is also to be noted that the assessment of deformations

associated with deep excavation depends if there is a building in the vicinity of the excavation or

not. For the case of no buildings, the ground deformations are designated as free-field or

greenfield. The presence of the building modifies the induced deformation due to the building

weight and stiffness. Heavy flexible buildings may have more deformations that the expected

greenfield while light rigid building may have less deformations that the anticipated greenfield

(Chang, 1969; Chandrasekaran & King, 1974; Clough & Manna, 1976; Brown & Booker, 1986;

Powrie & Li, 1991; Ng, 1992; Abdel-Rahman, 1993; Morrison, 1995; Bentler, 1998; El-Nahhas

et al., 1989, 1994 & 1998; Seok et al., 2001; Fayed, 2002; El-Nahhas & Morsy, 2002; and

others)

The traditional single, fully developed design with no intention to vary the design during

construction does not exist in geotechnical engineering, particularly, in deep excavation and

tunneling projects. Peck (1969b) coined the observational approach to be adopted in geotechnical

projects. In this approach, the instrumentation and monitoring are required to be carried out to

provide confidence to the administratively controlling authorities and the affected third parties

such as the owners of the adjacent buildings. Monitoring results often integrate with the design

and enhance the reliability of the design assumptions by validating the design parameters as the

construction proceeds. Inverse analysis of the monitoring data provides the appropriate tool to

combine observational and analytical approaches to enhance risk mitigations and managements

(Clough, 1975; Powderham, 1994, 1998 & 2002; Powderham & Nicholson, 1996; Powrie &

Kantartzi, 1996; Nicholson & Penny, 1999; Hashash et al., 2004 & 2010; Abdel-Rahman, 2007;

Lee at al., 2007; and others).

In this state-of-the-art report, the following issues are highlighted:

1. Factors affecting the deformations associated with deep excavations; 2. Assessment of the ground deformations outside the deep excavation using different

approaches (viz., empirical/semi-empirical, numerical; analytical, physical modeling and

ANN approaches);

3. Influence of the presence of buildings on the displacements; 4. Structural damage criteria; 5. Monitoring programs for deep excavation projects; & 6. Risk management and mitigation for deep excavation projects

In addition to the International studies presented in this state-of-the-art covering the

abovementioned points, National experiences in assessments of the deformations induced by

deep excavations, monitoring programs, risk assessment and risk mitigation are also highlighted.

14

2. FACTORS AFFECTING EXCAVATION DEFORMATIONS

Ground deformations associated with deep excavations are inevitable. The relaxation of the

horizontal stress by the excavation induces horizontal movements of the wall and the soil

towards the excavation accompanied by vertical deformations of the soil around the excavation.

The vertical deformations are mostly downward deformations (settlements); yet, sometimes

upward deformations (heaves) are measured adjacent to the wall or at far distances from the wall.

Settlement may be associated with the instability of the excavation base in clayey soils.

Deformations may also occur due to the increases in the effective stresses during lowering

groundwater table (Caspe, 1966; Goldberg et al., 1976; ORourke, 1981 & 1993; Clough and ORourke, 1990; Ou et al., 1993 & 2000; Hseih & Ou, 1998; Poh et al., 2001; Kung, 2003; and others).

Prior to the revolutionary state-of-the art paper of Peck (1969a) in which he demonstrated that

substantial deformations associated with deep excavations and tunneling may occur,

geotechnical engineers used to assume that that deformations are negligible if the excavation

have adequate factor of safety against potential failures. Later, ORourke et al., (1976) and Boscardin et al. (1979) reported that sensitive structures were damaged due to the deformations

induced by an adjacent deep cut in Washington D.C., even though the bracing experienced no

structural distress. Since then, it has been acknowledged that excavations are commonly

accompanied by significant deformations that may considerably affect adjacent facilities even if

they have adequate factor of safeties against possible failures.

It is a common practice to support deep excavations by continuous walls in urban areas to limit

the induced movements. The excavation support systems for deep excavations consist of two

main components: a wall, and its lateral supporting elements. Many types of walls and supports

have been used in deep excavations. Walls supporting deep excavation may be classified into

following three major categories according to the form of supporting measures provided for

them:

1. Cantilevered wall (usually for shallow excavation); 2. Strutted/braced wall; & 3. Tied-back or anchored wall

Under each of the above support category, the following wall types may be utilized:

1. Sheet pile wall; 2. Soldier pile and lagging wall (Berlin wall); 3. Contiguous bored piles wall; 4. Secant piles wall; 5. Diaphragm wall; & 6. Soil-mixing walls

Puller (2003) described the aforementioned systems and other less widely used support systems

in considerable detail. The excavation-induced deformations may be affected by a large number

of factors such as: wall stiffness, ground conditions, groundwater condition and control

measures, excavation depth, construction sequences, and workmanship. The following sections

address some of the important factors that profoundly affect the induced deformation and hence

the associated building damage.

15

2.1. Soil Type

Peck (1969a) showed that settlements next to deep excavations correlate to soil type. He

proposed three zones of settlement profiles based on the prevailing soil conditions as illustrated

in Figure 6. In general, larger wall deflection and ground deformations are induced due to

excavations in soils with lower strength and stiffness. The same conclusion was reached in many

other following studies (e.g., Goldberg et al., 1976; Clough & ORourke, 1990; Bentler, 1989; and others). This aspect is further elaborated in Section 3 of this state-of-the-art addressing

empirical and semi-empirical method for assessment of the deformation induced by deep

excavation.

Figure 6. Effect of the soil type on the settlements induced by deep excavation (Peck, 1969a)

2.2. Wall Stiffness and Excavation Stability

Stability and deformation are interrelated. Walls with large factors of safety against potential

collapses have small strains around the excavation; consequently, the ground deformations are

also likely to be also small. Conversely, if the factors of safety (or some of them) are small,

strains around the excavation and ground deformations may become large. Additionally, the wall

stiffness greatly affects the induced ground movements. Goldberg et al. (1976) showed using

finite element and measured data that the maximum lateral deformations for deep excavations in

clays can be estimated using the stability number of the excavation H/cu (where is the soil unit weight, H is the depth of the excavation and cu is the undrained shear strength) and the stiffness

of the supporting system EwIw/h4 (where Ew is the youngs modulus of the wall, Iw is the moment

of inertia of the wall per linear meter, h is a representative unsupported length of the wall such as

the average distance between struts). Figure 7 illustrates the findings of Goldberg et al. (1976).

16

Figure 7. Effect of wall stiffness and soil stability number on the wall deformations in clays (Goldberg et al., 1976)

Mana & Clough (1981) utilized the finite element and the field measurements to relate the

maximum wall movements with the factor of safety against basal heave in clays as shown in

Figure 8. The quasi-constant non-dimensional movement are at high safety factor is an indication

of an elastic response. The rapid increase in movements at lower factor of safety is a result of the

induced plastic deformations.

Figure 8. Effect of the basal heave stability on the wall deformations induced by deep excavations in clays (Mana &

Clough, 1981)

17

Clough et al. (1989) and Clough & ORourke (1990) utilized the nonlinear finite elements and field measurements to determine the effect of the wall stiffness on the maximum lateral wall

movement in clays that is induced by excavation. They introduced a system stiffness factor,

similar to Goldberg et al. (1976), for estimating wall stiffness of unit thickness (plane strain)

which depends on wall material, section properties and support spacing; this factor is giving by:

4

avewh

EIk

(1)

where k = Dimensionless system stiffness

E = Youngs modulus of wall system I = Moment of inertia of wall system

have = average vertical distance between tiebacks/struts

w = unit weight of water = 9.81 kN/m3

The results of their analyses are shown in Figure 9.

Figure 9. Effect of the basal heave stability and the system stiffness on the wall deformations induced by deep

excavations in clays (Clough at al., 1989)

According to the introduction of the system stiffness factor, the retaining system can be

categorized into two-categories:

1. Flexible systems (e.g., sheet-pile walls, soldier beam and lagging): Generally the stiffness factors k for these systems are less than 40.

2. Stiff systems (e.g., secant pile wall, tangent pile wall, diaphragm walls): Generally the stiffness factors k for these systems are greater than 300.

The selection of system stiffness and spacing generally relies on economic as well as practical

issues such as minimum spacing to accommodate construction activities.

18

Clough at al. (1989) and Clough & ORourke (1990) concluded that the wall stiffness is less effective in reducing movements than in cases with high factor of safety against basal instability.

However, in case of having low factor of safety against basal heave, the wall stiffness affects the

deformation greatly. The aforementioned studies suggest that the maximum lateral wall

movement for stiff systems (i.e., thick diaphragm walls or secant piles walls) in stable soils (i.e.,

factor of safety against bottom heave is greater than 3) is limited to approximately 0.2% of the

excavation depth regardless of the system stiffness.

Clough et al. (1989) ignores the increase of stability due to wall embedment. Hashash et al.

(2008) showed that the wall embedment and stiffness may limit the soil movements to much

lower magnitudes than what is predicted in Figure 9.

Long (2001) analyzed 296 case histories and checked Clough et al. (1989) chart against the study

data. Substantial scatter was noted as shown in Figures 10 & 11. He concluded that the wall

stiffness does not affect the deformation if the excavation has a factor of safety against basal

heave more than 3.

Figure 10. Normalized field measurements of the lateral deformations against Clough & ORourkes (1990) system

stiffness and basal heave factor of safety for cases with low factor of safety (FOS

19


stiffness and basal heave factor of safety for cases with high factor of safety (FOS>3) (Long, 2001)

Moormann & Moormann (2002) and Moormann (2004) reached the same conclusion of Long

(2001) that Clough et al. (1989) and Clough & ORourkes (1990) system stiffness factor needs to be revisited after reviewing more than 500 case history in both soft and stiff clays. Figures 12

& 13 show the substantial scatter of the database points with respect to Clough et al.s (1989) curves. Moormann (2004) attributed the lack of dependency of lateral movements on system

stiffness as predicted by to the factors like:

1. Soil conditions at the embedment portion of the wall; 2. Groundwater conditions; 3. Effect of the surrounding buildings or geometrically irregularities; 4. Workmanship; 5. Unforeseen events and excavation sequence; 6. Pre-stressing of struts and anchors; & 7. Time-dependent effects.

20


stiffness and basal heave factor of safety for soft clay (Moormann, 2004)


stiffness and basal heave factor of safety for stiff clay (Moormann, 2004)

21

Zapata-Medina (2007) proposed a revised system stiffness factor which gives more reliable

results with the data using the data of 30 case histories that comprise soft, medium and stiff

clays. A graph showing the favorable correlation between the maximum lateral deformation, the

factor of safety and revised system stiffness is shown in Figure 14. The recommendations of

Zapata-Medina (2007) are further elaborated in the Section 3 in this state-of-the-art report.

Figure 14. Normalized lateral wall movements vs. relative stiffness ratio, R, for deep excavations in cohesive soils

(Zapata-Medina, 2007).

It is to be noted that Zapata-Medinas (2007) utilized Ukritchon et al.s (2003) factor of safety (FS) against basal heave as shown in Figure 14. The factor of safety could reach as low values as

0.65 in the analyses without having a failure of the excavation; instead, large ground

deformations were observed. This note was not clarified by Zapata-Medina (2007)

Juang et al. (2011) explained the lack of dependence of the induced deformations on the system

factor by stating that the ground movements are essentially functions of the following six

parameters in addition to the system stiffness:

1. Excavation depth; 2. Excavation width; 3. The depth from the bottom of excavation to the hard stratum; 4. The normalized clay layer thickness (Hclay /Hwall) where Hclay is the sum of the

thicknesses of the clay layers and Hwall is the wall depth;

5. The ratio of shear strength over vertical effective stress (su /v); & 6. The ratio of initial Youngs tangent modulus over vertical effective stress (Ei /v)

The factor of safety against basal failure also affects the shape of the settlement trough

associated with deep excavation. Mana and Clough (1981) found by numerical analyses that the

width of the settlement trough increases with the increase of the factor of safety as shown in

Figure 15.

22

Figure 15. Effect of the factor of safety on the settlement trough width (Mana and Clough, 1981)

2.3. Overconsolidation (OCR) and At-Rest Earth Pressure Coefficient (Ko)

Overconsolidated soils generally have higher at-rest lateral pressure (Ko) than normally

consolidated soil (Mayne & Kulhawy, 1982). Potts & Fourie (1984) studied the behavior of a

single propped retaining wall has been using elasto-plastic finite element method. They

concluded that by increasing the at-rest coefficient (Ko), the deformations, forces and bending

moments in the wall substantially increase and even may exceed those calculated using the

simple limit equilibrium approach which is in common use. The behavior of excavated walls in a

high-Ko soil is dominated by the vertical unloading forces caused by the excavation as shown in

Figure 16. Additional horizontal restraint in the form of multi-propping, while reducing

horizontal movements of the wall and soil, has a much smaller effect on vertical movements.

Peck (1969a) noted that in highly overconsolidated clays, soil tends to heave near to the wall.

Figure 16. Contours of stress level at an excavation depth of 13.26m: (a) Ko=2; (b) Ko=0.5 (Potts & Fourie, 1984)

23

2.4. Groundwater Conditions and Control Measures

Groundwater develops hydro-pressure against the walls of the deep excavation supporting

system causing them to deform which adds to the ground deformations associated with deep

excavations. Additionally, soils under water are generally weaker than being above them due to

the effect of water in reducing the effective stress. Moreover, the flow of groundwater towards

the excavations may endanger the excavations and the surrounding buildings, particularly if it

occurs through the wall itself in lieu of the dewatering system. The different groundwater flow

patterns associated with deep excavations are shown in Figure 17 (Clough & ORourke, 1990).

Figure 17. Groundwater flow patterns encountered in deep excavations (Clough & ORourke, 1990)

Settlements are generated by the groundwater table lowering as the soil is passing from a

submerged to a saturated unit weight which leads to an increase of the effective stress as shown

in Figure 18. The settlement value depends on the drawdown of the water table and the soil

stiffness. In sands, excessive pumping out the groundwater from a deep excavation results in a

significant drop of the groundwater table within the surrounding areas with possible excessive

settlement of the adjacent buildings and other structures and piping if the exist hydraulic gradient

at the bottom of excavation exceeded the safe value. Puller (2003) summarized the groundwater

control measures for deep excavations as shown in Figure 19.

24

Figure 18. Influence of the dewatering works on the ground settlement

Figure 19. Groundwater control measures for braced excavation (Puller, 2003)

25

Examples of groundwater-related failures and problems that occurred to deep excavations due to

improper groundwater considerations in design and construction:

1. The collapse of a deep excavation for an underground metro station in Cologne, Germany in 2009, Figures 20 & 21, which in-turn caused the collapse of the historical

City Archive Building. This failure is anticipated to be a piping failure induced by the

groundwater high velocity that was not considered during the design of the dewatering

system (Rowson, 2009).

2. A diaphragm wall leaked during the construction of a deep exaction for a new underground station of the North-South Train Line in Amsterdam, the Netherlands. This

leakage caused washing of sand below the foundations of surrounding buildings and a

subsequent subsidence of 23 cm as shown in Figure 22. The predicted costs have gone

up from 1.5 to 3 billion euros and the project completion was shifted from 2011 to 2017

(Van Tol, 2010; Van Baars, 2011).

3. In 2005, a diaphragm wall leaked and surrounding houses started to subside in a deep excavation for a garage in Middelburg, The Netherland. To stop the subsidence, the pit

was filled with water until 2009, Figure 23, till new walls were placed in the pit and the

pit was filled with 13,350 m3 of concrete; a loss of almost half the volume of parking

space (Van Baars, 2011).

4. In 2007, a well-known failure of the diaphragm for The Infinity Tower in Dubai occurred due to piping by seepage through a diaphragm wall joint as shown in Figure 24.

Figure 20. Collapse of City Archive Building in Cologne (Germany) due soil piping induced by dewatering

(Rowson, 2009)

26

Figure 21. The collapsed City Archive Building in Cologne (Germany) (Rowson, 2009)

Figure 22. Damage due to Subsidence along an underground station of the North-South Train Line in Amsterdam

(Van Baars, 2011).

27

Figure 23. Leakage and damage at the building pit in Middelburg, the Netherland (Van Baars, 2011)

Figure 24. Failure of a diaphragm wall in The Infinity Tower in Dubai in 2007. The chronological sequence of

events is (a) to (d)

(a) (b)

(c) (d)

28

To avoid problems associated with groundwater and to minimize the effect of groundwater

lowering on the adjacent buildings, the concrete diaphragm walls in the Greater Cairo Metro was

extended deeper without reinforcement and a low permeability grouted plug is provided at their

toes as shown on Figure 25-a to avoid the possible effects of the large groundwater drawdowns

as schematically shown in in Figure 25-b. The grouting materials were injected in two stages:

bentonite-cement slurry and soft-silica gel, in order to reduce the permeability of the sand to 10-6

m/s. Thickness of the grouted plug and its elevation are selected to satisfy a safe limit of the

average hydraulic gradient within the plug (less than 3) and an average buoyancy factor of safety

of 1.1 of the remaining soil mass below the final excavation level (El-Nahhas, 2003 & 2006; El-

Nahhas et al., 2006).

(a) With plug (utilized in Greater Cairo Metro)

(b) without plug causing large drawdowns

(not utilized in the Greater Cairo Metro)

Figure 25. Schemes for groundwater control in a deep excavation (El-Nahhas, 2006).

2.5. Strut/Tie-back Prestressing

Support systems for deep excavations consist of two main components: The wall and the support

provided for the retaining wall as struts (braces), rakers, and tieback anchors. Clough (1975)

demonstrated the effects of pre-stressing of braces to control wall deformations. The wall

movement is plotted against the normalized prestressing force for sands and stiff clays as shown

in Figure 26. For both sands and stiff clays, the movements decrease with increasing prestressing

force of the tie-backs. Clough (1975) suggested that the optimum effect of prestressing in

reducing movements is achieved by using pressure levels slightly greater than those of Terzaghi

& Peck (1967).

ORourke (1981) observed that the effective stiffness of braces could be as low as two percent of the ideal stiffness due to compression of the bracing and its connections without imposing an

initial prestressing. Mana & Clough (1981) showed that increasing the stiffness of the

strut/anchor/raker reduces the deformation 40% as shown in Figure 27.

29

Figure 26. The effect of prestressing on the wall deformations (Clough, 1975)

Figure 27. The effect of the strut stiffness on the maximum lateral deformation of the wall and the maximum

settlement (Manna & Clough, 1981)

30

2.6. Construction Sequence

Generally, the following two different approaches are frequently utilized in deep excavations:

Conventional (down-top) construction: The excavation between the supporting walls (i.e., pit excavation) starts after installing the supporting walls and operating the

groundwater control measures. The excavation proceeds sequentially with the

installation of the struts, tie-backs and/or rakers to the foundation level of the permanent

structure. After that, the construction of the permanent structure starts from bottom to

the top. The first element of the permanent structure to be cast is the raft foundations. An

example of this method of construction is the construction of the Greater Cairo Metro -

Line 1 as show in Figure 28. The supporting wall may or may not be integrated with the

permanent structure. If the walls are be integrated with the structure, then, they should be

diaphragm walls.

Figure 28. Construction procedure steps for the Greater Cairo Metro - Line 1 (El-Nahhas et al., 1988)

Top-down construction: In this method of construction, the basement slabs are formed and poured on the existing subgrade. The top slab of the basement in the permanent

structure is cast after installing the supporting walls (walls should be diaphragm walls).

The top basement slab is considered the first support to the wall. After that, operation of

the dewatering system and pit excavation under the top slab proceed till reaching the

level of the second slab which is to be cast against the subgrade at this stage. Temporary

supports are also installed while excavating. Excavation shall continue to reach the

foundation level and then the raft foundation is to be cast. Excavation supporting walls

are always integrated within the permanent structure. An example of the top-down

construction is Rod El-Farag Station in the Greater Cairo Metro Line 2 as illustrated in Figure 29.

31

(a) configuration of the station

(b) stages of construction

Figure 29. Rod El-Farag Station (Ahmed and Abd El-Salam, 1996)

32

It is anticipated the top-down construction has much less deformations than the conventional

down-top construction due to the early installation of the top slab which acts as a support for the

wall. However, since the tope slab cannot be prestressed, it appears that the conventional (down-

top) construction with prestressed anchors/struts gives less cantilever deformations than the top-

down construction in soft clays especially as the top slab may suffer from shrinkage after its

casting and this limits its efficiency (Long, 2001).

It is also to be noted that the top-down construction helps to eliminating the top supports such as

tie-backs which may interfere with the foundations of the adjacent buildings (especially if they

are shallow foundations) and the nearby utilities. On the other hand, top-down construction

reduces the rate of excavation since excavations works start under the cast slabs in a restricted

narrow space.

2.7. Wall Lateral Deformation Patterns

Goldberg et al (1976) identified different settlement patterns following the wall lateral

deformations patterns as shown in Figure 30. They showed that the settlement behavior do not

only depend on soil type but also on the wall lateral deformations as well.

Figure 30. Settlement patterns associated with different wall deformation modes (Goldberg et al. 1976).

33

Clough and ORourke (1990) According to the method of construction the wall deform in two modes: cantilever mode, and bulging mode. The settlement troughs associated with each mode

are different as shown in Figure 31. Boone (2003) and Boone & Westland (2005) concluded the

same effect of wall deformation on surficial settlement trough as shown in Figure 32.

Figure 31. Modes of deformation of the wall (Clough and ORourke, 1990)

Figure 32. Lateral and vertical displacement patterns: concave on left, spandrel on right (Boone 2003; Boone &

Westland, 2005).

ORourke (1981) envisaged a factor called the Coefficient of Deformation (CD) which is defined

as the ratio of the cantilever deformation component (Sw) to total deformations (Sw + Sw) where Sw is the bulging component of the wall displacement. Figure 33 shows the relationship between CD and ratio of the maximum wall lateral deformation to the maximum ground settlement

relationship for clays. Accordingly, the maximum surficial settlement associated with the

cantilever mode (CD=1) is about 0.63 times the maximum lateral cantilever deformation of the

wall; while, the maximum settlement associated with the wall bulging mode (CD=0) is about 2

times the maximum lateral wall bulging deformation. Mana & Clough (1981) suggested that the

maximum vertical cumulative deformation is ranged between 0.5 & 1 times the maximum lateral

deformation of the wall based on field measurements as shown in Figure 34.

34

Figure 33. The ratio between the maximum horizontal to vertical displacement as a function of the Coefficient of

Deformations (ORourke, 1981)

Figure 34. The ratio between the maximum horizontal to vertical displacement (Mana & Clough 1981)

In the following sections, the settlement patterns associated with cantilever and bulging modes of

deformations of the wall are elaborated. The empirical and semi-empirical patterns associated

with the cumulative pattern of the wall are demonstrated in Section 3 of this-state-of-the-art.

35

2.7.1. Settlement pattern associated with the wall cantilever deformation mode

Caspe (1966), Bowles (1988), Aye et al. (2006) utilized analysis for the induced settlement that

is anticipated to be associated mainly with the wall cantilever mode as shown in Figure 35. The

lateral wall deflection are to be determined using the 1D beam-spring model (refer to Section 4.1

in this state-of-the-art report) and numerically integrated to obtain the volume of the wall

deflection (Vo) utilized in this method.

Figure 35. Deformations prediction from lateral wall deflection values proposed by Aye (2006):

(a) settlements; (b) lateral deformations

Ou et al. (1993) presented a tri-linear settlement profile called spandrel-type settlement based on

10 case histories of deep excavation in soft clays from Taipei, Taiwan. The maximum settlement

is located at the wall when the wall deforms as a cantilever. The settlement trough is shown in

Figure 36.

36

Figure 36. Spandrel-type settlement trough (Ou et al., 1993)

Lee et al. (2007) proposed that lateral Sh and vertical Sv deformations associated with the wall

cantilever mode can be presented in terms of the maximum wall deformations Sw and the trough

width W using Gaussian distribution, Figure 37, as follows:

(3)

(4)

Where is the ratio between the maximum wall deflection and the maximum surface settlement and can be assumed to be 0.5 for diaphragm wall & 1 for sheet pile wall.

Figure 37. Assumed Gaussian distribution for lateral and vertical ground deformations (Lee et al., 2007)

37

2.7.2. Settlement pattern associated with the wall bulging deformation mode

Hsieh & Ou (1998) presented a concave settlement profile for the bulging mode of wall based on

analysis of 9 case histories. The maximum settlement is assumed to occur at 0.5 He, where He is

the excavation depth from the wall. The settlement at the wall is approximated to 50% of the

maximum settlement as shown in Figure 38.

Figure 38. Concave settlement profile (Hsieh & Ou, 1998)

Karlsrud (1997a) proposed a relationship between the maximum wall deformation and the

surficial ground settlement concave pattern, Figure 39, based on data from sites with soft clays

and loose to medium dense sand and silts. The dashed lines close to the wall reflects impact of

the potential for movements of the tip of the wall. Thus for structures laying at distances from the

wall smaller than 0.2 times the depth to zero lateral displacement, the settlements may be quite

uncertain.

Figure 39. Relationship between wall movement and ground settlements for soft/loose soils (Karlsrud, 1997).

38

Schuster et al. (2009) proposed a concave settlement pattern along with its associated lateral

deformation patterns as shown in Figure 40. The settlement at the wall is about 20% of the

maximum settlement. The lateral deformation affecting nearby building changes from concave

shape at the ground surface to spandrel shape to depth of 5m depending on the foundation depth

of the building.

Figure 40. Vertical and horizontal ground movement patterns as a function of the excavation depth (He) and the

distance from the wall (d) (Schuster et al. 2009)

For the subsurface settlement associated with concave settlement trough, Aye et al. (2006)

proposed a vertical distribution similar to their recommendations for the spandrel-type settlement

as shown in Figure 41.

39

Figure 41. Subsurface settlement distribution for concave settlement profiles (Aye et al. 2006)

2.8. Time-Dependent Effects

For an excavation in clays, longer durations for installing the strut or constructing the floor slab

may cause larger wall deflection due to the occurrence of consolidation or creep of clay. Studies

that addressed that aspect by assessing the soil consolidation, as one of the components of the

wall and ground deformations, were carried out based on finite element analysis since it is not

possible to separate the consolidation deformation component out of the total deformations from

the field data.

Osaimi & Clough (1979), Yong et al. (1989), Finno & Harahap (1991), and Ou & Lai (1994)

showed that significant consolidation can take place during the construction of a deep excavation

in clay and that the effects of consolidation are significant. Consolidation and swelling during

excavation result in changes in the shear strength of soils and time-dependent deformations. The

negative water pressure dissipates with time generated by the excavation at the base of the

excavation which causes loss of some passive resistance that occurs immediate after excavation.

This leads to time-dependent deformations in the wall and the soil behind the wall.

2.9. Excavation Geometry and Three-Dimensional Effects

2.9.1. Excavation dimensions and depth to firm layers

Manna and Clough (1981) utilized non-linear finite elements to study the effect of the excavation

dimensions and found that increasing the width of the excavation and the depth to firm layer

increase the maximum ground settlement and the maximum wall deflection as shown in Figures

42 & 43. Similarly, Hsiao (2007) demonstrated that the maximum wall deflection has to be

modified by deflection reduction factor (K) due to presence of hard stratum. The deflection

reduction factor (K) is related to the ratio of the depth to hard stratum, measured from the current

40

excavation level, over the excavation width (T/B). At smaller T/B ratios (T/B0.4, the influence of the hard stratum is negligible as shown in Figure 44.

Figure 42. Effect of the excavation width on the maximum ground settlement and the wall deflection (Mana &

Clough, 1981)

Figure 43. Effect of the depth to firm layer on the maximum ground settlement and the wall deflection (Mana &

Clough, 1981)

41

Figure 44. The Effect of the hard stratum on the computed wall deflection (Hsiao, 2007)

2.9.2. Corner effect

Ou et al. (1996) performed parametric three-dimensional finite element analyses to investigate

the features of three-dimensional deep excavation behaviors. They found that close relationships

existed between the aspect ratio for excavation geometry (B/L) and wall deformation. B and L

are the excavation dimensions in horizontal plane in the direction of lateral wall measurements

and the perpendicular direction, respectively. Increasing the B/L decreases the wall deformation.

Additionally, the wall deformation of a deep excavation is directly related to the smallest

distance from the corner (d). The smaller is the value of d, the less is the wall deformation.

Ou et al. (1996) defined a ratio called the Plane Strain Ratio (PSR). PSR is defined as the ratio

of the maximum wall deformation of the cross section at a distance (d) from the excavation

corner to the maximum wall deformation in the plane strain conditions of the same geometry.

They established the relationship between (PSR), (B/L) & (d) based on the results of parametric

studies, as shown in Figure 45.

Figure 45. Plane strain ratio (PSR) as a function of the aspect ratio (B/L) and distance from the corner (d)

(Ou et al., 1996)

42

2.9.3. Parallel distribution

Finno & Roboski (2005); and Roboski &Finno (2006) studied deep excavations in soft to

medium clays based on the settlements that were observed using optical survey around a 12.8 m

deep excavation in Chicago. The excavation was supported by a flexible sheet pile wall and three

levels of regroutable anchors. They suggest a parallel distribution for the deformation to account

for the corner effect. They found that the complementary error function (erfc) can be used to

define the three-dimensional settlement distributions of ground movement around excavation of

finite length.

(3)

where max can be either maximum settlement or maximum lateral movement, L is the length of the excavation, and H is the height of the excavation as presented in Figure 46.

Figure 46. Three-dimensional distribution of settlement and lateral movement around finite deep excavation (Finno

& Roboski, 2005; Roboski &Finno, 2006)

43

2.10. Wall Installation Effect

The wall installation process can cause significantly movements in the surrounding ground. The

assumption of negligible deformations associated with wall installation may lead to a substantial

underestimation of excavation-related lateral movements (Ng and Yan, 1999; Gourvenec and

Powrie, 1999; Abdel Rahman and El-Sayed, 2002a, 2002b & 2009; El-Sayed and Abdel-

Rahman, 2002).

In a survey of the problematic deep excavations in The Netherlands carried out between years

2007-2012, Korff & Tol (2012) noted that many problematic deep excavation cases have been

reported as the designer of the wall supporting the deep excavation disregarded the installation

effects of the walls and foundations. Although a lot of efforts are often not saved into the design

of the wall stiffness and related assessment of possible damage to properties, the installation and

the associated deformations are often excluded which caused many problems later.

Morton et al (1980), Budge-Reid et al (1984), Cowland & Thorley (1984), and Thorley & Forth

(2002) reviewed the settlements induced by the construction of the diaphragm walls in Hong

Kong, particularly for the Mass Transit Railway project where soils are generally fill, marine

deposits and alluviums underlain by decomposed granite. Settlement values up to 150mm were

reported for shallow foundations while less settlement was reported for deep foundations as

shown in Figures 47, 48 & 49.

Figure 47. Settlement associated with trenching in Hong Kongs MTR (Morton et al., 1980)

44

Figure 48. Maximum building settlements due to slurry trench excavation for diaphragm walls as a function of

foundation depth in Hong Kongs MTR (Cowland & Thorley, 1984)

Figure 49. Building settlement due to diaphragm wall installation in Hong Kongs MTR (Budge-Reid et al., 1984)

45

Clough & ORourke (1990) showed that significant settlement may occur behind a diaphragm wall after installation (up to 0.15% of the trench depth) as shown in Figure 50. Deep trenches in

Hong Kongs marine and alluvial deposits controlled the data presented by Clough and ORourke (1990); therefore, it is anticipated that Figure 50 overestimates the ground movements in most cases.

Figure 50. Settlement due to installation of a diaphragm wall (Clough and ORourke, 1990)

Finno et al. (2002) observed that 25% of the total lateral movement occurred after installation pf

secant piles wall in soft to medium Chicago clay, as can be shown in Figure 51. It was concluded

that lateral movements of this magnitude cannot be neglected and must be taken into account

when designing support systems, especially when sensitive structures are nearby.

Figure 51. Lateral deformation associated with trenching for secant piles installed in Chicago clay

(Finno et al., 2002)

46

Poh and Wong (1998) investigated the influence of specific construction methods utilized to

install the diaphragm wall on the magnitude of lateral displacements. They found that the lateral

displacements decrease only slightly (approximately 10 percent) as the slurry level increases;

while the lateral displacements by approximately 50 percent if the slurry level decreases. They

also noted that increasing the holding time (i.e. time after the completion of the trench, but

before concreting) slightly the lateral soil movements (approximately 20 percent after 24 hours)

as shown in Figure 52.

Figure 52. The effect of slurry level variation and its holding time on the lateral deformations associated with

trenching (Poh and Wong, 1998)

CIRIA report 580 (Gaba et al., 2003) summarizes horizontal and vertical wall movements due to

installation of diaphragm walls and bored pile walls in stiff clays as shown in Figure 53. While

Clough & ORourke (1990) predicted that the maximum settlement could reach 0.15% of the trench depth, Gaba et al. (2003) found out that the maximum settlement is 0.04-0.05% of the

trench depth. The maximum lateral deformation is about 0.04 to 0.08% of the maximum trench

depth.

47

. Figure 53. Vertical deformations due to diaphragm wall installation (Gaba et al. 2003)

Gourvenec and Powrie (1999) investigated the influence of panel length and construction

sequence on the lateral deformations of a diaphragm wall. Figure 54 shows the lateral

displacements, normalized with respect to the maximum lateral displacement corresponding to

the plane strain case, versus depth, normalized with respect to the wall depth, for different panel

lengths. It can be seen in the figure that the maximum lateral displacements for panel lengths of

2.5, 3.75, 5 and 7.5 m are approximately 90, 75, 65 and 40 percent of the displacements obtained

for plane strains conditions ( L = ), respectively.

Figure 54. Influence of Panel Length on Lateral Displacements (Gourvenec & Powrie, 1999).

48

Abdel-Rahman & El-Sayed (2002a & 2002b), El-Sayed & Abdel Rahman (2002) and Abdel-

Rahman & El-Sayed (2009) studied a case history of diaphragm wall trenching and pit

excavation in Nile alluviums of the Greater Cairo. They augmented the field data with 2D and

3D finite elements. They have concluded the following:

Using 3D finite elements, the maximum settlement due to trenching was estimated to be about 0.048% of the maximum height of the trench for deep foundations and 0.03% of

the maximum height of the trench for shallow foundations.

Using 2D finite element, the maximum trenching settlement is estimated as 0.045% of the trench depth for both shallow and deep foundations as shown in Figure 55.

The maximum lateral deformation due to trenching is about 0.077% of the trench depth for piles and 0.047 % of the trench depth for the case of shallow foundations.

The maximum settlement in both cases was estimated to be 61% of the lateral displacement as shown in Figure 56.

Figure 55. The settlement envelopes for shallow and deep foundation due to trenching to a depth of 21m in the Nile

Alluviums in the Greater Cairo (Abdel-Rahman & El-Sayed, 2009).

49

Figure 56. The relationship between the lateral deformations and the maximum settlement due to trenching in the

Nile Alluviums in the Greater Cairo (El-Sayed & Abdel-Rahman, 2002).

2.11. Building Stiffness and Weight

There is a mutual influence between a building located nearby deep excavations and the induced

deformations. Both stiffness and weight of the building affect the final shape of the

deformations. The building stiffness tends to flatten the deformation across the building; while

the building weight increases the deformation especially in location close to the deep excavation.

Potts & Addenbrooke (1997) found that deformation induced by tunneling building deformation

is an interactive problem that can be solved using two relative stiffness ratios: a ratio expressing

for the bending stiffness of the building and the other is for the axial stiffness of the building.

Goh (2010) and Goh & Mair (2011) modified the relative stiffness ratios that were initially

proposed by Potts & Addenbrooke (1997) for tunneling to be utilized for deep excavations. They

introduced design charts that allow considering the effect of building stiffness on the induced

deformations. Mair (2011) showed that field data confirmed the trend according to Goh (2010)

and Goh & Mair (2011). The approach of relative stiffness is elaborated later in Section 10.3.3 in this state-of-the-art.

Burd et al. (2000) studied the deformation associated with tunneling and found the following

differences between the building influence in sagging and hogging ground deformation modes:

1. The stiffness of the building reduces the differential settlement in sagging deformation. They suggest that the ground provides a certain amount of lateral restraint when the

building is subjected to sagging deformation similar to the conclusions of Burland &

Wroth (1974 & 1975).

2. In hogging mode, such a restraint is not provided and the structure behaves more flexibly leading to higher degrees of damage than in sagging. Burd et al. (2000) related this

behavior to the imposition of building weight which alters the settlement behavior

compared to the greenfield deformations.

50

Elshafie (2008) performed centrifuge tests on model buildings subject to excavation-induced

ground displacements as shown in Figure 57. Buildings with two foundation types: raft and

isolated footings, were introduced near the deep excavation. Simulated buildings were made

from micro-concrete with variable stiffness, weights and interface roughness. He noted the

following:

1. Horizontal displacements are clearly influenced by a smooth interface, leaving the green field soil displacements intact, even for higher axial stiffness. Rough interfaces restrained

the horizontal movements of the building.

2. The roughness of the buildings-soil significantly affects by the axial stiffness of the blocks. Increasing the roughness increases the axial stiffness of the building. The effect

of the interface between the soil and the building is seen especially for buildings with low

bending stiffness. Stiff buildings tend to tilt regardless of the interface roughness.

3. The effect of building weight (up to 40 kPa) was small (maximum about 10% increase in deflection ratio) as long as a high factor of stability (> 1.4) of the wall was maintained.

This conclusion is in line with the findings of Franzius et al. (2004) for the deformations

induced by tunneling.

4. Buildings with individual spread footings experience large differential deformations, because footings outside the zone of influence do not follow the influenced part of the

building. This results in significant distortions and tensile strains concentrating at the

weak parts of the buildings.

Figure 5

STATE-OF-THE-ART REPORT: EFORMATIONS ASSOCIATED WITH DEEP EXCAVATION AND THEIR EFFECTS ON NEARBY...

Documents

Transcript of STATE-OF-THE-ART REPORT: EFORMATIONS ASSOCIATED WITH DEEP EXCAVATION AND THEIR EFFECTS ON NEARBY...