Gulf /Artelia International. Associate Professor - Ain Shams University. Presented in âUnderground Infrastructure & Deep Foundations UAE Summitâ, 7-10.
Deformations Associated with Deep Excavation and their Effects on Nearby Structures (State-of-Art) BY
Sayed Mohamed El-Sayed Elaraby Associate Professor - Ain Shams University
Hossam Eldin Abdallah Ali Associate Geotechnical Manager at SogreahGulf /Artelia International Associate Professor - Ain Shams University
Presented in “Underground Infrastructure & Deep Foundations UAE Summit”, 7-10 December 2014, Dubai, UAE
CONTENTS 1.
Effects of Deformations Induced by Deep Excavations on Nearby Buildings
2. 3. 4. 5. 6. 7.
Factors Affecting the Induced Deformations Prediction of the Induced Deformations Building Damage Assessment
Observational Method and Monitoring Risk mitigation and Risk Management
Summary
2
CONTENTS 1.
Effects of Deformations Induced by Deep Excavations on Nearby Buildings
2. 3. 4. 5. 6. 7.
Factors Affecting the Induced Deformations Prediction of the Induced Deformations Building Damage Assessment
Observational Method and Monitoring Risk mitigation and Risk Management
Summary
3
1. Effects of Deformations Induced by Deep Excavations
Failures due to instability of the excavations or large deformations associated with unbraced excavation (rare)
Aesthetical and serviceability problems due to induced deformations (frequent)
4
5
1. Effects of Deformations Induced by Deep Excavations
CONTENTS 1.
Effects of Deformations Induced by Deep Excavations on Nearby Buildings
2. 3. 4. 5. 6. 7.
Factors Affecting the Induced Deformations Prediction of the Induced Deformations Building Damage Assessment
Observational Method and Monitoring Risk mitigation and Risk Management
Summary
6
Factors Affecting the Induced Deformations
Soil type
Wall stiffness and overall system stability
GW Control
Strutting system
Construction system
Time
Excavation dimensions
Building characteristics
7
2. Factors Affecting the Induced Deformations
Soil Type Peck (1969)
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2. Factors Affecting the Induced Deformations
Soil Type
O’Rourke et al. (1976) The maximum surface settlements observed in deep excavations in Washington, which is characterized by stiff clays interbedded with dense sand, were equal to or less than 0.3% of the excavation depth near the edge of the cut and 0.05% at a distance equal to 1.5 times the excavation depth.
For Chicago soft clay, the maximum settlements were in agreement with Peck’s (1969a) recommendations. Three zones of ground displacement can be distinguished and related to the characteristics of construction.
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2. Factors Affecting the Induced Deformations
Soil Type
Goldberg et al., (1976) •
The maximum surficial settlement behind the wall was found to lie between 0.5-2.0 times the maximum horizontal wall deflection.
•
The maximum settlements behind the wall are generally about 0.171% of the excavation depth in sands, gravels and very stiff to hard clays and 1.22% for soft to stiff clays. The settlement envelopes are:
10
2. Factors Affecting the Induced Deformations
Wall stiffness and stability
Goldberg et al., (1976) • • •
Lateral deformation in Clay Using FE and field measurements Using Stability Number
Manna & Clough (1981) • • •
Lateral deformation in clay Using FE and field measurements Using FoS against Basal Heave
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2. Factors Affecting the Induced Deformations
Wall stiffness and stability
Clough et al. (1989); Clough and O’Rourke (1990) • • • • •
Lateral deformation in clay soils Using Non-linear FE and field measurements Using System Stiffness factor (K1) Varying inter-relation between wall stiffness and basal heave FoS. Ignoring wall embedment
Flexible systems
Rigid systems
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2. Factors Affecting the Induced Deformations
Wall stiffness and stability
Long (2001) • • • • •
Lateral deformation in clay soils Using 296 case histories Verification of Clough’s work. Using same System Stiffness factor (K1) No impact of wall stiffness for basal heave FoS >3.
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2. Factors Affecting the Induced Deformations
Wall stiffness and stability Moormann (2002 & 2004) • • • • •
Lateral deformation in soft and stiff clay soils Using 500 case histories Verification of Clough’s work. Using same System Stiffness factor (K1) Stressing on the impact of : •
Embedment, GWT, surrounding buildings, workmanship, excavation sequence, type of struts and anchors and time.
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2. Factors Affecting the Induced Deformations
Wall stiffness and stability
Zapata-Medina (2007) •
Lateral deformation in soft medium and stiff clay soils.
•
Using 30 case histories.
•
The database was backanalyzed using 3D FE for a base for parametric analysis.
•
Verification of Clough’s work.
•
Using revised System Stiffness factor (R)
•
Ukritchon et al.’s (2003) factor of safety was used
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OCR & K0
2. Factors Affecting the Induced Deformations
Mayne and Kulhawy (1982)
• •
Higher K0 leads to higher forces and deformation In high K0 soils, strutting system may not so effective for reducing vertical movements
Peck (1969) •
Higher OCR may leads to heave near the wall
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Dewatering and Groundwater Control
2. Factors Affecting the Induced Deformations
Clough and O’Rourke (1990)
El-Nahhas (2006)
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2. Factors Affecting the Induced Deformations
Dewatering and Groundwater Control
Failure due to soil erosion due to improper dewatering
The Collapse of City Archive Building in Cologne - Rowson (2009)
Leaking joints Leakage and damage at the building pit in Middelburg, the Netherland (Van Baars, 2011)
Excessive settlement due to improper filter design
Damage due to Subsidence along an underground station of the North-South Train Line in Amsterdam (Van Baars, 2011). 18
2. Factors Affecting the Induced Deformations
Dewatering and Groundwater Control
Failure of a diaphragm wall in The Infinity Tower in Dubai in 2007 in chronological sequence
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Strut/Tie-back Prestressing & Stiffness
2. Factors Affecting the Induced Deformations
Clough (1975)
Manna & Clough (1981)
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Construction Sequence
2. Factors Affecting the Induced Deformations
Down-top (Conventional) Construction
Top-down Construction
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2. Factors Affecting the Induced Deformations
Wall Deformation Patterns Clough & O’Rourke (1990)
spandrel
concave
Lateral and vertical displacement patterns (Boone 2003; Boone & Westland, 2005).
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2. Factors Affecting the Induced Deformations
Wall Deformation Patterns
Spandrel-type settlement trough (Ou et al., 1993) •
A tri-linear settlement profile representing 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
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2. Factors Affecting the Induced Deformations
Wall Deformation Patterns
Spandrel-type settlement trough (Lee et al., 2007) •
proposed a Gaussian distribution to represent lateral Sh and vertical Sv deformations associated with the wall cantilever mode in terms of the maximum wall deformations Sw and the trough width W
•
Where b is the ratio between the maximum wall deflection and the maximum surface settlement (assumed to be 0.5 for DW and 1.0 for steel SPW).
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2. Factors Affecting the Induced Deformations
Wall Deformation - Patterns Aye et al. (2006) • • •
Analysis for the induced settlement associated with wall cantilever mode and braced mode. Lateral wall deflection determined using 1-D beam-spring model Numerically integrated to obtain the volume of the wall deflection (Vo)
Concave settlement profile
Spandrel-type settlement trough
Lateral deformations
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2. Factors Affecting the Induced Deformations
Wall Deformation Patterns Concave settlement profile (Karlsrud, 1997) •
Relationship between the maximum wall movement and surficial ground settlements
•
From sites with soft clays and loose to medium dense sand and silts.
•
for structures laying at distances from the wall smaller than 0.2 times the excavation depth, the settlements may be quite uncertain.
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2. Factors Affecting the Induced Deformations
Wall Deformation Patterns
Concave settlement profile (Hsieh & Ou, 1998) • • • •
Concave settlement profile for the bulging mode of wall Based on analysis of 9 case histories. Maximum settlement assumed to occur at 0.5 excavation height . Settlement at the wall is approximated to 50% of the maximum settlement
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2. Factors Affecting the Induced Deformations
Wall Deformation Patterns
Concave settlement profile (Schuster et al., 2009) •
proposed a concave settlement pattern along with its associated lateral deformation patterns.
•
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.
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2. Factors Affecting the Induced Deformations
Time-Dependent Effects
•
Longer construction time increases wall deformation due to creep and consolidation
•
The negative pore water pressure dissipates with time generated by the excavation at the base of the excavation causes changes in soil shear strength
•
loss of some passive resistance occurs immediately after excavation.
•
This leads to time-dependent deformations in the wall and the soil behind the wall.
Excavation Geometry and Three-Dimensional Effects Mana & Clough (1981) & Hsiao (2007)
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Three-dimensional Effects
2. Factors Affecting the Induced Deformations
Corner effect (Ou et al., 1996)
Parallel distribution (Finno & Roboski, 2005; Roboski &Finno, 2006)
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2. Factors Affecting the Induced Deformations
Wall Installation Induced Movement
• • • •
Morton et al (1980), Budge-Reid et al (1984), Cowland & Thorley (1984), and Thorley & Forth (2002)
Clough and O’Rourke (1990)
Gaba et al. (2003)
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Wall Installation Induced Movement
Lateral deformation associated with trenching for secant piles installed in Chicago clay (Finno et al., 2002)
Influence of Panel Length on Lateral Displacements (Gourvenec & Powrie, 1999).
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2. Factors Affecting the Induced Deformations
Wall Installation Induced Movement
Trench Depth D = 21 m
• •
El-Sayed & Abdel Rahman (2002) Abdel-Rahman & El-Sayed (2009)
• •
Combined field data with 2D and 3D FE. 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. 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. Maximum settlement estimated to be 61% of the lateral displacement
•
•
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2. Factors Affecting the Induced Deformations
Building Weight and Stiffness Burd et al (2000)
The effect of building weight is small as long as a high factor of stability of the wall is maintained. The stiffness of the building reduces the differential settlement in sagging deformation. In hogging mode, such restraint is not provided and the structure behaves more flexibly leading to higher degrees of damage. Burd et al. (2000) related this behavior to the imposition of building weight which alters the settlement behavior compared to the greenfield deformations.
Elshafie (2008) Minimum impact if building induced bearing stress is less than 40 kPa as long as a high factor of stability (> 1.4) of the wall was maintained. Buildings with individual spread footings experience larger differential deformations. 34
2. Factors Affecting the Induced Deformations
Wall-Soil Interface Yu & Gang (2008)
•
the variation of the maximum lateral deformation, maximum settlement and their ratio impacted by the variation of the interface friction angle.
•
For smooth wall, the deformations (viz., maximum wall deflection is 0.2% and maximum settlement is 0.27% of the excavation depth) compared to rough walls (viz., maximum wall deflection is 0.1-0.125% and maximum settlement is 0.04 - 0.1% of the excavation depth).
•
The ratio between the maximum settlement and the maximum wall deflection also decreases from 1.35 in smooth walls to 0.5-0.75 in rough walls.
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2. Factors Affecting the Induced Deformations
Workmanship
•
Earlier warning by Peck (1969).
•
Workmanship can be considered as the human and/or experience factors which plays an important role in the success or failure of a certain project.
•
About 10% of the problematic deep excavation cases in the Netherlands for the projects done between 2007-2012, poor workmanship was a main factor in the encountered problems; it was related to the installation of diaphragm wall, piled walls or anchors (Korff & Tol, 2012).
•
Sowers (1993) demonstrated that out of 500 well documented foundation failures, the majority (88%) of failures were due to human shortcomings; only 12% of the failures were due to lack of technology.
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CONTENTS 1.
Effects of Deformations Induced by Deep Excavations on Nearby Buildings
2. 3. 4. 5. 6. 7.
Factors Affecting the Induced Deformations Prediction of the Induced Deformations Building Damage Assessment
Observational Method and Monitoring Risk mitigation and Risk Management
Summary
37
i- Empirical and semi-empirical approach
3. Prediction of the Induced Deformations
i- Empirical and Semi-Empirical Approaches
• F: Flexible walls (SPW) • S: Stiff walls (diaphragm walls, secant pile walls, tangent pile wall) • M: Mix types (flexible + stiff)
• A: All activities (Pit excavation + Wall Installation) • P: Pit excavation • W: Wall installation
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Boone (2003)
Zapata-Medina (2007)
i- Empirical and semi-empirical approach
3. Prediction of the Induced Deformations
Based on Manna and Clough (1981) and Clough et al. (1989)
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i- Empirical and semi-empirical approach
3. Prediction of the Induced Deformations
Hsiao (2007)
40
ii- Numerical modeling Beam-Column on Elastic Winkler Springs
Reference Deflection Method (Weatherby et al., 1998)
ii- Numerical modeling
3. Prediction of the Induced Deformations
Pfister et al. (1982)
41
The Finite Element Method
ii- Numerical modeling
3. Prediction of the Induced Deformations
Abdel-Rahman (1993); Hashash & Whittle (1996)
Gutierrez et al. (2002)
Kung (2010)
42
Material Parameters
•
Mesh Sizing
•
Constitutive Model
•
Model Dimension (2D/3D)
BC / FoS
•
Upper-Bound Solution
No of Elements Deformation
ii- Numerical modeling
3. Prediction of the Induced Deformations
The Finite Element Method: Main Considerations
Lower-Bound Solution No of Elements
43
iii - Analytical approach
iii - Analytical approach
3. Prediction of the Induced Deformations
Mobilizable Strength Method
•
Osman and Bolton (2004, 2006 & 2007);
•
Bolton et al. (1989, 1990, 2008 & 2010) ;
•
Bolton (2011)
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iv- Physical and Centrifugal Modeling
3. Prediction of the Induced Deformations
iv- Physical and Centrifugal Modeling Lam et al. (2011)
Laefer (2001)
45
v- Artificial Neural Networks (ANNS)
3. Prediction of the Induced Deformations
v- Artificial Neural Networks (ANNs) o ANN is a powerful data modeling (computational) tool capable of capturing and representing complex input/output relationships;
o Development of ANNs was motivated by desire to develop an “artificial neural system” that can perform "intelligent" tasks similar to human brain; o ANNs resemble human brain functions in the following two ways; • •
Acquires knowledge through learning; Storing knowledge within inter-neuron connection strengths known as synaptic weights;
o The ability to represent both linear and non-linear relationships and in their ability to learn these relationships directly from available databases.
46
v- Artificial Neural Networks (ANNS)
3. Prediction of the Induced Deformations
Rod El-Farag Station
After (Fayed, 2002) ANN Deformation Predictions near Several Metro Stations of Greater Cairo El-Dokki Station
El-Behoos Station
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CONTENTS 1.
Effects of Deformations Induced by Deep Excavations on Nearby Buildings
2. 3. 4. 5. 6. 7.
Factors Affecting the Induced Deformations Prediction of the Induced Deformations Building Damage Assessment
Observational Method and Monitoring Risk mitigation and Risk Management
Summary
48
2. Differential or relative settlement (dS) is the difference between two settlement values. The maximum differential settlement is denoted as (dSmax).
Deformation Measures
4. Building Damage Assessment
1. Settlement (S) is the vertical movement of a point. The maximum settlement is denoted as (Smax).
3. Rotation or slope (q) describes the change in gradient of the straight horizontal line defined by two reference points embedded in the structure with respect to their initial horizontal orientation. The maximum rotation is denoted as (qmax). 4. Angular distortion (b) is an angle that produces sagging (or upward concavity) when it is a directed downward from the building titled as a rigid body, or hogging (or downward concavity) when is directed upward from titled rigid body building. The maximum angular distortion is denoted as (b max).
5. Deflection Ratio (DF=D/L) is defined as the quotient of relative defection (D) and the corresponding length (L). 6. Tilt (w) describes the rigid body rotation of the whole superstructure or a well-defined part of it. 7.
Average horizontal strain eh develops as a change in horizontal length over the corresponding length; i.e., eh = (L2 – L1)/L.
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50
Building Deformational Modes
4. Building Damage Assessment
i- Angular Distortion (b)
i- Angular Distortion (b) L)
4. Building Damage Assessment
Skempton and MacDonald (1956) for Buildings with no excavation 1. 2. 3.
4.
Structural damage b < 1/150 (40 mm / 6m span). Aesthetical damage b< 1/300 (20 mm / 6m span). Recommended angular distortion in excess of 1/500 to avoid cracking. (12 mm / 6 m spans) To ensure that no cracking will occur the limit should be at least 1/1000) (6 mm / 6 m spans)
Bjerrum (1963) More levels of serviceability damages
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ii- Deflection Ratio (DL=D/L)
4. Building Damage Assessment
ii- Deflection Ratio (DL=D/L) Polshin and Tokar (1957) for unreinforced load bearing walls 1. Sagging mode - (L/H ≤ 3), Maximum deflection ratio D/L< 1/3300 to 1/2500 2. Sagging mode - (L/H ≥ 5), Maximum deflection ratio D/L< 1/2000 to 1/1400 L is the distance between two joints H is the Building Height
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iii- Deep Beam Model
iii- Deep Beam Model
4. Building Damage Assessment
Burland & Wroth (1974 & 1975); Burland et al. (1977)
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iii- Deep Beam Model
Threshold of damage for sagging of load bearing walls
iii- Deep Beam Model
4. Building Damage Assessment
Burland & Wroth (1974 & 1975); Burland et al. (1977)
Sagging mode, E/G = 2.6
D L H t
G E
Threshold of damage for hogging of load bearing walls
Hogging mode, E/G = 2.6
is the mid span deflection is the length in sagging / hogging is the height of the building from foundation to roof is the distance of the neutral axis to the edge of the beam. • for unreinforced bearing walls undergoing settlement sagging mode (t=H/2). • For the hogging, unreinforced bearing walls building (t=H). • For reinforced walls and frame structure (t=H). is the shear modulus of the beam representing the building is young's modulus of the beam representing the building
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iii- Deep Beam Model
4. Building Damage Assessment
Damage criteria according to Burland et al. (1977) & BRE Digest 251 (1995)
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iii- Effect of horizontal strains
iii- Effect of horizontal strains
4. Building Damage Assessment
Damage criterion according to Burland (1997)
Relationship of Damage to Angular Distortion and Horizontal Extension Strain according to Boscardin & Cording (1989)
1/1000
1/500
1/300
1/200
1/150
Boscardin & Cording (1989) developed damaging criterion for buildings adjacent to excavations in form of multi-dimensional relationship between the angular distortion b, the horizontal strain eh and the expected tensile strain/degree of severity Their criterion was based on the state of strain of a simple deep beam with L/H=1, E/G=2.6, and neutral axis at the bottom of the beam. The critical tensile strains for different damage levels were determined considering the field observations of damage associated with deep excavations and tunnels.
56
iii- Effect of horizontal strains
iii- Effect of horizontal strains
4. Building Damage Assessment
Damage zones with different critical tensile strains according Son & Cording (2005)
Tensile strain components due to horizontal strain, angular distortion and tilting for wall with L/H=1 & E/G =2.6 (Son & Cording, 2005)
57
Risk categories according to Rankin (1988)
1
Risk category Negligible
Maximum rotation (qmax) Less than 1/500
Maximum Settlement (max) > 10 mm
2
Slight
1/500-1/200
10 – 50 mm
3
Moderate
1/200-1/50
50 – 75 mm
4
High
Greater than 1/50
Greater than 75 mm
iii- Effect of horizontal strains
4. Building Damage Assessment
No.
Description of the risk Superficial damage unlikely Possible superficial damage which is unlikely to have structural significance Expected superficial damage and possible structural damage to building, possible damage to relatively rigid pipelines Expected structural damage to buildings. Expected damage to rigid pipelines, possible damage to other pipelines
The Damage Potential Index DPI thresholds (Schuster et al., 2009) Level of damage caused by excavation
DPI for sagging settlements (d/He ≤1.4)
DPI for hogging settlements (d/He >1.4)
1. Negligible
0-15
0-10
2. Slight
15-25
10-20
3. Slight to moderate
25-35
20-30
4. Moderate
35-60
30-50
5. Severe
60-85
50-80
>85
>80
6. Very severe
DPI = ec / (1/200) x 100 Remedial measures
Damage levels 1 and 2 are considered as tolerable, and no scheme to protect adjacent buildings is required. At damage level 3, possible damage to adjacent buildings might be intolerable. A protection scheme might be required in the design stage. If not implemented, great caution must be exercised to monitor the building during the construction. Damage levels 4, 5, and 6 are definitely intolerable. The excavation design should be reexamined and possibly changed. Or, a proper protection scheme must be implemented to protect adjacent buildings. 58
iv- Three-phase building damage assessment
4. Building Damage Assessment
iv- Three-phases building damage assessment Mair et al. (1996) Son & Cording (2005) a systematic procedure for damage assessment of buildings. The design approach consists of three stages:
1. Preliminary assessment 2. Second stage assessment 3. Detailed evaluation.
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vi- Factors affecting the structural response vi- Factors affecting the structural response
4. Building Damage Assessment
Ratio of the building’s Young modulus to its shear modulus E/G Burland & Wroth (1974 & 1975) and Burland et al. (1977) E/G =
2.6 12.5 0.5
for masonry walls, for frame & for little or no tensile restraint
Finno et al. (2005) Developed more detailed procedure for analysis of framed structures that accounts for the distribution of the stiffness of the slabs and the columns.
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Grade beams vi- Factors affecting the structural response
4. Building Damage Assessment
Boscardin & Cording (1989) Investigated the effect of grade beams to reduce the greenfield horizontal tensile strain egh to less strain eh, where EgA is the stiffness and area of the grade beam foundation, Es is the soil stiffness, H is the height of excavation or the length of the section of the foundation being strained, and S is the spacing between grade beams. A great benefit is noticed by using ground beam. More than 90% of the greenfield direct tensile strain is eliminated with the presence of a light grade beam; heavy grade beams do not add substantial reduction to the direct tensile strain induced by deep excavations.
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CONTENTS 1.
Effects of Deformations Induced by Deep Excavations on Nearby Buildings
2. 3. 4. 5. 6. 7.
Factors Affecting the Induced Deformations Prediction of the Induced Deformations. Building Damage Assessment
Observational Method and Monitoring Risk mitigation and Risk Management
Summary
62
i- Conventional deformation & stress monitoring
5. Observational Method and Monitoring
Deformations
Stresses
Surface points
Piezometers
Extensometers
Strain gauges
Inclinometers 63
64
i- Conventional deformation & stress monitoring
5. Observational Method and Monitoring
ii- Continuous Monitoring
5. Observational Method and Monitoring
A Reflectorless Robotic Total Station (RRTS) measuring RSPs and prisms (Tamagnan & Beth, 2012)
Terrestrial Laser Scanning (TLS)
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CONTENTS 1.
Effects of Deformations Induced by Deep Excavations on Nearby Buildings
2. 3. 4. 5. 6. 7.
Factors Affecting the Induced Deformations Prediction of the Induced Deformations Building Damage Assessment
Observational Method and Monitoring Risk mitigation and Risk Management
Summary
66
6. Risk mitigation and Risk Management
Risk Mitigation Proper Planning and Design Proper Monitoring Critical Validation Detailed risk mitigation and control plan
67
6. Risk mitigation and Risk Management
Geotechnical-related Risks Ground and groundwater conditions can be spatially extremely variable. Unlike other construction materials, unexpected ground conditions are common.
Events associated to ground-related problems often have a disproportionate impact on the Project cost and progress. Less than 1% of the Project cost usually spent on soil investigation.
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(after Abdel-Rahman, 2007)
69
6. Risk mitigation and Risk Management
6. Risk mitigation and Risk Management
Example of a risk plan (after Abdel-Rahman, 2007)
Risk source Contingency plan of action Excessive lateral movement of the wall and Increase the number of lateral supports ground settlement Instability of the grout plug Refill the excavation pit with water up to the level that adequately re-stabilize the situation, or perform heavy dewatering to lower the water table as needed. Insufficient drawdown to the water below Increase the number of wells excavation level Lateral leaking from the support system Inject grout columns behind the leaking locations
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7. Summary
Concluding Remarks
Deep excavations rarely cause failures of adjacent structures yet they often produce serviceability problems to nearby buildings.
More sophisticated approaches to be followed in design of underground works.
The induced deformations depend on many aspects (e.g. the soil strength and stiffness, time-dependent behavior, wall stiffness, method and sequence of construction, prestressing of the struts and anchors, the presence of nearby structures, etc.).
A well-designed support systems for deep excavations do not only ensure the stability of the excavation itself but also warrant less possibilities of damages to the adjacent buildings and utilities.
Numerous empirical methods are available to estimate the deformations associated with deep excavations based on the worldwide databases of the monitoring observations but not based on local measurements.
Computational methods such as Artificial Neural Networks and the empirical and semiempirical approaches can be utilized to validate the findings of the numerical methods such as the finite element method.
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7. Summary
Concluding Remarks (II)
The deformations patterns associated with deep excavations depend of the mode of the wall deformations.
Many damage criteria have been set to assess the effect of the ground deformations induced by deep excavations. They account for the effects of the differential settlements and the horizontal strain caused by deep excavations.
Monitoring programs are powerful “essential” tool in the observational approach and to allow for design validation/rectification/re-calibration, future feedback and more importantly as an early warning tool.
Proper and comprehensive soil Instigation is not a luxury.
Detailed risk management is essential to proceed smoothly in the face of the numerous risks associated with deep excavation, particularly the risks associated with unforeseen geotechnical conditions or construction problems.
The design of important deep excavations require independent checking (IDC).
Good Workmanship has to be maintained.
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