1. Construction Innovations and Future Infrastructures Research Center, Department of Civil Engineering, Faculty of Engineering, King Mongkut’s University of Technology Thonburi, Bangkok 10140, Thailand 2. Department of Civil Engineering, School of Engineering, King Mongkut’s Institute of Technology Ladkrabang, Bangkok 10520, Thailand 3. Soil Engineering Research Center, Department of Civil Engineering, King Mongkut’s University of Technology North Bangkok, Bangkok 10800, Thailand
Deep excavations in dense urban areas have caused damage to nearby existing structures in numerous past construction cases. Proper assessment is crucial in the initial design stages. This study develops equations to predict the existing pile bending moment and deflection produced by adjacent braced excavations. Influential parameters (i.e., the excavation geometry, diaphragm wall thickness, pile geometry, strength and small-strain stiffness of the soil, and soft clay thickness) were considered and employed in the developed equations. It is practically unfeasible to obtain measurement data; hence, artificial data for the bending moment and deflection of existing piles were produced from well-calibrated numerical analyses of hypothetical cases, using the three-dimensional finite element method. The developed equations were established through a multiple linear regression analysis of the artificial data, using the transformation technique. In addition, the three-dimensional nature of the excavation work was characterized by considering the excavation corner effect, using the plane strain ratio parameter. The estimation results of the developed equations can provide satisfactory pile bending moment and deflection data and are more accurate than those found in previous studies.
unloading/reloading stiffness from drained TX test
kPa
?
12000?27000
104000?158000
?
reference shear stiffness at very small strains
kPa
?
9000?20300
78300?118800
?
threshold shear strain at which
(?)
?
0.0001
0.0001
?
Poisson’s ratio for unloading/reloading
(?)
?
0.33
0.33
?
power of the stress level dependency of stiffness
(?)
?
1
1
?
effective cohesion
kPa
8
?
?
0
soil undrained shear strength
kPa
?
15?34
87?132
?
effective friction angle
°
22
0
0
36
dilatancy angle
°
0
0
0
0
failure ratio
(?)
?
0.9
0.9
?
reference stress for stiffnesses
kPa
?
100
95
?
-value for normally consolidated soils
(?)
0.625
0.625
0.625
0.412
Tab.1
Fig.2
Fig.3
parameter
symbol
unit
range
normalized parameter (dimensionless)
excavation depth
m
2, 5, 8, 11
excavation width
m
20, 40, 60, 80
thickness of diaphragm wall
m
0.6, 0.8, 1.0, 1.2
pile diameter
m
0.50, 0.75, 1.00, 1.25
pile length
m
15, 18, 23
pile distance from primary wall
m
0.6, 1, 3, 5, 10
pile distance from complementary wall
m
10, 20, 30
relative undrained shear strength ratio for soft clay
(?)
0.27, 0.30, 0.35, 0.38, 0.40
relative undrained shear strength ratio for stiff clay
(?)
0.45, 0.60, 0.75, 0.90, 1.05
relative shear stiffness ratio for soft clay
(?)
123, 158, 210, 263, 315
relative shear stiffness ratio for stiff clay
(?)
375, 525, 675, 825, 975
thickness of soft clay layer
m
11, 14, 16.5
Tab.2
Fig.4
Fig.5
design parameters included in predicted equations
symbols
Poulos and Chen [7]?
Liyanapathirana and Nishanthan [38]?
Zhang et al. [31]?
this study?
excavation depth
√
√
√
√
excavation width
×
×
√
√
wall thickness
√*
×
×
√***
strut stiffness
√
√
×
×
strut spacing (average value)
√
√
×
√***
unsupported depth of excavation
×
√
×
×
pile diameter (or width)
√
√
√
√
pile length
×
×
√
√
pile distance from excavation
√
√
√
√
pile-head fixity
×
×
√
√
axial load exerted on pile head
×
×
√
×
undrained shear strength of soft clay
√**
√**
×
√
undrained shear strength of stiff clay
√**
√**
×
√
shear stiffness of soft clay
×
×
×
√
shear stiffness of stiff clay
×
×
×
√
thickness of soft clay layer
×
×
×
√
Tab.3
Fig.6
No.
input variables,
coefficients of Eqs. (2), (5?7)
model A1 for predicting
model A2 for predicting
model B for predicting
β
a
b
c
α
a
b
c
η
a
b
c
0
?
?32.456
?
?
?
?14.613
?
?
?
?0.215
?
?
?
1
0.889
?83.340
70.909
4.864
1.067
?19.837
18.690
1.225
0.016
?
?
?
2
1.735
?
?
?
1.673
?0.066
0.465
2.262
0.726
?0.00019
0.00213
0.00999
3
0.717
0.318
?4.506
32.106
0.638
0.447
?6.839
28.132
0.614
0.00049
?0.00745
0.03876
4
0.509
3.793
?77.632
401.420
0.266
2.135
?53.457
338.350
1.079
0.00677
?0.14466
0.77826
5
?0.398
?
?
?
?0.174
?
?
?
?0.001
?
?
?
6
0.772
60.353
?56.828
24.013
0.912
?8.160
?0.463
6.021
0.819
?0.00788
?0.00916
0.01616
7
?5.396
?
?
?
?3.558
?
?
?
0.974
0.03095
?0.02983
0.01732
8
?1.255
?
?
?
?0.142
?
?
?
11.985
3.14 × 10?4
?6.71 × 10?4
0.00854
9
?0.038
?
?
?
?0.017
?
?
?
1.328
2.14 × 10?8
?4.60 × 10?5
0.02855
10
?0.007
?
?
?
?0.001
?
?
?
3.601
1.81 × 10?9
?5.00 × 10?6
0.01097
11
17.998
?
?
?
6.254
?
?
?
0.021
?
?
?
Tab.4
Fig.7
Fig.8
No.
input variables,
coefficients of Eqs. (2) and (8)
ω
a
b
c
0
?
?2.702
?
?
?
1
0.992
?0.03238
0.03900
0.84641
2
0.982
0.12381
?0.17917
0.91069
3
0.189
?0.15261
0.26377
0.74332
4
0.996
0.08356
?0.14026
0.87659
5
1.001
?0.37632
1.06570
0.22809
Tab.5
Fig.9
Fig.10
input variable,
value
remark
0.325
data from Goh et al. [8]: = 6.5 m
1
data from Goh et al. [8]: B = 20 m
4.761
data from Goh et al. [8] and Zhang et al. [31]: = 0.8 m, = 2.5 m and = kPa
11.562
data from Goh et al. [8]: = 1 m and assuming =
2.3
data from Goh et al. [8]: = 46 m
0.15
data from Goh et al. [8]: = 3 m
0.2825*
data from Zhang et al. [31]: = 25°
0.4698*
data from Zhang et al. [31]: = 40°
268**
data from Xuan [64]: = 700 and assuming = 100 kPa, , and
431**
data from Xuan [64]: = 700 and assuming = 100 kPa, , and
0.9
data from Zhang et al. [31]: = 18 m (base level of soft marine clay layer)
Tab.6
estimation method
observed and estimated values of (mm) at = 6.5 m
observed
estimated
error
proposed method of this study
15
14.84
1.05%
PC method
15
9.49
36.7%
LN method
15
65.52
336.8%
ZZG method
15
12.70
15.3%
Tab.7
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