基坑降水引起的相邻建筑物直接经济损失预测的研究

1
outline
• Background • Ground water table after pumping • Ground settlement caused by water pumping • Ground settlement and settlement gradient • Adjacent building direct loss prediction • Practical application
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Adjacent ground settlement and crack caused by ground water pumping in construction pit
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Pipeline cut by ground settlement that resulted from
ground water pumping
obtained S1, the modification factor ψ has to be determined first
s

n i 1
w
2Esi
(H
2 i

H
2 i 1
)
(3.1)
modification factor ψ: _determined by local engineering geology condition.
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Residential buildings damaged by ground settlement that resulted from ground water pumping
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How far? Magnitude? Is settlement magnitude the only factor?
125.6
35.5
6
14.52
119.94
29.7
7
14.76
122.12
34.8
8
14.62
120.83
36.3
9
15.14
125.51
37.5
ψ
0.2956 0.2797 0.3331 0.2965 0.2826 0.2476 0.2850 0.3004 0.2988
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modification factor ψ
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3 Ground settlement caused by water pumping
3.1 Algorithm-soil compression accumulation (SCA)
For the convenience of engineers, the algorithm stipulated in
national codes system
This must be taken into consideration!
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Determining of ground water table after pumping
Assumptions: 2-dimension stable flow, without water cutting wall
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Zhengzhou International Conference and Exhibition Center (ICEC)
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Zhengzhou ICEC Hotel
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Zijingshan Metro Station: In the future, the L-2 Metro line will run beneath this station. Here will be a busy transfer center for travelers.
-10.95
Distance to the edge of pit (m)
-26
-9.69 -40
-9.69 -40
-8.74 -52
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Calculated water table and monitored water table
After verification in six projects, it is found that the Dupuit's equation can be used to determine the water table after pumping
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Modification factor
No. Water table Calculated
Monitored
settlement (mm) settlement (mm)
1
10.79
91.35
27.0
2
10.43
89.03
24.9
3
12.16
100.87
33.6
4
13.84
114
33.8
5
15.15
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4.2 Algorithm
(1) The ground near the construction pit is divided into a series of donuts.
(2) Equation (3.1) is employed to determine the settlement of each donut (the middle line of each donut is taken as target).
29.7
1.71%
7
35.41
34.8
1.77%
8
35.04
36.3
3.47%
9
36.40
37.5
2.94%
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4 Building loss results from ground settlement 4.1 Main assumption
Only direct loss is taken into consideration
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However, these algorithms are too complicated to be applied in practical
project! On the other hand, most of the Chinese civil engineers are used to following the
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4.4 ground settlement gradient
No. Gi No. Gi No.
2
1 Study background
●More and more skyscrapers: deep foundation pits ●more and more underground projects
Metro underground shop mall Result in: Deep excavation
surrounding the pit
The ground water table may be obtained by
Snw lgRlg(rD)
Sw
lgRlgr
(Dupuit's equation)
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Loess geological area
Alluvion geological area
Ground settlement gradient
Adjacent building direct loss prediction
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2 Ground water table and contour after pumping
2.1 General algorithm for water table determining A-Solution of fluid mechanism: strict analytic solution
Chinese National Code (SCA) is employed:
s1

n i 1
w
2 Esi
(H
2 i

H
2 i 1
)
s2

m jn

wH EsiLeabharlann n(Hj H ji )
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S2-usually very small, may be neglected According to the National Code, in order to
Direct loss Prediction on Buildings around Construction Pit Caused by Ground Water Pumping
SONG Jianxue in collaboration with SONG Danju
Zhengzhou University
Pore water pressure numerical simulation-1
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Pore water pressure numerical simulation-2
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Ground settlement numerical simulation-1
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Ground settlement numerical simulation-2
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Construction pit ground water pumping
Determining of ground water table and contour after pumping
Building direct loss vs. ground
settlement gradient
Determining of ground settlement and contour
No. Modified calculation
Monitored
error
settlement (mm) settlement (mm)
S=ψS1
1
26.49
27
1.88%
2
25.82
24.9
3.69%
3
29.25
33.6
2.94%
4
33.06
33.8
2.19%
5
36.42
35.5
2.60%
6
34.78
(3) Settlement gradient between bordered donuts is obtained. (4) Economic loss rate vs. ground settlement gradient is set up. (5) A certain scope around the pit is chosen, all buildings loss in the
scope is accumulated.
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4.3 Donuts 4.3.1 Usually, the geometric center of pit is set as the center of all donuts 4.3.2 The affecting scope (taken as 5Sw, Sw-the depth of water table falling beneath the pit ground ) is divided into a series of donuts with the increment as 0.2Sw
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22
23
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Calculated water table and monitored water table
location monitored water table(m)
SW-70 -10.62
SW-67 -11.47
SW-68 -12.02
SW-69 -10.8
Calculated water table (m)
B-Solution of hydraulics: approximate solution
2H 2H 2H x2 y2 z2 0
(3-D stable flow)
H(TH)(TH)W (2-D stable flow)
t x x y y
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C- Numerical simulation
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Before applying, the validity of the formula has to be checked
Six projects are chosen as cases study, and only one is discussed here
Zhengzhou Metro Station: Athlete Center Station
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，
Presume ψ comply with the standard normal distribution
p()
1
e
( u )2 2 2
2
0.291
0.021
CV0.0217.2%10% 0.291
0.29
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Take ψ as 0.29, then the settlement calculation error