1. School of Highway, Chang’an University, Xi’an 710064, China 2. China Electric Construction Group Northwest Survey and Design Institute Company, Xi’an 710064, China
Centrifugal model tests were used to analyze the effects of cave height changes when the foundation slope is certain under the vertical load at the pile top on the load-settlement curve of the pile foundation, the ultimate bearing capacity of the pile foundation, the pile axial force and the pile side resistance in order to analyze the vertical bearing characteristics of bridge pile foundations crossing the karst cave in the steep slope area. The key parameters affecting the vertical bearing characteristics of the pile foundation were given. Results show that the vertical ultimate bearing capacity of pile foundation decreases with the increase of karst cave height, and the decrease of ultimate bearing capacity increases with the increase of karst cave height under a certain pile length and total depth of the pile foundation into the rock. The decrease of ultimate bearing capacity is not obvious when the karst cave height is less than 1.2 times the pile diameter. The decrease of ultimate bearing capacity increases significantly when the karst cave height is larger than 2.4 times the pile diameter. The decay rate of pile axial force is slower in the pulverised clay layer, faster in the bearing stratum, and does not decay in the range of the karst cave. The decay rate of axial force in the range of the bearing stratum increases significantly after the karst cave height is larger than 2.4 times the pile diameter. The pile side resistance in the holding layer is significantly larger than that in the upper rock and soil layers, and zero in the karst cave. The proportion of pile side resistance in the vertical ultimate bearing capacity of pile foundation gradually decreases as the karst cave height increases. The pile side resistance is reduced by 65.5% when the cave height is larger than 2.4 times the pile diameter, and the pile foundation is gradually transformed from a friction pile to an end-bearing pile.
Yujie LI,Zhongju FENG,Jingbin HE,Cong ZHANG,Siqi WANG. Centrifugal test on vertical load bearing characteristic of pile foundation crossing karst cave in steep sloping area. Journal of ZheJiang University (Engineering Science), 2024, 58(11): 2384-2392.
Fig.2Location relationship of steep slope - pile -karst cave
Fig.3TLJ-3 centrifugal model machine
物理量
量纲
原型
离心模型
尺寸l
L
1
1/n
水质量分数w
—
1
1
密度ρ
ML?3
1
1
应变ε
—
1
1
应力σ
ML?1T?2
1
1
质量m
M
1
1/n3
力F
MLT?2
1
1/n2
土压力p
—
1
1/n
重度γ
—
1
n
加速度a
LT?2
1
n
时间t
T
1
1/n2
角度α
—
1
1
变形u
L
1
1/n
Tab.1Similarity relationship of physical quantity in centrifugal model test
Fig.4Pile model and karst cave model of centrifugal model test
类型
A/m2
E/GPa
EA/GN
误差/%
原型桩
3.14
30.00
94.20
1.2%
模型桩
207.24×10?6
46.00
95.33
Tab.2Compressive stiffness of model pile and prototype pile
类别
ww/%
γ/(kN·m?3)
E/MPa
φ/(°)
c/kPa
粉质黏土
30
18
28
22
28
中风化灰岩
1.3
25
6000
—
—
Tab.3Foundation soil parameter of model
类别
ww /%
γ/(kN·m?3)
E//MPa
φ/(°)
c/kPa
粉质黏土
30
19.5
29.2
19.8
27.8
中风化灰岩
1.5
27
6000
—
—
Tab.4Foundation soil parameter of prototype
l/mm
α/（°）
L/mm
H/mm
200
45
60 (2.4D)
无溶洞
200
45
60 (2.4D)
30 (1.2D)
200
45
60 (2.4D)
60 (2.4D)
200
45
60 (2.4D)
90 (3.6D)
200
45
60 (2.4D)
120 (4.8D)
Tab.5Condition setting of centrifugal model test
Fig.5Measuring device of pile top vertical displacement
Fig.6Schematic diagram of pile measurement point layout
Fig.7P-S curve of pile foundation under different karst cave height
Fig.8Vertical ultimate bearing capacity of pile foundation under different karst cave height
Fig.9Axial force distribution of pile at different cave height
Fig.10Effect of cave height on pile axial force distribution
Fig.11Distribution of pile lateral resistance at different cave height
Fig.12Effect of cave height on pile lateral resistance distribution
Fig.13Effect of cave height on pile foundation sub-load capacity
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