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浙江大学学报(工学版)
Journal of ZheJiang University (Engineering Science)  2024, Vol. 58 Issue (11): 2384-2392    DOI: 10.3785/j.issn.1008-973X.2024.11.020
    
Centrifugal test on vertical load bearing characteristic of pile foundation crossing karst cave in steep sloping area
Yujie LI1(),Zhongju FENG1,*(),Jingbin HE2,Cong ZHANG1,Siqi WANG1
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
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Abstract  

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.

Key words： steep slope      karst      bridge pile foundation      centrifugal test      load-bearing characteristic     
Received: 24 August 2023      Published: 23 October 2024
CLC:  U 443  
Fund:  国家自然科学基金青年科学基金资助项目（4190070568）；国家重点研发计划资助项目（2018YFC1504801-04）.
Corresponding Authors: Zhongju FENG     E-mail: lyjie2022@163.com;ysf@gl.chd.edu.cn
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Yujie LI
Zhongju FENG
Jingbin HE
Cong ZHANG
Siqi WANG
Cite this article:

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.

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https://www.zjujournals.com/eng/10.3785/j.issn.1008-973X.2024.11.020     OR     https://www.zjujournals.com/eng/Y2024/V58/I11/2384


陡坡段穿越溶洞桩基竖向承载特性离心试验

为了研究陡坡段桥梁桩基穿越溶洞时的竖向承载特性，利用离心模型试验，研究陡坡坡度一定时，桩顶竖向荷载作用下溶洞高度变化对桩基础荷载-沉降曲线、桩基极限承载力、桩身轴力及桩侧阻力的影响，给出影响桩基竖向承载特性的关键参数. 结果表明，在桩长及桩基入岩总深度一定的情况下，桩基竖向极限承载力随溶洞高度的增大而减小，极限承载力减幅随溶洞高度的增大而增大. 当洞高小于1.2倍桩径时，极限承载力的减幅不明显. 当洞高大于2.4倍桩径时，极限承载力的减幅显著增大. 桩身轴力的衰减速度在粉质黏土层内较小，在持力层内较大，在溶洞范围内基本不衰减. 当洞高大于2.4倍桩径时，持力层范围内的轴力衰减幅度显著增大. 桩侧阻力在持力层内显著大于上部岩土层，在溶洞范围内几乎为零. 随着溶洞高度的增大，桩基础竖向极限承载力中桩侧阻力的占比逐渐减小，当洞高大于2.4倍桩径时，桩侧阻力减小了65.5%，桩基由摩擦桩逐渐向端承桩转化.


关键词： 陡坡,  岩溶,  桥梁桩基,  离心试验,  承载特性 
Fig.1 Pile foundation of pier 2#
Fig.2 Location relationship of steep slope - pile -karst cave
Fig.3 TLJ-3 centrifugal model machine
物理量量纲原型离心模型
尺寸lL11/n
水质量分数w—11
密度ρML?311
应变ε—11
应力σML?1T?211
质量mM11/n3
力FMLT?211/n2
土压力p—11/n
重度γ—1n
加速度aLT?21n
时间tT11/n2
角度α—11
变形uL11/n
Tab.1 Similarity relationship of physical quantity in centrifugal model test
Fig.4 Pile model and karst cave model of centrifugal model test
类型A/m2E/GPaEA/GN误差/%
原型桩3.1430.0094.201.2%
模型桩207.24×10?646.0095.33
Tab.2 Compressive stiffness of model pile and prototype pile
类别ww/%γ/(kN·m?3)E/MPaφ/(°)c/kPa
粉质黏土3018282228
中风化灰岩1.3256000——
Tab.3 Foundation soil parameter of model
类别ww /%γ/(kN·m?3)E//MPaφ/(°)c/kPa
粉质黏土3019.529.219.827.8
中风化灰岩1.5276000——
Tab.4 Foundation soil parameter of prototype
l/mmα/（°）L/mmH/mm
2004560 (2.4D)无溶洞
2004560 (2.4D)30 (1.2D)
2004560 (2.4D)60 (2.4D)
2004560 (2.4D)90 (3.6D)
2004560 (2.4D)120 (4.8D)
Tab.5 Condition setting of centrifugal model test
Fig.5 Measuring device of pile top vertical displacement
Fig.6 Schematic diagram of pile measurement point layout
Fig.7 P-S curve of pile foundation under different karst cave height
Fig.8 Vertical ultimate bearing capacity of pile foundation under different karst cave height
Fig.9 Axial force distribution of pile at different cave height
Fig.10 Effect of cave height on pile axial force distribution
Fig.11 Distribution of pile lateral resistance at different cave height
Fig.12 Effect of cave height on pile lateral resistance distribution
Fig.13 Effect of cave height on pile foundation sub-load capacity
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