下伏溶洞桩基竖向承载特性研究

杨柏; 肖康; 潘宗源; 覃超; 黄翔

doi:10.11932/karst2025y027

下伏溶洞桩基竖向承载特性研究

doi: 10.11932/karst2025y027

杨柏^{1, 2,},
肖康¹,
潘宗源³,
覃超¹,
黄翔^4, ,

1.
桂林电子科技大学建筑与交通工程学院, 广西桂林 541004
2.
西南交通大学地球科学与工程学院, 四川成都 611756
3.
中国地质科学院岩溶地质研究所/自然资源部、广西岩溶动力学重点实验室/中国地质调查局岩溶塌陷防治重点实验室, 广西桂林 541004
4.
桂林理工大学土木工程学院, 广西桂林 541006

基金项目: 广西自然科学基金（2024GXNSFBA010011）；广西高校中青年教师科研基础能力提升项目（2024KY0212）；广西重点研发计划（桂科AB25069410）；国家自然科学基金（42067044）

详细信息

作者简介:
杨柏（1989－），男，博士，讲师，硕士研究生导师，在站博士后，主要从事地基基础工程方面的研究。E-mail：ayangbai@163.com

通讯作者:
黄翔（1989－），男，博士，助理研究员，主要研究方向：地基基础工程、环境岩土工程。E-mail：guthuang@163.com。

中图分类号: TU473.1；P642,25
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- 文章访问数: 6
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- 被引次数: 0
出版历程
- 收稿日期: 2025-04-15
- 录用日期: 2025-11-12
- 修回日期: 2025-10-09
- 刊出日期: 2026-06-25

Study on vertical bearing behavior of pile foundations overlying karst cavities

YANG Bai^{1, 2
,},
XIAO Kang¹,
PAN Zongyuan³,
QIN Chao¹,
HUANG Xiang^{4
, ,}

1.
School of Architecture and Transportation Engineering, Guilin University of Electronic Technology, Guilin, Guangxi 541004, China
2.
Faculty of Geosciences and Engineering, Southwest Jiaotong University, Chengdu, Sichuan 611756, China
3.
Institute of Karst Geology, CAGS/ Key Laboratory of Karst Dynamics, MNR & GZAR/ Key Laboratory of Karst Collapse Prevention,CGS, Guilin, Guangxi 541004, China
4.
School of Civil Engineering, Guilin University of Technology, Guilin, Guangxi 541006, China

摘要

摘要: 为了研究下伏溶洞桩基承载特性，开展了模型试验和数值模拟研究，并将两种方法的研究结果进行对比分析。结果表明：（1）桩与岩土体呈复合破坏模式：在岩土层中发生圆柱面剪切破坏，溶洞顶板发生喇叭形冲切破坏；下伏溶洞桩基荷载–位移曲线为陡变型，无溶洞桩基荷载–位移曲线为缓变型。（2）下伏溶洞桩基为端承桩，桩身阻力整体呈现为“L”型。在各级荷载作用下，桩身轴力沿深度方向逐渐衰减，岩层中的桩身轴力衰减速率远大于土层；土层中桩侧阻力随着竖向荷载的增加很快充分发挥，岩层中桩侧阻力和桩端阻力随着竖向荷载的增加不断增大。（3）数值模拟结果与模型试验结果较吻合，桩基极限承载力相对误差为−22.2%~15.8%；基桩极限承载力随顶板厚度增加而增大，随嵌岩比增大而减小，当顶板厚度超过6D或嵌岩比达到0.6后，极限承载力变化趋势逐渐变缓。
- 下伏溶洞 /
- 嵌岩桩 /
- 承载特性 /
- 模型试验 /
- 数值模拟
Abstract: Karst regions are extensively distributed acorss China, where rock-socketed pile foundations are widely adopted in the construction of bridges, buildings, and other infrastructure owing to their high bearing capacity, minimal settlement, and favorable deformation control performance. However, when a karst cave exists beneath the pile tip, its load transfer mechanism, failure mode, and ultimate bearing capacity may deviate markedly from those of conventional pile foundations. Consequently, the stability of the cave roof and the interactions among the pile, overlying soil, bedrock, and underlying cavity constitute critical determinants of foundation safety. To investigate the vertical bearing behavior of pile foundations with underlying karst caves, this study integrates physical model tests with three-dimensional numerical simulations to examine the effects of cave roof thickness and rock-socketed ratio on failure characteristics, load–displacement response, axial force transfer, lateral resistance distribution, and ultimate bearing capacity.The physical model tests were designed based on the geological conditions of a karst site in Jiangnan District, Nanning, Guangxi, where the overlying layer is mainly red clay and the bedrock is moderately weathered dolomite. With a geometric similarity ratio of 30 and a volumetric weight similarity ratio of 1.2, nine model piles were fabricated in total. In the cave-roof-thickness test series, five piles shared a constant rock-socketed ratio of 0.5 while the cave roof thicknesses varied from 1D to 5D. In the rock-socketed-ratio test series, five piles maintained a uniform cave roof thickness of 3D with rock-socketed ratios ranging from 0.2 to 0.6; one specimen was shared between the two test series. The slow maintained load procedure was adopted to obtain the load–displacement curves at the pile top and the internal force responses along the pile shaft. Concurrently, a corresponding full-scale (1∶1) numerical model was developed using PLAXIS 3D. The Mohr–Coulomb constitutive model was assigned to both soil and rock masses, whereas the pile body was simulated as a linear elastic material. Interface elements were embedded at the pile shaft and pile tip to characterize the pile–soil and pile–rock contact behaviors. The interface strength reduction factors were determined via direct shear tests, yielding values of 0.5 for the pile–soil interface and 0.8 for the pile-rock interface.The results indicate that pile foundation with underlying karst caves exhibit a composite failure mode: columnar shear failure occurs along the pile shaft within the surrounding soil and rock mass, accompanied by trumpet-shaped punching failure of the cave roof beneath the pile tip. The displacement contour plots derived from numerical simulations are generally consistent with the failure morphology observed in the physical model tests, demonstrating that the established numerical model can effectively reproduce the failure mechanism of the pile-rock–cavity system. As the cave roof thickness increases, both the height and the scope of influence of the failure zone expand; conversely, these dimensions diminish with increasing rock-socketed ratio. These findings reveal that the roof thickness and the socketing condition collectively govern the diffusion of pile-tip loads within the rock mass and the subsequent punching failure process of the cave roof.The load-displacement curves of pile foundations with underlying karst caves exhibit distinct abrupt-failure characteristics. During the initial loading stage, the pile-head displacement increases approximately linearly with the applied load.Upon reaching the ultimate bearing capacity, any further load increment triggers a sharp surge in displacement, indicating sudden punching failure or instability of the cave roof. In contrast, piles without underlying cavities display a gradual load-displacement response without any pronounced inflection point. This discrepancy reflects the competitive relationship between the shaft resistance mobilized along the pile-soil/rock interface and the punching resistance offered by the cave roof. When the cave roof is relatively thin, the stress-affected zone beneath the pile tip readily penetrates the roof, rendering punching failure the dominant failure mechanism. Conversely, when the roof thickness is sufficient, the pile-tip load diffuses more effectively within the rock mass, leading to stable bearing behavior of the pile foundation.The axial force and shaft resistance profiles further elucidate the load transfer mechanism of pile foundation with underlying karst caves.At various load levels, the axial force along the pile shaft decreases progressively with depth, exhibiting a notably higher attenuation rate within the rock mass than within the overlying soil layer. Piles with underlying cavities predominantly behave as end-bearing piles. The distribution of shaft resistance displays a characteristic L-shaped pattern. Owing to the relatively low cohesion and internal friction angle of the red clay, the shaft resistance in the soil layer remains modest and mobilizes rapidly with increasing vertical load. In contrast, the rock mass possesses superior strength parameters; once relative shear displacement occurs at the pile-rock interface, the rock shaft resistance increases substantially, forming a distinct inflection point near the soil-rock interface. Both the rock shaft resistance and the pile tip resistance escalate continuously with rising vertical load, indicating that the bearing capacity of such piles is collectively governed by the rock shaft resistance, the pile tip resistance, and the stability of the underlying cave roof.The numerical results show good agreement with the physical model tests, with relative errors in ultimate bearing capacity ranging from −22.2% to 15.8%. Upon validating the reliability of the numerical model, parametric analyses were further extended to cover cave roof thicknesses from 1D to 10D and rock-socketed ratios from 0.2 to 1.0. The results indicate that the ultimate bearing capacity increases with cave roof thickness, exhibiting an approximately linear growth trend within the 1D–6D range; beyond 6D, the increase gradually plateaus. Conversely, the ultimate bearing capacity decreases with increasing rock-socketed ratio, showing an approximately linear decline as the ratio rises from 0.2 to 0.6; when the ratio exceeds 0.6, the rate of decrease diminishes markedly. These findings provide valuable references for evaluating the bearing behavior of rock-socketed piles in karst regions, determining rational design parameters, and implementing effective safety control measures.
- underlying karst cave /
- rock-socketed pile /
- bearing behavior /
- model test /
- numerical simulation

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图 1 试桩试验设计图（mm）

Figure 1. Test pile layout and design drawings（mm）

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图 2 试验加载装置

Figure 2. Test loading apparatus

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图 3 三维模型建立图

Figure 3. Schematic diagram of 3D model development

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图 4 试样剪切破坏前后图

Figure 4. Images of shear failure specimens before and after testing

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图 5 试桩桩顶荷载-位移曲线结果对比

Figure 5. Comparison of load-displacement curves at the pile top for test piles

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图 6 无溶洞基桩桩顶荷载-位移曲线

Figure 6. Load-displacement curve at the pile top for piles without karst caves

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图 7 桩身轴力曲线数值–试验结果对比

Figure 7. Comparison of axial force profiles between numerical simulations and physical model tests

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图 8 桩侧阻力分布曲线

Figure 8. Shaft resistance distribution curve

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图 9 极限承载力–顶板厚度关系曲线

Figure 9. Relationship between ultimate bearing capacity and cave roof thickness

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图 10 极限承载力–嵌岩比关系曲线

Figure 10. Relationship between ultimate bearing capacity and rock-socketed ratio

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表 1 试桩试验方案

Table 1. Test pile sheme

模型桩号	嵌岩深度H_p/mm	顶板厚度H_r/mm	嵌岩比l
RTP1	10/(0.5D)	20/(1D)	0.5
RTP2	20/(1.0D)	40/(2D)	0.5
RTP3 (ETP4)	30/(1.5D)	60/(3D)	0.5
RTP4	40/(2.0D)	80/(4D)	0.5
RTP5	50/(2.5D)	100/(5D)	0.5
ETP1	12/(0.6D)	60/(3D)	0.2
ETP2	18/(0.9D)	60/(3D)	0.3
ETP3	24/(1.2D)	60/(3D)	0.4
ETP5	36/(1.8D)	60/(3D)	0.6

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表 2 数值模拟实体材料参数表

Table 2. Material parameters for numerical simulation

实体材料	容重/（kN·m⁻³）	弹性模量MPa	泊松比	黏聚力/kPa	内摩擦角/°	界面强度系数R_inter	本构模型
土体	18	10	0.35	19.1	11	0.5	Mohr Coulomb
岩体	23	340	0.30	270	40	0.8	Mohr Coulomb
桩	25	30000	0.20	—	—	0.8	线弹性

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表 3 RTP3、RTP5、ETP1、ETP3试桩破坏模式数值-试验结果对比

Table 3. Comparison of failure modes between numerical simulations and physical model tests for test piles RTP3, RTP5, ETP1 and ETP3

试桩编号	试桩与岩土体位移云图	模型试验结果	顶板底面位移云图	模型试验结果
RTP3
RTP5
ETP1
ETP3

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表 4 试桩极限承载力

Table 4. Ultimate bearing capacity of test piles

试桩编号	数值模拟结果/N	模型试验结果/N	相对误差/%
RTP1	400	450	−11.1
RTP2	1000	1100	−9.1
RTP3 (ETP4)	1500	1500	0
RTP4	2100	2700	−22.2
RTP5	2500	3100	−19.4
ETP1	2500	2300	8.7
ETP2	2100	1900	15.8
ETP3	1800	1650	9.1
ETP5	1300	1200	8.3

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