Influence of multiple karst caves at the pile end on the bearing capacity of pile foundations based on ABAQUS
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摘要: 岩溶区地基中往往含有多个溶洞，当前对含多溶洞桩基－地基承载机理的研究落后于工程实践。因此，针对含多溶洞地基－桩基承载机理，依托某岩溶桩基工程，应用大型有限元分析软件ABAQUS建立模型，通过对桩基荷载－位移曲线的分析，探讨不同溶洞顶板厚度下溶洞形状、溶洞几何特性及溶洞间距对桩基极限承载力的影响。结果表明：相同工况下，方形溶洞对桩基承载力的不利影响大于圆形溶洞；随着溶洞单一尺寸的增大，溶洞对桩基极限承载力的不利影响逐渐增大。桩端存在双溶洞时，侧溶洞洞高对桩基极限承载力的影响大于洞跨对其的影响；随着溶洞间距的增大，侧溶洞对桩基承载力的影响降低，当间距达到5倍桩径时，侧溶洞对桩基承载力的影响可忽略。Abstract:
As an important load-bearing structure of buildings, the stability of pile foundations will directly impact building safety. With the expansion of engineering construction, foundations are frequently laid in an encounter with multiple karst caves. However, research on the influence of complex geological conditions with multiple karst caves at the pile end on the ultimate bearing capacity of pile foundations lags behind engineering practice. Therefore, studying this impact is crucial for engineering practice. In this study, a model of pile end containing multiple karst caves was established by the large finite element analysis software ABAQUS, with reference to a specific karst pile foundation project in the Hongshan district, Wuhan City, Hubei Province. This study aimed to explore the influence of cave shape, geometric characteristics, and spacing between karst caves on the ultimate bearing capacity of pile foundations under complex geological conditions with multiple karst caves at the pile end. This study involved the following steps. 1. Geological models of piles and karst caves were established. This involved firstly determining the premise assumptions for finite element analysis, selecting appropriate constitutive models, setting relevant parameters of pile foundations and engineering geological conditions based on a specific karst pile foundation project; secondly, setting constraints and boundary conditions, performing grid division, and determining calculation analysis; finally, establishing the model of comparative working condition groups according to the research purpose. 2. The finite element analysis was conducted with ABAQUS to simulate the displacement process of pile foundations under various karst geological conditions subjected to external forces. 3. Data compilation and analysis were completed. Load-displacement curves of pile foundations under different karst geological conditions were compiled. Based on Technical Code for Testing of Building Foundation Piles and the failure mode of pile foundations in simulation, the standard for selecting the ultimate bearing capacity of pile foundations was determined. Ultimate bearing capacities of pile foundations under different working conditions were extracted, organized, and graphed to analyze the influence of different cave parameters on the ultimate bearing capacity of pile foundations. The results indicate that under the same conditions of a single karst cave, square caves exert a greater adverse impact on the ultimate bearing capacity of pile foundations than circular ones. However, when the cave cap thickness reaches 5 times the pile diameter, the impact of cave shape on the pile foundation becomes negligible. As the single-direction size of the karst caves increases, their adverse effect on the ultimate bearing capacity of the pile foundation gradually intensifies. If two karst caves are present at the pile end with centroids at the same elevation, the appearance of a side cave will significantly reduce the ultimate bearing capacity of the pile foundation. The ultimate bearing capacity of the pile foundation when both caves are elliptical is greater than when they are rectangular. If a constant change of single-directional size for the side cave maintains, when the thickness of the cave cap H is ≤3d, the change in cave height will exert a much greater impact on the ultimate bearing capacity of the pile foundation than the change in span; when H is equal to 5d, the influence of the change in the span of side cave on the ultimate bearing capacity of the pile foundation will exceed that of change in the cave height. As the cave spacing increases, the influence of side caves on ultimate bearing capacity gradually decreases; when the spacing reaches five times the pile diameter, this effect can be ignored. This study employs the numerical simulation method with ABAQUS to analyze the ultimate bearing capacity of pile foundations with multiple karst caves, delving deeper into the influence of geometric characteristics of side caves and cave spacing on the ultimate bearing capacity of pile foundations. It provides theoretical support and technical guidance for practical engineering. Additionally, it offers valuable references and insights for the design and construction of pile foundations under similar complex geological conditions. -
Key words:
- karst /
- pile foundation /
- ultimate bearing capacity /
- ABAQUS
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图 1 桩基参数及工程地质条件
Figure 1. Pile foundation parameters and engineering geological conditions
表 1 桩和岩土体物理力学参数
Table 1. Mechanical parameters of pile and rock
岩土名称 层厚/m 密度ρ/kg·m−3 弹性模量E/MPa 泊松比µ 内聚c/kPa 内摩擦角 φ/° 粉质黏土 7.3 1 940 15 0.4 38 15 含碎石黏土 29.2 1 970 23 0.4 40 17 红黏土 5.3 1 960 27 0.4 35 12 中风化石灰岩 18.2 2 550 2e4 0.25 1e4 45 桩 43.8 2 500 3.55e5 0.2 
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表 2 G1、G2组模拟工况参数表
Table 2. Table of parameters for G1 and G2
溶洞数 分组 溶洞特征 顶板厚度H 桩端溶洞 桩侧溶洞 溶洞间距D 形状 洞高h 洞跨l 高跨比h/l 形状 洞高h' 洞跨l' 高跨比h'/l' 单 G1 d/2d/3d/4d/5d 矩形椭圆 3d 3d 1 / 6d 1/2 9d 1/3 12d 1/4 15d 1/5 双 G2 2d/3d/4d/5d 椭圆 3d 6d 1/2 矩形椭圆 3d 3d 1 d 6d 2 9d 3
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表 3 G3组模拟工况参数表
Table 3. Parameters for G3
溶洞数 分组 溶洞特征 顶板
厚度
H桩端溶洞 桩侧溶洞 溶洞
间距
D形状 洞高h 洞跨l 高跨比h/l 形状 洞高h' 洞跨l' 高跨比h'/l' 双溶洞 G3 2d/3d/4d/5d 椭圆 3d 6d 1/2 椭圆 3d 3d 1 d 6d 1/2 9d 1/3 6d 3d 2 9d 3
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表 4 G4组模拟工况参数表
Table 4. Parameters for G4
溶洞数 分组 溶洞特征 顶板
厚度
H桩端溶洞 桩侧溶洞 溶洞
间距
D形状 洞高h 洞跨l 高跨比h/l 形状 洞高h' 洞跨l' 高跨比h'/l' G4 2d 椭圆 3d 3d 1 椭圆 3d 3d 1 d
2d
3d
4d
5d6d 2 6d 2 9d 3 9d 3 矩形 3d 3d 1 矩形 3d 3d 1 6d 2 6d 2 9d 3 9d 3
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