Numerical simulation analysis and evaluation of stability of the karst foundation with developed joints and fissures
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摘要:
岩溶一直是困扰工程建设的大问题，对工程地基稳定性有着重大影响。为了有效获取节理裂隙发育溶洞地基稳定性相关参数，本文以西南某机场节理裂隙发育溶洞地基为研究对象，结合现场勘查，定性分析岩溶影响因素及发育规律，通过ABAQUS非线性有限元数值模拟计算和定量分析，探讨外荷载下节理裂隙对岩溶地基的影响，评价岩溶地基稳定性状况。分析结果表明：溶洞塑性破坏主要发生在溶洞两侧和节理裂隙处拉应力较大的部位，溶洞顶板厚度大于5 m时是稳定的。数值模拟结论和定性分析结果具有很好的一致性，为后续溶洞地基处理设计提供有力数据支撑。 Abstract:Karst has always been a big problem troubling engineering construction， which poses a great impact on the stability of engineering foundation. Therefore， it is of great significance to find out the law of karst development and seek effective treatment methods. In order to obtain the parameters related to the stability of karst cave foundation with developed joints and fissures， this paper takes the karst cave foundation in an airport in Southwest China as the research object. Combined with the field investigation， the impact factors and development law of karst are qualitatively analyzed. It is found that there are different manifestations of surface and underground karst， mainly in the form of stone bud， karst ditch， karst trough， funnel， sinkhole， concealed stone bud， karst hole， karst crack and karst cave. Karst is obviously developed near the fold axis， which is mainly controlled by the lithology of crystalline limestone stratum and longitudinal tensile joint fissures. The karst development of crystalline limestone with complete crystallization in the northeast and siliceous limestone in the southwest is weak， and the karst development of bioclastic and fine-grained limestone in the middle is strong. Geological structure affects the development trend of karst. Surface and underground karsts are extremely developed along the fold axis with certain directionality. The long axis of karst depression and karst funnel is basically consistent with the trend of structural line， and underground karst caves also have the characteristics of centralized development along the axial line of the fold. Groundwater affects the karst development intensity， which is manifested in the area where surface water is easy to gather， and collapse and funnel are well developed. It is found that there are many factors affecting the stability of karst foundation， including joint fissure， rock strength and rock occurrence， hole shape and burial， form and size of external load， groundwater and filling in the hole， etc. Therefore， on the basis of investigation and analysis as well as the karst cave drilling profile， this paper selects the most characteristic karst cave shape and diameter， aircraft external load， building load and the optimal roof thickness according to various factors， and establishes a qualitative evaluation system to assess the stability of karst caves revealed in this study area. At the same time， the stability of single typical karst cave and multi-layer complex karst cave in the study area is simulated through ABAQUS nonlinear finite element numerical simulation calculation and quantitative analysis to discuss the influence of joint fissures on karst foundation under external load， and to evaluate the stability of karst foundation. The analysis results show that the plastic failure of karst caves mainly occurs at the parts with large tensile stress on both sides of karst caves and joint fissures. When the thickness of karst cave roof is greater than 5 m， it is stable. The analysis shows that the overall stability of karst caves in the study area is good. 275 karst caves are exposed in boreholes， and 79 are in unstable state， accounting for 33.5% of the total. The results of numerical simulation analysis are in good agreement with the results of qualitative and semi-quantitative evaluation， which shows that the semi-quantitative conclusions have good guidance and can provide strong data support for the subsequent treatment design of karst cavern foundation. -
Key words:
- karst /
- development law /
- foundation stability /
- ABAQUS /
- analysis /
- evaluation
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图 3 研究区不同岩溶类型分布图
Figure 3. Distribution of funnel, fall-water hole, collapse, earth hole and stone bud in the field area
图 8 3 000 kN下总体位移图（单位：mm）
Figure 8. Overall displacement map under 3，000 kN (unit: mm)
图 9 3 000 kN下竖向位移剖面图（单位：mm）
Figure 9. Vertical displacement section under 3，000 kN (unit: mm)
图 10 3 000 kN下竖向位移曲线图（单位：m）
Figure 10. Vertical displacement curve under 3，000 kN (unit: m)
图 11 3 000 kN下X方向位移剖面图（单位：mm）
Figure 11. Displacement section in X direction under 3，000 kN (unit: mm)
图 12 3 000 kN下Z方向位移剖面图（单位：mm）
Figure 12. Displacement section in Z direction under 3，000 kN (unit: mm)
图 13 3 000 kN下最大主应力剖面图（单位：MPa）
Figure 13. Section of the maximum principal stress under 3，000 kN (unit: MPa)
图 14 3 000 kN下最小主应力剖面图（单位：MPa）
Figure 14. Section of the minimum principal stress under 3 000，kN (unit: MPa)
图 15 3 000 kN下竖向应力剖面图（单位：MPa）
Figure 15. Vertical stress section under 3，000 kN (unit: MPa)
图 16 3 000 kN下屈服应力剖面图（单位：MPa）
Figure 16. Lower yield stress section under 3，000 kN (unit: MPa)
表 1 岩土体物理力学参数
Table 1.
Physical and mechanical parameters of rock and soil 岩土体名称 弹性模量/GPa 泊松比 密度/kN 内聚力/MPa 内摩擦角/° 剪胀角/° 抗拉强度/MPa 填筑（土石） 0.067 5 0.25 2 160 0.4 18.2 — — 灰岩（破碎） 18.20 0.28 2 620 4.2 40.5 10.0 0.072 灰岩（完整） 30.25 0.20 2 650 4.9 42.2 10.0 1.831 水泥混凝土 20 0.20 2 500 — — — — 节理/裂隙 0.025 4 0.17 — 0.20 40 40.0 — 
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表 2 溶洞稳定性判据
Table 2.
Criteria for judging the stability of the cave 序号 影响程度 评判依据 稳定性等级 处理 1 无影响 溶洞顶板上中下均未发生过大变形，破坏区面积很小。 稳定 可作持力层，不需处理。 2 轻微影响 溶洞顶板的下部发生过大变形，但中部和上部均未发生过大变形，破坏区面断续，分布积小。 较稳定 采用注浆加固或扩大基础一般处理后可作持力层，以减小附加应力等。 3 中等影响 溶洞顶板的下部、中部均发生较大变形，但上部未发生过大变形，破坏区断续分布面积较大。 较不稳定 对规模较大的溶洞建议进行全面处理；对规模较小的溶洞作一般处理。 4 强烈影响 溶洞顶板的底部、中部和顶部均发生过大变形，破坏区连续呈贯通状分布。 不稳定 采取填充、桩穿越等，全面处理
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