下伏溶洞对桥梁桩基极限承载力的影响分析

Analysis of the Influence of Underlying Karst Cave on the Ultimate Bearing Capacity of Bridge Pile Foundation

为研究串珠状岩溶区桥梁桩基下伏溶洞对桩基极限承载力的影响因素,基于某高速公路桥梁桩基础工程,运用有限元方法建立溶洞区桩土一体化仿真模型,分析串珠状岩溶区下伏溶洞数量、下伏溶洞尺寸、持力岩层风化程度等因素对桩基极限承载力的影响规律。结果表明,下伏溶洞数量及下伏溶洞高度的变化对于桩基极限承载力影响较小;离桩基最近的下伏溶洞半径对桩基承载力的影响较大,其半径增大会引起桩基极限承载力的减小,半径从8 m增大至12 m时,桩基极限承载力降低1 587.08 kN,下降了25.2%;持力岩层风化程度越弱,桩基极限承载力越大,未风化岩层工况下桩基极限承载力为12 569.51 kN,而高度风化岩层工况下极限承载力为4 717.48 kN,仅为未风化岩层的37.5%。若下伏溶洞顶板厚度大于3倍桩径、溶洞半径较小、且溶洞顶板风化程度较弱时,可考虑将溶洞顶板作为桩基持力层。

In order to study the influence factors of the underlying karst cave on the ultimate bearing capacity of the pile foundation in the beaded karst area.Based on a highway bridge pile foundation project,the finite element method is used to establish a pile-soil integrated simulation model in the karst cave area.The factors such as the number of underlying karst caves,the size of the underlying karst caves,and the weathering degree of the bearing rock layer in the beaded karst area are analyzed on the ultimate bearing capacity of the pile foundation.The law of influence of force.The results show that the changes of the number of underlying karst caves and the height of the underlying karst caves have little effect on the ultimate bearing capacity of the pile foundation.The radius of the underlying karst cave closest to the pile foundation has a greater impact on the bearing capacity of the pile foundation,and the increase of its radius will cause the pile foundation when the ultimate bearing capacity decreases.When the radius increases from 8m to 12m,the ultimate bearing capacity of the pile foundation decreases by 1 572.73kN,a decrease of 25%.The ultimate bearing capacity of the pile foundation is 12 581.68kN under the condition of highly weathered rock stratum and the ultimate bearing capacity of the pile foundation is 4 718.15kN which is only 37.5% of the unweathered rock stratum.If the thickness of the underlying karst cave roof is greater than 3 times the pile diameter,the radius of the karst cave is small,and the weathering degree of the karst cave roof is weak,the karst cave roof can be considered as the bearing layer of the pile foundation.