岩溶区高速公路路桥基础稳定性评价方法

Stability Analysis and Evaluation of Cave Foundation under the Role of Groundwater in Karst Area

岩溶区路桥基础稳定性分析与评价是目前国内外高速公路建设的重大技术难题之一。目前,对溶洞地基稳定性评价研究多集中在塌陷发育机理及预防等定性评价方面,少见定量评价。在弹塑性力学基本理论基础上,首先分析地基中溶洞洞壁周围土体的应力状态,判别应力集中影响范围,再利用莫尔-库仑强度准则对溶洞地基稳定性计算模型进行改进,最后,以沪蓉国道主干线K198+189.85花石板1#大桥桥基稳定性评价为例,验证了该改进模型的可行性和可靠性。并进一步研究了基础底面尺寸、埋深、溶洞洞体形状以及地下水位埋深对溶洞稳定性的影响,揭示了该类溶洞塌陷破坏的机理。研究表明,改进模型是可行的,基础底面尺寸越小、埋深越浅、洞形越尖、地下水位埋深越浅,溶洞稳定性系数越大,越有利于溶洞地基的稳定,且地下水位对溶洞稳定性影响较为敏感,地下水位小幅度下降就可能导致溶洞由稳定变为破坏失稳。因此在溶洞地基稳定性评价中,应重视定量评价,尤其是地下水环境下的溶洞地基,同时计算所得的溶洞基础最大尺寸、临界埋深、最大水位埋深对溶洞地基的治理与设计具有较强的指导性作用。

It is one of the important technique problems of expressway construction to analyze and evaluate the stability of roadbed and bridge fundations in karst region at home and abroad.Currently,the stability evaluation of cave foundation is mostly focus on the quantitative evaluation,such as the collapse mechanism and prevention,while the qualitative assessment is rare.Based on the plastoelasticity theory,firstly analyze the stress state of the cave wall-surrounding body in the foundation,distinguish the stress concentration influence area,then improve the cave foundation stability computation model by using Mole coulomb strength criterion,finally,take a cave foundation stability evaluation as the example in Shanghai and Chengdu backbone of the Road,confirming the feasibility and reliability of the improvement model.The influence of the foundation bed size,buried depth,cave shape and groundwater level depth was further studied,which reveals the mechanism of the cave collapse destruction.And the research indicated that the improved model is feasible,when the foundation bed size is smaller,the buried depth is shallower,the hole shape is more spiky and the groundwater level depth is shallower,the cave stability coefficient will be bigger,which is more advantageous to the stability,and the influence of groundwater level depth is more sensitive to the cave stability,once the groundwater level depth dropped a little,the stable cave will become into failure and instability.Therefore,the quantitative evaluation should be paid more attention in cave foundation stability evaluation,particularly under the ground water environment,simultaneously,the calculation results,like cave foundation maximum size,the critical buried depth,the maximum water level buried depth,have the strong directive function to the cave foundation treatment and design.