桥梁桩基荷载下溶洞顶板稳定性研究

RESEARCH ON STABILITY OF CAVE ROOF UNDER PILE LOADING IN BRIDGE CONSTRUCTION ENGINEERING

基于Hoek-Brown准则,考虑溶洞顶板和桩基相互作用受力特性,针对岩溶地区溶洞地质条件的固支、简支圆板和矩形板4种模型,应用弹性力学推导溶洞顶板在桩基荷载下的最大应力计算式;引入Hoek-Brown准则作为判定顶板破坏的依据,得出顶板在不同简化模型下的顶板厚度理论计算公式以及在冲切、剪切破坏下的安全厚度计算公式。以江肇高速公路西江特大桥南引桥5号墩C桩桩基为研究对象,结合Hoek-Brown准则参数到Mohr-Coulomb准则参数的等效转换方法,得到不同板模型和抗剪切、冲切顶板安全厚度的计算结果。此外,应用有限元数值模拟方法得到不同板模型顶板安全厚度的数值模拟结果。通过比较理论验算和数值模拟结果不难发现:引入Hoek-Brown准则可以准确地分析溶洞顶板稳定性;所得到的4种不同简化力学模型下岩溶地区桥梁桩基荷载下溶洞顶板安全厚度计算公式可以进一步充实现有规范的内容,有效地服务于工程实践。

The present research is focused on the cave roof safety thickness and stability under pile loading in karst areas. Through the analysis of the interaction between the cave roof and pile foundation,four models were introduced to be as simply-supported,clamped circular plates and rectangular plates. Firstly,the force characteristics of cave roof under pile load in karst areas were analyzed. Based on the method of elasticity mechanics and introduction of Hoek-Brown criterion,a variety of simplified models were selected under consideration of the interaction between pile and cave roof. The maximum stress of the roof was then induced for different models following the theory of elastic mechanism. After the induction of the maximum stress,the theoretical formula of safety thickness was obtained,including the cases of four simplified models and anti-punching,shearing. Within the analysis of the stability for the cave roof,an equivalent conversion method for parameters was employed from the Hoek-Brown criterion to the Mohr-Coulomb criterion. In addition,compressive,tensile strength and other calculation parameters of the pile were determined,based on Hoek-Brown criterion,according to the detailed geological data of the West River Bridge. The cave roof thickness of different simplified models under different load conditions were then calculated by the theoretical formula. Using the finite element method,the theoretical results were identified to be the same as data from the numerical simulation. The results show that,it was feasible and effective to use the Hoek-Brown criterion to determine the stability of cave roof. Meanwhile,the results can be included in the national guideline for the design of piles in the bridge engineering in Karst areas.