广州市岩溶上覆砂土层塌陷特征及其内在机制

Destruction mechanism of sand-covered karst collapse in Guangzhou

本文以广州实际工程地质资料和工况为基础,建立了钻探等工程洞穿岩溶顶板后溶洞上覆砂土层塌陷的有限元数值模型。采用欧拉-拉格朗日耦合法(CEL)模拟岩溶上覆砂土层塌陷过程,借鉴正交实验法进行了多组数值模拟,研究了不同覆盖土层厚度、溶洞空腔大小和砂土内摩擦角对岩溶上覆砂土层塌陷发展模式的影响,阐释了砂土覆盖层坍塌的机理。研究表明,随砂土覆盖层厚度增大,砂土层的地表最大位移和塌陷速率均呈减小趋势,中心塌陷区域明显较小。随溶洞空腔尺寸的增大,塌陷范围和地表最大位移增大。钻探等工程洞穿岩溶顶板后,靠近岩溶空腔的竖向范围土体先失稳破坏,其影响范围主要受砂土覆盖层厚度影响,且塌陷速率主要受失稳的土体范围影响。在塌陷中心土体失稳后,周围土体才受到剪切应力的影响破坏而向溶洞空腔中心产生位移,周围土体向溶洞空腔运移量主要受溶洞空腔尺寸影响,且此部分砂土呈现出近似塌陷休止角的塌陷形态。

Based on realistic engineering geological data in Guangzhou,this study establishes a finite element model for simulating the collapse of the overlying sand stratum after drilling through karst caves roofs.The coupled Euler-Lagrange method(CEL)is employed to simulate the collapse process of the sand stratum.Multiple sets of numerical simulations are conducted using orthogonal experimental design to investigate the influences of different sand stratum thicknesses,cave sizes,and friction angles on the development pattern and to elucidate the mechanism of collapse in the overlying sand stratum.The results indicate that as the thickness of the sandy soil cover layer increases,both the maximum surface displacement and collapse rate of the sand stratum decrease,and the central collapse area becomes noticeably smaller.With an increase in cave size,the collapse range and maximum surface displacement increase.After drilling through karst cave roofs in engineering projects,the vertically adjacent sand near the karst caves undergoes initial instability and failure,with its influence range primarily affected by the thickness of the sand stratum,and the collapse rate mainly influenced by the range of unstable soil.Once the soil in the central collapse area becomes unstable,the surrounding soil is subjected to shear stress and fails,causing displacement towards the center of the karst cave.The amount of soil migration towards the karst cave is mainly influenced by the size of the karst cave,and this portion of the sand exhibits a collapse morphology similar to the angle of repose.