At present,there is no unified,systematic cognition regarding the mechanism of karst collapse as research achievements are mainly concentrated on the causes and influential factors of karst collapse in qualitative sense rather than quantitative approach.In this paper,the process of karst collapse covered with sand layer was investigated quan-titatively,and the barrier effect of clay layer covering the karst was studied by sampling (keeping the pressure head unchanged during the process of sampling) and pressure monitoring on a physical model. Results showed that:1) in the structure of rock covered with sand,three times of karst collapse happened during the steady decline of groundwa-ter level,with the critical seepage-breakage gradients rcaching 0.525,2.500 and 3.400,respectively;the maximum collapse rate gradually decreased, yet the durations and degrees of collapse gradually increased; moreover, the process of the first karst collapse was more complicated than that of the second and the third collapse;2) the seepage theory of liquefaction has been verified by the results of karst collapse of rock covered with sand layer;3) groundwa-ter level fluctuation exacerbates the formation of karst collapse;4) the seepage-breakage gradient increased from 0. 525 to 48.300 in the presence of clay layer,indicating that clay layer could significantly improve the safety of karst o-verburden layer and effectively inhibit karst collapse. The results of this study could improve the understanding of karst collapse mechanism in a quantitative sense.%岩溶塌陷研究成果主要集中于岩溶塌陷原因与影响因素等方面的定性研究,缺乏对岩溶塌陷机理的定量研究,导致目前对岩溶塌陷机理仍未形成统一的、系统的认识.因此,有必要利用物理模型试验,采用恒压取样与剖面压力监测技术,定量研究砂土覆盖岩溶口的岩溶塌陷全过程以验证"渗流液化论"塌陷机理,并研究黏土层对岩溶塌陷的阻隔作用.结果表明:①对粉砂-基岩结构地层,在岩溶管道水位持续下降过程中,发生了3次岩溶塌陷,其临界渗透破坏比降分别为0.525,2.500,3.400,单次岩溶塌陷最大塌陷速率逐渐降低,但其持续时间和塌陷程度增加,且初始岩溶塌陷过程明显比第2次和第3次岩溶塌陷过程复杂;②砂土覆盖岩溶管道的塌陷机理为"渗流液化论";③地下水位波动加剧岩溶塌陷的形成;④黏土层的存在将岩溶塌陷的临界渗透比降由0.525增加至48.300,说明黏土层能显著提高岩溶覆盖层的安全性,可有效抑制岩溶塌陷发生.该研究成果弥补了目前在定量研究岩溶塌陷机理方面的不足,为岩溶塌陷防治提供理论支撑.
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