江苏徐州地区岩溶塌陷致塌力学模型及水位控制红线

Mechanical model of karst collapse and red line of groundwater level of Xuzhou Region in Jiangsu Province

岩溶塌陷实际是覆盖层土体变形破坏的一种特殊类型。通过调查研究,将徐州地区岩溶塌陷概化为"单一透水型盖层"、"透—阻型盖层"以及"单一阻水型盖层"三种地质模式,破坏模式为渗透变形破坏和剪切变形破坏,致塌模式分别为"潜蚀渗透-超临界水力梯度致塌"、"潜蚀软化—吸蚀—渗透力致塌"以及"真空吸蚀致塌"。建立了内部塌陷阶段以及地表塌陷阶段的综合力学模型,经新生街塌陷和溶剂厂塌陷验证,计算结果与实际情况基本吻合。以徐州典型塌陷区为例,分别对不同覆盖层厚度(40 m、30 m、20 m、10 m)、不同溶洞直径(4 m、2 m、1 m、0. 2 m)、不同下伏黏性土厚度(5 m、10 m、15 m、20 m、25 m、30 m、35 m、40 m)的稳定性进行试算,得到稳定性系数随水位降深的变化关系曲线,结果表明:覆盖层厚度越大、下伏黏性土厚度越大、溶洞直径越小、水位降深越小,稳定系数越高,越不容易塌陷;当洞穴直径小于1 m时,自然条件下土体均处于稳定状态;以稳定系数等于1为变形破坏的极限平衡条件,确定了最大水位降深及其空间分布,并据此作为岩溶塌陷的水位控制红线,为研究区岩溶水安全合理开采提供指导意义。

Karst collapse is actually a special type of cover-layer soil mass deformation and failure.According to the investigation and research,the karst collapse in Xuzhou can be turned into three geological models,as single permeable type cap,permeable-resistant type cap and single resistant type cap.The faliure models are the seepage deformation damage and the shear deformation damage.Three corresponding collapse-causing models are subsurface erosion and permeation-supercritical hydraulic gradient to collapse,subsurface erosion to soften-suck erosion-penetration to collapse,and vacuum pumping to collapse.The collapse mechanical model was established,which contains the inter-collapse phase and surface-collapse phase.Meanwhile,evaluations of Xinshengjie karst collapse and Rongjichang karst collapse were carried out by using this collapse mechanical model.The results prove that the model is in accord with the fact.Taking the typical collapse of Xuzhou as an example,we calculated the stability under the conditions of different cover-layer soil thickness(40 m、30 m、20 m、10 m),karst cavity diameter(4 m、2 m、1 m、0.2 m),and bottom-layer cohesive soil thickness(5 m、10 m、15 m、20 m、25 m、30 m、35 m、40 m),and obtained the stability coefficient curve along with the change of water level drawdown.The results show that the greater of cover-layer soil thickness,the greater of bottom-layer cohesive soil thickness,the smaller of karst cavity diameter,and the smaller of water level drawdown will lead to the greater of the stability coefficient.When the karst cavity diameter is less than 1 m,cover-layer soil is stable under the natural conditions.When the limit equilibrium condition with deformation coefficient equal to 1 is considered,we calculated the maximum water level drawdown,which is taken as the Red Line of groundwater.It can provide guidance of reasonable exploitation of groundwater.