土洞型岩溶塌陷发育过程气体示踪试验研究——以广州金沙洲为例

Experimental study of gas tracer simulation of karst collapse development process:An example of Jinshazhou,Guangzhou

运用气体示踪进行土洞型岩溶塌陷监测预警是一种比较新的技术方法,其原理是通过气体在不同形状、规模的土体孔隙、裂缝和土洞中的运移规律研究,分析气体特征值与土体变形破坏的关系,进而间接判断土洞的发育情况,实现岩溶塌陷监测预警。本文以广州市金沙洲岩溶塌陷区为例,通过室内物理模型试验再现了土洞发育、形成到地面塌陷的全过程。运用气体示踪技术,按照土洞形成、土洞发育、土洞堵塞、土洞扩大和土洞塌陷五个过程,研究气体浓度、气体聚集时间等参数指标与土洞不同发育阶段的关系。结果表明:(1)土洞型岩溶塌陷发育程度与示踪气体浓度存在对应关系,气体浓度升高反映了土体变形破坏的进一步发育;(2)土体变形破坏程度与示踪气体浓度总体呈正相关关系,距离地面塌陷点越近浓度越高;(3)土体变形破坏程度与示踪气体浓度达到峰值浓度时间存在对应关系,距离地面塌陷点越近,气体浓度达到峰值的时间越快。根据以上试验结果,运用气体示踪技术进行土洞型岩溶塌陷监测预警是可行的,后期应探索预警阈值并进行野外现场实际验证。

Karst collapse is one of main geological hazards in karst areas in China,which can be generally divided into two types:sinkhole and karst collapse.Sinkhole is widely distributed and numerous,and how to monitor them and make an early warning is a focused issue.The primary characteristic of sinkhole development is that un‐der the action of groundwater and other factors,the internal structure of soil is deformed and damaged and then produces cracks and caves.The common monitoring and early warning methods include physical exploration,groundwater dynamic condition monitoring and other nondestructive detection tools.A relatively new technical method in this aspect is to use gas tracer.Its principle is to analyze the relationship between gas characteristic val‐ues and soil deformation and damage based on observation to gas transport in soil pores,cracks and holes of differ‐ent shapes and sizes,and then indirectly judge the development of sinkhole to achieve karst collapse monitoring and early warning.In this work,taking the karst collapse area of Jinshazhou,Guangzhou as an example,the whole process from sinkhole development to ground collapse was reproduced by indoor physical model tests,and then the relationship between gas concentration,gas accumulation time and other parameter indexes and different development stages of karst collapse was studied by using gas tracing technique in five processes of a sinkhole:for‐mation,development,blockage,expansion and collapse.The results show that(1)there is a correspondence be‐tween the development of sinkhole and tracer gas concentration,and the increase of gas concentration reflects the further development of soil deformation and damage.(2)There is a positive correlation between the soil deforma‐tion and damage and tracer gas concentration in general,and the closer to the ground collapse,relatively higher the concentration.(3)There is a correspondence between the soil deformation and damage and the time of tracer gas concentration reaching peak concentration,and the closer to the ground collapse,the faster the gas concentration reaching the peak.These experimental results demonstrate that it is feasible to use gas tracer technology to conduct monitoring and early warning of karst collapse.Later on we will conduct further research on early warning thresh‐olds and carry out practical verification in the field.