Experimental Study Of Gas Tracer Simulation Of Karst Collapse Development Process

Karst collapse is one of the 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 and warn them has been the focus of attention.The biggest characteristic of sinkhole development is that under the action of groundwater and other factors,the internal structure of soil will be deformed and damaged and then produce cracks and caves.The premise of its monitoring is that the monitoring means cannot produce secondary damage to the soil,the common monitoring and early warning methods mainly include physical exploration,groundwater dynamic condition monitoring and other nondestructive detection methods.That's a relatively new technical method to use gas tracing for karst collapse monitoring and early warning.Its principle is to analyze the relationship between gas characteristic values and soil deformation and damage through the study of gas transport law in soil pores,cracks and holes of different shapes and sizes,and then indirectly judge the development of sinkhole to achieve karst collapse monitoring and early warning.In this paper,taking the karst collapse area in Jinshazhou,Guangzhou as an example,the whole process from sinkhole development to ground collapse was reproduced by indoor physical model test,and then the relationship between gas concentration,the time at which the concentration of the gas begins to change and other parameter indexes and different development stages of karst collapse was studied by using gas tracing technique in five processes: sinkhole formation,sinkhole development,sinkhole blockage,sinkhole expansion and sinkhole collapse.In addition,by using numerical simulation software,the geological conditions of the karst collapse area in Jinshazhou,Guangzhou,were modeled and simulated with software calculations,and the transport of tracer gas in different stages of sinkhole development and the effect of different injection rates on gas tracer tests were analyzed.The results show that:(1)there is a correspondence between 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 deformation and damage and tracer gas concentration in general,and the closer to the ground collapse relative higher the concentration;(3)there is a correspondence between the degree of soil deformation and damage and the time of change of tracer gas concentration at the monitoring location,the closer the monitoring point is to the ground collapse point,the faster the time of change of tracer gas concentration;(4)there is a better correspondence between the tracer gas concentration of surface monitoring and the location of karst collapse,and the location of karst collapse can be predicted by contour analysis of tracer gas concentration on the surface;(5)there is a link between the tracer gas injection method and the monitoring results,and a suitable tracer gas injection method needs to be selected.Based on the above experimental results,we believe that it is feasible to use gas tracer technology for monitoring and early warning of karst collapse in soil cavities,but the practical application of related technology needs to be analyzed and designed in conjunction with the actual situation of each study area.