Research And Application Of Comprehensive Geophysical Exploration In The Exploration Of Glauberite In Chengdu

In the urban context,the use of conventional geological survey methods is limited,which geophysical survey methods can achieve the refined exploration of urban underground space has become a research difficulty.In Chengdu area,Glauber's salt is widely distributed,and Glauber's salt is easy to dissolve in water.Under the dynamic action of groundwater,it may form ground fissures or collapses,posing a threat to the healthy development of the city.In this paper,based on the exploration of urban underground space resources in Chengdu,the high-density electrical method,ground penetrating radar,mixed element surface wave and equivalent antimagnetic flux transient electromagnetic method are applied to the exploration of glauberite in Chengdu as a comprehensive geophysical method to explore the joint exploration effect of the above four geophysical methods;in addition,the inversion resolution of high-density electrical method is explored by experimental simulation.The research results are as follows:From the experimental simulation:1)The electrode spacing is less than 20m,the resistivity of the resistivity of the buried depth is 5m and the geological scale is different(The resistivity of the anomalous body=100?·m,and the resistivity of the buried environment=10?·m).The inversion resolution of the winner-?device is greater than that of the wenner-?device and wenner-?device.When the electrode spacing is less than 12.75m,the inversion resolution of the winner-?device is greater than that of the wenner-?device.When the electrode spacing is greater than 12.75m,the inversion resolution of the wenner-?device is greater than that of the winner-?device.When the electrode spacing is more than 5 times than the transverse side of the electrical abnormal body,electrical abnormalities cannot be reversed.2)The electrode is within 2~8m,the electrical characteristics of the section area of 4×4(m~2)are highly resistive(The resistivity of the anomalous body=100?·m,and the resistivity of the buried environment=10?·m).The maximum restraint depth increases with the increase of electrode distance and then decreases.Under the same electrodes,The maximum depth of wenner-?device>the maximum depth of wenner-?device>the maximum depth of wenner-?device.According to the application study:(1)according to the analysis of drilling and comprehensive geophysical data,the main aquifer in the survey line section is the Quaternary sand gravel layer.The strongly-moderately weathered mudstone and silty mudstone of Guankou formation are good aquicludes.The pores of the silty mudstone layer rich in glauberite are not developed and the water content is poor.The comprehensive analysis shows that the Glauber's salt layer within the survey line does not have the conditions to form a large-scale corrosion cave and will not affect the stability of the engineering buildings on the ground.(2)based on the analysis of drilling data,four geophysical methods,namely,ERT,surface wave,OCTEM and GPR,can realize high-precision detection of glauberite layer,bedrock and quaternary system interface and obtain some basic geological,hydrogeological and engineering geological characteristics under the background of urban strong interference source.