Application Of Electrical Resistivity Imaging In Geophysical Prospecting Of Shallow Covered Karst Cave

In the practice of shallow covered cave geophysical prospecting,the resolution of the profile is affected by the thickness,electrical property of the overburden and the selection of electrical array.In urban engineering or other small field geophysical exploration activities,the arrangement of electrical resistivity imaging is limited by site conditions,which greatly reduces selection of the Wenner(?????)array.At present,There are few systematic study of the geophysical resolution of the shallow covered karst caves of three kinds of deep sounding array(Inline Dipole-Dipole,Pole-Dipole and Pole-Pole array).Based on the above problems,this paper bases on previous research,studies the basic principles of electrical resistivity imaging through literature research.It mainly studies and analyzes the working principle and sensitivity characteristics of four array(Wenner,Inline Dipole-Dipole,Pole-Dipole and Pole-Pole array).Nine sets of numerical models are established by using forward and reverse software,The inversion profile characteristics of four array under different karst cave models and affected by the overburden are studied,It provides model reference for shallow covered karst cave geophysical prospecting array and effective determination of karst location,and makes evaluation on the adaptability of geophysical prospecting.Finally,the engineering application verification is carried out,the geological data of the study area is collected,and two groups of control experiments are set up on two known boreholes to study the engineering application effect of the four arrays,and the edge detection application is carried out to prove the reliability of the numerical simulation conclusion.The following conclusions are obtained in this paperThe difference of electrical properties between cave and surrounding rock,the depth of cave buried and the distance between electrodes per unit have the same influence on the resolution of Wenner,Inline Diploe-Dipole,Pole-Dipole and Pole-Pole array.The buried depth of cave and the distance between electrodes have the most serious influence on the resolution of the electrical array.The lateral resolution of the Wenner array is high,the Inline DipoleDipole array has the best resolution for vertical anomaly and the most sensitive response for low resistance anomaly.The Pole-Dipole array has high resolution for lateral uneven arrangement and the most sensitive response for high resistance anomaly.and the Pole-Pole array can provide more geo electric information but the resolution is poor.In shallow covered cave geophysical prospecting,the resolution of the four array is affected by the thickness and electrical properties of the low resistance cover layer,and the Inline Dipole-Dipole array and the Pole-Dipole array are less affected than the Wenner and the Pole-Pole array.This four array can effectively reflect the overburden and bedrock interface in the geophysical exploration of shallow covered karst caves.Under the condition of thin low resistance cover,the abnormal cave can be effectively reflected.The lateral resolution of the Wenner array is high,the response to the position and shape of the cave is great,and the formation information is accurate;The vertical resolution of Inline Dipole-Dipole array is high,and the vertical dimension of cave is close to the drilling exposure,which is suitable for solving the uneven geological problems of vertical variation;The Pole-Dipole array can solve the problem of blind area at the edge of the site,and the resolution of the cave is lower than that of the Wenner and Inline Dipole-Dipole array;The information of the Pole-Pole array is the most abundant,but there are differences in the location judgment of the cave,and the resolution is poor,which is suitable for the detection range and effectiveness of the array.Under the condition that the thickness of low resistance cover is more than 10 m,the Wenner and the Pole-Pole array are seriously affected by the low resistance cover,which can not effectively reflect the karst cave anomaly under the bedrock;Although Inline Dipole-Dipole array can effectively respond to cave abnormality,the signal of the array is affected by depth;The Pole-Dipole array can take into account the resolution,detection signal and depth,and is an ideal array for geophysical exploration of cave under the condition of low resistance cover layer greater than 10 m.This study can provide a theoretical basis for the selection of geophysical prospecting array and interpretation of results of shallow covered cave geophysical prospecting by electrical resistivity imaging,and has a good application value.