A Study On The Two-Dimensional Entoptic Prospecting Method Of ERT For The Water Flow Process Around Cavity

In the field of hydrogeology,the research of water transfer in unsaturated zone of cavity surrounding is lacking of intuitive and dynamic monitoring method,in order to make up for the inadequacy of the status quo,based on the numerical model and physical model,using the high-density Electrical Resistivity Tomography method,a new high-density Electrical Resistivity Tomography method named entoptic prospecting Electrical Resistivity Tomography(eERT)is proposed for monitoring the cavity surrounding area.In a different way with traditional method,it is using non-invasive prospecting way under the circular boundary conditions.From the scale of laboratory-model test,the cross section of the cavity is simulated.Water and moisture migration were prospected based on eERT,which is also a brand new way to understand the process of water migration around the cavity area,including the relationship between the resistivity of porous media under two-dimensional condition and water infiltration in different media.The specific results of this study are as follows:(1)The effectiveness of the eERT is verified.Through numerical simulation research method,this part of study obtains the response characteristics of apparent resistivity in annular-electrodes-arrangement using entoptic prospecting method under the condition of limited space.Results show that when columnar abnormal bodies and the zonal distribution abnormal bodies appear in the test area,the imaging results on the position and distance present a reasonable correspondence,and this has been able to meet imaging requirements for a limited range of measurement.(2)The unsaturated process around the cavity is successfully monitored.The saturated zone and unsaturated zone in the physical model test are identified accurately based on entoptic prospecting method,and the process of water transfer can be monitored by the electrical resistivity tomography image.We establish the relationship between resistivity and volume water content based on Archie's formula which can be linked with the moisture content,and this is the basis for the distinction between saturated and unsaturated regions.Eventually the saturated zone and unsaturated zone in the water migration process of are accurately identified.(3)The dynamic monitoring of water migration is realized.In the physical experiment,results show that the space-time variation of the apparent resistivity could not only reflect the process of moisture migration in test,at the same time also can identify the location of the fault zone.Electrode arrangement is made within the ring of visual monitoring method for homogeneous and heterogeneous medium moisture migration process and identify abnormal body is feasible.