Research On Transient Electromagnetic Method And Responses Of Tunnel Water-bearing Structures Using Surface-tunnel Configuration

The tunneling construction in china is faced with serious threats of water and mud gush,advanced geological borehole and geophysical method is used to determine the geological situation in front of the tunnel.But current geological forcast method can only obtain limits depth in front of the tunnel,and can't indentify massive adverse geological structure,and can't easily find out water-bearing structure in the tunnel roof and floor.Affected by car,steel and so on in the tunnel,electromagnetic method is fragile to noise effection.In the investigation of tunnel line selection,there is a shortage of geophysical method that can detect large adverse geological structure.Therefore,compared with earth-air transient electromagnetic(TEM),a new configuration,which put the source on the earth and collect data in the land and tunnel,is researched.The soure is located on the ground and is far from the metal anomaly in the tunnel,which can improve the signal-to-noise ratio.This configuration can detect geological structures of hundreds of meters and can detect roof and floor water-bearing structures of tunneling tunnel.This configuration can be used to detect large-scale abnoemal body when doing line selection,and detection depth can reach more than 1km.Earth-underground TEM expands the detection range in tunnel geological forecast,and it is expected to be a new method.Earth-underground TEM is expected to be used in tunnel geological forecast and line selection,and this configuration characteristic is comprehensively elaborated about receiving both earth and underground data.In order to researth water-bearing structures response in front of the tunnel,firstly,multi-resolution grid algorithm is developed,this algorithm redefined the small grid iterative formular and achieve the unity of time and space domain after boundary conditions constraints.Then,the basic regular of earth-underground TEM is researched by changing the receiver depth,resistivity and distance,and line optimization is researched by five line data receiving.Finally,the response regular of tunnel cavity,vertical filling fault,inclined filling fault,water filling cave,fault broken belt and large-scale underground river is researched.On the basic of numerical calculation,physical model test is used to get earth launching-underground receiving TEM.Firstly,different distance,height and source location are researched to get basic regular.Then,the response characteristic of roof,floor,vertical abnormal response is obtained by different steel platform position.Finally,the response of upright,inclined and cubic water body is obtained by different water body in front of the tunnel,and different water amount response is also obtained to analyse and induce the regular.Field test is carried out based on numerical test and physical model test,firstly,earth-underground TEM's feasibility is compared by known water storehouse model.Then,commom tunnel TEM and CSEM method are used to compare earth-underground TEM by detecting unknown area.After dong numerical test,physical model test and field test,we find the conclusion that earth-underground TEM is sensitive to water-bearing body.Based on multi-resolution grid algorithm,numerical test,physical model test and field test,response regular of different water abnormal body is obtained,which laid a solid foundation for TEM inversion.