| The research direction of this paper is derived from the National Natural Science Foundation of China(NSFC),"Research on the Rapid Detection Method of Transient Electromagnetic Diseases inside High-speed Railway Tunnel Structures"(Project No.51478395).As the mileage of high-speed railway construction in China,as well as the complexity and diversity of the traversed terrain,keeps increasing,especially in the rugged and mountainous areas in the west,the proportion of high-speed railway tunnels is getting higher and higher.And at the same time,the proportion of groundwater-related diseases in the constructed high-speed railway operation tunnels is also getting higher and higher.Based on the available data,it can be expected that in the next five to ten years,groundwater-related diseases in high-speed railway tunnels will become more frequent and more serious.In order to ensure the safety of high-speed railway tunnels,fast and accurate groundwater disease diagnosis and maintenance tools are urgently needed.Based on this background,combined with the non-contact detection characteristics of the transient electromagnetic method,this dissertation proposes the application of train-borne transient electromagnetic method for groundwater disease detection inside high-speed rail tunnels to meet the requirements of rapid and efficient detection.Through a variety of different research methods such as data comparison,theoretical calculation,computer simulation and indoor full-size physical model test,research work has been carried out on the three-dimensional forward study of water-bearing anomalies behind the lining involved in train-borne transient electromagnetic detection,comparative study of antennas of train-borne detection systems,study of mutual induction between train-borne detection antennas,study of detection angle and distance of train-borne detection antennas,interference and identification of train bodies and train tracks on the detection of water-bearing anomalies in close proximity and optimization study of the detection results of water-bearing anomalies in close proximity,etc.The main research results and conclusions achieved are as follows:1).The electromagnetic response law of water-bearing anomalies behind the tunnel lining to different physical parameters is studied by using numerical calculation software for groundwater defects in close proximity targeted by train-borne transient electromagnetic.The influence and sensitivity of the relevant parameters of the water-bearing anomalies on their electromagnetic characteristics are summarized,and the electromagnetic response time of the water-bearing anomalies is concentrated in the range of 0.1 us to 100 us.Thus,the corresponding instrument parameters suitable for train-borne system are proposed to provide technical guidance for the selection of vehicle detection equipment in the later stage.2).For the train-borne transient electromagnetic antenna system of close range detection,the electromagnetic response law of three different antenna type combinations is studied,and the electromagnetic induction law of the relative position change of the three antenna combinations is compared.The conclusion can be summarized as when the antenna is arranged in central loop configuration,the induction electromotive force of 8-shaped transmitting coil is the smallest but not with stability;the induction electromotive force of square transmitting coil is the most stable;the circular coil has the largest induction electromotive force,but also without stability.Combined with the working environment limitation of the train-borne transient electromagnetic system and the long-term stability requirement of the antenna,the optimal antenna configuration is finally selected as a multi-turn square wire frame with the central loop configuration.3).For the transient process of the train-borne transient electromagnetic detection antenna,the induction law between the transmitting and receiving antennas after step turn-off is studied from the perspective of transmitting current,coil turns and coil size.It is concluded that the transmitting current,coil turns and coil size all have influence on the transient process,while the current factor does not affect the curve shape of the transient process,but only changes the amplitude of the curve.Then through the equivalent circuit analysis of the receiving antenna,the influence law of the damping coefficient on the performance of the receiving antenna is studied,and it is obtained that in the critical damping state,namely damping coefficient equal to 1,the output curve overlaps with the theoretical curve at the earliest,that is,in this case the receiving system takes the least time to output the effective signal,and can reflect the effective geological information at the earliest.Therefore,in order to ensure the effectiveness of the received signal,the detection system should be as close as possible to the critical damping state,in order to avoid the oscillation phenomenon as much as possible.4).For the problem of uncertainty in the distribution of water-bearing anomalies in operating high-speed railway tunnels,the electromagnetic response law of water-bearing anomalies under different spatial distribution conditions is studied,and the conclusion is that the electromagnetic response of water-bearing anomalies is most obvious when the train-borne detection antenna is facing the water-bearing anomalies;the farther the water-bearing anomalies deviate from the detection antenna,the smaller the electromagnetic response of water-bearing anomalies.In order to ensure the detection efficiency of a single train on a single side of the tunnel,the vehicle transient detection antenna should be oriented at an angle of 45 degrees to the ground.5).For the metal interference between the train body and train track on the water-bearing anomalies in close proximity behind the lining in the operating high-speed railway tunnel,firstly,the respective electromagnetic response characteristics of the train body and train track are analyzed and calculated,and then the interference law of the water-bearing anomalies is studied,and it is concluded that the electromagnetic response of the train body is much larger than that of the train track in the same tunnel space,and when the train body exists,the water-bearing anomalies electromagnetic response is completely covered.Therefore,only high resistance materials can be used to manufacture the train body to exclude this interference term.Due to the non-excludability of the train tracks in the operating tunnel,the weak electromagnetic influence can only be used as a background field for anomaly detection.6).A multi-level comparative study is performed using multiple square coils combined with train track interference based on indoor isometric water-bearing anomaly detection tests.This includes:(1).The model materials are selected using the physical similarity criterion,and the electromagnetic response interval of the close water-bearing anomalies is verified by the equiproportional experimental field arrangement;(2).The effect of coil damping state on detection results is confirmed by comparative detection of different coil sizes and turns;(3).The electromagnetic response of the water-bearing anomalies in close proximity under the metal interference of train tracks confirms the relative weakness of the electromagnetic response of train tracks and the feasibility of the detection of water-bearing anomalies in close proximity after backgrounding the electromagnetic interference of train tracks;(4).By changing the angle between the water-bearing anomalies and the detection antenna,it is verified that the 45° angle between the detection antenna and the ground has the highest detection efficiency,which can ensure that the transient electromagnetic train running in a single trip can detect the anomalies with different spatial distribution in a single side of the tunnel;(5).Finally,for the problem of early data loss in the detection of actual water-bearing anomalies,the difference between the original data and the restored data after considering the coil response is compared,which confirms the importance of the coil response in the close transient electromagnetic detection and provides an important basis for the restoration of early data in the later stage. |
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