The Research Of Application Of The Comprehensive Physical Methods To Detect The Railway Roadbed And Tunnel Disease In The Karsts Area

China has complex topographical and geological conditions, with the development of economy and society, the demands and requirements for transportation are also increasing, of which there are many railway through the mountains and hills. At the same time, China is a country which the distribution of karsts geology is broad, especially in the southwest of China. In these karsts regions, at the early construction of the railway and the future course of operations, there are potential disaster problems such as Surface subsidence, collapse substrate, inrushing water and gushing mud and so on. Timely detection and treatment of these issues is very important.Currently, there are many geophysical methods of detecting cavities or underground water, such as electromagnetic method, high-density electrical, acoustic methods,ground penetrating radar method,radiation method etc. Each method has its own advantages and limitations. In the railway lines of the karsts area, the roadbed and mountain tunnel is a unified whole, for the detection of disease problems which existed, usually divided into two in the past. Based on the karsts survey work of a railway line in the southwest of China, I read and sort a lot of documents information, and hope to make a set of comprehensive geophysical methods, which can quickly and cost-effectively solve a variety of diseases issues that exist in the roadbed and tunnel.Theoretical basis and application characteristics of several methods were studied in this paper, and then combined with the actual work, the key technology of data collection, data processing and data interpretation in each methods were studied, the existing interference and common problems in the work were summarized, theoretical and technical supports for the application of related work provided in this paper. Combined with the geological and geophysical conditions of the actual work area, I analyze the feasibility of the method chosen to build a typical physical model of diseases geological body, through the analysis of the application of this group of geophysical methods to detect different targets to give the common diseases geophysical anomaly map, and describe, analyze and summarize typical anomalies of common diseases to provide a reference for the interpretation of the relevant exception.Combining with the work area geological, geophysical characteristics and the existing constraints, I study and use synthetically a high density resistivity method, ground-penetrating radar method,seismic imaging method in this paper. Because of a close link between Karsts and groundwater and large differences in resistivity between voids or water-rich geological and normal surrounding rocks, high density electrical method can be the effective way to reflect more intuitively and accurately the distribution and variation of subsurface resistivity; Because of the different propagation and attenuation of electromagnetic wave in different media, ground penetrating radar method by emitting electromagnetic pulses into the ground detect subsurface, where there is a big acoustic impedance difference between air or water in karsts fissures and other media, which also makes ground-penetrating radar method effectively detect karsts fissures. Because the cavity and broken structure formed by karsts tectonic can produce a greater elasticity difference in the surrounding medium, by studying the characteristics of elastic waves, seismic imaging methods can effectively determine underground voids and fracture zones.Through analyzing results in practical work, as opposed to the more flexibility and accuracy of a single method, but compared to other survey methods, this comprehensive set of geophysical methods described in this paper have the characteristics of the relatively low exploration costs, the high exploration efficiency and the rich detection information. This combination of geophysical methods used in this paper solved a variety of problems detected in disease detection of karsts Railway Bed and tunnels. In the karsts groundwater advanced prediction, checking roadbed covered karsts, detecting the end of the tunnel karsts fracture zone, detecting karsts cement grouting effect and detecting tunnel lining etc. This method also has a good detection results, making due contributions for guaranteeing the construction safety and reducing unnecessary losses.