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

With the accelerated pace of China's railway construction, in the process of construction, more and more railway lines are built to pass through complex karst geological conditions inevitably. When encountered in some complex terrain conditions affect the mountain construct these lines need to Dig tunnel. To protect the karst area of railway safety, along the railway to carry out inspections to identify karst position, excluding the impact on railway safety karst generated.This paper combined with the geological and geophysical characteristics, choose high-density electrical method, ground penetrating radar(GPR) method, the seismic image method, the transient Rayleigh wave method to research and application. There is a close relation between the karst and the underground water, and there is a great difference between the karst cave or the water rich geological body and the normal surrounding rock. High density resistivity method can intuitively and accurately reflect the subsurface resistivity distribution and variation, which is an effective method for the detection of Karst. Electromagnetic wave propagation in different medium is different and attenuation regularity, Ground penetrating radar(GPR) method, through to the underground pulse electromagnetic wave to detect the underground medium, the karst caves in the air or water with a big wave impedance differences of surrounding rock medium, it also makes the ground penetrating radar(GPR) method can effectively detect karst caves. The void and broken structure formed by the karst structure make it have a large elastic difference in the surrounding medium. By studying the characteristics of the elastic wave, the seismic imaging method can effectively find the underground karst cave. Karst is commonly due to loose clayey soil cave, water filling the cavity filling and filling of karst cave, the cave where the surface wave compared to surrounding rock surface wave, the wave velocity is lower, generally for the lower body, so can be an effective detection of karst by surface wave.At the same time for different filling the cavity with a high density electrical method, ground penetrating radar(GPR)method and seismic imaging method of numerical simulation, and its performance characteristics are analyzed and summarized.By geophysical prospecting methods and the combination of engineering geological conditions,the advantages and disadvantages of methods and physical parameters of combining, integrated the three aspects to consider and choose the most appropriate comprehensive and combination method to satisfy the detection requirements, through comprehensive or combined geophysical interpretation of the joint to improve the detection accuracy and reduce the the uncertainty of a single geophysical exploration.Through the above research, the selection of geophysical methods for detection of karst work area and optimum operating parameters; Geophysical methods for railway basal karst detection, are analyzed and explained, after explaining the abnormal spot drilling verification, summarized under the specific geological conditions of geophysical exploration of the original data collection technique, parameters selection and the interpretation of the data processing method. After comprehensive geophysical prospecting method of integrated interpretation and drilling validation, proved that using comprehensive geophysical prospecting method for railway basal karst cave detection relative to a single method has stronger adaptability and accuracy,overcome the multiple solutions of the single geophysical method, compared with other exploration methods, geophysical prospecting method has the characteristics of low cost, high exploration efficiency and abundant information.