| In recent years,with the continuous development of China's economy and the continuous improvement of urbanization,China's urban rail transit construction has achieved unprecedented development.At present,in order to improve the construction efficiency and shorten the constructing time,the shield method construction has been widely used in urban subway construction in China.However,due to the complicated urban geological environment,ground subsidence and boulders during rail transit construction and operation,geological safety accidents have occurred from time to time,posing a huge threat to the lives and property of the people.The hidden danger of geological safety has become the main factor restricting the safety and high-efficiency construction of China's rail transit,and is an engineering problem to be solved urgently.Urban geological hazards mainly include underground caves and boulders.Underground caves will cause the ground to collapse,threatening the safety and property of the people;and the underground boulders will wear the shield machine cutter head and affect the construction progress of the tunnel shield machine.Geophysical detection technology plays an important role in the detection and monitoring of geological hazards of rail transit due to its economic,rapid and non-destructive characteristics.However,it is extremely challenging to do such work,because the detection accuracy of geological hazards such as underground caves and boulders is high,and the interference of geophysical field detection on urban ground is very large.Meanwhile,the detection effect of a single geophysical field is very uncertain,and it is difficult to meet the requirements of accurate detection of shallow geophysics in cities.This dissertation proposes a three-dimensional parallel electrical observation system with multiple boreholes and ground synchronously arranged.The observation system includes an electrode group for three-dimensional measurement of high-density resistivity on the ground and vertical electrode arrangements in multiple boreholes to form a full range of ground and holes.The three-dimensional observation system has wider coverage and greater data information.Ground high-density resistivity three-dimensional imaging(CT)and simultaneous porous three-dimensional cross-hole electrical CT detection effectively improve the longitudinal resolution of electrical CT and realize the fine structure detection of urban geological hazards.The observation system is also suited for three-dimensional cross-hole seismic CT observation,which realizes the rapid diagnosis of three-dimensional seismic CT and three-dimensional electrical CT with porous(larger than 3 holes)and large spacing(larger than 20m)along the rail transportation.Using the upper and lower parallel dual transmitting coils,a set of ground transient electromagnetic data correction processing methods has been developed.This device can effectively reduce the mutual inductance caused by the current changes in the transmitting and receiving coils,improve the signal to noise ratio,and largely reduce the influence of various types of pipelines and strong metal induction bodies on the transient electromagnetic signals.The blind zone of transient electromagnetic detection is changed from the normal 20m,and the detection blind zone is within 2m,which significantly improves application effect in the detection of geological hazards of transient electromagnetic method in environment.In view of the anomalous characteristics of geophysical fields of underground holes and boulders,this dissertation finally developed a set of comprehensive geophysical detection technologies based on shallow seismic method,direct current method,electromagnetic method and three-dimensional cross-hole method,and independently developed a set of suitable for the ground Multiple geophysical field exploration and diagnosis system for urban rail transit geological hazards.Based on the collation of engineering geological and hydrogeological data of cities in mainland China,the thesis carries out the zoning,classification and precise expression of engineering geological and hydrogeological types along the line,and summarizes the current geophysical response characteristics of collapse and boulders disaster sources along the rail transit.Its accuracy and reliability are further verified by the three-dimensional numerical simulation of seismic and DC resistivity and laboratory tests in this dissertation.On the basis of independently developing a seismic,electrical and magnetic integrated multi-geophysical exploration system and three-dimensional imaging software,firstly use surface shallow seismic,direct current method and transient electromagnetic multiple geophysical detection to quickly scan the surface,and then Accurately locate geological hazards through the three-dimensional resistivity cross-hole CT or three-dimensional seismic cross-hole CT method to form a fast,reliable,and intelligent multi-geophysical expert diagnosis and analysis system suitable for the exploration of ground hazards along rail transit.The system has been initially applied in the exploration of geological hazards in new cities such as Hefei,Shaoxing and Xiamen,and has achieved good engineering application results,providing a new technical means for the exploration of geological hazards in urban rail transit in China. |
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