| With the development of the economy,the subway has become an important part of urban transportation,and the operating mileage of the subway has increased significantly year by year.About one-third of China's areas are karst-developed areas.Common karst diseases include karst caves,karst depressions,and subsidence columns.Underground esoteric rivers are often formed in areas with strong karst development.Reports of urban karst caves and surface subsidences are not uncommon,and the existence of such unfavorable geological bodies such as karst seriously jeopardizes the safety of ground buildings and people's lives and property.The subway's geological structure,stratigraphic structure,and development degree of karst diseases directly affect the subway construction progress and the post-operation safety of the subway.Therefore,accurate and efficient exploration techniques are used to find out the stratum structure of the metro work area,and the type and size of karst diseases.The specific location in space is of great significance for ensuring the construction progress of the line,operational safety and the safety of people's lives and property.Conventional geophysical methods are difficult to meet the high-precision detection of karst diseases in subways.Crosshole seismic CT technology can accurately image the stratum structure of subway stations.Combined with other geological data,the type,scale and shape of karst in the field can be accurately determined.prediction.In this thesis,a systematic study on cross-hole seismic CT technology is carried out on tomography theory,numerical simulation and application effects.The three-dimensional model of non-uniform medium between pores is established by using single caves with different filling media,different beaded caves with different filling media,and karst fissures with different dip angles.The karst caves with different karst types are simulated by crosshole seismic CT technology.When to go.By analyzing the traveling wave travel characteristics of the forward simulation,the following conclusions are obtained: the travel time of the seismic wave will be longer as the diameter of the karst cave increases;for the same diameter cave filled with different media,the wave velocity of the filling medium and the surrounding intact rock The greater the difference in body wave velocity,the easier it is to identify the karst features.As far as the single-shot record is concerned,the larger the diameter of the cave,the more the number of different paths,ie the larger the diameter of the cave,the larger the area affected by it;The seismic wave travel characteristics of the semi-filled karst caves of the two materials are between the fully-filled karst caves;for the karst fissures with different dip angles,the travel time characteristics are closely related to the spatial arrangement of the observation system;the observation system selection and the line layout must be combined.The geological data of the previous period is as perpendicular as possible to the direction of the strike.The measured results of the pore formation were analyzed.Using on-site measured crosshole seismic CT data,combined with previous numerical simulations and geological data,inversion of the formation velocity structure of the site,division of stratigraphic structure and formation of unfavorable geological bodies.According to the image characteristics of the inter-hole seismic CT profile,the complete limestone region,tunnel hole instability problem,karst cave and karst fissure water-rich problem,ground collapse problem and uneven settlement of foundation are summarized and analyzed.In addition,the application of crosshole seismic CT technology is analyzed from the aspects of data acquisition,observation system and noise.In the future engineering practice,it is hoped that the error can be reduced and the accuracy of engineering prediction can be improved. |
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