Research On Multi-wave Seismic Fine Detection Technology Of Urban Ground Fissures

Ground fissure refers to the deformation of underground rock and soil under the action of internal and external stress.When the external force exceeds the internal binding force of rock,it breaks up and forms fissures.Then under the pressure of surrounding rock,cracks occur on the upper surface along the free surface,showing cracks.This common geological hazard has the characteristics of strong concealment,extensive development,different scales and difficult exploration.It can induce landslides,debris flows and other serious disasters under rainy weather,endangering the safety of building infrastructure and public.Therefore,it is of great significance to detect ground fissures and find out the causes and morphological characteristics of existing urban ground fissures.Up to now,the predecessors have identified the formation mechanism of most ground fissures through InSAR,GPS,leveling,soil loss theory,surface wave exploration,numerical simulation and other methods.Among many methods for detecting ground fissures,the comprehensive geological survey method can only judge the outcropped ground fissures;drilling and trench exploration can observe the joint shape of ground fissures,but the exploration scope is limited;geophysical means are often used to detect ground fissures;surface wave exploration and ground penetrating radar can detect the structure of shallow surface strata with high resolution,but the detection depth is limited.Ground fissures are essentially different from geological structures,and their development patterns are quite different,which greatly increases the difficulty coefficients of seismic exploration for ground fissures.Seismic exploration has achieved good exploration results in the morphological characteristics,genetic analysis and controlling factors of ground fissures,but most of them are structural ones.The detection of complex profiles of medium and small-sized complex-genesis ground fissures can no longer be based on the characteristics of traditional faults such as reflection event axis dislocation and fault characteristics,so a new method suitable for ground fissure detection needs to be put forward.The main content of this study is to analyze the formation mechanism and development process of ground fissures in the regional geological background,summarize the plane profile characteristics of ground fissures,analyze the geological conditions and physical properties of existing ground fissures developed areas,and design three geological models of ground fissures,i.e.tracking fracture type,ladder type and Y type ground fissures.Their seismic forward records are obtained by forward simulation of higher order finite difference equation,and then the frequency spectrum and attribute characteristics of seismic single shot are analyzed and studied.The morphological characteristics of three ground fissure models on single shot record and superimposed profile are distinguished and identified.Then,combined with the characteristics of forward summary,the problems existing in actual ground fissure data are analyzed and studied,and the final mining is carried out.The multi-wave interpretation of ground fissures in the study area is carried out by means of superimposed section,attribute analysis,first break wave tomography and Rayleigh surface wave inversion.The method is proved to be effective and feasible by drilling holes.