The Application Of Geological Radar In The Detection Of Underground Space

In recent years,with the continuous construction of cities and the full development and utilization of underground space,the environment of urban roads,municipal pipelines and underground buildings has also gradually deteriorated,resulting in potential disasters such as cavities and loose underground bodies,leading to the collapse of urban roads.The collapse of urban road surface occurs suddenly and has a wide range of influence,which often causes huge property losses and seriously threatens the safety of the city.With the prosperity of the social economy and the needs of urban construction,the construction of projects in the city has become more frequent.The underground pipelines distributed in the underground of the city test the construction ability of the builders.In order to avoid the potential damage to underground pipelines in the construction of the project,the census activities of the underground pipelines in the city are imperative.GPR is a widely used method for engineering geophysical exploration,which uses high frequency electromagnetic waves to detect the distribution law of media under the surface and identify abnormal geological bodies.Therefore,according to the two-way travel time,waveform data and amplitude of the received wave,the structure of the underground medium or the spatial position of the geological body can be inferred through appropriate data processing.GPR has been widely used in geological survey and engineering survey due to its simple principle,strong operability and low loss.It plays an important role in the detection and analysis of road surface subsidence.With the prosperity of social economy and the need of urban construction,the urban engineering construction is more and more frequent.In order to avoid the potential damage to the underground pipeline in the construction,it is imperative to survey the underground pipeline in the city.This paper mainly explores the role and effect of GPR in urban integrated pipeline detection,introduces the working principle of GPR,the working process and method of GPR in integrated pipeline detection,establishes forward models of various GPR and analyzes the influence of medium,target size and buried depth on numerical simulation results.The forward results of numerical simulation are compared with the measured results in the work area,and the effect of them in engineering exploration is evaluated.This paper mainly introduces the research background,basis and significance of the topic,the research status at home and abroad,the research content and expected results of GPR.This paper discusses the application of GPR in underground space,such as ground collapse,pavement collapse,karst development area,etc.The distribution and development of ground subsidence,the formation mechanism of karst and the characteristics of GPR in detecting nonmetal pipeline are also introduced.Consult the relevant literature,understand the application of GPR in geological disaster investigation,and summarize the research status of GPR.Understand the application scope of FDTD method in forward modeling of GPR.As a detection method of underground space,GPR is introduced.According to the difference of dielectric constant of underground material,the working principle of detecting underground space target is introduced.In the process of GPR detection,the transmitting antenna transforms the electrical signal into high frequency electromagnetic signal,and sends it to the underground space in the form of broadband short pulse signal.The basic law of electromagnetic wave propagation is introduced.This paper introduces the influence of dielectric properties of media on GPR and three technical parameters of GPR,including GPR equation,resolution and detection distance.As well as three criteria for judging anomalies: amplitude,coaxial,and amplitude.The application of GPR method is affected by many factors and effective detection distance.According to the geological environment and working environment of the working area,select the measurement method,measurement instrument,measurement network layout,determine the appropriate parameter information,and detect the target body.The purpose of GPR data processing is to eliminate noise interference and improve the resolution of energy reflection of the main body of the target.FDTD is widely used in various fields of numerical simulation because of its simple principle,easy to master and parallel computing.The stability of the difference scheme in numerical stability analysis is introduced.It is introduced that the calculation of the electromagnetic field value on the grid boundary needs the electromagnetic field value outside the boundary and special difference scheme,namely boundary condition.An important task of FDTD method in electromagnetic field analysis is to simulate the excitation source,that is,to select the appropriate incident wave to add to the FDTD iteration.In the forward numerical simulation,it is very important to select the appropriate excitation source in the iteration.This chapter mainly introduces 2D-FDTD forward modeling of radar electromagnetic wave propagating in various underground structures to study the propagation characteristics of GPR wave,and verifies the effectiveness of finite difference method in GPR forward modeling.The software gprmax 2D is used to complete the numerical simulation through gprmax 2D,and then through MATLAB mapping,the results are obtained,and then the forward results are analyzed.This paper introduces the forward modeling of the shape and size of the underground object and the different media,the forward modeling and result analysis of the nonmetal pipeline under the different pavement,the forward modeling and result analysis of the common diseases in the underground space.At the end of this chapter,it mainly introduces the application of GPR in a specific project.This paper introduces the situation of airport geological exploration area.The main purpose of geophysical exploration is to find karst caves and karst fracture zones.GPR has a great attenuation on clay layer.The reflection coefficient of radar reflected wave depends on the difference of relative dielectric constant of corresponding medium.The greater the difference,the greater the reflection coefficient and the better the detection effect.According to the strength and waveform of the reflected wave,the complete lithology,cavity,loose body and water injection can be determined.The shape characteristics of karst caves on GPR images mainly depend on the shape,size and properties of the filling,which is generally composed of many hyperbolic strong reflection waves.This paper introduces the road surface disease phenomenon in the road collapse work area,which has many reasons.Using GPR as detection means,through the analysis of radar profile,the location and distribution of underground collapse can be accurately detected,the collapse mechanism can be analyzed,and the disease can be reduced.Through the GPR investigation of road collapse,we can understand the mechanism of road collapse,and detect whether there are cavities and broken zones.Based on the difference of relative permittivity between underground pipeline and surrounding medium,the ground penetrating radar(GPR)is introduced to find and analyze anomalies.It has the advantages of high resolution,strong anti-interference ability,easy to carry and operate.