| Finding out the distribution of urban road underground space targets and ensuring the sustainable development of urban roads is an important task for maintaining urban road safety.Ground penetrating radar plays an important role in urban road safety and quality inspection by virtue of its advantages of fast data acquisition,low cost,high imaging resolution,high efficiency,and non-destructive testing.This article focuses on the non-destructive testing technology of ground penetrating radar,starting from the principle,using the latest open source software gpr Max3 D to carry out the numerical forward simulation of ground penetrating radar,analyzing the propagation law of electromagnetic wave in different physical parameter models,and providing reference and basis for actual data analysis.I participated in the ground collapse detection project in Shenzhen throughout the whole process,and used the ground penetrating radar comprehensive detection vehicle to detect hidden dangers on the conventional urban roads in various large districts of Shenzhen according to the ground collapse prevention and control plan of Shenzhen in 2019.I picked out the ground penetrating radar data with better quality for comprehensive processing and analysis,and described,distinguished and summarized the abnormal signals of common urban road ground penetrating radar,and provided a direct basis for the follow-up ground collapse prevention and control work.The main conclusions are as follows:(1)The reflected wave at the end of the underground model body is in the form of a hyperbola,and the vertex position of the hyperbola is the center position of the end point of the model body.Electromagnetic waves cannot effectively penetrate metal conductors,and metal conductors have a shielding effect on electromagnetic waves.The electrical conductivity of the model material affects the energy propagation and attenuation of electromagnetic waves,the smaller the electrical conductivity,the smaller the electromagnetic energy attenuation.The greater the difference in relative permittivity between dielectric materials,the greater the reflected wave energy.The relative permittivity of the underground model is smaller than that of the underground half space,the reflected wave and the incident wave have the same phase.The detection depth and resolution of the ground penetrating radar are related to the center frequency of the antenna and the electrical properties of the dielectric material in the underground half space.The greater the center frequency,the shallower the detection depth,and the higher the resolution,the smaller the center frequency,the deeper the detection depth,and the lower the resolution.(2)The main types of ground collapses in Shenzhen are engineering collapses,which are mainly caused by water supply,sewage,rainwater,concealed channel damage,improper construction,rain erosion,and roadbed settlement,etc.,and most of them occur within 2m below the ground.Radar data interpretation results should include underground cavities,voids,loose soil,etc.The ground collapse accident in Shenzhen showed the characteristics of concealment,suddenness,mass occurrence,and serious damage.Interfering objects on the ground have a long radar reflection signal,which shows a deep regular abnormal signal,even exceeding the detection depth of the antenna.The signal energy is generally not large,low frequency information is displayed,and the abnormal signal display range is usually large,Such as interfering objects like viaducts,tunnels,street lights or billboards.Generally,the radar profile of surface and underground anomalies show different regular reflection waves with the structure of the anomaly.Anomaly bodies such as manhole covers,ground steel plates,and bridges show columnar and regular strong reflection radar waveforms.Cables,pipes,and steel mesh show regular hyperbolic radar waveforms.Artificial structures,geologically porous,voids or cavities are displayed as irregular radar signals,which change with the changes of underground structures. |
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