The Study On Forward Ground-penetrating Radar Simulation And Detection Method For Railway Subgrade Defects

The core idea of the geological radar is non-destructive testing.The geological radar has a high resolution and can quickly obtain the detection result.The result is highly reliable and does not involve the working status of the measured object.It can achieve continuous imaging and is internally There are practical applications for defects and shallow fine stratigraphic structures.Due to the particularity of roadbed diseases under the railway,the use of geological radars to identify roadbed diseases is a cost-effective method.However,due to the particularity of the railway track and the dense steel mesh arranged inside the ballastless track,the reflection signal of the electromagnetic wave at the lower target of the steel bar received by the radar receiving antenna is weak,which brings difficulties to the detection work.In this paper,a systematic study of the process of detecting groundbreaking of railway subgrade by geological radar is carried out.Combined with numerical simulation,physical model test and field test,the characteristics of ground-based radar response of different types,different characteristics and different conditions are analyzed.The main research contents and results are as follows:(1)Analyze the types of railway roadbed diseases,study the working principle of the geological radar and set principles of the acquisition parameters,and provide the basis for the numerical simulation,physical model test and field test process.(2)Using gprMax 3.0 geological radar simulation software to establish a common railway subgrade disease model for forward modeling,analysing the anomalous characteristics of subgrade diseases under different conditions,and clarifying the fundamental characteristics of radar submarine radar detection maps.The circular cavity presents a hyperbolic feature with a small radius.The rectangular cavity exhibits a horizontal arc at its upper boundary.The reflection energy is strong,while the two ends of the horizontal section have hyperbolic characteristics with weak reflection.(3)For the distribution of reinforcing bars in high-speed railway ballastless track,the forward modeling study was conducted on the roadbed diseases distributed under the steel bars,and the influence of steel bars on the underlying diseases was analyzed.Due to the large conductivity of the steel bars,the geological radar will enter electromagnetic waves.Attenuation occurs at this location,and only part of the electromagnetic waves are incident on the lower layer through the gaps between the surface reinforcing bars,which will affect the detection of the disease area under the reinforcement.However,when the ratio between the spacing of rebar and its diameter reaches a certain value,it can be considered that it has little effect on the detection of the underlying disease.(4)Simulate the typical subgrade disease form through physical model test,collect the typical geological radar profile image of the test model,study the difference of geological radar image in different types of subterranean disease areas,analyze the image characteristics of typical subgrade disease,and obtain the geological data.Comparing the radar profile image with the forward simulation result image,the feasibility of the forward modeling is verified,which provides a basis for the further use of forward modeling for more complex geological radar detection and analysis.(5)Through on-the-spot test of ballastless track slabs,the analysis of the signal representation of the rebar signals in ballastless track slabs was studied.The effect of rebars in track slabs on the detection of anomalous target bodies below was studied;Geological radar scanning,combined with existing research results,identified the geological radar image.Through on-site testing of ballasted tracks,the distribution of roadbed subgrade damages was obtained.