The Research On Detection Method Of Void Area Under Road Based On Elastic Wave Method

The roadbed is the load-bearing part of the road and bears the load of passing vehicles and its own weight on the upper part of the road.If the stability of the roadbed is reduced,the road superstructure will be affected and the road will have potential safety hazards.If the roadbed becomes unstable,the superstructure of the road will not be able to maintain stability,this leads to the occurrence of road diseases.The compressive stress will be generated by the passing vehicles and the weight of the road.When the compressive stress acts on the roadbed,the roadbed will be continuously deformed.If the deformation exceeds the limit value,the roadbed will be damaged and eventually lead to road instability.Underground works such as subways and pipelines that the city has vigorously developed will also affect the roadbed.The excavation of soil will cause the settlement of the upper soil.Precipitation will lead to soil erosion;the loose soil will gradually form a void.Underground pipes,especially water pipes,are damaged fractured,this lead to water leakage.The surrounding soil is washed away,the roadbed of the road formed holes and looseness and other diseases,and then developed into a roadbed emptying,causing the road to collapse.In this paper,the principle of subgrade voiding is studied to determine the causes and types of subgrade voiding.The existing detection theory is summarized.Based on the advantages and disadvantages of traditional detection methods,combined with the theoretical study of elastic waves,the propagation law of elastic waves is analyzed,and then a new detection method for the detection of subgrade voids-the elastic wave detection method is proposed.Firstly,a numerical model is established based on the finite difference theory.The model includes numerical models of voids of the same depth and different scales and numerical models of the same size and different depths,analyze the propagation law of elastic waves in different voids and then use the software to simulate the elastic wave data for frequency domain and time domain analysis,and explore the vibration characteristics of different void areas.The surface acoustic wave data processing is performed on the simulation record to obtain the dispersion curve,and the characteristics of the wave dispersion under the different voiding states are analyzed.Numerical simulation of subgrade voids in different states,and the corresponding changes in elastic waves based on numerical simulations,the theory and method for quickly and accurately detecting and effectively identifying the location and character of the void area are designed.Using a hand hammer as a source,using the single-channel detector picks up the elastic wave vibration signal,using the seismic wave instrument to collect,The rapid detection device for roadbed was studied by designing data acquisition and processing integrated system and changing the coupling method of the detector and the ground,and then combines the results obtained by numerical simulation to design empty model,The emptying model includes several models with the same depth and different sizes,and a model with the same size and different depth.Based on theories and methods of elastic wave detection,the actual different state void detection is performed.The collected data was analyzed by software in frequency domain and time domain.The surface wave detection is performed by means of transient excitation multi-channel reception.The surface wave data is subjected to F-K transformation to obtain the dispersion curve,and the variation characteristics of the dispersion curve are analyzed.Through different data collection methods and data processing methods,the optimal void detection scheme and data processing scheme are determined to verify the vibration characteristics obtained in the actual void area.Finally,according to the work have be done,two data acquisition and processing integrated systems,a portable electromagnetic source and two sets of rapid detection receivers were designed.The numerical simulation and actual test results show that when the subgrade is voided or there is a hole in the deep,elastic waves can cause the incident wave of the reflected wave to be broken during the hole detection,and the seismic records appear diffracted and oscillated.The presence of a cavity in a certain area can be determined by combining the continuous condition of the reflected wave event axis with the diffraction arc and the waveform oscillation.The spectrum and time-frequency analysis of the obtained seismic records,analysis of changes in the main frequency and amplitude,and the characteristics of frequency changes at different times can also determine the existence of voids.An abnormal inflection point appears in the surface wave dispersion curve of the de-vacuum area,and the existence of a certain depth de-emption area can be determined by the abnormal change of the dispersion curve.Therefore,in the actual void detection,the surface wave detection and the common offset elastic wave detection method can be combined.The horizontal range of the void area can be determined by the common offset elastic wave method,and the depth range of the void can be determined by the surface wave method.The void is identified qualitatively and quantitatively.