| In highway engineering,the compaction degree of road base is an important index to determine the quality of the project.The subgrade conforming to the standard of compaction can reduce the occurrence of water infiltration,subgrade subsidence and so on,and improve the carrying capacity and service life of the road.The traditional compactness detection methods,such as ring knife method,sand filling method and nucleon instrument method,etc.They have the disadvantages of damage to road structure,rough detection and slow speed.Reflective cracking is a common disease of semi-rigid base asphalt concrete pavement.The cracks are often produced in the semi-rigid base.Under the repeated action of driving load and temperature load,the cracks quickly reflect to the surface layer;the water seep down into the subgrade along the crack,and makes the subgrade out of the roadbed under the action of driving load and shortens the service life of the road.Therefore,we need new and effective methods to complete the fast and accurate detection of subgrade compaction and pavement crack depth.As a geological detection method,transient Rayleigh Wave method has been widely used in industry,engineering and other aspects because of its characteristics of rapid detection,nondestructive and high resolution.It is a kind of surface wave,with medium propagation characteristics along the free surface.The exploration in Rayleigh Wave mainly uses the characteristic that the wave velocity of Rayleigh Wave is closely related to the physical properties of the propagating medium,so it can be used to detect and analyze the internal conditions of the medium.Based on the virtual instrument technology,the transient Rayleigh Wave detection system is developed with the graphical programming language LabVIEW as the development platform,and the common calculation methods of the physical characteristics of Rayleigh Wave,the frequency dispersion curve and the inversion of the dispersion curve are analyzed.The compaction degree of clay is detected by the characteristics of the wave velocity of Rayleigh Wave and the physical properties of the medium.In this paper,the compaction degree of clay is detected by tamping test.The maximum absolute error of compaction degree measured by the Rayleigh Wave method is 0.5% compared with the sand ring knife method.The results show that the system is used to detect the compaction degree of clay.There is a high accuracy.The propagation mechanism of cross fracture in Rayleigh Wave is analyzed,and the detection of crack depth is realized by the time path mathematical relationship of the cross seams of Rayleigh Wave.The system is used to detect the transverse cracks in a section of Yexian County highway in Lanan high speed,and the calculation depth of the crack is basically consistent with the result of the core sampling.In addition,good experimental results have been obtained. |
