| With the rapid development of China's high-speed railway, long-term effects of environmental loads and train loads, ballastless track has presented different types and different degrees of diseases. The detachment, looseness and void diseases of the CA mortar layer, which is the lubrication layer between the track slab and the supporting layer, are the main forms in the slab ballastless track. The long-term development of these diseases will inevitably lead to deformation and dislocation of the track, thereby affecting the service life of the structure, reducing the quality of the train running, and threatening the driving safety and durability of the structure. Therefore, it is great significant to study the rapid and nondestructive method to detect interlayer detection of ballastless track, which can guarantee the operation safety of high-speed railway and develop the maintenance strategy.Taking void disease in CA mortar for research objects and GPR as technical method, this study established direct wave, reinforced bar (rebar) and void disease echo model to analyze the affection of rebar echo on the lower part of the void disease echo and discuss the algorithm to suppress direct wave, and on the basis of studying the characteristic of wave velocity and directional characteristics of target echo, a directional filter is proposed to detect and identify the void disease in CA mortar. Based on the analysis, some main conclusions can be drawn.(1) Strong echoes of rebar are the main obstacles in the detection of void diseases in CA mortar. The influence of rebar echo on void disease echo mainly includes strength attenuation, signal delay and echo aliasing. The amplitude of void disease echo is inversely proportional to the diameter of covered rebar, and the greater the diameter of rebar, the weaker the void echo amplitude. The delay occurs between the rebar-covered void disease and uncovered void disease. And the overlapping interference is produced when the distance between the steel bar and the cavity disease is close.(2) Ground direct wave is an important component of GPR echo energy. With the increasing of relative permittivity, the energy Eigen vectors of ground direct wave and GPR echo signal converge to the same vector space. And the proposed energy adaptive analysis can effectively suppress the ground direct wave while retaining the target echo of the steel bar and the cavity disease.(3) The energy of target echo has the feature of maximum value and axial symmetry, the instantaneous phase of target echo has the feature of even symmetry in time and odd symmetry in space. The algorithm of wave velocity estimation based on feature fusion of energy features and instantaneous phase features can eliminate the error caused by pseudo vertex in the calculation of the wave speed of the reinforcement structure of ballastless track, and can estimate the wave velocity more accurately.(4) The directivity of echo signal is an important feature of GPR target echo. The main directional feature of point target echo is the hyperbolic asymptote direction, and the main directional feature of infinite target echo is the horizental direction. The energy statistical feature of Curvelet transform in Scale scale 3 is an important representation of directional difference of different targets.(5) The main directional feature of rebar echo is the hyperbolic asymptote direction,and the main directional feature of void disease echo is the horizontal and hyperbolic asymptote direction. The horizontal feature is the main difference between the echo of rebar and the echo of void disease. The horizontal filter based on the directional selection of Curvelet transform effectively eliminates the influence of rebar interference,and realizes the detection and identification of void disease in CA mortar. The simulation results show that the proposed horizontal filter can effectively identify the void of CA mortar at 4 cm length under the condition of 2 mm trace spacing, and the detection speed can reach 34.2 km/h. |
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