An Experimental Study Of The Mechanical Impedance Method For Detecting The Disengaging In The CA Mortar Layer Of Ballastless Track

The past several years has witnessed the skyrocketing development of the Chinese high speed railway. It has been more than seven years since the operation of the first high speed railway. As the operation time gradually leveled up, there emerged a range of issues in the CA mortar layer of the ballastless tracks, including damage, disengaging, etc.The existence and development of these issues would pose potential threat to the safety of the high speed train and passengers. As a consequence, the defect detection of the CA mortar layer became an urgent priority.The ballastless tracks of the high speed railway are typically presented as layer structure. The disengagement of CA mortar would result in an alteration of support distribution the track plates.Defect detection of the CA mortar layer could be realized by the analysis of the vibration properties of the track plate structure. In order to study the vibration response properties of the track plates on impact, multilayer mathematical models of the normal and defective ballastless tracks were established, respectively.Multilayer structure models of the conventional ballastless rails and the defective ones were initially established by the finite element model. Features of the speed response were studied by analyzing the frequency spectra of the speed under two different working conditions. Feasibility of the detection of the cavity in CA mortar layer by the mechanical impedance method was discussed as well.In this paper, the optimal test coefficient and defect identification coefficient of the disengagement in the CA mortar layer were studied by using the mechanical impedance method. The defective CA mortar layer model was tested by the impact transient pulse response tester. The experimental result was well in consistence with that of the theoretical simulation, indicating the feasibility and accuracy of the mechanical impedance method in the defect defection of CA mortar layer. The CA mortar layers in theoretical model and practical operation were tested, respectively. The available minimum average admittance of void points was selected as the threshold of the voidance. Prediction of the support distribution in the unknown test points was realized by the analysis of the threshold.The detailed procedure in practice could be conducted as follows:(1) detection of the CA mortar layer in balastless rails by the transient mechanical impedance method;(2) repairment of the defective parts in the rails;(3) assessment of the repair effectiveness of its repair.In terms of the mechanical impedance method, an overall detection was firstly conducted, then came the locally refined inspection. Location and scale of the cavities could be precisely detected if there were defects in the structure.