Experimental Study On Fatigue And Fracture Property Of Rock-Concrete Interface

During the service period,the concrete gravity dam will be subjected to the periodic changes of water pressure and temperature stress.The weak interface between the concrete dam body and the bedrock will accumulate damage under such cyclic load,and even produce interface cracks in severe cases,which will reduce the load-carrying capacity of the dam and seriously threaten the safe operation of the dam.Therefore,it is necessary to study the fracture characteristics of rock-concrete interface under fatigue load.Normally,the load on the dam is far lower than its design value,and cracks will not occur at the interface,but damage will accumulate,and the bonding performance of the interface will change accordingly.However,in another case,when the load on the dam is at a high level,cracks will appear at the interface and continue to expand along the interface,eventually leading to the overall collapse and failure of the dam.Therefore,the study of fatigue fracture characteristics of rock-concrete interface under different load levels is of great significance to the safety assessment of dams.In this paper,the fatigue fracture characteristics of the rock-concrete interface in the above two cases are studied as follows:(1)Study on the influence of low-stress fatigue load on the fracture properties of rockconcrete interfaceThree-point bending fatigue tests were carried out on a series of 100 × 100 × 500 mm rockconcrete composite beams under low-stress level.The load vs.crack mouth opening displacement(P-CMOD)curves were obtained in the test to monitor the stiffness change and the deformation of the specimens.After the fatigue tests,the static three-point bending tests were carried out,the initial cracking loads were determined according to the strain gauge and the critical crack length was measured by arranging clip gauges along the ligament of the specimens.The initial fracture toughness and the unstable fracture toughness of the specimens were calculated by ANSYS finite element analysis software.The influence of low-stress fatigue load on the fracture characteristics of rock-concrete interface was discussed.(2)Investigation on the effect of low-stress fatigue load on the evolution of the fracture process zone using digital image correlation methodUsing the digital image correlation technology(DIC),the evolutions of the fracture process zone of rock-concrete composite beams after low-stress fatigue tests were observed and compared with that of the specimens under static load.The test results show that the influence of low-stress fatigue load on the evolution of fracture process zone of rock-concrete interface is mainly concentrated in the stage before the peak load.Before the peak load,the crack growth length and crack opening width of the composite beam after fatigue load are smaller than those under static load.The difference decreases gradually after the peak load.(3)Crack growth rate of rock-concrete interface under high-stress fatigue loadThree-point bending fatigue tests were carried out on 100 × 100 × 500 mm rock-concrete composite beams under high-stress fatigue load.The load vs.crack mouth opening displacement(P-CMOD)curves were obtained during the fatigue process to determine the change of specimen compliance during the fatigue process.The compliance calibration method based on digital image correlation technology(DIC)was used to determine the crack growth curve of the specimen during the fatigue process,and the fatigue crack growth rates of the specimens were calculated by using the Matlab calculation program.Finally,the Pairs formulas of the rock-concrete interface under different stress levels were obtained by fitting.