Experiment Study On Strain Rate Dependence Of Concrete/Rock Interface Fracture Behavior

The concrete structures built on the rock base are often subjected to dynamic loads during the working period,and the safety design of the structures depend more on the performance under the dynamic load.With the full deployment of the western development strategy in the 21 st century,a number of concrete high dams will be constructed in the southwest with high-intensity seismic regions.Therefore,the seismic response analysis and aseismic characteristic analysis of the dams are particularly important.In this paper,based on the aseismic characteristic of the concrete structure on the rock foundation,and combined with the National Natural Science Foundation Project(51579033),the experimental researches on the fracture behavior of the concrete/rock interface in the range of seismic strain rates are carried out in the following aspects.1.In order to study the strain rate effect of interfacial fracture of concrete and rock,the axial tensile tests,split-tension fracture tests and three-point bending tests have been performed on rock/concrete interface specimens with MTS testing machine under different strain rates.The axial tensile tests and the three-point bending tests also include pure rock specimens and pure concrete specimens.The load-crack opening displacement curves were obtained,from which the peak load and the energy absorption capacity were obtained(the fracture energy of the specimens were calculated in the three-point bending tests).The rate effect mechanism of concrete/rock composite specimens that in the middle and low strain rates has been analyzed,with special emphasis placed on the difference between the interfacial fracture and the fracture of parent materials.2.The four-point shear tests have been carried out on the concrete/rock composite specimens.By adjusting the relative length of parent materials,the tests were divided into three modes.According to the different strain rates,four groups of experiments were carried out in each case to study the mechanical property of the concrete/rock interface under different stress conditions.The load-crack opening displacement curves were obtained,and the crack opening displacement,crack shear displacement and the displacement of two loading points with time were collected.Based on the experimental results,the strain rate effect and the modal ratio correlation of the peak loads were analyzed,and the time history curves of the open dynamic stress intensity factor and the shear dynamic stress intensity factor under different modes were calculated.3.The cyclic loading tests of concrete and rock three-point bending beam specimens with prefabricated cracks have been carried out by MTS testing machine to study the fracture behavior of concrete and rock under seismic strain rates.The full curves of load-crack opening displacement were obtained,from which the common point trace curves of the testing curves were obtained.Meanwhile,the envelope curves of cyclic loading tests and the monotonic loading test curves were compared,and the fracture energy of the specimens were calculated as well as the dissipated energy of hysteresis loops.At last,the acoustic emission characteristics of concrete and rock specimens under the load history were analyzed by collecting acoustic emission signals of cyclic loading tests.