Experimental Research On Composite Fracture Of Ordinary Concrete Under Hydraulic Fracturing

In recent years,Chinese water conservancy engineering industry has developed faster and faster,the number of large reservoirs and dams have increased dramatically,compared with ordinary small and medium-sized dams,the bearing water pressure is greater.The concrete dams which are built have developed to level 300 meters,the high water pressure generated after water storage by these dams are likely to cause hydraulic fracturing.With the increasing of dams' height,the water pressure on the dams are also increasing,which make the problem of hydraulic fracturing of dams become more and more obvious.Therefore,it is an urgent issue to solve the problem that concrete dams are prone to hydraulic fracturing.This paper depends on the National Natural Science Foundation of China project—constrained joint tests and real-time simulation of RCC arch dam considering multiple factors(51479168),and the common concrete I-II composite fracture test under the combined action of water pressure and external force.On the basis of summarizing the shortcomings in the existing hydraulic fracturing test device,this paper developed a hydraulic fracturing test device based on axial force experiment,which can prefabricated the crack of specimens through the crack and carry out the concrete I-II composite fracture test,under the combined action of water pressure and external force can not only accurately simulate the destruction condition of concrete dams under water pressure,but also effectively observe extending of crack.At the same time,when the hydraulic fracturing test is carried out by using the device,the thickness direction of specimens are small,which can reduce the volume of the entire specimens.This paper is based on the prefabricated crack and the width of specimens were fitted to making the angel formed by the batches of 24 specimens to be 0 degree,30 degree,45 degree and 60 degree respectively,then adopt the hydraulic fracturing test device developed by myself,experimental study on composite concrete fracture under two different loading conditions: the water pressure is applied when the axial tensile force is constant and the axial tensile force is applied when the water pressure is constant.Through the experiment,we obtained the curves of load-strain,the curves of load displacement,the cracking angle of the composite fracture.The crack initiation and instability fracture toughness of concrete specimens under two different loading conditions were calculated by double K fracture criterion.Through the experiment,the following conclusions are obtained:(1)In a certain load range,the displacement and strain increase with the increasing of the load,when the load exceeds a certain range,the strain,displacement and load are no longer simple linear relationship.(2)I initiation and instability fracture toughness in concrete I-II composite fracture decrease with the increasing of specimen width and angle of prefabricated crack,while II crack initiation and instability fracture toughness increase with the increasing of specimen width and angle of prefabricated crack.(3)Based on the theoretical analysis of the test results,try to fit the fracture toughness and the instability fracture toughness curve of concrete I-II composite fracture under different loading conditions.