SIFs-based Crack Propagation Criterion Of Interface And Its Application On The Fracture Analysis In Dam

Concrete gravity dams play very significant roles in flood control,environmental conservation and power generation.In practice,many factors,incloding strss concentration loading etc.,could trigger the generation of the micro-cracks between concrete dams and rock foundations.The micro-cracks in the heel of the dam and rock foundations are growing and enlarging under the loads,which affect the safe operation of concrete gravity dams.The continuous penetration of the micro-cracks on the interface may lead to failure of concrete gravity dam and cause serious loss of personnel and property.As a result,it is of great practical significance to study fracture charateristics of cracks at the interface and predict the propagation paths of interfacial cracks.A lot of experiments and numerical studies have been carried out in the academic community,and corresponding interface crack propagation criteria have been proposed.In order to verify the crack propagation criteria of concrete-rock interface proposed by Dong et al.,the following work is carried out:(1)Three-point bending beam tests of different kinds of concrete-rock composite specimens.In this paper,granite,sandstone,C30 and C50 were employed to compose the concrete-rock composite specimens.Experimental tests were conducted on the homogeneous material specimens and the composite rock-concrete specimens to study the interfacial fracture process under three-point bending conditions.The initiation loads,peak loads,the curves of P-? and P-CMOD was obtained from the tests directly.K1ini and K2ini were got by numerical calculation based on the initiation loads.Fracture energy was obtained based on the curves of P-?.The results indicate that the properties of the materials on both sides of the interface affeet the fracture characteristics of the concrete-rock interface.Among them,the higher the concrete strength,the higher the bonding strength of the interface was.(2)Four-point shear beam tests of different kinds of concrete-rock composite specimens.Four-point shear beam tests were carried out on the obove three concrete-rock composite specimens,C30-sandstone,C 50-sands tone and C50-granite.A wide range of mixity of interfacial crack under four-point shear beams test were obtained by changing rock length.A unified interfacial crack initiation criterion expressed by the stress intensity factors(SIF s)was fitted by the SIFs corresponding to the interfacial crack initiation based on the experimental data.The results indicate that the values of K1ini and K2ini under four-point shear conditions were elliptically distributed that the ratio of long axis to short axis of the ellipse was 1.6,and the propagation paths of the interfacial crack obtained by experiment were in in agreement with the crireria proposed by Dong et al.(3)Numerical simulation of concrete-rock specimen tests.Combining with the fictitious crack model,the crack initiation criterion can be tons formed into the crack propagation criterion by considering the contributions of the cohesive forces in the fracture process zone.By assessing the relationships of the interfacial propagation criterion and the maximum circumferential stress criteria of the rock and concrete,the potential interfacial crack propagation paths can be predicted.Furthermore,a numerical method was developed by introducing these criteria to simulated the whole fracture process of the rock-concrete interface based on finite element software ANSYS,in which the predicted P-CMZD curves and crack trajactories showed a good agreement with the experimental ones.(4)Numerical simulation of the concrete gravity damFinally,taking a classic gravity dam in the practical engineering as an example,the variation of SIFs of the interface between dam heel and rock foundation under body forces,hydrostatic pressure and uplift pressure with the crack length was studied,and the effects of the water levels,initial crack length and crack propagation length on the fracture behaviour were investigated.The whole fracture processes under various fracture parameters of the rock,concrete and their interface were simulated numerically,three typical modes of interfacial crack propagation were obtained by numerical simulation.The application of three existing interfacial crack propagation criterion in the dam was analyzed and compared.The results indicated that the proposed method was effective in the safety assessment of the gravity dam in practical engineering as well as the application of the these propagation criteria is convenient because only the initial fracture toughness of the rock,concrete and their interface are necessary.