Experimental And Numerical Investigations On Crack Propagation In Jointed Rock Mass Under Water Pressure Based On Direct Shear Tests

At present,many large-scale rock engineering projects in China,such as national defense,transportation,hydropower and mining,are under planning or construction.The design,construction,operation and post-maintenance of these projects are closely related to the mechanical properties such as the strength of the rock mass to which the project depends.Rock mass,in the tectonic movement,internally produced a large number of weak interlayers,structural planes and micro-cracks,which we define as jointed rock masses.Now many projects have proved that basically all rock mass engineering instability failure,not just at the beginning,but in the process of rock mass engineering excavation,with the change of load inside the jointed rock mass,the weak part inside the jointed rock mass creates cracks and expands,and the cracks penetrate each other,and finally the macroscopic failure surface is formed.The strength of the rock mass is reduced,which seriously affects the stability of the rock mass engineering.Whether it is the collapse of the Malpasai dam with a height of 66 meters in France in 1959,or the large landslide of the Vaughan Reservoir with a dam height of 262 meters in Italy in 1963,the crack,under the coupling of the geostress and fissure water,initiation,propagation,coalescence and failure are closely related.Therefore,we need to strengthen the study of the failure process of jointed rock mass,and the role of water in joints also needs to be considered.The research work of this paper is as follows:(1)A kind of rock-like material which is very close to the natural rock mechanics parameters is prepared.The geometrical position of the cracks is arranged according to the requirements,and a large number of rock-like specimens with through-cracks are prepared.(2)Direct shear tests were carried out on rock-like specimens with complete single crack,parallel double cracks,parallel triple cracks and non-parallel double cracks,the complete process of crack initiation,propagation,coalescence and failure.The shear stress and displacement data were recorded in real time,and the analysis was carried out later.(3)The numerical simulation of the direct shear test was performed using two-dimensional particle flow(PFC2D)software.The shear stress in the simulation process were recorded by measuring the circular module,and the analysis on displacement field was introduced to further investigate the whole process of crack initiation,propagation,coalescence and failure.(4)With the aid of water sealing fixture and water injection equipment,the filling of water pressure of flaw in the pre-existing crack was completed,and the direct shear test was carried out under the action of water pressure of crack to explore the influence of water pressure on the crack expansion process in the direct shear of the specimen.(5)By improving the domain model of particle flow(PFC2D)software,the contact between particles is eliminated due to the model failure in version 4.0 of PFC2D software,so as to eliminate the disadvantages of disconnected domain.In the fluid calculation of the new domain model after particle fracture,the domain remains connected,and water can enter into new cracks and continue to flow.Furthermore,according to the characteristics of low permeability of rock particles,the calculation rules of interaction between fluid and particles are corrected,and the calculation of the parameters of the convective area is improved.A more suitable model in fluid-solid coupling for rock is proposed.