Experimental Study On Hydraulic Fracture Mechanism Of Rock Mass And Numerical Simulation

A big puzzle was uprising on the study of natural rock mass mechanical effect and its permeability because of its structural uncertainty. When rock mass stability was studied in the scope of engineering district, big inner structures, like large faults, could be described in detail. But a mass of relatively small structures couldn't be described in numerical analysis mesh grid. Moreover, it was just this small structures could make a non-neglectable effect in rock mass permeability. And seepage was a prominent factor for stability of rock mass and constructions on the rock mass.As known, seepage may debase rock mass' stability. But how about the mechanism was? In soil mechanics research, effective stress theory was used as the base. In which buoyancy was taken into account in fact. Under high water pressure action, water current in rock mass couldn't be restricted in crannies. Water with high potential energy could pierce into rock block. So that. Some new crannies were created to deplete the water potential energy. Which, vitiation of water to rock mass, just was the nucleus of hydraulic fracture research. It also was one side problem of seepage stress couple research.Rock mass hydraulic fracture mechanics was studied in this dissertation based on continuum elasto-brittle damage theory. Some achievements were drawn as follows. In the category of elastic brittle mechanics, a tense-shear competing model for rock mass failure judging was put forward. In which the viewpoint was that rock mass failure might like tense or shear. In a certain condition, rock mass failure might as one of the both or all of the both. Even though the both happened simultaneously, There was only one style, shear or tense, happened in a little time slicing such as 1 second. Nobbut one style in this second might change to another in the next second. The failure style of rock mass in an idiographic time of day lied on which trend was in the ascendant. A normal triaxial hydraulic fracture test was done in seepage laboratory of Hohai university. The sample was thick-cylinder made from cement mortar. An anisomerous deformation was gained in the condition of symmetrical load and symmetrical restraint. And the stress state of sample failure couldn't satisfy the thick-cylinder theory. The concept of asymmetry coefficient was put forward to describe material distribution asymmetry.The viewpoint in rock mass hydraulic fracture mechanism in this dissertation was that strain (stress) concentration was the core concept. Under such a notion, Failure of brittle rock mass was from a certain local point. Crack appears from local. Cracks enlarging and connecting was the reason of rock mass failure. Fracture mechanics and brittle elastic damage mechanics were suitable in local crack enlarging research. Stress concentration was striking in the local zone of crack tip. A kind of smashing failure took place by tense or shear in a little local zone of crack tip with a free surface of crack. And strain concentration was striking in the local zone also.Fracture enlarging and connecting in rock mass went with pressured water inrush consequentially. The new fracture was supposed interconnected in this dissertation. So, once fracture enlarged, pressured water swarmed into right away. The face pressure from water on fracture surface reinforced the stress concentration. Which was the reason why hydraulic fracture intimidates rock mass stability.Some research in rock mass hydraulic fracture numerical simulation was done in this dissertation. A Finite Element Method(FEM) program code was worked out. In the FEM program, computing process was divided in two parts, mechanics and seepage. The two parts had a certain relationship. And intercross iterative computing was done following the relationship between the two parts. Several key problems were studied as follows. (D Weibull distribution and normal distribution were used to give values to elements' Young's modulus in FEM mesh grid. By which, the material asymmetrical distribution was simulated. The research shown that the frac...