Testing Study On Damage And Fracture Properties Of Typical Rock In Chongqing

Damage and fracture failure of rock is a serious global scientific problem about geological disaster prevention and mitigation in rocky area. Damage and fracture properties of rock partly decide deformation, strength and stability of rocks, which often cause geological disasters including collapse, landslide and tunnel roof, etc. Taken typical rock including sandstone, mudstone and limestone in Chongqing as research objects and combining laboratory experiments with theoretical analysis as research means, rock mechanics, elastic-plastic mechanics, damage mechanics and fracture mechanics as theoretical basis, thesis systematically analyzes damage and fracture properties of typical rock in Chongqing area. The main researches achieved are as follows:(1) Based on static uniaxial compression test, mechanical strength parameters of three kind of typical rock in Chongqing area are measured. This thesis analyzes deformation characteristic of rock in the compression process, and the failure modes and fracture surface morphology.(2) According to test on rock fatigue damage property, thesis analyzes deformation feature for three kind of typical rock under cyclic loading with different frequencies by axial stress-strain curve. Based on morphology and distribution of cracks on rock failured, fatigue failure modes and failure mechanism of rock under cyclic loading with different frequencies are analyzed, and constitutive model describing fatigue deformation of rock is established.(3) By using the energy theory, thesis reveals dissipation trend of energy for different lithology rock under cyclic loading with different frequencies. Combining fatigue damage test with static uniaxial compression test, fatigue deformation curve is completely controlled by the static stress strain curve. Control strain of fatigue failure is equal to the strain at which maximum stress of cyclic loading corresponds to strain soften stage after the peak value of static stress strain curve.(4) Based on accumulated plastic strain rate and damage energy dissipation rate, fatigue damage model of rock is established. Then, piecewise hyperbolic model is used to deduce rock damage variable expression. In addition, thesis put forward fatigue damage evolution equation for rock, and reveals damage evolution trend of rock under cyclic loading with different frequencies. (5) According to experiment on fracture characteristics of rock, fracture toughness KIC of three kind of typical rock in Chongqing area are measured. Fracture failure mechanism of rock is discussed, and energy conversion in the fracture process is also understanded. At the same time, this article analyzes crack morphology, its distribution and fracture surface morphology.(6) Based on fracture mechanics, crack tip stress component expressions is obtained. Taking use of maximum circumferential stress theory, failure criterion of rock fracture is proposed by Drucker-Prager criterion. On this basis, thesis brings forward a new variable for the first time, that is crack growth variables, which can describe the development situation of cracks in rock ligament area, and reveals the evolution trend of fracture failure process for rock under the influence of loading.