Study On Mechanics Characteristic Of Damage Due To Freeze-thaw Action In Fractured Rock Masses And Failure Mechanism

It always induces geological disasters such as frost heaving and thawing settlement, mud-rock flows, landslide, collapse and so on by repeated freeze-thaw effect in the cold region. The joint fractured rock mass is a kind of complicated medium which exist everywhere in rock engineering, for example, dam foundation, slope and underground cavern, due to repeated freeze-thaw, its strength becomes damaged and weaken, and growing deformation in the rock mass. These problems will directly affect the design and construction of rock engineering and normal operation after the engineering was finished. As the rise of engineering construction in western cold region, a number of freeze-thaw problems of geotechnical are urgent to be solved. The paper closely research on damage mechanics of joint fractured rock mass under freeze-thaw condition, we prefabricated fissure in model material to simulate jointed rock mass, then freeze-thaw cycling test and uniaxial and triaxial compression test were conducted of fracture rock samples, freeze-thaw damage mechanics characteristics of fractured rock mass was discussed, and revealed the evolution process of crack initiation, crack propagation and failure of rock mass, damage evolution equation and the constitutive relation under the effect of freezing and thawing and load coupling of freeze-thaw fractured rock mass were established. the main research contents and results are as follows:(1) According to the similarity theory, combined with the rock’s mechanics properties of the scene, the similar modeling material similar to rock-cement silica fume mortar was prepared successful; the method of prefabricating crack in the modeling material was used to simulate the jointed rock mass, ten kinds of integrated rock specimens and fractured rock samples with different geometric characteristics were made totally.(2) The freeze-thaw tests of different freeze-thaw cycles and uniaxial compression test on the prefabricated fractured rock samples were carried out, then analyzed the fracture geometry parameters (crack length, crack dip, the number of cracks) on the effects of the mechanical properties of the freeze-thaw fractured rock, and discussed the failure mechanism of the freeze-thaw fractured rock samples; the paper also summarized the three damage modes of the fractured rock:particles shattered mode, crack mode and fracture along the prefabricated crack mode.(3) The affecting factors of freeze-thaw damage were divided into external factors, internal factors and other factors. Based on mesoscopic damage theory and macroscopic statistical damage model, the freeze and thaw damage evolution, the external load damage evolution and the freeze-load coupling damage evolution were developed. The damage evolutions aim at researching the damage mechanism of jointed rock mass under the load condition of freeze-thaw and external load, then building damage constitutive models of rock.(4) Triaxial compression test was carried out of rock specimens, by this way, the mechanical character with different confining pressure, the influence law of fracture spacing with different freeze-thaw cycles, different confining pressure was analyzed.(5) Based on the theory of the damage fracture mechanics, new computing formulas about the crack condition, extending direction and the length of the wing crack are deduced. Analyze the three different fracture penetration modes of stretch-draw, shear and tensile-shear. Take the initial damage caused by native fissure and freeze thawing and the additional damage caused by crack growth of fractured rock mass into consideration, From the view of crack propagation of damage equivalence, Research on the equivalent model of crack extension of the rock mass under freezing and thawing cycle.(6) Combined with the results of rocklike samples under freeze-thaw cycle and mechanical test, the digital simulation has been taken to the typical rock slope of the Tianshan highway. Computes and analyzes the changes of the displacement, the maximum principal stress and the plastic zone development of rock slope after several freeze-thaw cycles. Research the impacts on slope stability brought by the changes of the mechanical properties under freeze-thaw cycles. Basic and key technologies of slope protection will be provided for the slope of mountainous area in freezing and thawing cycle conditions.