| Research on fracture mechanism for fractured rock mass under water-rock interaction is one of the most basic issues in nuclear waste treatment, storage and exploitation of fossil energy resources, earthquake mechanism and estimation of long-term stability of rock and soil structures. It is also one of the leading subjects of rock mechanics. The influence of water-rock interaction includes mechanical effect and chemical corrosion. On the one hand, with aggravating the branch cracks seeding, propagation and coalescence, seepage pressure in fractures leads to progressive failure of rock engineering. And on the other, the link between the mineral particles is weakened and the microstructure of rock mass is changed because of chemical corrosion effect. At the same time, the deformation of rock increases and the strength decreases. The result of water-rock interaction is that the mechanical properties of rock are changed due to the change of micro-components and the destruction of micro-structure in rock. So, it is necessary and important to research the principle of the interaction between multiple cracks and the quantitative methods for the chemical damage of water-rock interaction. Meanwhile, the fracture criterion for fractured rock mass is built. The study results can be used to offer an effective parameter for exactly estimating the safety and stability of many rock engineering projects which are related to hydrochemistry.The studied title is come from National Science Foundation Project (grant number:50774093—Coupling theory of rheology-damage-fracture in fractured rock masses and application under water-rock interaction) and Doctoral Innovation Project of CSU(grant number:2009bsxt060—Study on fracture mechanism of multi-crack in rock mass under complex conditions). The research work involving several aspects as follows:(1)The macro-mechanical experiments on regular cracks body in rock-like materials have been made. Using white cement as the similar materials, the rock like specimens in which the cracks were arranged in different echelon design through pre-installed steel slice were produced, the research on the models of fracture propagation and coalescence, as well as the low of strength variation with the cracks collocation and crack numbers under uniaxial loading were summarized systematically.(2)Using Three-dimensional topography measurement instrument of Talysurf CLI 2000 type, the topography change of rock surface under the action of the chemical corrosion was measured. Five kinds of rock were used to made specimen. The specimen were scanned first and then immersed in chemical solution 30days and then scanned again. By comparing the test results, it shows that the discreteness of rock's surface height, the deviation degree of datum plane and the roughness are increased after water-rock interaction. Meanwhile, the distribution probability of highness is more concentrated, and the highness difference of the rock surface is decreased and becomes more coordinated.(3)Using Instronl 1342 type electro hydraulic servo test machine, the constant displacement load relaxation method of double torsion(DT) specimens made of five kinds of rock were applied to study subcritical crack growth. The DT specimens were divided into two groups which one group was immersed in groundwater and the other in air. The relations of the stress intensity factor K1versus the subcritical crack growth velocity V were obtained by test. The subcritical crack growth parameters A and n were also obtained. The behavior of subcrtical crack growth law under different environment was analyzed, and the subcritical crack growth parameters were compared. The results show that lgKI-lgV curves of specimens after chemical corrosion locate top left corner of those of air specimens. The slope of curve is smaller and the intercept is bigger. It suggests that the subcritical crack growth speeds up because of water-rock chemical corrosion. Meanwhile, the fracture toughness KIC also decreased obviously due to water chemical corrosion, for example, the KIC of amphibolite decreased 39.46%and for marble,27.19%.(4) According to the theory of fracture mechanics, the mechanical model of multi-crack in infinite-plane is set up. Based on principle of superposition, the formula for calculating stress intensity factor(SIF) was built. The stress intensity factor of cracks in different conditions, such as different crack distance, different crack angle and different seepage pressure. The results suggest that, with the crack distance increases, the SIF is close to a fixed value which is calculated without considering the interaction between cracks. The results also show that the KIof crack tip increases along with seepage pressure increasing.(5)Researching the seepage-stress coupling process of crack rock mass is very important to disclose crack's initiation rule. By analysis the stress of crack tip, the mechanism of crack's initiation and propagation is bulit and the formular is also established. Then, the equation to calculate stress intensity factor at the wing crack tip is derived based on the energy criterion. At the same time, the length of wing crack could be extrapolated. On the basis of this analysis, the fracture failure criterion of rock multi-crack body is set up.(6) Based on the change of rock micro-structure under chemical corrosion, corrosive effect of water and chemical solutions on crack is studied. Using geochemical kinetics of mineral-water interactions and checking ion concentration in chemical solution under different periods, the ways of quantitative methods for equivalent crack propagation under chemical corrosive of water-rock interaction were approached. According to conservation of mass, the evolution equation of crack was obtained and chemical corrosive of water-rock interaction was equivalent to effective crack length and the computational formulation of equivalent crack propagation was set up. A new thought way to quantitative study the micro-mechanism of fractured rock mass in the interaction of water-rock is suggested.
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