Research On Time-Dependent Failure Of Soft Surrounding Rock In Higher Humid Environment

Higher requirements are proposed for mining safety with development of science and technology and the change of energy resources condition. Due to the presence of water for construction and groundwater in rock mass, the soft rock roadway is always in water-enriched environment During the interaction process of water and soft, the physical and mechanical properties of soft rock are changed dramatically. Coupled with the impact of time, the damage caused by water is possibly more serious than the damage caused by mechanical factors. Therefore, research on the time-dependent deformation of soft rock roadway under water-enriched environment is necessary. On one hand, it is helpful to better understand the effects of water on the mechanical properties of soft rock, such as, deformation, damage, strength and rheology. On the other hand, it provides a new explanation for the formation mechanism of time-dependent deformation in roadway, and also provides a more reliable basis for determining the theoretical support of soft rock roadway.Based on NSFC (NO.51174039), named "Study on the formation mechanism and analysis method of EDZ in vapor environment", and NSFC (NO.51004020), called "the mechanism of time-dependent deformation and damage under the conditions of moisture transformation", this dissertation include two parts. On the part of theory, a creep damage constitutive equation is proposed by introducing the weaken effects of water on rheological parameters. On the other part, by using the rock failure process analysis system, the failure process of rectangular roadway under water-enriched environment, and the phenomenon of floor heave are represented, and the formation mechanism of EDZ are discussed at last. The main research results are as follows:(1) By reading a large number of relevant papers, the current achievements of the water effect on soft rock are summarized in, the aspects of theory, physics experiments and numerical simulation(2) In theory, the mechanical properties and rheology theory are summarized. Based on the generalized Kelvin model, the moisture-related variable Dω and time-related variable Dt are presented to established the creep damage model of soft rock at different moistures, because of the time-dependent rheological parameters of soft rock as well as the effects of moisture on the physical and mechanical characteristics of rock. According to the uniaxial creep test results of Tab2siltite under different water conditions, the mechanical parameters of the model are obtained in the use of parameters inversion method, and the significant effect of the moisture content on the creep characteristics are analyzed. By comparing the results obtained from the creep damage model with the creep test data, it’s found that the model could well describe the creep properties in whole process. Then the rationality and correctness of the creep damage model are identified.(3) In numerical simulation:(a) Applying a humidity-mechanical-damage coupled model, Realistic Failure Process Analysis (RFP A) humidity diffusion edition is used. Three kinds of layered rectangular coal roadway and three kinds of coal-rock roadway with different quarrying positions are simulated. The failure process of the rectangular roadway under humidity environment is represented. By analyzing the characteristics of time-dependent deformation, the evolution rules of surrounding rock in humidity field is explained. For coal roadway, the cracks occur from both sides of the laneway, then expand to coal roof or floor with lower strength, finally to the higher strength rock. For coal-rock roadway, the displacements of floor are related to the positions of coal, and even though the cracks start in the coal as the same as coal roadway, they extend to the roof or floor near the coal.(b) With the significant expansion characteristics of soft rock, water in the roadway often leads to the phenomenon of floor heave. By the inversion method, the parameters are obtained, which are required in numerical simulation, including diffusion coefficient, expansion coefficient, and the reduction coefficient of strength and elastic modulus. Applying the rock failure process analysis system, the evolution of the floor heave are simulated. The conclusions show that water transformation is a time-dependent process, so the floor heave in roadway is dependent on time. At the beginning of the excavation, the floor deformation increases slowly with time. During the development of floor heave, the concentration extends to the internal rock mass with humidity diffusion. And when the rock strength after weakened lower the stress value, damage occurs. The presence of damage speeds water into internal rock, and exacerbates the weakness of roadway with a sharp increase in the floor displacement.(c) On the basis of Realistic failure process analysis (RFPA) code, considering the relationship between the increase of humidity and degradation of rock mechanical properties, the humidity-stress-damage coupling model is proposed in the code to represent the time-dependent deformation and failure in rock under high humidity environment. The humidity version of RFPA is used to simulate the development of EDZ in soft rock when the roadway exposed to high moisture environment. By studying the influence of parameters in the numerical model, the time-dependent deformation and failure processes of the roadway under high humid condition are discussed in detail. It can be predicted that the higher degradation coefficient of elastic modulus and the expansion coefficient, the larger thickness of EDZ. By studying the influence of moisture on the surrounding rock, the numerical results provide a better understanding of the time-dependent behavior of EDZ and it is good for thinking about a new way of drift support.