| Brittleness and rupture mechanism of rockmess under complicated multi-field coupled effect is a frontier topic of rock mechanics and rock engineering.Due to the spate of rock burst disasters in the hard brittle rock tunnel,its complex geo-stress environment and mechanics characteristics of rock under the influence of high temperature,high osmotic pressure and high geostress have become one of the key problems of underground rock engineering.Therefore,carrying out the reseach of brittlness and failure process of rockmess under the complexed multi-field coupled condition to predict and prevente rock burst has the research and practical significance.In view of this,to meet the demand of engineering construction and the demands of the development of the discipline theory,this article reseach the brittleness of rock under Themol-Hydro-Mechanical coupling mechanics experiments,using the theory of rock strength,elastic-plastic mechanics,and percolation mechanics theory system study and put forward the double parameters characteristic of brittle rock brittleness indexes.In this paper,the research work mainly focused on the following several aspects:?1?THM coupling of sandstone in the triaxial compression?conventional and unloading?characteristics of strength and deformation in the process of evolution.?2?Evolution of permeability with temperature characteristics and permeability in the process of sandstone fracture evolution characteristics.?3?Acoustic emission technology monitoring sandstone rupture process affected by temperature and osmotic pressure.?4?Research the mechanism of energy absorption,energy dissipation and energy release in the fracture process of sandstone.?5?Established a dual-parameter brittle index based on the stress-strain curves.Based on the above research ideas and experiments,we obtain the following results and research progress:?1?The rock fracture characteristics are type I,and combined type II.The high temperatured causes the expansion stress in the rock,which improves the brittleness of the rock.Strain has a high dependence on temperature and osmotic pressure.There is a critical turning point in the influence of temperature on rock,which is shown as the reinforcement of the transition from brittleness to plasticity.The peak stress is less sensitive to osmotic pressure,and the residual stress shows a linear decrease with the increase of osmotic pressure.The fracture of rock is shown as macro shear failure in this experimental tests.?2?The relationship between permeability and strain can be expressed as an exponential functionK=aeb?1.In the residual stress stage,Crack coalescence in rock leads to the seepage channel becoming smooth,and the permeability of rock mass increases and the relationship between the rock mass permeability and confining pressure is negative exponentK=ae-b?3.?3?The progressive failure process of rock can be divided into 8 stages:Linear elastic deformation;Microcrack initiation;Microcrack propagation;Microcrack;Macroscopic crack propagation;Macrocrack;Destruction.AE counts and cumulative counts have a high sensitivity to temperature.High temperature stimulated the activity of rock AE activity.AE cumulative counts increase with osmotic pressure increasinig,indicating that osmotic stimulation of rock crack generation and propagation,while the growth rate of cumulative counts increasing and the value increasing with osmotic pressure.Introducing A-FRE and RA value to identify the failure mode of rock microcrack and the macro failure of rock performance is shear failure.The inside microcosmic of rock rupture point is complex fracture?tensile and shear mode?,for the master characteristics of the rock,the rupture point of the fault or shear fracture also exist at the same time,with the increase of osmotic pressure,the rupture type gradually by the shear rupture to tensile rupture of the type of conversion and increased.?4?The energy behavior of rock peak is mainly reflected by the energy accumulation,and the elastic energy growth rate is changed from slow to fast.Low permeability and high permeability rocks have better energy storage capacity and energy release ability.The limit of rock storage energy decreases with the increase of osmotic pressure.At the stage of storage,the growth rate of elastic performance decreases with the increase of osmotic pressure,but the elastic energy release rate of rock under different osmotic pressure is approximately the same.The energy dissipation rate of the rock with different osmotic pressure is roughly equal to that of the energy dissipation rate.The dissipation energy ratio of the rock can react with the internal damage state,and the ratio of the dissipated energy to the time changes first and then decreases,then increases steadily,and then the law of the sudden change is large.The effect of temperature on the dissipation energy is mainly reflected in the change of the peak stress value point,the lower the energy density of the rock under the high temperature condition is lower than the low temperature condition.The peak feature point after energy dissipation is affected by temperature is not obvious.?5?Summarize the current description of some domestic and foreign scholars on the brittle characteristics—brittleness index,generalize brittle the key factors from the basic characteristics of brittle rock:?1?High stress drop difference;?2?Low strain growth differential.A new brittleness index based on the stress drop and strain difference is proposed,and the rationality of the brittleness index is analyzed by comparing with the brittleness index based on the law of energy consumption. |
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