Research Of The Rupture Characteristics And The Rock Burst Ejection Process Of Hard Rock Under Hydro-mechanical Coupling Conditions

By reason of the hard fractured rock in deep tunnel always meets high ground stress,high water pressure,and some other complexly compling stress field,the unexpected geological hazards occurred continually have become a major threat to the underground projects.Studies about micromechanical behavior have shown that the hard rock failure has a complex process,including microcrack gestation,initiation,expansion,macroscopic rupture and so on.After that,the energy inside rock can easily instantaneous release,and then induced geological disasters.Therefore,it is important to research the deformation behavior,rupture properties and constitutive model of the hard rock with different environmental conditions.What's more,there else has great practical significance to preventing and mitigating disasters,reducing casualties and mechanical losses,and controlling the tunnel catastrophic damage by studing the ejection process of rock burst though.numerical simulation.The main work about the research is dedicated to analyzing triaxial unloading test data under nature state and H-M(Hydraulic-Mechanical)coupling condition,tensile test and its analysis under water-saturated state,related constitutive relation study,and the analysis of rock burst ejection numerical simulation under coupling conditions.For sandstone,the macroscopic and microscopic deformation characteristics,failure characteristics,mechanical characteristics are described in detail.On the basis of above,the change rule under H-M condition is analyzed.Then,the unloading constitutive model is created.After that,the paper thinks about how to confirm the parameter of initiation point,calculate the initiation level,and find the functional relationship between the initiation level and brittleness index.At last,the numerical simulation with DEM is used to research the rock burst ejection process and the difference with/without water pressure.Study achieves the following key results:(1)Based on the different conditions of confining pressure and water pressure under triaxial unloading tests,the typical stress points are confirmed from the deviator stress-strain curve.Combining these special points in the unloading curve under hydraulic condition,the whole process is analyzed,including microcracks compression,closure,initiation,compassion,until creating the macrocracks.(2)It shows that the water pressure increases the typical stress values in the stress path of each phase though analyzing different H-M tests.What's more,this paper researches the change rules in the condition of different confining pressure and hydraulic pressure,while announces the special meaning of location transformation of the typical points,especially about initiation threshold,rupture condition,stress-strain curve shape,etc.There exists a study result is that,under the continuous hydraulic pressure influence,the higher water pressure causes the stronger brittleness characteristics.(3)The confining pressure is the key factor to control the failure characteristics of the sandstone under H-M coupling function,which has higher influence than hydraulic pressure.(4)To demonstrate the nonlinear deformation afer the expansion point,the volumetric strain difference and the deformation modulus are used to calculate the relative expansion strain and the deformation difference.Though fitting the two parameters,the function graph is obtained,which is used to estimate the extent of the damage after expansion and judge the occurrence time of the expansion limit.The related results are applied in the constitutive model.(5)Article defines the initiation level,which reflects the difference between the size of the rock discontinuities and microstructure.By building a functional relationship between the initiation level and typical brittleness index B,the paper got a conclusion that B5 and B6 are representative.Especially,the brittleness index B5 and B6 are calculated by compressive strength and tensile strength,while the brittleness index B3 is calculated by peak strength and residual strength.What's more,the result indicates the initiation level and the brittleness index are generally direct ratio relationship.(6)The results of ejection simulation of hard rock by discrete element method shows that the failure process of rock sample can be divided 4 stages,including calm period,stress concentration period,local failure period and final ejection period.High confining pressure works significantly to rock burst ejection.(7)The mechanical calculation of numerical simulation under H-M coupling condition is complicated.Water reduces the initial kinetic energy of the ejection block,while the ejection distance is shortened.Since hard rock is affected by water fracturing,the block launch earlier.Therefore,water play a positive role,for rock,in terms of micro-cracks developing,stress state change,reducing the energy,and so on.(8)Combined with microscopic analysis and numerical simulation results,the rock failure characteristics affected by water divided into two aspects.On the one hand,rock in the water-saturated state has smaller ejection kinetic energy than which has no water pressure.On the other hand,the higher water pressure accelerates rock fracture,which decreases the typical stress values with increasing pressure.