Study On Failure Process And Energy Mechanism Of Hard-brittle Rock Under Hydro-mechanical Coupling Action

At present,the failure process and energy mechanism of hard brittle rock under the action of high geo-stress and high underground water pressure is forefront topic of rock mechanics and engineering fields.But the rock mechanism under hydro-mechanical coupling action is very complex and few previous related research work.In view of this and a typical engineering as the research background,conducting a series of hydro-mechanical coupling test of hard brittle rock.The mechanical properties and permeability characteristics,deformation and failure rule,law of internal fracture development process,the mechanism of energy evolution and energy consumption are researched.On the basis of these experimental studies,use particle flow code,study the failure process and energy mechanism from the perspective of mesoscopic mechanics and macro phenomenon.The main results are displayed as follows:(1)With the increase of moisture contents,the AE activity is more concentrated and strength is higher,the increase rate of total energy absorbed by rock and its amount decrease.The increase rate of elastic energy decrease with the increase of moisture content,but their release rate differ slightly.The energy storage limits decrease with the increase of moisture content.The dissipated energy decrease as the moisture content increase,but the increase rate of dissipated energy before and after peak strength differ slightly.The stress point A who represent from the compaction stage into the elastic deformation stage and the crack initiation point B who represent from the elastic deformation stage into elastic-plastic stage decrease with the increase of moisture content.These results reveal the plasticity mechanism of rock enhanced and brittle characteristics weakened with the increase of moisture content.(2)With the increase of water pressure,the AE activity is more concentrated and strength is higher.The AE counts and total energy increase as the water pressure increases.It reveals water pressure could stimulate rock crack and promote the release of strain energy.As the water pressure increases,the number of crack enhances and the degree of concentration of crack is higher in the 3-D location of AE figures when the rock unstable failure.At the same time,the failure angle decreases on the macroscopic failure morphology.These results reveal the mechanism of rock failure change from suppression of shear to suppression of rifting,plasticity weakened and brittle enhanced under hydro-mechanical coupling process.(3)The peak strength of saturated rock is lower than the dry rock,and it decreases with the increase of water pressure.The peak strain of the saturated rock is higher than dry rock,but it decreases with the increase of water pressure.On the one hand,the water pressure rise is equal to the confining pressure is reduced On the other hand,the water pressure could stimulate rock crack deformation and accelerate the process of rock failure,the higher the pressure,the more obvious effect,resulting in the rock failure occurs under small deformation.(4)The peak strength and peak strain of the rock decrease with the increase of unloading rate,unloading rate have a significant impact on the circumferential dilatation deformation.The circumferential dilatation is more remarkable with the increase of the unloading rate.The circumferential strain and volume strain curves are relatively gentle when the unloading rate is lower,which indicate that the circumferential dilatation and crack propagation are gradual process of development.With the increase of unloading rate,the inflexion of the circumferential strain and volume strain curves are more sudden,which indicate that the brittle property of rock increases with the increase of unloading rate.(5)In the process of deformation and failure of rock,the law of the permeability evolution is the results of the interaction of mesoscopic damage evolution and macroscopic crack.The rock has a certain extent of permeability during the initiation of loading,and then decrease slightly with the compaction of crack and the increase of stress.After entering elastic-plastic deformation stage,along with the expanding of crack,the permeability is getting better and better.The permeability of rock increases sharply when the rock reaches failure phase.At various stages,the permeability of rock increases with the increase of water pressure.This is because the water pressure can stimulate rock crack extension and promote seepage path.(6)The acoustic emission rate change slightly under different unloading rate or different water pressure condition,while the AE energy rate increases with the increase of water pressure.Which indicate that the water pressure can promote the release of strain energy and strengthen the brittle failure characteristics of rock.Comparing with conventional triaxial compression test,the AE energy rate of unloading triaxial compression test is higher,and it increases with the increase of unloading rate.(7)Under the action of hydro-mechanical coupling test,the energy storage limit of granite is lower,and the rate of energy storage decrease with the increase of water pressure.After rock reach stress strength,the increased with the increase of water pressure.The higher the unloading rate,the greater energy release rate.This is because the brittle fracture characteristics of rock and the speed of crack propagation enhanced with the increase of water pressure and unloading rate,and this could promote the elastic energy release.(8)Analyzed the failure process and energy mechanism by PFC3 D.Under the condition of no water pressure,the inside of the rock energy release cause by particles bond rupture is integrity.After applying the water pressure at the bottom of the rock,the crack number and energy release of the bottom is obvious more than the upper.It shows that water could stimulate rock crack and accelerate the process of rock failure.Under the action of hydro-mechanical coupling test,the internal crack and energy release are more concentrated.With the increase of water pressure,the energy proportion of tensile rupture improved significantly.(9)The impact kinetic curve of hard brittle rock show obvious characteristics of main shock type.Maximum instantaneous impact kinetic energy increases with the increase of water pressure,shows that the water pressure can enhance rock internal energy release.The elastic energy extreme value decreases with the increase of water pressure.Under the condition of different water pressure,the elastic energy drop rate and dissipated energy growth rate differ slightly.