Study On True Triaxial Rockburst Test And Rockburst Criterion Under Hydro-Mechanical Coupling Action

At present,the prediction and prevention of rockburst disasters have become a frontier problem in engineering geology,which is under the coupling of the high ground stress and high groundwater pressure.However,there exists the less research on the true triaxial rockburst test with different moisture contents and the rockburst criterion which is under hydro-mechanical coupling action.In view of this,the true triaxial rockburst test with different moisture contents was carried out in this paper,the influence of moisture content on rockburst was analyzed.On the basis of this,the humidity effect and water pressure effect of the existing rockburst criterion were analyzed,and the rockburst criterion under hydro-mechanical coupling action was preliminarily explored by combining the previous research results.The main research results are as follows:(1)The moisture content has a great influence on the peak compressive strength and tensile strength of red sandstone.With the increase of moisture content,there is a clear downward trend with the peak compressive strength and tensile strength of red sandstone.(2)With the change of moisture content,the failure characteristics of the true triaxial rockburst specimens are obviously different: 1)with the extension of soaking time and the increase of moisture content,the sound becomes gradually lower when the destruction is occurred;2)the vertical crack and the size decreases,and the coexistence of multiple cracks eventually turns into a single shear crack;3)the level of destruction also decreases with the increase of moisture content;4)the destruction can be described from a complex failure mode contained tension,splitting,shearing and rockburst to a shear-rockburst failure mode,then to a saturated specimen single shear failure mode.These characteristics of failure indicate that,with the increase of moisture content,the level of rockburst destruction of red sandstone has a decreasing tendency,the probability of rockburst is decreased,and water plays a positive role in reducing the risk of rockburst.(3)Different changing characteristics can be shown through three-direction stress and strain and volumetric strain of the three moisture contents and true triaxial rockburst specimens.These characteristics show that with increase of moisture content,the brittle failure degree gradually weakens,the plastic deformation characteristics are becoming significantly obvious.It can be inferred that the probability and intensity of occurrence of rockburst are becoming smaller.(4)The results of acoustic emission characteristics of true triaxial rockburst test show that: with the increase of soaking time,the moisture content becomes higher,and the acoustic emission count is gradually changed from two stages to three stages.The acoustic emission activity is becoming active with the increase of the moisture content before the abrupt burst;for the two rockburst specimens with the increase of moisture content,the release of energy before the destruction is increased.The final release of energy is reduced,the degree of brittle failure is reduced,and the plastic deformation becomes more and more obvious.The saturated specimen,due to the plastic enhancement,the whole acoustic emission activity is relatively active,cracks can be seen during the continuous stage,which can be specifically performed by the acoustic emission parameters are relatively higher,the yield failure stage appears before the destruction,and it is ultimately failed to happen rockburst;with the increase of moisture content,plastic deformation characteristics of specimens are becoming reinforced,the probability and intensity of the occurrence of rockburst is declining.(5)Compared with the features of fragments of the two rockburst specimens,some conclusions can be drawn: from the perspective of the shape,with the same length and width scale,flake features of the rockburst are more obviously existed with the low moisture content of the specimens;the mass distribution characteristics indicate that the formation of fragments rockburst in the dry red sandstone specimens consumes more energy than the aqueous specimens.This also indirectly shows that with the extension of the soaking time,the increase of moisture content,the energy provided by the specimen is relatively reduced during the rockburst,and the intensity of the rockburst is also reduced;the value of fractal dimension of rockburst is decreased with the increase of soaking time and moisture content.From the point of view of fractal results,after a long soaking time,the formation energy of fragments rockburst is smaller than dry specimen's.Specimens in dry conditions are conducive to accumulating energy and releasing them instantly,which leads to the formation of fragments rockburst,and the larger energy consumption.(6)Moisture content and water pressure are important factors affecting the mechanical properties of rock.Because of the limitation of single index factor,the variation degree of each rockburst criterion index varies greatly with the change of moisture content and water pressure.(7)Based on the influence of moisture content and water pressure on rockburst and the results of previous studies,the concept of new hydro-mechanical coupling rockburst vulnerability index(HMRVI)is preliminarily explored.Humidity control factor,water pressure control factor,system stiffness factor and geological structure factor are selected to construct the expression of HMRVI.(8)Based on the analysis of the hydraulic effect of the existing rockburst criterion,the stress intensity ratio,the brittle index and the rockburst vulnerability index are selected to describe the influence of moisture content on the rockburst vulnerability.The stress level and energy index are selected to describe the influence of water pressure on the rockburst vulnerability,and the expressions of humidity control factor and water pressure control factor are constructed by the form of the integral quotient.