Study On Propagation And Attenuation Law Of Blasting Stress Wave In Jointed Rock Mass Under Different In-situ Stresses

With the continuous development of the national economy and the vision of the people's better life,the demand for clean energy and convenient transportation is becoming stronger.Meanwhile,China's Western Development Program,Southto-North Water Diversion Project,National Long-term Railway and Highway Planning,"The Belt and Road" and other national level policy and planning had been laid down and implemented,the construction of underground engineering under deep buried,long span and complex geological conditions has become the "new normal" in the field of hydropower,railway,highway and energy exploitation.At present,the excavation of underground rock mass is still dominated by the drilling and blasting method,and the loading of underground engineering rock mass under blasting excavation is a dynamic disturbance under a certain initial stress.The influence of the in-situ stresses must be considered when studying the propagation law of blasting stress wave in underground rock mass in the construction of underground engineering.As everyone knows,the natural rock mass is a geologic body composed of intact rock and joints,it is necessary to study the propagation characteristics of blasting stress wave in the intact rock and joints in order to obtain its propagation law in the jointed rock mass.Based on this,this paper takes the view of "rock mass structure" as the premise that the jointed rock mass is a geological structure consisting of the intact rock and joints.On the basis of revealing the influence of the change of in-situ stresses on the propagation characteristics of the stress wave at the intact rock and joints,the propagation and attenuation laws of stress wave in jointed rock mass under different in-situ stresses were studied in three aspects: model test,theoretical derivation and numerical simulation.The main works of this paper are as follows:(1)Several representative surrounding rock mass of deep underground engineering in China were synthetically analyzed,and the selection range of physical and mechanical parameters of the original rock was determined.Based on the similarity theory,mix ratio test and laboratory test,the matching ratio and the detailed physical and mechanical parameters of model material were obtained.A largegeomechanical test device was selected to apply two-dimensional equal and unequal static loading,and a large size model test block(1600 mm×1300 mm×400 mm)was made,while the blasting load was produced in the center of the test block with a cylindrical charge detonator,and the blasting stress wave propagation test of large-size block under different static loads was realized.Considering the influence of joint angle and number on the propagation law of blasting stress wave,the single-joint,double-joints and multi-joints test blocks were designed and made respectively,the blasting load in the model test remains unchanged and repeatedly applied on the test blocks,and the propagation and attenuation law of blasting stress wave in intact rock and jointed rock mass under different in-situ stresses was studied.(2)For the blasting stress wave vertically incidenting rock mass under in-situ stress,the influence of confining pressure and joint number on the propagation of stress wave were studied based on the experimental results of different twodimensional equal static loading.Meanwhile,considering the effect of in-situ stresses on the initial stiffness of joints,and based on the discontinuity deformation method and time-domain recursive method,the propagation equation of one-dimensional stress wave passing through multiple parallel joints under in-situ stress was derived,and the theoretical and experimental results were compared from the two aspects of wave form and transmission coefficient.(3)For the blasting stress wave obliquely incidenting rock mass under in-situ stress,the propagation tests of blasting stress wave under two-dimensional equal and unequal confining pressures were carried out in the single-joint and double-joints test blocks,based on the theory of cylindrical wave propagation,the influence of confining pressure,lateral pressure coefficient and joint angle on the propagation of stress wave were analyzed.Considering the effect of in-situ stresses on the joint stiffness and the physical and geometrical attenuation of cylindrical stress wave propagation in the intact rock,and combined with the discontinuous deformation method and time-domain recursive method,and the attenuation of cylindrical wave in the intact rock between joints,the propagation equation of cylindrical wave in jointed rock mass under in-situ stress was derived,and the theoretical and experimental results were compared.(4)Based on the time-history curves of stress and strain measured at the samedistance from the blast source in different test models,and combined with the stress wave propagation theory,and the stress wave energy transfer coefficient was derived.The energy transfer law of blasting stress wave in jointed rock mass with vertical and oblique incidence under different static loads was analyzed,and the effects of confining pressure,lateral pressure coefficient,joint angle and number were studied respectively.(5)The variation law of the initial damage variable was determined by the change of the stress wave velocity in the intact rock under different two-dimensional equal static loading in the model test,and combined with the Mohr-Coulomb strength criterion,the elastoplastic Mohr-Coulomb constitutive model of the intact rock considering the initial damage was established.Moreover,the established constitutive model was numerically implemented using the UDEC fish language,and combined with the joint nonlinear deformation model,the numerical simulation of two-dimensional equal static loading conditions in the model test was conducted,and then the rationality of the constitutive model was verified by comparing with the test results.Finally,based on the above numerical simulation method,the numerical calculation of the stress wave propagation in jointed rock mass with different angles and numbers was carried out,and the influence of confining pressure,joint angle and number on the propagation of stress wave was further studied.