Experimental Study On Stress Wave Propagation Characteristics And Energy Dissipation Of Jointed Rock Mass

The jointed rock mass is a complex medium often encountered in an underground,tunnel,slope,and other geotechnical engineering construction.Due to the changes in in-situ stress,geological structure,weathering erosion,and human activities,rock mass has nonlinearity,heterogeneity,and anisotropy.As the rock mass' s weak structural plane,the study of stress wave propagation characteristics and energy dissipation of jointed rock mass is of great significance in tunnel excavation,support,tunnel excavation,and large-scale reclamation.In this paper,the joint red sandstone is taken as the research object.The experimental study and numerical simulation software ANSYS / LS-DYNA are used to study the influence of joint thickness and dip angle on stress wave propagation and its energy dissipation law.Meanwhile,the influence of parameters C and N in numerical simulation on the jointed rock mass' s dynamic mechanical properties is analyzed.The main conclusions are as follows:(1)The uniaxial compression test of red sandstone with a loading rate of0.002mm/s is carried out.The results show that the stress-strain curve of red sandstone can be divided into five stages from the beginning of stress to failure,and the failure is mainly caused by the extension of tensile crack and the connection with shear crack.(2)The stress-strain curves and failure modes of different parameters C and N in the simulated impact process are analyzed,and the rules are analyzed to improve the parameters of the HJC model.The results show that the peak strain of jointed,red sandstone changes in cubic function with the increase of C and N values,and the specimen's failure time shifts with the increase of C value.(3)Under different joint dip angles,the reflection coefficient and reflection energy ratio of stress wave increase linearly with the increase of joint dip angle,while transmission coefficient,transmission energy ratio,peak strain decrease linearly,and dynamic peak stress-energy absorption rate decrease.The failure modes of jointed red sandstone can be divided into two types: one is that the specimen only has cracks on the surface and does not break;the other is that the specimen is seriously damaged and forms fragments of different sizes.(4)Under different joint thickness,the reflection coefficient and reflection energy ratio of stress wave increase linearly with the increase of joint thickness,and the dynamic peak stress decreases as a whole,while the transmission coefficient and energy absorption ratio decrease first and then increase,and the transmission energy ratio decreases as a quadratic function.In the process of failure,stress concentration first appears around the intact rock,and a failure circle is formed.The damage degree of the middle part is small,and the initial unit failure occurs at the back end of the rock.When the joint thickness is thin,the damage degree of the back end of the rock is more serious than that of the front end.(5)Under different impact velocities,the incident energy increases linearly with the increase of impact velocity,and the reflected energy,transmission energy,and damage variable all change in quadratic function.When the joint thickness is 8 mm,the rock failure is mainly concentrated in the front end;with the increase of impact velocity,the time of the rock's first macro failure gradually decreases,and the degree of rock failure is related to the impact velocity.The greater the impact velocity is,the greater the degree of rock failure is.