Study On Shear Characteristics Of Rock Mass With Serrated Joints Based On Particle Flow Method

A jointed rock mass is a three-dimensional fracture body composed of a block of continuous medium and a discontinuous medium jointed surface.The strength,deformation and stability of jointed rock masses are often controlled by the jointing surface.Under the action of external load,microfractures gradually develop and penetrate each other near the jointing surface,which reduces its bearing capacity and then causes serious engineering disasters.With the advantages of simple morphological parameters,easy quantification,and intuitive description of shear properties and damage modes,serrated joint surfaces are widely used in the study of shear properties of jointed rock masses.Therefore,the study of shear mechanical properties and damage characteristics of sawtooth jointed rock masses is an important prerequisite for the construction and safety assessment of rock masses.Compared with model tests,numerical simulations,especially those based on the discrete element program PFC2 D,have the natural advantages of low cost,high regularity,and the ability to analyze the damage process from a detailed viewpoint.The fracture can develop in any direction and cause damage to the model,which can visualize the development pattern of climbing damage,climbing gnawing damage and direct gnawing damage,and see the damage area and damage trajectory.Based on this,this thesis adopts the numerical simulation technology of PFC2 D program as the research object to systematically carry out the research on the effects of joint geometry,muddied interlayer and sinusoidal cyclic loading on the shear mechanical properties and damage characteristics of jointed rock masses,and the main research results are as follows:(1)The working conditions with different sawtooth undulation angles and single sawtooth length ratios were set up to investigate their effects on the shear strength and damage characteristics of the jointed rock masses,and a two-factor ANOVA was conducted using SPSS software.It is shown that the climbing damage occurs at 10°and 20°,the climbing gnawing damage occurs at 30° and the direct gnawing damage occurs at 40° and 50°,and the shear strength of the jointed rock is the highest near 40°;The shear strength increases nearly linearly with the increase of single serration length ratio,the growth rate of shear strength is lower and tends to be the same for the undulation angle of 10° and 20°,and the growth rate of shear strength is higher and tends to be the same for the undulation angles of 30°,40° and 50°,and the growth rate remains at about 15%;Compared to the single sawtooth length ratio,the sawtooth undulation angle is the main influencing factor for the shear strength of the jointed rock mass.(2)A model containing muddied interlayer of different thicknesses was established to investigate the effects of interlayer thickness and filling degree on the shear strength of the jointed rock mass.The study shows that when the filling degree is less than 100%,the mud layer is intermittently filled,and the shear strength of the jointed rock body containing mudification interlayer decreases rapidly with the increase of the filling degree,and its strength is controlled by the thickness of the interlayer and the roughness of the joint surface together.When the filling degree is between 100% and 200%,the interlayer thickness is higher than the saw tooth height,and it is continuous filling,the damage of the joint surface is mainly by the abrasion of the interlayer,and the shear strength is mainly provided by the filling.When the filling degree is greater than 200%,the shear damage occurs completely in the muddied interlayer,and the difference of shear strength of different interlayer thicknesses shrinks and eventually tends to be the same,and the shear strength at this time is mainly determined by the material properties of the interlayer itself,and the effects of the roughness of the joint surface and the thickness of the interlayer are negligible.(3)The stress damage model was introduced to consider the deterioration effect of rock mechanical parameters with loading time,and the damage curve characteristics of the jointed rock mass under cyclic loading were investigated.The study shows that the damage curve of sine wave stress cyclic loading shows the evolution of "sparsedense-sparse-continuous sparse",and the loading amplitude,loading frequency and normal stress all have different degrees of influence on the shear stress hysteresis curve.With the increase of loading amplitude,the number of cycles when the test block reaches damage decreases,the hysteresis curve becomes more sparse and the spacing between curves is larger;with the increase of loading amplitude,the damage caused by dynamic stress increases,the force chain inside the system makes adjustments,the horizontal normal contact force increases significantly,the maximum increase of normal contact force is 110.15%,part of the weak force chain turns into a strong force chain,the number of contacts with high tangential contact force increased significantly.