Numerical Study Of Joint Rock Mass Compressive Strength Based On UDEC

During the long-term existence of the rock mass in nature,various types of irregular structural surfaces have been formed by geological and weathering processes.These structural planes are randomly distributed and cross each other,making the rock mass form an intricate fractured structure.The existence of joint surfaces makes the strength of rock mass present complex anisotropy.This thesis obtains the mechanical parameters of rock specimens through rock mechanics tests on a rock sample in a mining area in Jiangxi and applies the Hoek-Brown Criterion to estimate the rock mass mechanical parameters.A two-dimensional discrete element UDEC numerical model is established to systematically study the anisotropy of three types of jointed rock masses.The main research results are as follows:（1）The effect of joint occurrence on the compressive strength of a single jointed rock mass is studied through the controlled variable method.The results show that when the joint position（distance from the joint tip to the compression surface）and the dip angle are the same,the compressive strength presents a nonlinear decreasing trend as the ratio of the joint trace length increases,which can be fitted as a quadratic function relation;when the joint position and the ratio of the joint trace length are the same,the compressive strength first decreases and then increases when the dip angle increases,which fits a"U"shape change trend;when the joint dip angle and the ratio of joint trace length are the same,the compressive strength increases linearly as the distance between crack tip and compression surface increases.（2）To study the mechanical characteristics of only one set of superior jointed rock masses,the compressive strength experiment was carried out by changing the joint dip angle and joint spacing under the action of confining pressures.The results show that unlike single-joint rock masses,as the joint dip angle of the joint surface increases from15^°to 90^°,theσ₁-βcurve presents an asymmetrical"spoon"shape.The failure modes of the rock mass are crushing failure,shear slip failure,and split failure;when the dip angle of the joint surface is close toφ_j（angle of internal friction of the joint surface）or at 90^°,even if the joint spacing is changed,its compressive strength will not change significantly;when the dip angle of the joint surface is betweenφ_j and 90^°,the rock mass will fail along the joint surface,compressive strength decreases with the decrease of joint spacing,and gradually tends to a constant value,which approximates to a negative exponential change relationship;As the confining pressure increases,the compressive strength of the rock mass increases linearly,and the anisotropy decreases accordingly.（3）Combining the fractal theory and the Monte Carlo method,a jointed rock mass network is generated,and jointed rock mass simulation specimens are taken using the center of the jointed rock mass network as the base point.This step is used to explore the anisotropy of the complex jointed rock mass.The results show that controlling for the sampling angle and confining pressure,the increase in rock mass size correlates with the weakening of the anisotropy of the jointed rock mass.The compressive strength of the jointed rock mass shows a non-linear decrease trend and tends to a certain value,which can be fitted into a negative exponential change relationship;controlling for the confining pressure and size,the increase in the sampling angle（the angle between the intercepted rock mass specimen and the horizontal direction）will result in a slight fluctuation of the compressive strength of the jointed rock mass,which can be explained by the fractal characteristics of the joint distribution.The size effect and confining pressure effect of the jointed rock mass are more obvious when the sampling angle is at 60^°,where the compressive strength value is slightly higher.