Study On Macro-micro Mechanical Behavior And Failure Evolution Characteristics Of Rock Mass With Non-uniform Structural Planes Under Uniaxial Compression

After a long geological evolution,various scales and different occurrences of fracture structural planes are generally developed inside the rock mass.Under the disturbance of the project,the structural plane is prone to cracking,expansion and penetration,resulting in rock mass instability,which brings serious safety hazards to the project construction.In the past,many scholars have carried out a lot of research work on the mechanical properties and failure modes of fractured rock mass,but mainly for the two-dimensional structural fractured rock mass with the same strike of structural plane,while the structural plane of engineering rock mass often has complex strike diversity characteristics in three-dimensional space.Therefore,it is of great theoretical significance and practical value to study the failure behavior of rock mass with inconsistent strike of structural plane.In view of this,this thesis is in combination with the National Natural Science Foundation of China（42202322）’Study on true triaxial unloading mechanical response and failure mode of rock mass with non-uniform structural plane’.The rock mass with a pair of non-uniform structural planes is taken as the object.The mechanical properties,crack propagation,failure mode and energy evolution characteristics of fractured rock mass with different fissure deflection angles,fissure inclination angles and rock bridge lengths under uniaxial compression are systematically studied by means of laboratory test and numerical simulation.The main conclusions are as follows:（1）The fissure deflection angle and the fissure inclination angle have significant influence on the mechanical properties of fractured rock mass.With the increase of the fissure deflection angle from 0°to 80°,the uniaxial compressive strength and elastic modulus of the fractured rock mass increase,and the growth rate gradually decreases.When the inclination of the two structural planes is consistent,the mechanical strength of the fractured rock mass is the smallest,and the mechanical strength is the largest when the inclination of the two structural planes is opposite.The uniaxial compressive strength,elastic modulus and deformation modulus are positively correlated with the fissure inclination angle,and are about’W’type with the increase of the length of the rock bridge.The influence of the length of the rock bridge on the mechanical properties of the rock mass is less than the fissure deflection angle and fissure inclination angle.Most of the stress-strain curves of rock mass with non-uniform structural planes have stress rebound phenomenon in the post-peak stage.（2）In the process of uniaxial compression,the crack first initiates at the tip of the structural plane,and then it is easy to expand to the end of the specimen to form a tensile wing crack,and the cracks often overlap and connect along the near tip of the structural plane.When the fissure deflection angle is small,the failure modes of the front and rear surfaces are close to each other,showing shear splitting failure.As the fissure deflection angle increases,the specimen undergoes tensile-shear mixed failure,and the rock bridge penetration situation shows the change rule of penetration-not direct penetration-penetration.The failure mode of rock mass samples under different fissure inclination angles is mostly tensile-shear mixed failure.When the length of the rock bridge is large,the failure mode of the sample is tensile failure.（3）According to the energy conversion curve,the characteristic stress of sandstone samples at each stage under uniaxial compression is determined,and the variation characteristics of energy at each stage are analyzed.The characteristic strength of the intact rock sample is greater than that of the fractured rock sample,and the structural plane weakens the strength of the rock sample.The elastic energy rate decreases-increases-decreases with the strain,and the dissipation energy rate and dissipation energy coefficient have the opposite change rule.Before the peak stress,the input energy is mainly converted into elastic energy accumulated inside the rock sample.In the post-peak failure stage,the elastic energy decreases sharply.The stored elastic energy drives the crack propagation and releases rapidly in the form of dissipated energy,and finally the rock sample loses the bearing capacity.（4）PFC^3Dparticle flow code is used for numerical simulation.Firstly,the significant influence of mesoscopic parameters on macroscopic parameters is obtained by orthogonal test design,and the mesoscopic parameters are calibrated.Then the numerical model of rock mass with non-uniform structural plane is constructed,which is the same as the indoor test scheme.The results of numerical simulation of uniaxial compression show that micro-cracks initiate around the structural plane,and then appear at the end of the sample.A large number of cracks are generated at the tip of the structural plane,and they expand around the rock bridge area.According to the internal cross section of the failure sample,the micro cracks around the structural plane are more concentrated.In the early stage of loading,the model sample is dominated by strain energy storage.After the peak stress,the friction slip energy increases sharply,indicating that the contact,dislocation and friction between particles are the main factors causing energy loss.The increase of the deflection angle or the inclination angle of the structural plane will increase the energy storage level of the sample.