Study On Mechanical Characteristics Of Fractured Rock Mass Based On Discrete Element Of Particle Flow

The rock is a solid aggregate of one or more minerals with a stable shape.After experiencing a series of complex geological tectonic movements,a large number of fractures have been formed inside the rock.Under the action of external force,the growth and development of fractures will affect the mechanical properties of rock.In engineering practice,rock with fractures will affect the safety and construction quality of geotechnical engineering.Therefore,the study of mechanical properties and deformation and failure characteristics of rock with fissures is of great practical significance to the stability evaluation and risk control of rock mass.Considering that the process of sampling fractured rock in situ is difficult,And the artificial processing of fractured rock blocks may bring uncontrollable damage,Then it will influence the results of the experiment,Therefore,this paper takes rock similar materials as the research object,The mechanical properties of rock materials with cracks are studied by means of laboratory test and numerical simulation.Firstly,uniaxial compression tests were carried out on rock specimens with cracks,and the macroscopic mechanical parameters,such as peak strength,elastic modulus and Poisson's ratio,were obtained;Then,the sensitivity analysis of PFC^3Dmeso-parameters was carried out to study the influence of its changes on the macroscopic physical properties of rocks,and the calibration of meso-parameters of uniaxial compression model was carried out;Then,the numerical simulation of the uniaxial compression test of rock specimens with single fractures is carried out,and the data obtained from laboratory tests are compared and analyzed.The reliability of the discrete element method based on PFC^3D used in the study of mechanical properties of rock specimens with fractures is verified;Finally,the strength,deformation,failure characteristics and size effect rules of rock with double fractures are further studied.The main research results are as follows:(1)With reference to the rock-like material mix ratio obtained by the predecessors,a rock-like specimen composed of water,high-strength gypsum,sand,silica fume and superplasticizer was produced.After testing,the specimen shows typical brittle failure characteristics,and the conventional mechanical parameters are basically close to slate,showing similar mechanical properties,so it can be used to simulate brittle rocks.The specific mixing ratio of rock-like specimens:water:high-strength gypsum:sand:silica fume:superplasticizer=0.34:1:1.4:0.1:0.011.(2)The influence of poisson's ratio mesoscopic parameters mainly straight joint stiffness than kn/ks;The main mesoscopic parameters that affect the elastic modulus are flat joint modulus Ec and flat joint stiffness kn/ks,and the influence of Ec is more obvious.Affect the compressive strength of the mesoscopic parameters is more,there are mainly straight joint tensile strength of sigma,cohesion,internal friction Angle?b and rigidity than kn/ks,which are greatly influenced by Cb with sigma?b.(3)The uniaxial compression test study of the indoor rock-like specimens shows that the stress-strain curve fluctuates greatly before the specimens with single cracks reach the peak compressive strength,and the yield platform can be observed.The same as the complete specimen is the development of tensile microcracks during the entire stage of uniaxial compression.The growth of microcracks is faster as the stress approaches the peak.The difference is that the initial cracks of the intact specimens originate from the upper and lower edges of the specimens,and there are very few shear cracks,and tensile failure dominates,which is manifested as brittle splitting failure;the initial cracks of the specimens containing cracks originate from Within the tensile stress range near the crack.In general,the stress and deformation changes of the fractured rock specimen and the complete specimen are basically the same during the entire uniaxial compression process.They both reach the nonlinear stage through elastic deformation,and then fall quickly after reaching the peak stress.(4)The mechanical strength and deformation modulus of the rock-like specimens are affected by the thickness of the crack.With the increase of the crack thickness,the compressive strength and the deformation modulus show an obvious downward trend.When the thickness of the crack is small,a slight flaking phenomenon can be observed on the surface of the specimen.At this time,tensile failure occurs.When the thickness of the crack increases to a certain extent,the initial crack will continue to develop until it penetrates the specimen,and finally pull The shear mixed form is destroyed.(5)With the constant increase of fracture Angle,the peak strength decreases first and then increases,reaching the lowest value at 45°and the highest value at 90°,and the elastic modulus changes slightly.The influence of crack on strength and elastic modulus is greater when the vertical distribution changes than when the transverse distribution changes.The fracture Angle has little influence on the failure mode.(6)The peak strength of rock-like specimens under different fracture spacings is significantly lower than that of intact rock-like materials,and double fractures have a significant weakening effect on the properties of rock-like materials.As the distance increases,the strength curve shows a trend of first rising and then falling,reaching the highest value when the distance is 15mm,but the elastic modulus does not change significantly.Using the PFC^3D numerical simulation method,the uniaxial compression of a large-scale multi-cracked rock specimen is simulated,and it is found that the number of drops in the stress-strain curve increased with the increase of the number of cracks.The damage of the specimen is mainly caused by the shear failure of the diagonal cracks at 45°and 135°,However,the 90°and 0°crack surfaces have relatively slipped,and the final failure of the model is a comprehensive failure type composed of tensile,tensile-shear composite and shear.