The Anti-dip Layered Rock Mass Of Bending Failure Criterion And Numerical Implementation

Layered rock mass is the most important geological body involved in human engineering activities.Because of its strong compressive performance,it is often used as the basis for engineering materials and various engineering construction.but meanwhile,it has the characteristics of heterogeneity,discontinuity,inhomogeneity and anisotropy,so it has weak tensile performance and is prone to bending and tensile failure,such as the bulge at the bottom of the foundation pit,the bending of the tunnel side walls and the roof,the bending deformation of the roof in the goaf,and the deformation and failure of steep inclined layered slopes.That is serious harm to human engineering construction.Many research shows that the deformation failure characteristics of layered rock masses and their mechanical properties are closely related to their particular characteristics.Damage gradually occurs during the deformation and failure process,which usually manifests as the continuous deterioration of mechanical properties of rock masses.It assumes that bending failure of rock mass is pure tensile failure in conventional engineering design.Meanwhile,it also assumes that rock mass is homogeneous with constant mechanical parameters,which leads to deviations in the design results.Therefore,it is important to explore the bending deformation failure characteristics and mechanical degradation characteristics of layered rock.In order to further understand the bending deformation process and mechanical properties of layered rock masses,this paper establishes a damage constitutive model of limestone under three-point bending action based on the existing theory in laboratory through conventional rock mass mechanics and three-point bending tests.In the bending failure mode,the bending deformation numerical test is implemented by using FISH language in FLAC^3Dsoftware,and compared with existing experimental models to verify the rationality of damage constitutive model and the applicability of the bending failure criterion.It is used in the example of the collapse of goaf.The specific research content is as follows:?1?To obtain its basic mechanical strength parameters based on conventional rock mass mechanical tests on bedding limestone,and analyze the stress-strain curves corresponding to different tests and the corresponding deformation characteristics of layered limestone specimens under different stress states.?2?Through three-point bending and acoustic emission tests on three sets of layered limestone specimens with the same height-diameter ratio and different sizes,it analyze the load-displacement curve,stress-strain curve,and stress-cumulative ringing number-time.According to these curves,the deformation and failure under the three-point bending condition of the test sample is a local-to-integral process of compression.The acoustic emission phenomena at different bending deformation failure stages are different.?3?It establishes the bending and fracture failure criterion,then it is implemented by numerical simulation.Combined with the experimental results,the theory of mechanical bending of simply supported beam materials is used to simulate rock mass mechanics.The damage variable D is corrected through the rock microelement body hypothesis and Weibull distribution function.Based on the principle of Lemaitre strain equivalent and continuous damage theory,the damage of limestone under three-point bending is established.According to the deformation and failure characteristics of the inverted rock mass in the goaf slope,the failure criterion under the bending failure mode was constructed.With the help of the built-in FISH language of FLAC^3D,written the code of rock parameter degradation and internal bending force calculation in the process of bending deformation and failure,so as to realize numerical bending deformation test,and compared and verification with the laboratory test.?4?Based on the deformation characteristics and constraints of the roof in the goaf,and make the basic assumption and proper simplification,at the same time summarize the mechanical model of the anti-tilt rock structure under two kinds of constraints.It establish the mechanical failure criterion of the layered rock mass in the goaf.The relationship between the bending tensile stress and the cantilever length,thickness of rock beam was discussed using the control variable method.?5?A numerical analysis model of mining slope was established based on the Nayong Zuojiaying collapse in Guizhou,and the deformation of slope induced by underground mining was simulated based on the regular More-Coulomb model and the bending damage constitutive model respectively.The two calculation results were compared by the aspects of stress,displacement and failure area.The damage constitutive model and fracture criterion are further verified by comparing the bending stress at the top of goaf with the results of structural mechanics calculation.The mechanical properties and deformation and failure characteristics of layered rock masses are closely related to their special characteristics.It is very common to find that most of the collapsed geological disaster is related to layered limestone in Guizhou province.The layered limestone is brittle failure materials.The collapse related to layered limestone is often happened suddenly,and difficult to prevent.The paper establishes a damage constitutive model of limestone under the three-point bending action and a damage criterion under the bending failure mode,and carried out the numerical simulation,which plays an important role in correctly understanding the deformation characteristics of layered rock mass and provides a useful reference for the calculation of rock mass stability of mining slope and similar projects.