Study On Fracture Characteristics Of Hard And Brittle Rock Under High Stress

The mechanical study of rock fracture characteristics has always been an important subject for highway cutting slope,road engineering and railway engineering construction.Under the guidance of one belt,one road policy and the western region’s strategy of large scale development,the road engineering in China has also been developing rapidly in mountainous areas,and the engineering related to rock is increasing.Under the condition of high stress,the mechanical behavior of rock damage and fracture will be different from that of other rocks,and its deformation,damage and fracture characteristics will also be different.Therefore,it is necessary to carry out the research on the fracture failure characteristics of rock under high stress conditions,and the characteristics of input,accumulation,dissipation and release energy of high stress rock and the mechanical behavior caused by the complex environment It is of decisive significance for the occurrence of disasters in road engineering construction.In view of this,supported by the National Natural Science Foundation of China,this paper analyzes the fracture mechanism of hard and brittle rock materials under high stress conditions by using damage and fracture mechanics,energy dissipation principle and other related theories,and proposes a damage fracture constitutive model with energy as parameter suitable for high stress conditions,It provides a reliable theoretical basis for the construction of road engineering and disaster prevention.In this paper,through theoretical analysis,uniaxial,triaxial tests and numerical analysis,the mechanism of mechanical properties of hard and brittle rocks is studied,the achievements are divided into the following aspects:1.The definition and criterion of high stress are analyzed,and the transformation form of energy in the whole process of rock failure is explained from the angle of energy.In this paper,the mechanical model and constitutive model of high stress highway slope rock mass under unidirectional stress are analyzed,the wave velocity is used as an indirect physical quantity to characterize the stored energy of rock,the relationship between the wave velocity and the corresponding energy is studied,and the energy damage variable with the wave speed as the intermediate bridge is defined,the damage fracture constitutive model and damage fracture criterion of rock under uniaxial stress are established.2.The hard brittle rock material sandstone is selected as the research object,and the constitutive model is verified by uniaxial compression test.According to the test data,the energy evolution curve of the whole process of rock stress is drawn.From the curve results,we can see that the work done by the external load on the rock is stored in the form of elastic strain energy,the curve of total energy and releasable strain energy is almost parallel,only a small amount of energy is used for the compaction and slight expansion of internal cracks in rock,and the elasticity can be released after the peak strain After the peak strain,the bearing capacity of the rock decreases rapidly,and gradually decreases to zero,showing no residual deformation,showing brittle failure.The measured data are substituted into the constitutive model and compared with the test value,the model value is consistent with the experimental value The values of elastic ultimate strength(6.12MPa)and peak strength(13.53 MPa)of key joints are almost the same as the values of elastic ultimate strength(6.53 MPa)and peak strength(13.36MPa)obtained from test values.Therefore,the damage fracture evolution constitutive model in this paper can well explain the fracture evolution mechanism of rock under uniaxial stress.3.The mechanical characteristics of highway slope rock mass and the rock constitutive characteristics under three-dimensional stress condition are analyzed,and the stress and deformation characteristics of rock are characterized by energy,based on the damage fracture constitutive model under uniaxial stress,the energy form of rock under three-dimensional stress is studied,and the damage variable with energy as evolution is defined,the damage fracture constitutive model and damage fracture criterion of rock under three-dimensional stress are established.4.The hard and brittle rock material sandstone is selected as the research object,and the constitutive model is verified by three-dimensional compression test.Accordingto the test data,the damage variable curve and energy change curve are drawn,the test results show that the damage variable of the specimen changes in a "s" shape with the increase of strain when there is no confining pressure or low stress surrounding rock,before the peak strain,the total energy and releasable elastic strain energy increase nonlinearly with the increase of strain.The dissipative energy increases slowly at the initial stage of load loading.When the peak strain is near,the dissipated energy begins to increase.After the peak strain,the releasable elastic strain energy decreases sharply,and the internal crack expands rapidly.The dissipated energy increases greatly,and finally exceeds the releasable energy at a certain moment elastic strain energy,rock shows brittle failure.Under the high stress confining pressure,the damage variable changes in a "parabola" shape with the increase of strain,before the peak strain,the curves of total energy and releasable elastic strain are almost parallel,and the dissipated energy is almost unchanged with the increase of strain.After the peak value,the releasable elastic strain energy can reach the limit value and release gradually,due to the restraint of confining pressure,the releasable elastic strain energy eventually tends to a stable value and does not change.Under the high stress confining pressure,the rock shows ductile characteristics with residual stress.The total energy and dissipation energy increase linearly with the increase of strain,and the dissipated strain energy will exceed the elastic strain energy at a certain stage of residual deformation.When the dissipation energy curve is close to the residual strength,the curve will have an obvious inflection point,which is the precursor of rock failure.The results show that the stress-strain curve obtained by the model is consistent with the numerical curve obtained from the test.5.According to the engineering geological data of highway high and steep slope in high stress area,a three-dimensional calculation model is established by using numerical software.The displacement field analysis,stress field analysis and energy field analysis of the simulation results are carried out by using the constitutive model established in this paper,and the spatial distribution characteristics of displacement,stress distribution characteristics and elastic strain energy distribution characteristics are obtained.The numerical analysis results show that the model can reflect the mechanical behavior of hard and brittle rock under high geostress and meet the engineering practicability.The calculation results can be used to evaluate the stability of slope rock mass of road engineering in high stress area.