Mechanical Response And Engineering Application Of Sandstone Under Unloading Path

The underground roadway of coal mine passes through the abnormal area of geological structure(fault,collapse column,fracture zone,etc.),the excavation induces the unloading instability and failure of engineering rock mass in frequent disasters.The rock mass in the abnormal geological structure area is in three stress states of elasticity,plasticity and post peak.The change of stress field makes it difficult to control the surrounding rock in the abnormal geological area.Differential control technology should be adopted for zoning support of the surrounding rock.It is necessary to deeply analyze the rock mechanical response under the unloading stress path and the differential control technology of the surrounding rock from the internal mechanism.Taking the excavation unloading of engineering rock mass as the background,taking the unloading stress path of rock mass passing through the fracture zone as the main line,and using the methods of laboratory test,theoretical analysis,similarity simulation,numerical simulation and field measurement,this paper explores the mechanical behavior,energy evolution law and acoustic characteristics of sandstone under different unloading paths,and then deeply studies the mechanical properties of rock mass near the fracture zone,The zoning scheme of surrounding rock control is proposed.The research results have important theoretical significance and engineering value for revealing the fracture mechanism of rock under unloading path,perfecting and developing surrounding rock control theory and technology.This paper mainly carries out the following research work:(1)Based on the systematic study of the unloading stress path of rock mass passing through the fracture zone,the unloading paths of elastic,plastic and post peak stress states are designed,and the variation law of stress-strain curve and the evolution law of mechanical parameters of sandstone under different unloading paths are analyzed.With the increase of unloading amount,the volume strain increases,the unloading degree His negatively correlated with the deformation modulus E and positively correlated with poisson's ratio ?,the ? of dilatancy Angle and the normalized plastic shear strain conform to a single exponential function.The applicability of different strength criteria to describe the unloading mechanical properties of sandstone is explored.The relationship between unloading path and failure difficulty was analyzed by unifying confining pressure reduction parameters(2)Aiming at the energy evolution process of sandstone unloading failure,firstly,the law of energy accumulation,dissipation and release under different unloading paths was studied,and the influence of unloading paths on energy transformation mechanism was revealed.On this basis,the relationship between energy storage limit and unloading path was analyzed.The elastic energy storage limit increased linearly with the increase of confining pressure,and the unloading failure time met the limit energy storage law.The release rate of surplus energy was proposed and its evolution law was analyzed.The relationship between energy change rate,stress-energy increment ratio,deformation energy conversion ratio and unloading energy consumption under different unloading paths was explored.Finally,the relationship between surface energy,friction energy and dissipated energy is revealed,and the damage parameters represented by surface energy are deduced.(3)According to the acoustic characteristics of sandstone unloading failure,acoustic emission(AE)time-frequency parameters such as count,energy and peak frequency were selected to track and analyze the acoustic response and damage evolution law of rock under different unloading paths,and compared with the damage represented by energy.The calculation method of AE characteristic parameters is studied,and the reduction of b value and the disordering of sample entropy are obtained as the precursor information of rupture.Based on unloading mechanical parameters,energy parameters and acoustic parameters,the early-warning index system is established,and the early-warning level,weight and danger level of each parameter are given.(4)Based on the study of similar material ratio scheme,the characterization method of stress level(elastic and plastic)determined by stress-strain curve of similar samples was proposed,and the spatial stress distribution characteristics were studied.The similarity simulation test bench was used to carry out the excavation and unloading experiments of rock mass with different stress levels,and the effects of stress levels on the failure characteristics,mechanical properties and acoustic properties of surrounding rock were studied,which provided the basis for the differentiated control of surrounding rock under different stress levels.(5)Based on the elastic-plastic theory,stress-strain curves under different unloading paths and unloading expansion feature,the unloading constitutive model considering radial strain was derived.The reliability of the unloading constitutive model was verified by the fracture characteristics and curves of samples.The stress distribution of surrounding rock near the fracture zone is studied by using the derived elastic-plastic unloading constitutive model.On this basis,the numerical calculation of non-support,non-difference support and differential support was carried out to analyze the mechanical characteristics of surrounding rock in different areas,and the control efficiency of differentiated support scheme on surrounding rock was evaluated by displacement field,stress field,plastic zone and energy distribution,and the feasibility of differentiated support was analyzed by industrial experiment.Figure[136]Table[18]Reference[280]...