| Under the action of load,the defects of fractured rock mass continue to produce and expand,and the damage continues to accumulate,which seriously threatens the safety and stability of rock mass engineering.Revealing the mechanical properties and failure mechanism of fractured rock mass damage is the scientific basis to solve the problem of rock mass engineering disaster.On the basis of experimental research,this paper adopts the method of theoretical analysis,numerical calculation and intelligent analysis to study the evolution law of mechanical properties and behavior of rock mass under the fracture structural characteristics and confining pressure,and establishes a damage constitutive model that reflects the characteristics of the whole process of deformation and failure of fractured rock mass,and the strength prediction model of fractured rock mass was established to provide new ideas and theoretical basis for rock mass mechanics research and engineering stability evaluation.The main research contents and conclusions are as follows:(1)The influence of different fracture geometry characteristics and confining pressure on mechanical properties and failure modes of rock mass was studied.The results show that the rock mass resistance to deformation and failure is positively correlated with the confining pressure,decreases with the increase of fracture length,penetration and quan tity,and decreases first and then increases with the increase of fracture dip angle.With the increase of confining pressure,the rock mass changes from brittleness to ductility,the failure pattern of intact rock samples changes from tensile to shear,the failure pattern of rock samples with different fracture penetration degrees change from tension-shear to shear,the rock samples with different fracture length,quantity,and dip angle show shear failure.(2)According to the stress and deformation characteristics of the damaged and undamaged parts of rock mass,and a damage constitutive model which can reflect the whole process of deformation and failure of fractured rock mass is established to theoretically characterize the damage characteristics and macroscopic mechanical behavior of the rock mass.The results show that the stress-strain curve and damage evolution curve of rock mass correspond well with the macroscopic deformation and failure process induced by structural changes.The existence of fractures leads to the mechanical properties deterioration of rock mass,and the damage degree intensifies with the increase of fracture length,penetration and quantity,and increases first and then decreases with the increase of fracture dip angle.The increase of confining pressure can inhibit the internal damage of rock mass and improve the compressive strength,with remarkable plastic characteristics.(3)The whole process of fracture evolution of rock mass with different fracture geometry characteristics is numerically simulated by discrete element method,and the fracture mechanism of fractured rock mass is further expounded from the meso point of view.The results show that the failure process of rock mass can be divided into four stages:crack initiation stage,crack stable growth stage,pre-peak crack accelerated growth stage and post-peak crack accelerated growth stage;There are three types of rock mass fracture form:tensile failure,shear failure and composite through failure.The deformation and failure process and model simulation results of rock mass are basically the same as the indoor experimental results,in which different fracture lengths have the most significant effect on rock mass strength.(4)Comprehensively consider the relationship between fracture geometric characteristics,confining pressure,physical and mechanical parameters,12 characteristic parameters affecting rock mass strength are selected from the experimental results,and the strength of fractured rock mass is classified and predicted by machine learning-random forest algorithm,the prediction model of rock mass strength under multi-characteristic parameters is obtained,and the mapping relationship between strength and parameters is established,which provides an effective way to consider the randomness and correlation of rock mass strength parameters.The results show that the prediction effect of rock mass strength in class Ⅲ of[21～30]MPa,class Ⅳ of[31～40]MPa,class Ⅴ of[41～50]MPa and class Ⅵ of[51～60]MPa is the best;the prediction effect of rock mass strength in class Ⅱ of[11～20]MPa is good;the prediction effect of rock mass strength in class Ⅰ of[0～10]MPa is the second.The model can be extended to other rock mass strength prediction. |
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