Damage Mechanism Of Fractured Rock Under Force-Temperature Field And Analysis Of Time-dependent Slope Stability

After excavation of open pit mines,the slope will be exposed to the natural environment for a long time.Affected by temperature,seepage,mining,freezing and thawing,the structural integrity and the strength of the rock gradually decrease with the increase of the slope exposure time,and the slope stability has typical timeliness.This paper comprehensively uses open pit mining theory,slope engineering theory,fracture mechanics analysis,FLAC~3DD numerical simulation calculation,laboratory test,mathematical statistics and data analysis to systematically study the variation law and damage deterioration mechanism of the physical and mechanical properties of rock and soil in the unloading stress field and the temperature field.The extension criterion and damage model of rock micro-fracture under freezing-thawing and unloading effects are established.The concept of time-dependent strength parameter is introduced into the stability analysis of time-dependent slope.Based on this,the design schemes of long-term and short-term time-dependent slope are proposed.The main research work of this paper is as follows:(1)According to the mechanical characteristics of the rock mass inside the composite slope,the corresponding loading-unloading effect model of the composite slope is established,rock compression tests under different stress paths are designed,and the stress-strain curves and deformation characteristics of the rock under different stress paths are studied.Based on the theory of fracture mechanics,the unloading effect model of open pit excavation is established.The mechanism of crack propagation in rock mass under the action of loading-unloading stress field is analyzed.The functional relationship between the safety height of composite slope and the crack morphology is determined when the crack propagates near the slope surface.(2)Through the freeze-thaw cycle test of sandstone,the change rule of physical and mechanical indexes of rock samples experiencing different freeze-thaw cycles is studied.The phase change volume of water in micro-fissures of saturated rock samples during freeze-thaw cycles is taken as a variable,and the freeze-thaw damage degradation model of saturated rock is established based on the expansion factor of micro-fissures.According to the principle of stress superposition and strain energy density factor theory,the criterion of cracking of freeze-thaw fractured rock mass is determined,and the theoretical frost heave stress of freeze-thaw fissure is deduced.The sensitivity of fixed factors and variable factors to theoretical frost heaving force is discussed respectively.(3)The damage process of slope rock mass in open pit mine is a non-linear cumulative process closely related to time,and the slope stability has a typical timeliness.The sensitivity of influence factors of slope stability to damage degradation is studied by control variable method and orthogonal test method.Slope models with different time-dependent strength parameters are designed.The time-dependent slope angle corresponding to the given safety and stability factor is determined by functional fitting of safety factor.According to the difference of service life of different side slope in open pit mine,the concepts of long-term time-dependent slope and short-term time-dependent slope are put forward.Taking the non-working side and end slope of Beitashan open pit as examples,the time-effect design and stability calculation of long-term slope and short-term slope are carried out respectively.The results show that for the mine whose slope angle is too conservative,the resource recovery rate of the mine can be improved by the time difference design,and the economic benefit is obvious.This dissertation includes 63 figures,11 tables,and 135 pieces of reference.