Study On Effect Of Freeze-thaw Cycle On Dynamic Performance Of Improved Aeolian Sand And Fractal Law Of Damage

In recent decades,with the rapid development of China's economy and the increasing energy consumption,the proved shallow coal resources are gradually exhausted,and the acquisition of coal resources has entered the stage of deep mining.In the process of the construction of ultra deep mine and the gradual development of the mining roadway to the deep,in the face of the complex geological environment such as high ground stress,high seepage pressure and high ground heat,the self-supporting capacity of surrounding rock is reduced,the original support of the roadway is gradually invalid,which leads to the occurrence of rheological instability failure accidents of the roadway,which brings serious security risks for the mining of coal resources.In the process of roadway excavation,the surrounding rock is affected by geological structure movement,secondary stress redistribution and blasting disturbance,which leads to the expansion of the original fracture and the initiation of new fractures,which is one of the important factors causing the instability and failure of the roadway.Under the action of high permeability water pressure,it not only changes the stress state of the fissured rock mass medium,but also weakens the mechanical properties of the fissured rock mass medium,which directly affects the overall stability of the coal mine roadway.Therefore,the research on the mechanical properties of fractured rock mass under seepage has been paid attention to in the field of geotechnical engineering.Therefore,with the support of National Natural Science Foundation of China(51774166),taking the fractured rock mass as the research object,this paper uses taw2000 electro-hydraulic servo rock triaxial test system and GDS Rheometer,polarizing microscope CT scanning,acoustic emission high-speed camera and SEM scanning were used to carry out conventional rock mechanics test,polarizing CT scanning observation test,acoustic emission test,SEM test,full stress-strain permeability test and triaxial rheological test of rock under seepage,to explore the fracture damage evolution rule and creep failure mechanism of fractured soft rock under seepage.The main research work can be summarized as follows:(1)The taw2000 electro-hydraulic servo rock triaxial test system is used to test the basic mechanical parameters of sandstone samples and obtain the basic mechanical parameters of ultra deep mine sandstone.Prefabricate sandstone samples with single fracture in different spatial positions,and carry out uniaxial compression test to explore the influence of spatial position of fracture on the mechanical properties of rock samples.GDSTAS servo soft rock rheological test system was used to test the full stress-strain permeability and to explore the influence of seepage on the mechanical properties of rock samples.(2)The mineral structure and internal defects were scanned by polarizing microscope CT;the acoustic emission signals were obtained by acoustic emission instrument under different loads;the full field strain characteristics of rock specimen surface were obtained by non-contact full field strain measurement system;the micro morphology characteristics of rock fracture were observed by SEM scanning surface.Based on the theories of fracture mechanics,damage mechanics and fractal mathematics,a quantitative damage model is established to describe the fracture propagation and evolution of soft rock.(3)According to the law of crack evolution and rock failure mechanism,the fracture will occur when the fracture is in the state of supercritical propagation,and the seepage will weaken the rock medium,which will lead to the degradation of the yield boundary of the rock medium.Based on the classical mechanical theory,the D-P strength criterion under the seepage action is modified,and the seepage stress coupling effect is established according to the statistical damage theory Three dimensional constitutive model of rock.(4)GDSTAS adopted in the UK The mechanical parameters of uniaxial and triaxial creep tests of fracture soft rock in ultra deep mine are determined.The curve characteristics of triaxial creep tests of fracture soft rock in seepage field are analyzed in high stress state,and the initial creep strength parameters and strength parameters after creep failure are obtained.(5)Based on the damage factor,triaxial test data and creep curve of fracture soft rock specimen,the criterion of creep initiation and acceleration before and after the peak of fracture soft rock under high stress is determined.