Study On The Deterioration And Instability Characteristics Of Complex Fractured Rock Slopes In The Three Gorges Reservoir Are

Rock slope instability is one of the most common geological hazards in China,which often causes significant loss of life and property.Under long-term geological processes,many micro or macro defects,such as joints,faults,cavities,and cracks,occur inside natural rock formations.These defects make fractured rock mass a relatively complex and commonly encountered engineering medium.Numerous engineering practices have shown that the initiation,propagation,and coalescence of cracks can cause instability and failure of rock masses under engineering disturbances.Therefore,studying the crack propagation and failure patterns of fractured rock mass under stress is of great significance.In this paper,orthotropic proportion tests were conducted on rock-like materials to obtain the optimal proportion.Based on this,uniaxial compression tests were carried out on single and multiple cracked rock-like specimens to study their physical and mechanical properties and failure characteristics under different combinations of crack length,width,number,and dip angle.In addition,the required I and II type fracture toughness for numerical simulation were measured using the direct shear box and double torsion test.Finally,the stability of dangerous rock masses was analyzed using rock fracture theory,and the crack propagation pattern of dangerous rock masses was simulated using finite element numerical simulation software.The main research contents and conclusions are as follows:(1)The hazardous rock behind the Maritime District in Wanzhou district was selected as the specific research object.Basic physical and mechanical parameters of the target rock were obtained through indoor tests such as uniaxial compression and Brazilian splitting.Using the principles of similarity and orthogonal experimental design,25 sets of different material ratios of simulated rock materials were designed,and the optimal ratio of simulated rock was obtained as follows: water: cement: quartz sand: gypsum : waterproof agent : early strength agent = 1 : 0.25 : 0.54 : 0.024 : 0.054 : 0.056.(2)Based on the obtained optimal material ratio,prefabricated fractured rock-like specimens were made,including single fracture specimens with fracture inclination angles of 15°,30°,45°,60°,and 75°,fracture lengths of 10 mm and 20 mm,and fracture widths of 0.5mm and 2mm,as well as multi-fracture specimens with 1,2,3,4,and 5 fractures.Uniaxial compression tests were carried out on these specimens to investigate the influence of different fracture lengths,widths,inclinations,and numbers on the strength,fracture propagation,and failure modes of rock-like materials.The experimental results showed that for single fracture specimens,the fracture length had the greatest impact on the strength reduction,followed by the fracture width,and the fracture inclination had the smallest impact.For multi-fracture specimens,the degree of strength reduction gradually increased with the increase in the number of fractures.The influence of fracture length,width,inclination,and number on the type and propagation of cracks in the specimens was small,only affecting the direction of crack propagation.(3)Combining linear elastic theory and fracture mechanics,the methods for calculating the stress intensity factor at the crack tip and the I-II composite fracture criterion were summarized.The stability of the dangerous rock mass was analyzed using rock fracture theory.A numerical calculation model of the dangerous rock mass was established using finite element software,and the effects of different crack lengths on the crack stress intensity factor,stability,and crack propagation of the dangerous rock mass were compared.The results showed that as the crack length increased,the stress intensity factor and the degree of crack penetration of the dangerous rock mass gradually increased,the safety factor decreased,and the crack initiation time was advanced.