Study On Mechanical Properties And Vibration Fatigue Of Rock Cutting Slope On Shanghai-Kunming High-Speed Railway

For the service duration of cut slope in the karst region,it isn't only affected by the complicated geological conditions such as karst collapse and karst water erosion and so on,but also the vibration load of the train.With the increase of the traveling speed of the High-Speed Train and the rise of tractive tonnage,the long-term vibration of the train load during the operation period will inevitably result in the changes in the rock engineering properties.The study of the features of rock mass mechanics of karstification and the vibration fatigue damage for cut slope of karst region not only has active significance to the stability of long-term service duration of rock cut slope,but also provides a reference to the research of fatigue damage of karstificated rocks with the vibration of high speed train.The research is based on the National Natural Science Foundation of China.By systematically generalizing the karst distribution law,development characteristics and cut slope's instability mechanism for the roadbed of Shanghai-kunming high-speed railway(Guizhou Section),with risky factors of service duration of rock cut slope in the karst region as the starting point,the deformation features of karstificated rocks of typical structural surface of cut slope is researched through the on-site three-dimensional laser scanner and pressure-bearing plate test.We have studied the changes in the strength and mechanical parameter of the karstificated rocks under the action of karstic water and performed the fatigue damage test for the karstificated rocks under different loading conditions and hydraulic actions.By means of in-depth research on the models of fatigue damage of karstificated rocks,we try to the establish a series of estimation methods of low-cycle fatigue life for the rock cut slope during the service duration,and perform dynamic response analysis of rock cumulative fatigue damage caused by the vibration for the cut slope.The main contents of this paper are as follows:(1)We have conducted the in-situ deformation measurement of rocks with different karstic development and calculated and analyzed the rock viscoelasticity deformation under the bearing plate.Aiming at the cut slope in the area of typical structural surface obtained through the three-dimensional laser scanner,we have studied the deformation laws of rocks with different karstic developments through the pressure-bearing plate tests,and the research results showed that,at the same position under the pressure-bearing plate,as the applied load increases,the displacement increases gradually;as the degree of karstic development increases,the displacements of points under the bearing plates increase;the greater the karstic development,the larger the displacement value.(2)A series of tests and researches have been conducted for the karstificated rocks using karstic water(water and chemical solution),including compression strength,elasticity modulus,poisson ratio and variation of acoustic wave velocity and so on.The research showed that:under the action of karstic water,the rock displayed significant softening phenomenon,and the strength of peak values significantly decreases,especially,the more intense the degree of karstic development,the greater the softening degree;under the action of karstic water,the average elasticity modulus of all groups of specimen appeared a decreasing trend,and as the karstic development gets stronger,the average poisson ratio of all groups of specimen after saturation display increasing trend,that is,under the saturation effect,the circumferential deformation is more sensitive than the longitudinal deformation;the relationship between uniaxial compressive strength and wave velocity is established for karstificated rocks.(3)The fatigue damage test is performed for karstificated rocks under different loading conditions using the Shanghai to Kunming high-speed railway(Guizhou Section).The low frequency of 3Hz is taken as frequency values of rock loading while the sine loading wave is fatigue loaded wave.Based on the measured data,S-N curves are established and used to describe rock fatigue lives under different karstic development states.For the karstificated rocks,the threshold value of low-cycle fatigue loading is 78.4%.The fatigue life of karstificated rocks increases as the f,loaded frequency,increases,and it satisfies the linear relation under the log-log coordinate.(4)we have studied the axial and ultimate deformation laws of stress-strain curves in the process of fatigue loading for the karstificated rocks,and the entire stress-strain curves under the uniaxial compressive strength is compared with the stress-strain curves under fatigue load,which proved that,the fatigue rupture of karstificated rocks is completely controlled by the whole static process.(5)Based on the dynamic load vibration frequency of high speed train with different travelling speeds,we proposed the influence of loaded frequency on the mechanical property of rock fatigue damage with different karstic developments,and focused on the changes in threshold value,ultimate strain and elasticity modulus.Moreover,by introducing the Wohler model in the calculation of concrete fatigue loading and the correction factor,we have established the estimation method of fatigue life with loading conditions.(6)Based on the test results of fatigue mechanics of karstificated rocks under different loading conditions,saturations and karstic developments,we have adopted the regression analysis,and combined the linear Minear damage accumulation theory satisfying the engineering accuracy,and established the evolution model of cumulative fatigue damage based on the residual strain for the karstificated rocks;by combining the calculation method of fatigue life for the cut slopes with different engineering characteristics and loading conditions,we have introduced the calculation method of fatigue life of concrete,and set up a group of estimation methods of low-cycle fatigue life for the rocks of cut slope during the service duration.(7)The Fortran language is adopted to perform Abaqus secondary development of rock fatigue damage,and the three-dimension dynamic model of cut slope is established allowing for the accumulative fatigue damage of karstificated rocks,and the dynamic response analysis of cut slope is conducted under the fatigue damage.The research results showed that,by allowing for the fatigue damage of rock,the drawbacks of traditional elastoplasticity dynamic analysis can be overcome,and after the fatigue damage is introduced,the dynamic response of rock is even more significant.The low-cycle fatigue issue of rocks of cut slope caused by the train load is of active significance to the analysis of long-term service stability of rock cut slope of the high-speed train,which is an indispensable factor for the rock dynamic response analysis.