Experimental Study On Static And Dynamic Properties Of Red Clay Soil Reinforced With Rice Straw

Red clay is the product of weathering and lateralization of carbonate rocks,which is widely distributed in the south of the Yangtze River in China.Road and railway construction in these areas has created a large number of red clay slopes.Vegetation slope protection technology is a new slope protection technology,but the existing vegetation slope protection technology ignores the fact that its reinforcing effect cannot be played before the plant root system is developed,and the stability of the slope is difficult to be effectively guaranteed in the early stage.To address this shortcoming,the group chose environmentally friendly and economical rice straw as reinforcing material to strengthen the soil body in order to guarantee the preliminary stability of the slope.In this thesis,the static and dynamic characteristics of straw reinforced soil are studied by means of laboratory tests and theoretical analysis.The influences of confining pressure,reinforcement rate reinforcement length and water content on the static characteristics of soil are discussed and built the Duncan-chang model.The effects of confining pressure,reinforcement ratio and frequency on the dynamic characteristics of soils are analyzed,and the dynamic characteristics of soils are studied based on the H-D equivalent linear model.The research contents and conclusions of this thesis are as follows.(1)The basic physical and mechanical parameters of red clay and the direct shear strength index and compaction characteristics of straw reinforced soil were studied through laboratory soil tests.The natural water content of red clay is 25.7%,and the natural dry density is 1.47 g·cm-3.The addition of rice straw has little effect on the maximum dry density and the optimum moisture content of red clay.Under the condition of different reinforcing ratio,when the reinforcing ratio of rice straw is 0.2%,the friction angle and cohesion of the soil are maximum.(2)By carrying out static triaxial tests on the red clay reinforced with straw,the influences of failure form,stress-strain curve,reinforcement length and reinforcement rate on the shear strength of soil were studied,and Duncan-chang model of the red clay reinforced with straw was established.The shear failure of red clay is obvious,but the straw reinforced soil only has middle bulge deformation,and the stability of the whole structure is strong,which indicates that the straw reinforced soil has a strong restraint effect on the soil deformation.The stress-strain curves of plain soil and reinforced soil show the characteristics of hardening.Under the failure state,when the reinforced ratio is 0.2%and the length of rice straw is 20mm,the partial stress acting on the sample is the largest.With the increase of reinforcement ratio and length,the cohesion and internal friction angle of rice straw reinforced soil increased at first and then decreased.The fitting curve of Duncan-chang model matched well with that of experimental data,the results show that Duncan-chang model can simulate the static triaxial test results of rice straw reinforced soil.(3)By carrying out dynamic triaxial tests on red clay reinforced with rice straw,study the variation of hysteretic curves of red clay reinforced with straw under different reinforcement ratio,confining pressure and frequency.The morphological characteristics of hysteretic curves were quantitatively studied by using parameters such as slope k,area S,residual strain εp and ratio a of short axis and long axis of hysteretic ring.With the increase of dynamic stress,the k value of hysteresis curve decreases rapidly and then tends to be stable.With the increase of confining pressure and frequency,the k value increases,and the anti-deformation ability of soil is improved.At the initial stage of cyclic loading,S,εp and a change little with the increase of dynamic strain when the dynamic stress amplitude is small.At the later stage of loading,S,εp and a increase rapidly with the increase of dynamic stress amplitude,and decrease with the increase of confining pressure and frequency.When confining pressure and frequency were determined,the ultimate dynamic stress strength of reinforced soil was greater than that of unreinforced red clay.Reinforcement effect of rice straw significantly enhanced the dynamic strength of red clay.When the rice straw reinforcing rate was 0.2%and the frequency was 2Hz,the stiffness of red clay is the highest and the viscosity,residual strain and energy dissipation capacity are the lowest under the same dynamic stress.(4)By carrying out dynamic triaxial tests on red clay reinforced with rice straw,the dynamic elastic modulus and damping ratio of the clay were studied under different reinforcement ratio,confining pressure and frequency,and the H-D equivalent linear model of dynamic elastic modulus and damping ratio was established.When the straw reinforcement rate is 0.2%,the dynamic elastic modulus of the reinforced soil is the maximum and the damping ratio is the minimum.With the increase of confining pressure and frequency,the dynamic elastic modulus is improved.Under the same confining pressure and frequency,the dynamic elastic modulus firstly decreases and finally becomes stable with the increase of dynamic strain.Under the same dynamic strain,the damping ratio decreases with the increase of confining pressure and frequency.The damping ratio is affected by confining pressure and frequency,but is less affected by reinforcing ratio of straw.The above research results can provide reference for the theoretical research and engineering application of red clay soil reinforced with rice straw in the future.