A Study On Dynamic Characteristics Of Rubber Sand

With the further improvement and upgrading of Chinese high-speed rail network,the demand for road system is also higher,and the quality problems of Chinese transportation projects have also been exposed in the process of high-speed development and construction during the past 30 years.Geotechnical filler composed of waste rubber tire particles and sand has the characteristics of light weight and strong elastic deformation ability,which can be used in road engineering.The main purpose of this paper is to explore the use of rubber particles to alleviate the structural damage caused by earthquake and traffic vibration.The compression,shear,dynamic characteristics and vibration reduction performance of rubber sand are studied.The main work is as follows:In the first part,lateral confined compression test and direct shear test are used to study the compressive properties and shear strength characteristics of rubber sand mixtures under dry and saturated conditions.It is found that the compression and rebound of the mixed soil increase with the increase of rubber particles both in the dry and saturated state.Compression deformation of saturated mixed soil is obviously larger than that of dry mixed soil.The shear stress-shear displacement curve of pure sand shows obvious strain-softening trend,while rubber sand shows strain-hardening trend.The shear strength of the specimens increases with the increase of vertical pressure,but the influence of rubber particle content is not obvious.Duncan-Zhang hyperbolic model was used to simulate the pre-peak part of the shear stress-shear displacement curve of rubber sand in direct shear test.By comparing the predicted curve with the test results,the hyperbolic model was proved to be feasible and in good agreement.In the second part,the influence of rubber particle content and confining pressure on liquefaction potential and dynamic modulus damping ratio of saturated mixed soil under dynamic loading is discussed through dynamic triaxial test.It is found that the liquefaction potential of sand can be effectively improved by adding rubber particles,while the confining pressure has little effect on the dynamic strength of rubber sand.The liquefaction strength curves of mixed soils under different rubber particle contents and confining pressures conform to the power function relationship,and the normalized liquefaction strength curves of rubber sand mixed soils are obtained considering the influence of rubber content.The addition of rubber particles significantly affects the development of dynamic pore water pressure of mixed soil.The higher the rubber content,the more obvious the cyclic reciprocating and grooves appear in the process of dynamic pore water pressure rising.Considering the influence of initial dynamic stress ratio,rubber content and confining pressure,a dynamic pore water pressure ratio development model is established,which can be fitted by the same hyperbolic model under different test conditions.It was found that rubber particles would migrate and aggregate to the top of the sample under the condition of high rubber content and high initial dynamic stress ratio.The mechanism of particle migration was revealed based on the micro-contact state and particle movement mode of the mixed soil.The dynamic modulus damping test results of rubber sand can be fitted by Hardin model.The maximum dynamic shear modulus decreases with the increase of rubber content and increases with the increase of confining pressure.The third part is to simulate the dynamic response of buried pipeline under dynamic load,and discuss the feasibility of using rubber to reduce the dynamic damage of underground pipeline caused by traffic load.The test results show that the dynamic deformation of the top and bottom of the pipeline caused by dynamic load can be greatly reduced by adding rubber particles in both dry and saturated states,and the dynamic strain response of the pipeline is greatly affected by dry/saturated states of backfill soil.The uniform compressed response was observed in the top area of the pipeline under all working conditions.The dynamic load intensity and loading sequence had notable influence on the strain response in the bottom area of the pipeline.The strain in the side wall area of the pipeline was tensioned response and accumulated gradually in all working conditions.Rubber sand layer can better reduce dynamic soil pressure in dry state,and the soil pressure decreases with the increase of soil depth,while the peak value of soil pressure response in saturated state is generally smaller.The subsidence response of saturated soil is greater than that of dry soil,and the difference is more distinct in rubber sand.From top to bottom,the dynamic acceleration response of soil layer shows a trend of decreasing significantly first and then increasing sharply.At present,the research on scientifically use of rubber sand is in the ascendant in the field of civil engineering.However,there are some shortcomings in the research of some influencing factors.Considering the influence of pore water,it is worth exploring.In addition,the exploration of particle migration is also meaningful.It is a new idea to study the influence of rubber particle migration on dynamic strength and pore pressure development to explore liquefaction mechanism and avoid liquefaction damage.