Experimental Study On Dynamic Characterictics Of Fibre-reinforced Loess

Fiber soil is a new type of geocomposite material formed by uniformly mixing fine fiber materials with soil.The reinforcement of the fiber to the soil can effectively improve the mechanical properties of the soil.Morever,the fiber soil has the advantages of environmental friendly,low cost and simple construction process,which makes the fiber soil have broad application prospects in the seismic protection of the slope,the foundation of the roadbed and the construction of water conservancy and flood control.But the current research mostly focuses on the improvement of the static characteristics of the fiber soil,and there are few studies on its mechanical properties under dynamic loading.The dynamic deformation characteristics and dynamic strength characteristics of soil are important contents of soil dynamics research.In this paper,Yangling loess and basalt fiber were used as experimental materials to study the effects of fiber content,fiber length,moisture content and consolidation confining pressure on the dynamic stress-strain relationship,dynamic elastic modulus and damping ratio of fiber soil by indoor dynamic triaxial test.And analyze the dynamic strength and its parameter characteristics of fiber soil under different fiber content.The main contents include:(1)The maximum dry density and the optimum moisture content of loess under different fiber content were studied by light compaction test.The results showed that the maximum dry density and optimum moisture content of fiber loess decreased with the increase of fiber content.Compared with unreinforced loess,the maximum dry density and optimum moisture content of fiber loess with 0.6% content decreased by 4.0% and 7.3%,respectively.The research results provide sample preparation parameters for dynamic triaxial tests and provides a useful reference for improving the compaction effect of fiber loess in engineering.(2)Based on the dynamic deformation test,the effects of fiber content,fiber length,moisture content and consolidation confining pressure on the dynamic constitutive and its parameter characteristics of fiber loess are studied.The test results show that:(1)At the same dynamic strain,with the increase of moisture content,the dynamic stress and dynamic elastic modulus of fiber loess and plain loess gradually decrease,and the damping ratio increases.(2)The dynamic stress and dynamic elastic modulus of fiber loess and plain loess corresponding to the same dynamic strain increase with the increase of confining pressure.There is no obvious law of damping ratio with confining pressure under different moisture content conditions.(3)The improvement of fiber content on dynamic parameters of loess is also affected by both confining pressure and moisture content.When the moisture content is lower than the plastic limit,the higher the confining pressure is,the more obvious the dynamic stress of the fiber loess under the same dynamic strain higher than that of the plain loess.The fiber content has little effect on the dynamic elastic mode,and the damping ratio has no obvious regularity.When the moisture content is higher than or equal to the plastic limit,the dynamic stress,dynamic elastic modulus and damping ratio of the fiber loess under low confining pressure are significantly higher than that of plain loess.With the increase of confining pressure,the influence of fiber content is weakened.The improvement on the dynamic parameters of the fiber does not increase with the increase of the fiber content,there is an optimal fiber content.(4)With the optimal moisture content,when the confining pressure is low,with the increase of the fiber length,the dynamic stress and dynamic elastic modulus of the fiber loess increase,and the damping increases first and then decreases.As the confining pressure increases,the effect of fiber length decreases.(5)The dynamic stress-strain relationship of the 6-fibre loess is hardened and can be fitted by the Hardin-Drnevich hyperbolic model.The model parameters are influenced by the fiber content,moisture content and confining pressure.(3)Based on the dynamic strength test,the influence of fiber content on the dynamic strength characteristics of loess under the optimal moisture content is studied.It can be found that the dynamic shear strength curves of plain loess and fiber loess both decrease with the increase of vibration times.Under the same failure vibration level,the higher the confining pressure,the greater the dynamic shear strength of the loess.The dynamic shear strength increases with the increase of fiber content,but the increase reduces with the increase of confining pressure.Based on the dynamic strength curve,the dynamic strength parameters of loesss with different fiber content were obtained.The results show that the dynamic cohesion of plain loess and fiber loess decreases slowly and then stabilizes with the increase of failure vibration times.However,the internal friction angle is basically unchanged.The incorporation of basalt fiber mainly improves the dynamic cohesion of loess,and has little effect on the internal friction angle.