Strength And Deformation Characteristics Of Cotton Fiber Reinforced Soil Studied By Experiments

Fiber reinforced soil is an artificial composite soil formed by adding fiber materials with high tensile strength in soil.Most of the reinforcing materials of traditional reinforced earth are oriented,usually only controlling the lateral deformation.But fiber is able to control the possible deformation of the soil in all directions because of its randomness of the distribution direction in soil.The use of fibers can replace or minimize the use of curing agents such as traditional cement.Lightweight,flexible,high-strength fiber materials also have excellent performance in earthquakes.The superiority of fiber reinforced soil is favored by many scholars,and it is widely believed that it has application prospects in the foundations,slope reinforcement and other projects,and can become a kind of high-quality soil improvement technology.Fiber reinforced soil is one of the hot issues in geotechnical engineering research.The strength and deformation characteristics of cotton fiber reinforced soil were studied by conducting several unconfined compressive strength tests,UU tests,and CU tests.The interaction between fiber and soil was analyzed,and the reinforcing mechanism of fiber reinforcement was explored.The following conclusions:(1)The effective fiber content for cotton fiber reinforced soil is 0 ~ 1.5%.There is an optimal fiber content of 1.0% and an optimal fiber length(critical length)of D/2(D is the diameter of the sample).(2)The stress strain characteristics of the reinforced soil are strain hardening.The stress strain curve is nonlinear,and the plastic deformation of the sample occurs.When the strain is small,the reinforcement effect is weak.With the increase of axial strain,the reinforcing effect of fibers is enhanced.(3)At the optimum fiber content and fiber length,the strength is increased by 24.8% when the reinforcing fibers are added in the pattern of random distribution and decreased by 15.1% when added in layered one-way distribution,while it remains nearly the same if the fibers in layered cross distribution.Fiber distribution patterns has important influence on the strength of fiber reinforced soils.This experiment demonstrates that the reinforcing fibers will help restraining soil radial displacement,inhibiting the development of soil cracks under load and increasing soil strength if certain reasonable and practical means can be used to control their distribution patterns so as to keep them oriented along the local tensile stress.(4)With both fiber content and fiber length increasing,its average deformation modulus is increased first and then decreased,varying in the range of 0.56 ~ 1.26 MPa.(5)By UU tests,under the optimal reinforcement conditions,the unconsolidated undrained strength of saturated cotton fiber reinforced soil is 63.5% higher than that of unreinforced soil.By CU tests,as both fiber content and fiber length increases,the cohesion is increased first and then decreased.Under this optimum condition,the total cohesion and effective cohesion are increased by 48.4% and 112.3%,respectively,compared to unreinforced soil.Its internal friction angle is basically unchanged with the change of fiber content and fiber length.(6)By CU tests,the pore water pressure of fiber reinforced soil increases to the peak with the increase of the axial strain and then slowly decreases.And it increases with the increase of deviation stress,and finally tends to be stable.The pore pressure coefficient A of compacted fiber reinforced soil is 0.35 ~ 0.46.