Study On Strength Characteristics Of Ramie Fiber Reinforced Soil

At present,fiber reinforced soil has been used in civil engineering in various situations.It refers to improving the strength and stability of soil by uniformly adding fibers to the soil to improve the engineering characteristics of clay such as water deformation,water loss shrinkage and poor strength,so as to meet the current engineering needs and reduce the occurrence of natural disasters.Ramie fiber has good toughness,water resistance and corrosion resistance,and plant fiber has excellent isotropic mechanical properties and good tensile strength.It is also a green material and has no pollution to the environment.Therefore,it is of great engineering significance to study the mechanical properties of ramie fiber reinforced soil.On the basis of previous studies,this paper uses ramie fiber as a reinforced material to improve the cohesive raw soil.The data are obtained through unconfined compressive strength test and direct shear test.The effects of ramie fiber content and fiber length on the mechanical strength characteristics of fiber reinforced soil are studied.The main conclusions are as follows:(1)The liquid-plastic limit of the raw soil taken from the site was measured.The calculated results showed that the plasticity index of the raw soil in this test was 15.2According to the engineering classification of soil in the specification,the category of raw soil in Hefei area is low liquid limit clay,which belongs to the category of clay.(2)The raw soil test block was prepared with the raw soil in Shushan District of Hefei City as the raw material.According to the specification,the optimal moisture content of the raw soil was 15.1%,and the maximum dry density was 1.68g/cm~3.(3)In the unconfined compressive strength test,the effects of ramie fiber content and fiber length on the compressive strength and failure mode of reinforced soil specimens were investigated.The results show that the compressive strength of reinforced soil specimens increases first and then decreases with the increase of fiber content.The effect of fiber length on its compressive strength is similar to that of fiber content on its compressive strength,and the compressive strength of reinforced soil specimens is higher than that of plain soil specimens.It shows that ramie fiber can improve the unconfined compressive strength of cohesive raw soil.During the test,the plain soil specimens show that there will be a large number of vertical cracks through the specimen,and the soil sample will crack,while the fiber reinforced soil is a small failure surface of the through specimen,and the surface of the soil sample is slightly bulging.The failure of both plain soil and reinforced soil is shear failure,but the integrity of reinforced soil specimens is significantly better than that of plain soil.(4)In the direct shear test,the shear strength displacement curves of three ramie fiber lengths(5mm,10mm,15mm)and three fiber contents(0.1%,0.3%,0.5%)were studied,and the influence of these two factors on shear strength was analyzed.The test results show that the shear strength of ramie fiber reinforced soil is significantly greater than that of plain soil,and the increase of shear strength is proportional to the increase of fiber length and fiber content.The reinforcement effect of fiber on soil not only comes from the friction between fiber and soil,but also from the spatial constraint of uniform,multi-directional and interwoven fiber network structure.(5)The addition of fiber can greatly increase the cohesion of fiber improved soil,depending on the degree and content of fiber.With the increase of fiber content,the cohesion increases.At the same time,due to the interweaving and aggregation effect of fibers,the effective effect of fibers decreases,and the increase of cohesion is not obvious in the range of high fiber content.The effect of fiber length on cohesion is similar to that of fiber content.(6)Fiber length and fiber content have little effect on the internal friction angle of reinforced soil,and there is no obvious rule.Compared with the internal friction angle of reinforced soil without ramie fiber,the change range is about 3°.Ramie fiber reinforcement is a physical effect.Its addition does not change the properties of the soil itself and the external environment.It is only filled between the pores of the soil particles and cannot increase the bite force between the soil particles.