Experimental Study On Strength Characteristics Of Wheat Straw Reinforced Soil

Soil strength characteristics have been one of the hot spots in geotechnical engineering field,and various reinforcement and strengthening technologies have been widely applied.Fiber reinforcement can effectively improve the strengthf soil,reduce the expansive soil swelling shrinkage and degree of fracture,increase fracture toughness and soil permeability at the same time,which is widely used in engineering application.In recent years,many scholars and researchers have paid close attention to natural rubber because of its characteristics of environmental protection and good economic returns.As a natural fiber,wheat straw has differrent mechanical properties and different surface characteristics with rigid material such as bolt andflexible material such as geotextile,and also has different effect of reinforcement and the law of strength growth.In this paper,through a series of experiments,such as indoor soil test,large direct shear,three axial compression and unconfined compression test,the following contents and results are obtained:(1)in the three axial compression test,soil samples appear obvious shear failure,while the straw reinforced soil only central bulging,that reinforcement deformation has a binding effect on soil.the stress difference of soil increases with the increase of confining pressure,and the stress-strain curve shows hardening characteristic.The maximum stress appears in the reinforcement ratio of 0.2% and the fiber length is 10 mm.Under different confining pressure,the strength of reinforced effect coefficient of wheat straw reinforced soil are greater than 1,indicating the use of wheat straw reinforced soil can enhance the strength,at the same time when the confining pressure is lower the reinforcement effect is more obvious.(2)The large direct shear test results show that with the increase of normal stress,the peak value of shear stress also increases with the increase of normal stress.At the same time,in the lower normal stress,shear reinforcement rate of 0.3% soil samples have the higher stress value,which is about 1.5 times of unreinforced soil,while under the higher normal stress,the shear stress of the specimen with the reinforcement ratio of 0.2% is the highest,which is about 1.14 times of that of the non reinforced soil.by drawing the shear strength envelope diagram and and diagram of shear strength and vertical pressure,we found that the sample shear strength becomes larger,,reinforcement significantly improved the soil cohesion,but has little effectto the internal friction angle,and showed a negative correlation.(3)combined with unconfined compression test,the cracks appear time of reinforced soil is close to that of the unreinforced soil samples,the resistance to deformation characteristics of the reinforcement can gradually play in the larger axial displacement.The relationship between compressive strength and axial strain is softening.Consistent with the results of three axial compression and large direct shear test,the initial stiffness of the reinforced soil is not changed,and only when the reinforced soil has a certain axial strain,the effect of reinforcement will begin to show.The results show that the compressive strength of the0.3% rate and 15 mm length of sample is the laggest,which is about 2.1 times of that of the non reinforced soil.(4)Through the MATLAB software to draw the relationship between the strength of reinforced soil and reinforcement condition in the three-dimensional coordinate axis,we found that the reinforcing effect of straw on soil has very good,with the increase of fiber length and reinforcement ratio,the strength of reinforced soil increases first and then decreases.Multi factor analysis of variance was performed by using SPSS software.It was found that the reinforcement ratio can affect the strength of soil more than the length of fiber.Considering the mechanical properties and strength properties of soil,we determine the optimal reinforcement ratio of wheat straw fiber reinforced soil with reinforcement ratio of 0.2%-0.3%,and the optimal fiber length is 10-15 mm.This paper focuses on the influence of fiber length and the rate of wheat straw reinforced soil in proportion of reinforcement deformation,mechanical parameters and strength characteristics,analysis influence factor to find out the best mixing ratio.Carry out the research on the theory and technology of fiber reinforced soil,has important theoretical significance to improve the fiber reinforced earth theory and practical application value for highway engineering construction,loess cave disaster control and many other engineering applications.