Experimental Study On Strength Properties Of The Polypropylene Fiber Reinforced Cement Soil

As a new type of geotechnical material,because of its advantages of shear resistance,crack resistance,and good corrosion resistance,fiber reinforced soil is often used in structural reinforcement of embankment and retaining wall,and it is the hotspot of reinforced soil technology.This paper,taking Guangzhou Nansha solidified mud as the research object,based on the background of the lack of unified understanding of the soil reinforcement effect of fiber content,fiber length and the amount of admixture,is on the basis of the current reinforced soil strength theory to further explore the influence of above factors on fiber reinforced solidified silt strength and deformation,and studies the relationship between its strength in the coastal conditions and the number of dry wet cycles.On the basis of the study of the influence of the early cement admixture on the mechanical properties of Nansha silt,this paper will further study the strength and deformation characteristics of solidified soil reinforced by polypropylene fiber,thus providing important theoretical support for the actual projects.(1)The basic physical and mechanical indexes of Nansha silt in Guangzhou were measured by basic laboratory soil tests,and the physical,chemical and mechanical properties of polypropylene fiber were briefly introduced.(2)In this paper,the mechanism of the strength of fiber reinforced soil was introduced in detail.The principle of the fiber could be summed up as "bending mechanism" and " interweaving mechanism",and the physical and mechanical properties of the soil were improved obviously under the joint action of both.(3)The effect of fiber content,fiber length and cement content on the unconfined compressive strength of fiber reinforced soil cement was studied by means of single doped test,and the results were compared with those of previous studies.Based on the scanning electron microscope test and the strength theory of fiber reinfo rced soil,the principle of strength enhancement and its failure mode of fiber-cement soil were preliminarily analyzed.Finally,the optimum scheme of fiber-cement soil was obtained by orthogonal test.The test results indicated that with the increase of f iber content,fiber length and cement content,the unconfined compressive strength of fiber-cement soil increased to a certain extent,however,the enhancement effect of fiber length on the strength of soil cement was not as obvious as that of fiber conten t and cement content.The incorporation of fiber could prevent the development of cracks in the cement soil during compression failure.The optimum scheme of fiber cement soil was as follows: the fiber content was 0.4%,the fiber length was 3mm,the cement content was 18%.(4)The stress-strain characteristics of fiber-cement soil with different fiber content were studied by means of unconsolidated-undrained triaxial shear test,and the change characteristics of cohesion and internal friction angle of fibe r-cement soil with different fiber content were obtained.Beside,the constitutive model of soil with different fiber content was established,and the parameters of the correlated models were obtained through experiments.The experimental results showed that the incorporation of fiber could increase the failure strain of cement soil to a certain extent,in addition,with the increase of fiber content,the cohesion of cement soil was improved obviously,while the internal friction angle changed little.(5)The dry-wet cycling test was carried out under the condition of littoral,the relationship between the unconfined compressive strength,cohesion and internal friction angle of fiber reinforced cement soil with different fiber content and the number of dry wet cycles was also studied,thus,the variation regularity of the strength characteristics of fiber reinforced cement soil under the condition of dry-wet cycles was obtained.The results indicated that with the same fiber content,the unconfined compressive strength and cohesive strength of fiber reinforced cement soil increased at first and then decreased with the increase of the number of dry wet cycles.Unde r the condition of the same dry-wet cycles,the unconfined compressive strength and cohesion of fiber-cement soil increased with the increase of fiber content.