# Experimental Study on Strength of Polypropylene Fiber Reinforced Cemented Silt Soil
###### Abstract  
To improve the poor characteristics of low strength and high compressibility of weak silty soil, a series of samples with different cement dosage, fiber content, and fiber length was prepared in this experiment, and unconfined compressive strength (UCS) tests, triaxial tests, and scanning electron microscopy (SEM) tests were carried out to explore the influence of polypropylene fiber on the strength of cement-stabilized soil and analyze the curing mechanism of fiber-reinforced cement soil. The test results show that the factors affecting the UCS of the sample from high to low were: cement dosage, fiber content, and fiber length. An orthogonal test found that the optimal ratio of the sample was cement dosage of 18%, fiber content of 0.4%, and fiber length of 3 mm, and the UCS of the sample can reach 1.63 MPa. The triaxial test shows that when the cement dosage is 15% and the fiber length is 9 mm, the incorporation of fiber can significantly improve the toughness and strength of soil. When the cement dosage is 15%, the UCS with 0.4% fiber content is 1.6 times that without fiber. With the increase of fiber content, the peak stress and axial strain of fiber-cured soil are increased, and the cohesion and internal friction angle are also increased. The failure mode and SEM test of fiber-reinforced cement soil show that when the cement dosage is 15% and the fiber length is 9 mm, the addition of fiber can improve the deformation ability of cement soil and slow down the development of cracks. With the increase in fiber content, the number and width of cracks are significantly reduced, and the failure mode changes from brittle failure to ductile failure. polyproplane fiber; cement soil reinforcement; triaxial test; orthogonal test; fitting  
structure, which enhances the bonding force of the contact interface and improves the ability of soil to resist deformation. Studies have shown that fiber, as a commonly used soil reinforcement material, has been widely used in new curing agents combined with fiber-modified silt solidified soil, fiber-modified microbial solidified marine sand, fiber-reinforced cement solidified dredged soil, fiber-modified geopolymer solidified soil shrinkage/cracking and fiber application in concrete. [PERSON] et al. [30] improved silt solidified soil by using cement-slag-fly ash-gypsum curing agent and polypropylene fiber and found that the failure mode was improved, changing from brittle mode to ductile mode. The optimum fiber content and fiber length were 0.4% and 12 mm, respectively. [PERSON] et al. [31] used microbial-induced calcium carbonate precipitation technology combined with activated carbon to solidify marine sand, and brittle failure occurred when it was damaged. The incorporation of sisal fiber could improve this situation, and the optimal content of fiber was 0.2% with or without activated carbon. To improve the brittle fracture behavior of sand, [PERSON] et al. [32] used a polyurethane curing agent and sisal fiber. The addition of fiber can improve not only the tensile and compressive properties of sand but also the residual strength of sand. [PERSON] et al. [33] solidified dredged soil with high moisture content, low permeability, and low bearing capacity by using ordinary Portland cement and polyvinyl alcohol fiber. With the increase in curing age, the influence of fiber on internal friction angle decreased gradually, and the optimal fiber content and length were 0.1% and 6 mm, respectively. [PERSON] et al. [34] artificially improved the cracking problem of geopolymer-solidified soil and found that the fiber had a good anti-cracking effect in the continuous drying test and dry-wet cycle test by using ash-based polymer and coconut fiber-solidified soil. [PERSON] et al. [35] explored the improvement effect of sisal fiber and conducted experiments on plain expansive soil, fly ash-modified soil, and fly ash combined with sisal fiber composite modified soil.