# Experimental Study on Strength of Polypropylene Fiber Reinforced Cemented Silt Soil
## 3 Analysis of Unconfined Compressive Strength and Unconsolidated Underained Test Result
### Analysis of Unconfined Compressive Strength Results of Fiber Cement Soil
The optimal scheme is determined by the ratio of the maximum strength corresponding to the level of each factor to the best curing effect, where:  
Factor A: K\({}_{\rm 4}>\) K\({}_{\rm 3}>\) K\({}_{\rm 2}>\) K\({}_{\rm 1}\)  
Factor B: K\({}_{\rm 4}>\) K\({}_{\rm 3}>\) K\({}_{\rm 2}>\) K\({}_{\rm 1}\)  
Factor C: K\({}_{\rm 1}>\) K\({}_{\rm 2}>\) K\({}_{\rm 4}>\) K\({}_{\rm 3}\)  
Therefore, the optimal scheme was A\({}_{\rm 4}\)B\({}_{\rm 4}\)C\({}_{\rm 1}\), that is, the cement dosage was 18%, the fiber content was 0.4%, and the fiber length was 3 mm. This scheme was the 16 th group in the orthogonal table, and its UCS was the largest in the 16 groups, thereby verifying the correctness of the scheme obtained by range calculation. Effect of Fiber Content and Confining Pressure on Axial Strain--Deviatoric Stress Relationship of Cement Stabilized Soil  
Figure 5 shows the stress-strain curves of fiber cement soil under different confining pressures. The stress-strain curves under four different confining pressures were generally presented as follows: With the increase in the axial strain, the deviatoric stress first increases to the peak value, then decreases, and finally tends to be flat, and the curve was strain-softening. Under the same confining pressure, with the increase in the fiber content, the deviatoric stress and axial strain of the fiber-solidified body under failure were also gradually increasing. With the increase in the fiber content and confining pressure, the failure mode changed from brittle failure to ductile failure, and the residual strength increased accordingly. The test showed that friction occurs between the fiber and the soil particles mixed with cement soil, and the fiber can increase the contact surface between the fiber and the soil particles, which increased the friction resistance of the fiber cement solidified body. Therefore, the deviatoric stress increased gradually when it was damaged. In addition, the fiber connected the soil particles in the form of a network to improve the strength of the solidified body. When the fiber-solidified soil was damaged, due to the tensile characteristics of the fiber itself and the pulling effect between the soil particles, the fiber bore a part of the tensile force, thereby hindering the emergence of cracks and slowing down the failure process. With the increase in the fiber content, the deviatoric stress becomes larger, the failure cracks become smaller, and the strength was improved. With the increase in the confining pressure, the deviatoric stress and axial strain of the fiber-solidified body were also gradually increased, indicating that with the increase in the fiber content, the cracks in the soil were well filled. The network structure composed of fibers connected the soil together, which reduced the development of cracks and improves the ability to resist deformation. With the increase in the confining pressure, the connection between soil particles was closer. The disorderly fiber network structure bound the cracks of cement soil to carry out stress redistribution so that the stress distribution of fiber in cement soil was more uniform. The friction between fiber and soil particles and the tensile force of fiber itself can also improve the overall strength of the solidified body [45]. The interaction between fiber and soil particles was analyzed. As a result of the mutual restriction between fiber and soil particles in fiber-reinforced cement soil, fiber was wrapped by soil particles and hydration products, and the interface force, including normal force and tangential  
force, was generated on the interface. The normal force was formed by cohesion and extrusion force. The cohesion was related to the cohesion of the soil itself, and the extrusion force was caused by the external pressure of the soil. The tangential force was composed of friction, which was related to the normal force, and the friction increases with the increase in the normal force [29]. The stress-strain curve trend in Figure 5 was divided into four stages.