The physical and mechanical properties of grouting materials greatly affect the friction resistance and the bearing performance of a non-soil-squeezing PHC pipe pile. Orthogonal tests for four factors at five levels were carried out to optimize the proportion of the water–cement mixture by using Portland cement as a raw material and a water-reducing agent, expansion agent and early-strength agent as additives. The following conclusions were obtained: (1) Both the water–cement ratio and the dosage of water-reducing agent are positively correlated with the fluidity of the water–cement mixture and have the greatest influence on the fluidity, followed by the expansion agent and early-strength agent. The saturation point of the water-reducing agent is 1.5%. (2) The strength of the grouting body decreases linearly with the increase of the water–cement ratio, and the dosage of the water-reducing agent has no obvious effect on the strength. As the dosage of expansion agent increases, the strength of the grouting body decreases rapidly. The expansion agent mainly plays a key role in the middle and late stages of the hardening process of the slurry. Early-strength agents have a greater impact on the early strength, but less on the later strength. When the slurry is solidified for 3 h, the early-strength agent has the greatest impact on the strength with an optimal dosage of 5%. (3) The volume of the grouting body has an inverse relationship with the water–cement ratio, and the optimal amount of expansion agent is 12%. The incorporation of an expansion agent makes the volume increase of the grouting body exceed the volume shrinkage ratio caused by the hardening of the grouting body with a curing time of more than 3 days, ensuring a slight increase in the volume of the grouting body. After 3 days, even though the effect of the expansion agent is gradually weakened, it can still ensure that the volume of the grouting body does not shrink. With the increase of the amount of water-reducing agent, the volume of the grouting body gradually decreases. When the amount of water-reducing agent exceeds 1.5%, the volume of the grouting body no longer decreases. (4) The early-strength agent has almost no effect on the volume of the grouting body. When the curing time is 3 h, the water–cement ratio has the greatest influence on the volume of the grouting body, followed by the water-reducing agent, and, finally, the expansion agent. After 3 h, the water–cement ratio still has the greatest influence, and the influence of the expansion agent gradually exceeds that of the water-reducing agent. The water-reducing agent mainly affects the volume of the grouting body in the water separation stage, and the expansion agent mainly plays a role in the middle and late stages of the slurry solidification. After optimized ratio analysis, the fluidity of the water–cement mixture can be improved, the volume shrinkage ratio rate can be lowered and the early strength can be increased.

Numerical simulation is a good method for studying some academic problems in the engineering. Laboratory triaxial tests of composite soil were used widely in order to understand the stress-strain relationship. But the deformation of composite soil in laboratory triaxial tests is difficult to measure in some situation. Numerical simulation on laboratory triaxial test of composite soil with roots is carried out to see how the deformation of composite soil developed under the pressure on the specimen. Drucker-Prager constitutive model was used in the numerical simulation of finite element analysis. The results show that the numerical simulation of finite element method using Drucker-Prager constitutive model is suitable for studying the deformation development of composite soil with roots. The research results are important for understanding the deformation development of laboratory triaxial test of composite soil with roots.

Compared with pile-supported reinforced embankments, rigid-flexible pile composite foundation with geogrid reinforced cushion (RFPCFGRC) has its advantage of its economics. Piles play an important role in rigid flexible pile composite foundation with geogrid reinforced cushion. The bearing mechanics of RFPCFGRC is more complicated than that of pile-supported reinforced embankments because of addition of flexible piles. This paper discussed the diffence and the bearing mechanics of the two types of composidte foundation. The results show that addition of flexible piles has changed bearing mechanics of composite foundation and changes the load distribution among piles and soil. Soil arching degree of RFPCFGRC is larger than that of pile-supported reinforced embankments.

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