Settlement characteristics of soft soil subgrade reinforced by cement-mixed piles under traffic cyclic loading

Cement-soil mixing pile reinforcement technology has been widely employed in the construction of infrastructure such as railway and highway embankments. This study investigates composite foundations reinforced with cement mixing piles in subgrade engineering within tidal flat soft soil areas, with a particular focus on their settlement behavior under cyclic traffic loading. A three-dimensional numerical model was developed to reasonably predict the accumulation of embankment settlement under cyclic traffic loading, incorporating a single bounding surface constitutive model for clay. A systematic analysis was conducted to evaluate the reinforcing effect of cement-soil piles, as well as the influence of factors such as load amplitude, pile length, pile spacing, and pile elastic modulus on the cumulative settlement of the embankment surface. The results show that the amplitude of the traffic load significantly affects the cumulative settlement of the embankment surface. Compared with the unreinforced case, the total settlement after reinforcement is reduced by approximately 85% across different load amplitudes. Reducing the pile spacing effectively controls subgrade settlement, primarily by increasing the replacement ratio and thereby enhancing the strength of the foundation soil. Increasing the pile length and ensuring that the pile tip is embedded in a soil layer of higher strength also substantially reduces cumulative subgrade settlement. In contrast to pile spacing and length, increasing the elastic modulus of the piles has only a marginal effect on mitigating embankment settlement.