Research on the Bearing-Deformation Characteristics of Prestressed Concrete Thin-Walled Pipe-Pile Cement-Soil Cushion-Composite Foundation

Graded gravel or gravel is commonly used as the cushion material in composite foundations reinforced with prestressed concrete thin-walled pipe pile. For the road section without drainage requirements in highway engineering, it is proposed to replace gravel or the gravel cushion with cement-soil cushion, which can greatly reduce the project cost, but its engineering characteristics need to be further studied. Field test, numerical calculation and theoretical analysis were carried out on the composite foundation of prestressed concrete thin-walled pipe-pile cement-soil cushion. The results show that when the cement-soil cushion reaches a certain thickness, the settlement-control effect of composite foundation is better than that of gravel cushion. With the increase in cement-soil cushion thickness, cement content, pile length and pile-cap size, the pile-soil stress ratio increases, and the pile-soil settlement decreases. The larger the pile spacing is, the larger the pile-soil settlement is. Conversely, larger pile spacing leads to increased settlement. Among the influencing factors, the thickness of the cement-treated soil cushion is identified as the most significant parameter affecting the load-bearing and deformation behavior of the composite foundation. Beyond this apparent diminishing-return thickness, further increases in cushion thickness yield diminishing returns in settlement control. The settlement-control effect of double-layer reinforced-cushion-composite foundation is better than that of single-layer reinforced cushion. The position of reinforcement layer also has an important influence on the bearing deformation characteristics of composite foundation. Under the condition of single-layer reinforced cushion, placing the reinforcement at the bottom of the cushion proves more effective than at the top. From the perspective of settlement-control effect and economy, there is an optimal value for the ratio of pile spacing to pile-cap size, which is about 0.5. The above research results offer experimental data and practical engineering references for prestressed concrete thin-walled pipe-pile composite foundations with cement-soil cushions under the geological and loading conditions examined in this work.