Reinforcement and settlement calculation of pressure-cast-in-situ fluid-solidified soil pile composite foundation

To improve the foundation bearing capacity and reduce the differential settlement of the expressway, a new type of pressure-cast-in-situ fluid-solidified soil pile (PFSSP) is proposed to reinforce the composite foundation. Based on laboratory tests, an industrial solid-waste-based soil curing agent is developed to form pumpable fluid-solidified soil (FSS), and the mechanical properties of the resulting FSS are characterized. Using spraying, expanding, and injection construction technologies, the PFSSP is formed from pumpable FSS, and field tests are conducted on the PFSSP composite foundation to verify the reinforcement effect. Considering the strengthening effect of ribbed plates on the pile skin friction and the end-bearing resistance characteristics between the double frustums and the surrounding soil, the load–settlement calculation method for PFSSP composite foundations is established. The results show that the curing agent at 14% for the industrial solid-waste-based soil can be effectively applied in engineering construction. Comparing with the cement mixing pile (CMP), the material consumption of PFSSP decreases by 51 % under the same ultimate bearing capacity of composite foundation, and the average cement consumption per meter decreases by 42 %. Considering the price of raw materials and the construction coordination fee of the general contractor, the average cost per meter was reduced by 5 %. The comparison of calculated values with measured curves shows that the relationship between the pile head load and displacement of the PFSSP composite foundation is well described by the present method.