Mechanical Characteristics and Optimum Design of SMW Construction Method for a Comprehensive Pipe Gallery in a Water-Rich Weak Stratum

The K0+080-K0+275 bid section of the underground comprehensive pipe corridor on Wanxin Road in Binhai New City located in Fuzhou was considered in this work. The mechanical properties and optimal design of the soil mixing wall (SMW) construction method piles (steel-cement mixing piles) in the comprehensive pipe corridor in the water-rich, weak stratum were studied. In the K0+080-K0+275 bid section of the comprehensive pipe gallery, different construction parameters of the steel-cement-soil mixing piles were tested through pile tests. The construction parameters of the SMW construction piles were as follows: water-cement ratio of 1.3 and cement content of 20%. The finite element software MIDAS-GTS NX was used to establish a mechanical model of the SMW construction method piles. The variations in mechanical characteristics, such as the horizontal displacement of SMW construction method piles under different supporting pile diameters, steel layouts, steel sizes, and supporting axial forces, were analyzed. The optimal design of the SMW construction method piles was also determined. Results revealed that when the pile diameter of the SMW construction method increased from 0.55 m to 0.85 m, the horizontal displacement of the pile body decreased by 28.9%. The horizontal displacement of the pile body could be effectively controlled by increasing the pile diameter. Increasing the size of the flange and web of the section steel had little effect on the deformation of the foundation pit. The flange was sensitive to the deformation of the supporting structure because it was on the stressed side. The different layout forms of the steel section exerted a great influence on the deformation of the foundation pit. The maximum horizontal displacement of the pile body for the type of steel close insertion was 18.4% less than that for the plug-one-jump-one insertion type. Increasing the supporting pre-added axial force effectively reduced the deformation of the envelope structure, and adopting the value of 50%-80% of the designed axial force was reasonable. The K0+080-K0+275 bid section of the Wanxin Road underground comprehensive corridor was determined to be supported by φ650@450 cement-soil five-axis mixing pile interpolated with HM500×300×11×18 section steel, and the layout of the section steel adopts the plug-one-hop-one type. The on-site monitoring data of the optimal construction plan were in accordance with the change law of the numerical simulation and were successfully used in the underground comprehensive pipe corridor project. Ideal results were achieved.