The synchronous concentric construction of steel pipe-cement soil composite pile consists of steel pipe pile, inner cement-soil, and outer cement-soil. Its axial bearing behavior is closely related to the interactions between the three components and the surrounding soils, and its bearing and deformation mechanisms are very complex. Based on site excavation tests, the inner cement-soil and steel pipe pile were simplified into equivalent modulus solid piles by area. An elastic failure model was used to simulate the interaction between the steel pipe pile and the outer cement soil interface. The deformation of the outer cement soil and surrounding soil was considered as shear deformation, and the relationship between the pile end resistance and settlement was analyzed using a bilinear model. Taking into account the deformation characteristics of the steel pipe pile, cement-soil, and surrounding soil, the axial bearing capacity and deformation calculation formula of this new composite pile were derived, and the methods for determining the values of relevant parameters were provided. The feasibility of the above proposed method was verified through comparative analysis of engineering examples.

Shield tunneling method is widely used in subway tunnel construction because of its advantages such as not affecting ground traffic, high mechanization degree and short construction period. However, the problems of cracking and damage caused by uneven rising of segments are often encountered in the construction process of shield method, which affects the normal use of tunnel. However, the research on the mechanism and theoretical calculation of shield tunnel segment floating is relatively rare. In this paper, the floating mechanism of segments in the initial floating stage of shield tunnel is analyzed deeply, and the corresponding theoretical calculation formulas of upward buoyancy/anti-buoyancy and buoyancy are proposed. The theoretical calculation results are compared and analyzed with engineering examples. The results show that: The initial floating of the segment can be divided into two stages: rapid rising and slow rising, in which the rising amount of the rapid rising stage accounts for about 80%~90% of the total rising amount. The theoretical calculation value of the total floating amount is greater than the monitoring value, but the calculation error of the floating amount per ring is relatively stable, the theoretical calculation formula presented in this paper can provide reference for the calculation of the floating amount of the actual segment.