To investigate the impact of changes in end-bearing conditions, resulting from shield tunneling, on the bearing capacity of an upper cement-soil pile composite foundation, this study is conducted based on a specific section of the Zhengzhou Metro Line 5 where shield machines cut through cement-soil piles. According to the principle of similarity, a reduced-scale model test of a single cement-soil pile within a composite foundation was designed for laboratory testing. Based on this, a corresponding finite element analysis model was established. By comparing the results from the reduced-scale model test and numerical simulations, the variation patterns of side resistance and end-bearing resistance of the cement-soil pile composite foundation were analyzed as the pile characteristics changed. Studies indicate after the lower part of the cement-soil pile composite foundation undergoes shield tunneling while maintaining a constant vertical load above, there is primarily a redistribution of stress within individual piles, characterized by a transformation between side resistance and end-bearing resistance to balance the upper load. Simultaneously, the neutral point of the side resistance of the cement-soil pile composite foundation moves downward, and its position relative to the pile length is less than that observed in the case where only the pile length is shortened. The change in the length of the cut pile significantly influences the development of side and end-bearing resistances; the contribution of side resistance decreases with an increase in the cut length, whereas the extent to which end-bearing resistance is mobilized slightly increases as the cut length grows.

The experiments of lateral unloading were conducted on the Yellow River alluvial silt under different consolidation confining pressures and water contents using a true triaxial instrument. Its mechanical properties under plane strain state of lateral unloading were studied. The applicability of the classical strength criterion to the silt was compared and analyzed based on the test results. The results show that: The stress-strain curves of silt show a weak hardening type under plane strain state of lateral unloading. The curves show brittle failure at a low water content, and plastic failure at a high water content, with a failure strain between 1% and 6%. The unloading strength is affected by confining pressure significantly, whereas the water content has a relatively small impact on it. The initial change of small principal strain during unloading is small, and the small principal strain begins to grow almost linearly when the axial strain reaches about 1%. The medium principal stress is greatly affected by the confining pressure, and it decreases rapidly in the early stage of unloading. The value tends to stabilize and does not decrease when the axial strain reaches 0.5% to 1%. The medium principal stress coefficient decreases rapidly and then increases slowly with the increase of axial strain. It is between 0.27 and 0.37 when the sample is damaged. The Lade-Duncan strength criterion could predict the unloading strength of silt well under plane strain state of lateral unloading.