This paper presents observed arching-induced ground deformation and stress redistribution behind braced excavation using the top-down construction method. The soil properties around the excavation were determined by laboratory and field tests. The ground deformation, soil displacement vector, strain path, principal strain, maximum shear strain, lateral earth pressure, pore water pressure, and effective stress path are presented based on the measured data. The majority of soil behind the wall is under volumetric expansion, indicating consolidation, creep behavior, or a combination of both. Besides, two periods of increases in pore pressure are observed, due to stress transfer from the lower to the upper parts (i.e., soil arching effect). The deep inward movement of the wall and the nearby soil accounts for the distribution of lateral earth pressure acting on the wall. The soil located behind the area of maximum wall deformation and adjacent to the wall, as well as the soil below the excavation base intersected by the shear plane, is in an active stress state. The lateral earth pressure at 5 m from the left excavation wall showed minimal changes, due to the combined effects of soil arching from lateral excavation and shield tunneling.

To assess the stability of coral sand foundation in complex environments, the undrained monotonic and cyclic shear tests were conducted in the laboratory. The test results indicate that the coral sand exhibits pronounced inherent anisotropy in the vertical direction. Under complex consolidation conditions, significant stress-induced anisotropy can also be observed. With increasing generalized shear strain (gamma g), both the generalized monotonic and cyclic shear modulus (Ggm, Ggd) exhibit a decreasing trend irrespective of consolidation ratio (kc) and inclinations of major principal stress (alpha c). Additionally, a strong linear relationship is evident between Ggm and Ggd, suggesting a consistent reduction pattern of Gg for various loading modes. The investigation on the inclination of the failure line (phi FL) for monotonic and cyclic shear is also conducted. The test results show that consolidation conditions have minimal influence on phi FL during monotonic shear, but exert a significant impact on phi FL during cyclic shear. A novel index called the consolidation parameter (eta) is proposed to quantitatively assess the relationship between kc, alpha c and phi FL. The average values of phi FL for cyclic shear increase with increasing eta, indicating the non-failure zone of coral sand during undrained cyclic shear will shrink with higher values of kc and alpha c.

The back pressure saturation method, a widely adopted and efficient technique for enhancing soil saturation, can nonetheless introduce notable deviations in soil strength parameters. Standard spherical glass bead sand was utilized for conducting benchmark consolidated undrained (CU), consolidated drained (CD), and dry sample tests. Real-time accurate measurements and comparative analyses of deviatoric stress and pore pressure (or volumetric deformation) data were performed. Utilizing the p '-q q stress path diagram, the influence of back pressure application on soil mechanical properties was significantly demonstrated and quantitatively analyzed, thereby preliminarily elucidating the mechanism of back pressure influence. The setting of back pressure significantly impacts the results of CU tests, where the shape of pore pressure development governs the shape of deviatoric stress development, ultimately influencing the determination of strength parameters. However, the stress path remains constrained within the framework of the revised Cam-Clay model. The mode and rate of pore pressure development are primarily constrained by the magnitude of the back pressure setting and the relative density of the sample. As back pressure increases, the potential change in pore pressure also increases, resulting in a greater amplitude of deviatoric stress change. Similarly, a higher relative density leads to a faster development rate of pore pressure and an increased rate of deviatoric stress. Under identical initial conditions, the development of pore pressure in CU tests exhibits high consistency with the development of volume deformation in CD tests, revealing the common essence of the sample's volumetric deformation potential across different boundary conditions. A quantitative prediction formula for the residual strength of CU tests at the critical state is presented. The residual pore pressure value can be initially quantified based on the relative density and back pressure measurements, subsequently leading to the determination of the residual strength of CU.