The current research primarily focuses on the impact of full-ring expansion on tunnel safety, but the relationship between local expansion of the surrounding rock and initial water content is rarely studied yet. Therefore, this paper analyzes the mechanics and deformation characteristics of a tunnel passing through an expansive mudstone area in a tunnel project in China. The analysis considers different local expansion areas and the initial water content of the surrounding rock. The research findings indicate that the local expansion of the tunnel's vault and sidewall has the most significant impact on the deformation range of the surrounding rock. Compared to other expansion conditions, the deformation difference can reach a maximum of 156 mm. The order of expansion conditions leading to the development of plastic zone volume in the surrounding rock is as follows: full-ring expansion > vault expansion > local vault expansion > sidewall expansion > invert expansion. When the initial water content reaches a certain level, the expansion effect becomes less significant due to the upper limit of the surrounding rock's expansion capacity. However, an increase in water content will cause the surrounding rock to soften and intensify the expansion of the deformation range. The local expansion of the surrounding rock not only increases the bending moments on the preliminary lining at the directly affected by the expansive force but also significantly impacts other expansion areas. The local expansion of the vault and sidewall greatly influences the stability of the secondary lining, resulting in some areas having a safety factor lower than the allowed value. However, from the perspective of overall tunnel safety, the secondary lining still provides a certain safety margin.

There are countless engineering disasters induced by expansive strata in the tunnel project. Nowadays, most of the research focuses on the basic characteristics of expansive rock and soil, while the influence about coupling buried depth and different initial water content of surrounding rock on the tunnel lining is still rarely involved. Based on the principle of temperature and humidity equivalence, this paper discusses the behavior of rock as well as the mechanical properties of lining under the interaction of different buried depth and initial water content by using FLAC(3D) numerical simulation. It was found that the initial water content shows an obvious effect on the evolution about the plastic area of rock compared with the buried depth of the tunnel. For shallow tunnels with a water content of less than 10 %, the plastic zone of the vault will penetrate to the surface after water absorption and expansion. Under the coupling effect, buried depth inhibits the development of the plastic zone to a certain extent. For different initial water contents of the surrounding rock, the displacement of the tunnel adds with the burial depth. The swelling of rock will significantly reduce the safety of the primary support, and when the burial depths of the tunnel increase to 150 m, the security coefficients of some primary support structures are less than 2, which does not meet the need in standard. The safety factor of secondary support is mainly influenced by the expansion force, not the ground pressure (represented by buried depth). The findings may be valuable reference for the analysis as well as evaluation of the security as well as stability of tunnels in expansive mudstone.

In combination with the field monitoring data, PLAXIS3D finite-element software was used to numerically model the pull-pile supporting structure in a deep foundation pit. This structure was compared to the single-row pile support structure in order to learn more about the pull-pile supporting structure's force and deformation characteristics and how it works. The study found that the cumulative horizontal displacement curves of the supporting piles are integrated into an upward convex shape. The bendingmoment curve of the front-row piles presents an inverted S shape, and the bendingmoment curve of the back-pull piles presents a bow shape. The back-pull-pile effect can improve the unbalanced distribution of positive and negative bending moments in single-row piles by changing the stress condition of the soil. In other words, the pull-pile supporting structure has good safety and serviceability and can well control the lateral displacement of the foundation pit.

There is limited research on the interaction mechanism between the buckling load of the side pile top and the soil pressure behind pile (SPP) with the side pile. As the side pile serves as a crucial component of the lining structure in the metro, using the pile -beam -arch (PBA) method, it plays a vital role in maintaining the mechanical stability and deformation control of the station's lining system. Based on the Guangzhou Metro Line 11 project, this paper delves into the impact of mechanical characteristics and deformation of the side pile using the PBA method. It considers various factors such as different buckling loads, including horizontal load of arch (HLA), vertical load of arch (VLA) and SPP and offers corresponding construction suggestions. Our findings indicate that the lateral displacement and deformation of the side pile are primarily influenced by the HLA. The optimal HLA value stands at 1200kN. As the HLA increases, the side pile undergoes a transformation from a forward -inclined deformation mode to a belly distension deformation mode when moving towards the station's interior. The influence of HLA on bending moments about the side pile surpasses that of axial force. The VLA exerts a more significant effect on vertical settlement of the side pile, yet its impact on lateral pile body deformation is minimal. An increase in HLA significantly impacts the axial force of the side pile, but has minimal effects on bending moments. The SPP holds significant influence on the stability of the side pile; hence, it is recommended to implement appropriate lining measures to guarantee stability when dealing with exceptionally high SPP values.