Investigation of Passive Failure Mechanism of Shallow-Buried Inclined Shield Tunnels

Face stability of shallow tunnelling in sandy soil considering unsupported length

In order to study the variation law of support pressure and instability mode of excavation face under different soil parameters, a complete set of centrifugal model seepage test device is independently developed. The results of centrifugal tests with different C/D (where C is the overburden thickness of the tunnel and D is the tunnel diameter), internal friction angles, and heights of water head show that with the increase of the retreating displacement S of the excavation surface, the support pressure P of the excavation surface can be divided into three stages: rapid decline (S < 1.5D%), slow rebound after reaching the limit support pressure Plim (1.5D% ≤ S ≤ 3D%), and gradually reaching the stable value (3D% < S). With the increase of C/D, the limit support pressure on the excavation face gradually increases and tends to be stable. For different soil properties, when C/D > 1.5, the limit support pressure on the excavation face tends to be stable. With the increase of internal friction angle, the limit support pressure decreases gradually, and its influence on support pressure can be ignored when φ > 40°. With the increase of height of water head Hw, the limit support pressure increases linearly. By establishing a numerical analysis model and analyzing the instability modes of soil under different C/D, internal friction angles, and cohesion, the instability mode of soil in front of the excavation face can have a great correlation with C/D of the soil and internal friction angle, while the influence of cohesion is minimal. With the increase of C/D, the soil changes from overall failure to local failure, the change of C/D mainly affects the height of soil arching effect and the width of the wedge below, while the internal friction angle mainly affects the width of the wedge and the instability angle of soil.

An analytical model for face stability of shield tunnel in dry cohesionless soils with different buried depth

Analysis of face stability for a shield tunnel in the inclined strata with soft upper and hard lower layers

Limit support pressure on tunnel face at different construction line slopes by slip line method

Analysis of face stability for tunnels under seepage flow in the saturated ground

Numerical investigation and prediction of the excavation face stability for river-crossing shield tunneling: An intelligent prediction model for limit support pressure

Stability of tunnel face in unsaturated sand possessing apparent cohesion: A micro-macro analytical approach

Face stability analysis of cohesion-frictional soils considering the soil arch effect and the instability failure process

Assessment of tunnel face stability subjected to an adjacent tunnel

Stability Analysis of 3D Tunnel Face of Shallow Rectangular Shield Tunnel

Investigation on overburden thickness considering face and anti-floating stability of shallow shield tunnel

Face stability analysis of shallow shield tunnels in dry sandy ground using the discrete element method

ABSTRACTWith the continuous urban development, tunnels are increasingly designed with curved alignments to avoid existing structures and to make better use of the underground space. However, these tunnels are usually subjected to complex forces, and current research on the curved tunnels face stability remains incomplete. This paper presents a detailed face stability analysis of curved tunnels, both analytically and numerically. Initially, a series of 3‐D numerical simulations are performed to investigate the spatially asymmetric failure pattern of the soil ahead of the curved tunnel face and the stress transfer mechanism of the soil arching effect during the excavation process is explored. Subsequently, based on traditional limit equilibrium methods and the results from numerical simulations, an improved wedge‐prism model and corresponding theoretical calculation formulas for the limit support pressure are proposed. The validity of the improved model is confirmed through illustrative analyses, while sensitivity analyses are conducted on the impacts of soil internal friction angle, structural depth ratio, and tunnel curvature radius on the limit support pressure. This study can aid in the calculation of the stability of the tunnel face and the limit support pressure in curved tunnel excavation.

One of the significant challenges faced in shield tunnel construction is the risk of collapse resulting from abrupt changes in soil conditions in advance of the working face, particularly within the sandy cobble stratum. This study aims to effectively manage these sudden variations and to further investigate the failure mechanisms associated with shield tunneling. The limit support pressure, instability patterns, and soil arch ranges at the excavation face under varying burial depths were analyzed using PFC3D discrete element software, specifically in relation to the shield section of the Beijing Subway New Airport Line 06 cigezhuang~1# wind shaft project. The findings of this research indicate the following: (1) The limit support pressure at the shield excavation face in sandy cobble strata increases with the burial depth ratio; however, the ratio of the limit support pressure decreases as the burial depth ratio increases. (2) A burial depth ratio threshold of 1.0–1.5 suggests that no soil arch forms in the stratum ahead of the excavation face when the burial depth ratio is below this range. Conversely, a soil arch develops when the burial depth ratio exceeds this threshold. (3) When the burial depth ratio is less than the threshold range of 1.0–1.5, the longitudinal instability zone transitions from a wedge shape to a barrel shape, extending to the surface. Conversely, when the burial depth ratio surpasses this range, the longitudinal instability zone changes from a wedge shape to a bulb shape and does not extend to the surface. (4) This paper proposes a calculation model for determining the limit support pressure of the excavation face under both shallow and deep burial conditions in the sandy cobble stratum, providing a calculation formula for the limit support pressure and establishing a reference range for the calculation parameters.