Upper‐Bound Finite Element Adaptive Analysis of Plane Strain Heading in Soil with a Soft Upper Layer and Hard Lower Layer

Abstract

This paper investigates the stability of a rectangular tunnel face affected by surcharge loading in soil with a soft upper layer and hard lower layer using upper-bound finite element methods with a plastic-dissipation-based mesh adaptive strategy (UBFEM-PDMA). Seven different positions for the soil interface are selected to study this problem. The upper bounds on the ultimate surcharge loads σs are presented in terms of dimensionless stability charts. The σs increases with tunnel depth, and it increases when the position of the soil interface moves up along the tunnel face. The failure mechanism primarily involves a wedge-shaped zone around the tunnel face and two slip lines originating from the top and bottom of the tunnel face, and it is mainly influenced by three factors, i.e., the position of the soil interface, the soil properties, and the tunnel depth. In contrast to the failure mechanism for uniform soil, multiple slip lines exist in the tunnel face in soil with a soft upper layer and hard lower layer. The results compare reasonably well with those in the literature and those from the numerical method.

Towards an error indicator-based h-adaptive refinement scheme in kinematic upper-bound limit analysis with the presence of seepage forces

“…To achieve a fully automatic adaptive analysis, a novel termination criterion ensure that the mesh refinement automatically stops is thus proposed. Unlike previous adopted mesh refinement scheme (Nguyen-Xuan et al, 2016;Zhang et al, 2019a;Zheng and Yang, 2022) with a continuously significant growth in the refined elements, the later refinement criteria ensures that the total number of refined elements gradually increases initially and then continues to decrease with adaptive step. For this reason, the error indicator and refinement criteria proposed by Dezfooli et al (2022) are also preferred in this study and thus incorporated into the UBFEM.…”

“…Each of these indicators has its unique set of advantages and limitations. Among these indicators, the most commonly used technique is to determine a minimal set of active element that needs to be refined through a prescribed adaptive refining coefficient (Dörfler, 1996;Martin, 2009;Nguyen-Xuan et al, 2016;Zhang et al, 2019a;Zheng and Yang, 2022).…”

Influence of shield tunnel construction on ground surface settlement under the condition of upper-soft and lower-hard composite strata

“…Large-scale settlement remarkably challenges shield tunnel construction. Therefore, the influence of shield tunneling on strata under the condition of upper-soft and lower-hard composite strata should be investigated [29][30][31][32][33]. Deng et al [34] took Shenzhen Metro Line 2 as an engineering example, conducted a construction risk analysis under the conditions of upper-soft and lower-hard composite strata, and obtained the specific tunneling parameters through slag soil improvement and tool change with pressure; consequently, they provided valuable data for the theoretical study of shield tunneling under complex geological conditions.…”

Risk Analysis and Control Measures for Slurry Shield Tunneling Diagonally under an Urban River Embankment

“…Compared with clayey strata, the mechanical properties of sandy strata are more complex and less stable [4]. Instability is easily generated during surface excavation, and even surface collapses may occur [5].…”