Study on the Stress and Deformation Characteristics of Shield Tunneling Through Mining Tunnel Structure

Abstract

In the construction of shield crossing existing mined tunnel without load, it is imperative to develop corresponding design standards that reflect actual engineering force characteristics to ensure the successful completion of tunnel construction. This research uses The MIDAS-GTS finite element software to facilitate the creation of a numerical model of the shield structure for an air-push-over mine tunnel project in Changsha, China, investigating the stress field’s evolution during shield construction, and calculating the maximum positive and negative bending moments and maximum axial forces for different structures and other force states under various construction conditions. This study's findings informed the design and construction optimisation of the shield tunnelling empty-push method. The outcomes of this numerical simulation led to several key findings: (1) The soil density exerted a significantly greater impact on the internal forces of the initial support structure than both the tunnel depth and soil Poisson's ratio. Additionally, a sudden shift in internal forces occurred within the 300-350 mm range when the lining thickness was altered. (2) Factors such as the tunnel depth, soil density, soil Poisson's ratio μ, and lining thickness have a similarly influenced internal forces of the segment and the initial support. Notably, the backfill layer thickness significantly affected the segment’s maximum axial force causing an abrupt change of approximately 300 mm. (3) Under the shield machine equipment’s weight constraint, it is essential to control the guide rail’s thickness, to prevent it from becoming overly large.

Assessment of the Service Status of the Tunnel Structure Adjacent to the Station

“…Evaluating the dependability of connections within the segment structure involves considering several factors, which encompass water seepage at pipe joints, the extent of joint openings, and pipe misalignment. These variables play a pivotal role in categorizing the overall operational state of the pipe connections, aligning with wellestablished guidelines [8]. Figure 2 offers a comprehensive overview of the operational conditions of segment connections.…”

“…In accordance with the guidelines delineated in the "Assessment Code for Shield Tunnel Structural Integrity" (DGTJ-08-2123-2013) [8], the allowable allowance for joint openings is specified at 6 mm. After thorough inspection, it became evident that the longitudinal joints in all up-line segments displayed openings ranging from 1-2 times the allowable limit.…”

“…The evaluation of the structural condition of the tunnel encompasses two core aspects: the assessment of segment structures and the examination of segment connections. In accordance with the guidelines provided in the "Code for Assessment of Shield Tunnel Structural Integrity" (DGTJ-08-2123-2013) [8], a systematic categorization of the operational status of the intermediate tunnels in the impacted region has been meticulously executed, allowing for a comprehensive evaluation of the tunnel's structural soundness.…”

“…Furthermore, the tunnel's surroundings are characterized by a moderately humid environment. In strict accordance with the specified standards [8], the environmental impact is classified as Class B. Consequently, the assessment of the component's operational condition is determined by the presence of cracks and water leakage in the pipe segments, as depicted in figure 1. Evaluating the dependability of connections within the segment structure involves considering several factors, which encompass water seepage at pipe joints, the extent of joint openings, and pipe misalignment.…”

“…Figure 2 presents a comprehensive representation of the operational conditions of segment connections, taking into account factors such as water seepage, joint openings, and pipe misalignment. The classification system employed allows for a comprehensive assessment of the structural soundness of these connections, in accordance with the guidelines [8].…”