Three-dimensional centrifuge and numerical modeling of the interaction between perpendicularly crossing tunnels

TLDR

Combine all content per label. Background: two sentences: "Tunnel driving inevitably induces changes in stress and deformation in the ground, which could cause ultimate and serviceability problems to an adjacent tunnel. Maybe: "Tunnel driving alters ground stress and deformation, potentially causing ultimate and serviceability problems in adjacent tunnels, yet the effects of induced stress on existing tunnels and crossing‑tunnel interaction remain poorly understood." That covers both. Purpose: The sentence labeled Purpose, Mechanism: "In this study, a series of three-dimensional centrifuge tests were carried out to investigate the responses of an existing tunnel in sand to the excavation of a new tunnel perpendicularly below it." So Purpose: "The study investigates the response of an existing tunnel in sand to the excavation of a new tunnel perpendicularly below it using three‑dimensional centrifuge tests." That is fine.

Abstract

Tunnel driving inevitably induces changes in stress and deformation in the ground, which could cause ultimate and serviceability problems to an adjacent tunnel. The effects of induced stress on an existing tunnel and crossing-tunnel interaction are still not fully understood. In this study, a series of three-dimensional centrifuge tests were carried out to investigate the responses of an existing tunnel in sand to the excavation of a new tunnel perpendicularly below it. Three-dimensional tunnel advancement was simulated using a novel technique that considers the effects of both volume and weight losses. This novel technique involves using a “donut” to control volume loss and mimic soil removal in-flight. To improve fundamental understanding of the stress transfer mechanism during the new tunnel advancement, measured results were back-analyzed three-dimensionally using the finite element method. The maximum measured settlement of the existing tunnel induced by the new tunnel constructed underneath was about 0.3% of tunnel diameter, which may be large enough to cause serviceability problems. The observed large settlement of the existing tunnel was caused not only by a sharp reduction in vertical stress at the invert, but also by substantial stress transfer of overburden pressure at the crown. The section of the existing tunnel directly above the new tunnel was compressed vertically because the incremental normal stress on the existing tunnel was larger in the vertical direction than in the horizontal direction. The tensile strain and shear stress induced in the existing tunnel exceeded the cracking tensile strain and allowable shear stress limit given by the American Concrete Institute.