<p>Heavily squeezed deformation generally occurs in the tunnels excavated in deep soft rock masses due to high in-situ stress, resulting in boundary encroachment and compromising normal operations. A pilot tunnel and cross-sectional re-profiling technique is an effective measure to control the large deformation and release stress in the surrounding rock. Considering the strain-softening and geometric nonlinearity characteristics of rock mass, a finite strain solution of a circular tunnel in the strain-softening rock mass is derived according to the initial coordinate system. Using the mapping relationship between the current and initial coordinates of the surrounding rock, a numerical procedure for the ground response of re-profiling tunnels based on the equivalent re-profiling radius is developed. The proposed solutions are verified by the analytical and numerical finite strain solutions of circular tunnels in strain-softening rock masses. For a pilot tunnel method-constructed tunnel, a larger pilot tunnel radius results in a smaller support pressure, and vice versa. Once the secondary support stress is determined, the appropriate radius of the advanced pilot tunnel can be determined, which can economically reduce the tunnel squeezed deformation. As the ratio between the radius of the pilot tunnel and the designed tunnel <InlineEquation ID="IEq1"> <EquationSource Format="TEX">$R_{k} /R_{d}$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>R</mi> <mi>k</mi> </msub> <mo stretchy="false">/</mo> <msub> <mi>R</mi> <mi>d</mi> </msub> </mrow> </math></EquationSource> </InlineEquation> increases from 0.1 to 0.8, the relative reduction ratio of the tunnel wall displacement increases from 1.86 to 15.5%. The proposed solution is applied to the Haba Snow Mountain Tunnel project using the advanced pilot tunnel construction method, and the predicted displacement is in good agreement with that of the field-test result, with a relative error of 5.8%. The proposed solution can well reflect the re-profiling response of a heavily squeezed tunnel and can provide a theoretical basis for the structural design optimization and stability control of tunnels encountering heavily squeezed displacement.</p>

Re-profiling Response of Heavily Squeezed Tunnels in Strain-Softening Rock Masses: Numerical Solution and Pilot Tunnel Application

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发表日期：

2025年11月14日

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Kai Huang,
Qiang Zhang,
Peinan Wu,
Yapeng Li,
Shihao Yan

摘要

Heavily squeezed deformation generally occurs in the tunnels excavated in deep soft rock masses due to high in-situ stress, resulting in boundary encroachment and compromising normal operations. A pilot tunnel and cross-sectional re-profiling technique is an effective measure to control the large deformation and release stress in the surrounding rock. Considering the strain-softening and geometric nonlinearity characteristics of rock mass, a finite strain solution of a circular tunnel in the strain-softening rock mass is derived according to the initial coordinate system. Using the mapping relationship between the current and initial coordinates of the surrounding rock, a numerical procedure for the ground response of re-profiling tunnels based on the equivalent re-profiling radius is developed. The proposed solutions are verified by the analytical and numerical finite strain solutions of circular tunnels in strain-softening rock masses. For a pilot tunnel method-constructed tunnel, a larger pilot tunnel radius results in a smaller support pressure, and vice versa. Once the secondary support stress is determined, the appropriate radius of the advanced pilot tunnel can be determined, which can economically reduce the tunnel squeezed deformation. As the ratio between the radius of the pilot tunnel and the designed tunnel $R_{k} /R_{d}$ $R_{k} / R_{d}$ increases from 0.1 to 0.8, the relative reduction ratio of the tunnel wall displacement increases from 1.86 to 15.5%. The proposed solution is applied to the Haba Snow Mountain Tunnel project using the advanced pilot tunnel construction method, and the predicted displacement is in good agreement with that of the field-test result, with a relative error of 5.8%. The proposed solution can well reflect the re-profiling response of a heavily squeezed tunnel and can provide a theoretical basis for the structural design optimization and stability control of tunnels encountering heavily squeezed displacement.