• Title/Summary/Keyword: solid-fluid coupling

Search Result 53, Processing Time 0.017 seconds

Face stability analysis of large-diameter underwater shield tunnel in soft-hard uneven strata under fluid-solid coupling

  • Shanglong Zhang;Xuansheng Cheng;Xinhai Zhou;Yue Sun
    • Geomechanics and Engineering
    • /
    • v.32 no.2
    • /
    • pp.145-157
    • /
    • 2023
  • This paper aims at investigating the face stability of large-diameter underwater shield tunnels considering seepage in soft-hard uneven strata. Using the kinematic approach of limit upper-bound analysis, the analytical solution of limit supporting pressure on the tunnel face considering seepage was obtained based on a logarithmic spiral collapsed body in uneven strata. The stability analysis method of the excavation face with different soft- and hard-stratum ratios was explored and validated. Moreover, the effects of water level and burial depth on tunnel face stability were discussed. The results show the effect of seepage on the excavation face stability can be accounted as the seepage force on the excavation face and the seepage force of pore water in instability body. When the thickness ratio of hard soil layer within the excavation face exceeds 1/6D, the interface of the soft and hard soil layer can be placed at tunnel axis during stability analysis. The reliability of the analytical solution of the limit supporting pressure is validated by numerical method and literature methods. The increase of water level causes the instability of upper soft soil layer firstly due to the higher seepage force. With the rise of burial depth, the horizontal displacement of the upper soft soil decreases and the limit supporting pressure changes little because of soil arching effect.

Hydro-Mechanical Modelling of Fault Slip Induced by Water Injection: DECOVALEX-2019 TASK B (Step 1) (유체 주입에 의한 단층의 수리역학적 거동 해석: 국제공동연구 DECOVALEX-2019 Task B 연구 현황(Step 1))

  • Park, Jung-Wook;Park, Eui-Seob;Kim, Taehyun;Lee, Changsoo;Lee, Jaewon
    • Tunnel and Underground Space
    • /
    • v.28 no.5
    • /
    • pp.400-425
    • /
    • 2018
  • This study presents the research results and current status of the DECOVALEX-2019 project Task B. Task B named 'Fault slip modelling' is aiming at developing a numerical method to simulate the coupled hydro-mechanical behavior of fault, including slip or reactivation, induced by water injection. The first research step of Task B is a benchmark simulation which is designed for the modelling teams to familiarize themselves with the problem and to set up their own codes to reproduce the hydro-mechanical coupling between the fault hydraulic transmissivity and the mechanically-induced displacement. We reproduced the coupled hydro-mechanical process of fault slip using TOUGH-FLAC simulator. The fluid flow along a fault was modelled with solid elements and governed by Darcy's law with the cubic law in TOUGH2, whereas the mechanical behavior of a single fault was represented by creating interface elements between two separating rock blocks in FLAC3D. A methodology to formulate the hydro-mechanical coupling relations of two different hydraulic aperture models and link the solid element of TOUGH2 and the interface element of FLAC3D was suggested. In addition, we developed a coupling module to update the changes in geometric features (mesh) and hydrological properties of fault caused by water injection at every calculation step for TOUGH-FLAC simulator. Then, the transient responses of the fault, including elastic deformation, reactivation, progressive evolutions of pathway, pressure distribution and water injection rate, to stepwise pressurization were examined during the simulations. The results of the simulations suggest that the developed model can provide a reasonable prediction of the hydro-mechanical behavior related to fault reactivation. The numerical model will be enhanced by continuing collaboration and interaction with other research teams of DECOLVAEX-2019 Task B and validated using the field data from fault activation experiments in a further study.

Numerical modelling of Fault Reactivation Experiment at Mont Terri Underground Research Laboratory in Switzerland: DECOVALEX-2019 TASK B (Step 2) (스위스 Mont Terri 지하연구시설 단층 내 유체 주입시험 모델링: 국제공동연구 DECOVALEX-2019 Task B(Step 2))

  • Park, Jung-Wook;Guglielmi, Yves;Graupner, Bastian;Rutqvist, Jonny;Park, Eui-Seob
    • Tunnel and Underground Space
    • /
    • v.29 no.3
    • /
    • pp.197-213
    • /
    • 2019
  • We simulated the fault reactivation experiment conducted at 'Main Fault' intersecting the low permeability clay formations of Mont Terri Underground Research Laboratory in Switzerland using TOUGH-FLAC simulator. The fluid flow along a fault was modelled with solid elements and governed by Darcy's law with the cubic law in TOUGH2, whereas the mechanical behavior of a single fault was represented by creating interface elements between two separating rock blocks in FLAC3D. We formulate the hydro-mechanical coupling relation of hydraulic aperture to consider the elastic fracture opening and failure-induced dilation for reproducing the abrupt changes in injection flow rate and monitoring pressure at fracture opening pressure. A parametric study was conducted to examine the effects of in-situ stress condition and fault deformation and strength parameters and to find the optimal parameter set to reproduce the field observations. In the best matching simulation, the fracture opening pressure and variations of injection flow rate and monitoring pressure showed good agreement with field experiment results, which suggests the capability of the numerical model to reasonably capture the fracture opening and propagation process. The model overestimated the fault displacement in shear direction and the range of reactivated zone, which was attributed to the progressive shear failures along the fault at high injection pressure. In the field experiment results, however, fracture tensile opening seems the dominant mechanism affecting the hydraulic aperture increase.