Article

The face stability of slurry-shield-driven tunnels

Tunnelling and Underground Space Technology (Impact Factor: 1.59). 04/1994; 9(2):165-174. DOI: 10.1016/0886-7798(94)90028-0

ABSTRACT During the excavation of a tunnel through soft water-bearing ground, a temporary support is often required to maintain the stability of the working face. In a slurry shield, this support is provided by a pressurized mixture of bentonite and water. Slurry-shield tunnelling has been applied successfully worldwide in recent years. Under extremely unfavorable geological conditions, however, face instabilities may occur. This paper aims at a better understanding of the mechanics of face failure when using a bentonite slurry support. The complex interrelations between the various parameters (shear strength and ground permeability, suspension parameters, slurry pressure, geometric data of the tunnel, safety factor) are studied. Attention is paid to the time-dependent effects associated with the gradual infiltration of slurry into the ground ahead of the tunnel. Related topics, such as the stand-up time, soil properties and the effect of advance rate, are discussed quantitatively.

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    • "In this research, the value of grouting pressure is chosen as 150 kN/m 2 based on the measured data. The face support pressure is applied to avoid collapse of the soil at face of excavation [14] [15]. In case of Western Scheldt tunnel construction , the face pressure distribution was varying during excavation process. "
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    ABSTRACT: In this research, Finite Element (FE) method is applied to simulate the shield supported mechanized excavation of Western Scheldt tunnel in the Netherlands. Both 2D and 3D numerical models are created to predict the system behavior. Sensitivity analysis and parameter identification techniques are utilized to calibrate and validate the model based on field measurement. The mechanical behavior of the soil is modeled by an advanced elasto-plastic model, namely Hardening Soil model correlating small strain stiffness (HSS). Global sensitivity analysis is carried out in this paper to evaluate the relative sensitivity of model response to each input parameter. Thereafter, a parameter identification technique (back analysis) is employed to find the optimized values of the selected parameters. To accomplish this, the computationally expensive FE-model is replaced by a meta-model in order to reduce the calculation time and effort. Moreover, a soft soil constitutive model based on the modified Cam-clay model deals with primary compression of fine grained soils, is assigned to the clay layer to further improve the numerical prediction of system behavior. Due to the importance of model subsystems, such as face pressure and volume loss, the sensitivity of model response to subsystems has been evaluated. The results show that optimized parameters obtained via back analysis make the numerical simulation capable to well predict the ground settlement.
    Computers and Geotechnics 09/2015; 69:601-614. DOI:10.1016/j.compgeo.2015.07.003 · 1.65 Impact Factor
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    • "In this research, the value of grouting pressure is chosen as 150 kN/m 2 based on the measured data. The face support pressure is applied to avoid collapse of the soil at face of excavation [14] [15]. In case of Western Scheldt tunnel construction , the face pressure distribution was varying during excavation process. "
    [Show abstract] [Hide abstract]
    ABSTRACT: In this research, Finite Element (FE) method is applied to simulate the shield supported mechanized excavation of Western Scheldt tunnel in the Netherlands. Both 2D and 3D numerical models are created to predict the system behavior. Sensitivity analysis and parameter identification techniques are utilized to calibrate and validate the model based on field measurement. The mechanical behavior of the soil is modeled by an advanced elasto-plastic model, namely Hardening Soil model correlating small strain stiffness (HSS). Global sensitivity analysis is carried out in this paper to evaluate the relative sensitivity of model response to each input parameter. Thereafter, a parameter identification technique (back analysis) is employed to find the optimized values of the selected parameters. To accomplish this, the computationally expensive FE-model is replaced by a meta-model in order to reduce the calculation time and effort. Moreover, a soft soil constitutive model based on the modified Cam-clay model deals with primary compression of fine grained soils, is assigned to the clay layer to further improve the numerical prediction of system behavior. Due to the importance of model subsystems, such as face pressure and volume loss, the sensitivity of model response to subsystems has been evaluated. The results show that optimized parameters obtained via back analysis make the numerical simulation capable to well predict the ground settlement.
    Computers and Geotechnics 07/2015; 69(7):601-614. · 1.65 Impact Factor
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    • "Figs. 3–6 show results for TBM diameters D ¼ 1, 2 and 3 m and cover to diameter ratio C=D ¼ 0:5, 1, 2, 3 and 4. In the model by Anagnostou and Kovári (1994) the yield strength of the slurry s F influences the results. Results given here are for the minimal slurry Fig. 2. Definition of pressure distribution over penetration zone and excess pore pressures. "
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    ABSTRACT: Face stability of microtunnelling TBMs is an important aspect for a safe and controlled project execution. Lack of proper face support can lead to sudden collapse with resulting large settlements. Guidelines for minimal and maximal support pressures in most codes do not take the infiltration of bentonite suspension in coarser soils into account. Infiltration lowers the effectiveness of the face support. In loose sands infiltration can lead to excess pore pressures and induce liquefaction, with possible catastrophic consequences. This paper investigates the influence of infiltration and gives some guidelines for a proper selection of bentonite suspensions based on soil gradation.
    Tunnelling and Underground Space Technology 11/2014; 46. DOI:10.1016/j.tust.2014.09.015 · 1.59 Impact Factor
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