This was made possible by the use of a spatial discretization technique. The 3rd training course tunnelling in urban area prague, 45th may 2007 face stability in conventional tunnelling and epb soil conditioning d. Therefore, the design procedure for tunnels, as compared to aboveground structures, is much more dependent on such factors as the site situation, the ground characteristics, and the excavation and. Assessing face stability conditions for shallow tunnels in soft ground through the tunnel stability factor spyridon konstantis1 1 arup geotechnics and tunnelling, uk abstract the contribution discusses the use of the tunnel stability factor tsf for the preliminary. Tunnel face stability analysis in soft ground in urban. The correct evaluating of face pressure to avoid face instability depends on various factors, such as cohesion, friction angle and permeability of the ground, type of the machine, advance rate, unit weight of slurry or conditioned soil, tunnel diameter, overburden, and. The main methods for face stability analysis mostly focused on finite element method, limit equilibrium method, and numerical simulation method.
This method can be employed to define the safety factor and its corresponding critical failure mechanism for a given tunnel. Tunnel face stability investigation by means of 3d. Face stability analysis of circular tunnels driven by a pressurized shield. Analysis of face stability during excavation of doubleotube shield tunnel yuyouyang, 1 qinghongzhou, 1,2 honganli, 1 xueganghuang, 1 andxiaomingtu 1 school of engineering and technology, china university of geosciences beijing, beijing, china haikou forest farm, kunming, yunnan, china.
The first is the effective stress acting on the tunnel face calculated by upper bound solution, and the other is the seepage force calculated by numerical analysis under the condition of steadystate groundwater flow. We investigate the effects of the support pressure distribution and of the free unsupported span on the stability of the tunnel face by means of limit equilibrium computations, which are based upon the so. Stability of the tunnel face stability of the tunnel face is a function of many variables of which the more important appear to be. Face stability analysis of shield tunnel using slip line. In underground excavations the geotechnical evaluation of stability is fundamental. Upperbound solutions for face stability of circular. Several normalized charts are also presented for quick evaluation of tunnel face stability.
The sufficient support pressure is essential to guarantee the safe construction of shield tunnel. The stabilization of the excavation face of a shallow tunnel in difficult ground conditions p. These failures highlight the need for research into tunnel stability and improvement of how tunnel support is designed in practice. In addition, we provide normalized diagrams, which allow for a quick assessment of the stability of the tunnel face. The effect of seepage force on tunnel face stability with pipe roof reinforcement was studied based on the kinematic method of limit analysis. Uncertainty modelling and sensitivity analysis of tunnel face stability wolfgang fellina, julian kingb, ansgar kirscha, michael oberguggenbergerc, a unit of geotechnical and tunnel engineering, university of innsbruck, innsbruck a6020, austria bbreath research unit, austrian academy of sciences, a6850 dornbirn, austria cunit of engineering mathematics, university of. Research article upper bound solution for the face. In this study, two factors are simultaneously considered for assessing tunnel face stability. The contribution of horizontal arching to tunnel face stability. Tunnel, tunnel face, prereinforcement, longitudinal fiberglass dowel, presupport. Failure modes and face instability of shallow tunnels. Evaluation of the tunnel face stability through a ground. The construction of the intake tunnel of the darlington nu clear generating station is analyzed using threedimensional elastoplastic finite element analysis.
The analyses concentrate on the stability at the face as well as the circumference of tunnels excavated in high in situ horizontal stress conditions. Key factors in the face stability analysis of shallow tunnels. This chapter aims to investigate stability of a tunnel face in weak rock masses at the ultimate limit state in the context of the kinematical approach of limit analysis. Probabilistic evaluation of tunnel face stability in. For simplification, a tunnel face with an elliptic cross section is taken into account. Uncertainty modelling and sensitivity analysis of tunnel. Experimental investigation of face stability of shallow. Oreste politecnico di torino, italy abstract the stability of the excavation face of shallow tunnels excavated in difficult ground conditions is at present a.
Centrifuge model test on the face stability of shallow tunnel gregor idinger pelin aklik wei wu ronaldo i. The face stability of slurryshielddriven tunnels article pdf available in tunnelling and underground space technology 92. When it is not possible to ensure excavation face stability in natural conditions, it is in fact necessary to intervene with remarkably costly reinforcement operations. Stability assessment of tunnel face in a layered soil 473using upper bound theorem of limit analysis fig. The obtained ub solution is rigorous but its criticality depends on the constructed kinematically admissible velocity field. Face stability analysis of circular tunnels driven by a. Maintaining tunnel face stability is a key construction consideration in shield tunnel project, especially the tunnel below the river bed. Based on the limit equilibrium of soil in front of.
In order to stabilise the face in conventional tunnel ling, reinforcement of the ground ahead of the face. Face stability of tunnels in soft rocks request pdf. A shield tunnel under compressed air is considered which implies that the applied pressure is uniformly distributed on the tunnel face. The overburden pressure above the tunnel face is the counterforce of foundation, which can be obtained from reference 3.
Upperbound analysis on the face stability of a non. Tunnel design criteria common design guidelines 2015 c26. Increase of cohesionahead of tunnel face face improvement using grouting control of preconvergence by face pretreatment athens metro numerical analysis in the design of urban tunnels lecture outline 1. Two sets of failure mechanisms in the context of the limit analysis theory with. The effect of pore water pressure on tunnel face stability. This paper is an investigation of face stability on a smallscale tunnel model in a geotechnical centrifuge. The aim of tunnel face stability analysis is to ensure that the supporting pressure is sufficient to pretend the soil mass collapse in front of the tunnel face. For an approximate distribution of the hydraulic head in the ground around the tunnel face, we derive a closedform solution for the necessary face support pressure. This paper focuses on the face stability analysis of doubleotube shield tunnel. Some aspects on the collapse at tunnel face are investigated for different overburden. Oggeri ita aites world tunnel congress 2007 prague. The stabilization of the excavation face of a shallow.
In this work, the different failure models of face instability of the shallow tunnels were established based on the upperbound theorem of limit analysis for the formation of clayey and sandy soils, respectively, and the analytical equations for determining the limit support force for the face stability were also derived. Stability assessment of tunnel face in a layered soil. The water in river will reduce the tunnel face stability, and need greater. Face stability in conventional tunnelling and epb soil. The studies revealed that the existence of groundwater may seriously affect the face stability. Analysis of limit support pressure on tunnel face below. Stability analysis of shallow undrained tunnel heading using finite element limit analysis a dissertation submitted by mr.
This leads to a more reliable calculation of the required support pressure. A new calculation procedure is illustrated in this study for the analysis of the effect on the face stability in shallow tunnels of the following key factors. Table 4 and figure 3 summarize the results of all the investigated cases. Pdf the face stability of slurryshielddriven tunnels. Geotechnical stability analysis of san francisco tunnel. Face support pressure calculations for shield tunnelling in soft ground version 102016 page 6 of 64 list of variables a m2 crosssectional area of the silo aa m2 area aa bb m2 area bb b m length the silo c knm2 cohesion. Influence of pipe roof reinforcement on face stability of.
As mentioned before, many works adopted an equivalent circular shape for the stability design of a tunnel face. At the end of the paper, the influence of anisotropic permeability on tunnel face stability is also discussed, showing that the isotropic model leads to an overestimation of the necessary tunnel face pressure for anisotropic soils. Alexander bell in fulfilment of the requirements of bachelor of engineering civil october, 2016. Based on the kinematic method of limit analysis and the shear strength reduction technique, the threedimensional model for expressing the tunnel face stability with pipe roof reinforcement was established. This section aims to discuss the influence of the cross section of a tunnel face on the safety factor. Analysis of face stability during excavation of doubleo. Recommendations for face support pressure calculations for. Tunnel stability norwegian geotechnical institute ngi. Stability of the excavation face in shallow tunnels and in poor ground is at present a relevant problem in tunnelling.
The consequence of such unexpected failures with respect to risk to life and the trust of the public in tunnelling technology are so important that the profession needs to improve its methods and rethink its practice. The stability of a tunnel face with a free span and a non. Based on a real case biella tunnel, a parametric study has been developed to show the influence of the several elements that affect the tunnel face stability in shallow tunnels. The excavation process may lead to excess pore pressures in front of the tunnel boring machine, which lower the stability of the face. Research article analysis of face stability during.
Influence of seepage on tunnel stability pdf free download. This kind of analysis is significant to ensure the safety of workers and reduce the influence on the surrounding environment. Cornejo gave out a formula to determine the stability number of the tunnel face in clay based on the limit equilibrium method. It has been found that analytical stability solutions generally underestimate the required face support pressure and excessive deformation will take place in the ground near the tunnel heading when these solutions are used. The sparse polynomial chaos expansion is employed to perform a probabilistic analysis of the tunnel face stability in the spatially random soils.
Experimental investigation of face stability of shallow tunnels in sand. Facestability analysis of tunnels excavated below groundwater considering. For the face stability of a tunnel in undrained clay, the continuous velocity field proposed by mollon et al. Tunnelling methods in urban areas to control settlements 3. The required face support pressures are compared to the analytical solutions available from the literature. The tunnel to be built will help to solve the transport problem in lima city due to the population growth, which was the reason for the stability analysis of two alternative proposals a and b in the portals and tunnels, using software rocplane, swedge and.
Experimental investigation of face stability of shallow tunnels in sand ansgar kirsch to cite this version. View enhanced pdf access article on wiley online library html view download pdf for offline viewing. Tunnel face stability under seepage flow conditions. Water pressure in river will influence the stress redistribution of tunnel face in the process of excavating the tunnel. These excess pore pressures have been incorporated in a new stability model, that can also deal with heterogeneity of the soil. By making use of symmetry, half of the tunnel cross section was considered. The effect of a forepole umbrella system on the stability. Results for tunnel face stability investigation based on these results, it can be concluded, that the tunnel face is stable against plastic failure. The evaluation of the stability of the excavation face is an important aspect in the design of a tunnel.
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