Delayed failure at the Messochora tunnel, Greece

Geodetic and extensometer data are used to shed light on the poorly known effect of delayed tunnel deformation. Four weeks after full section excavation and without any evidence of gradual strain accumulation, significant convergence of the tunnel walls and cracking of the lining occurred along a 36 m long, weak rock zone in the Messochora tunnel (Greece). Deformation extended also to nearby, previously stabilized sections. This event is in variance with predictions of an exponential-type pattern of decrease of strain accumulation based on theoretical and field evidence; it can only be explained if we accept that at the weak zone the tunnel was at a critical stability level, and that some small-scale interventions, which would otherwise have no effects, triggered a new phase of deformation transferred to nearby sections. Evidence from this tunnel indicates that, especially in weak rock zones, post-excavation stabilization may only be transient, depending on the balance between stresses and the combined strength of the rocks/lining.     

Analysis of the behaviour of a yield-control support system in squeezing rock

Recent innovations in yield-control support systems allow to increase the rate of advance when tunnelling in difficult conditions is associated with severely squeezing rock. Such systems which imply the insertion in the lining of highly deformable concrete elements are being adopted successfully in tunnelling projects using conventional excavation methods. The Saint Martin access adit excavated in a Carboniferous Formation along the Base Tunnel of the Lyon-Turin rail line is presented as a case study. Numerical analyses are discussed to compare the results of computed and measured performance of a typical monitored section and to find out possible optimizations of the support system adopted.     

Squeezing loading of segmental linings and the effect of backfilling

Overstressing of the segmental lining is one of the major hazard scenarios related to shielded TBM tunnelling in squeezing ground. The present paper deals with this specific problem, addressing the key question of the ground pressure acting upon a segmental lining installed behind a single shielded TBM. Starting with a structured discussion of the influencing factors and their interactions, the paper investigates how the type, location and thickness of the backfilling play an important role with respect to the loading of a segmental lining. Secondly, it explains how to take due account of the actual thickness of the backfilling (which is not known a priori since it depends on the deformations of the bored profile) in a numerical simulation. Thirdly, the paper advances a number of theory-based decision aids which cover the relevant range of ground parameters, initial stress, segmental lining and backfilling characteristics, thus supporting rapid initial assessments of the ground pressure acting upon a segmental lining and making a valuable contribution to the decision-making process.     

Failure mechanism of tunnel lining joints and bolts with uneven longitudinal ground settlement

To simulate the failure mechanism of tunnel segmental lining joints and longitudinal bolts under uneven longitudinal ground settlement, a numerical model with 3D lining rings and bolts was established. The loads were divided into two parts: the soil pressure around the tunnel just after construction and a displacement loading according to field measurements of uneven longitudinal ground settlement. The interactions between the lining tenons, bolts and their holes, were determined. The results indicated that the deformation of the circumferential joints consisted of opening and dislocation, but the dislocation was dominant. The progressive failure of bolts and waterproofing measures were also revealed. The evaluation of structural integrity of circumferential joint and the mitigate measures were proposed in order to ensure the operational safety of a metro tunnel.     

Mechanical analysis of circular liners with particular reference to composite supports. For example, liners consisting of shotcrete and steel sets

This paper describes a methodology for the mechanical analysis of composite supports, such as liners consisting of shotcrete and steel sets. The methodology presented here is based on an established technique of structural analysis commonly referred to as the ‘equivalent section’ approach. This technique consists in treating the composite section of a straight beam as a homogenized section of equivalent mechanical properties. The equations presented in this paper have been derived from application of the theory of elastic shells (or curved beams) and therefore are more appropriate for the analysis of circular tunnel liners. The proposed methodology for the design of liners is based on the construction of capacity diagrams, another established technique of structural analysis and concrete design that can be conveniently extended to the analysis of composite sections for tunnel liners. When applying the theory of elastic shells to derive the equations that conform to the proposed methodology, the problem of determining the mechanical response of semi-circular arches treated with the theory of thin and thick formulations has been re-visited. Observations of practical interest arising from the comparison of results obtained with both approaches are discussed.     

Analytical algorithm for longitudinal deformation profile of a deep tunnel

To investigate the longitudinal deformation profile(LDP) of a deep tunnel in non-hydrostatic condition,an analytical model is proposed in our study.In this model,the problem is considered as a superposition of two partial models,and the displacement field of the second partial model is the same as that of the concerned problem.Therefore,the problem can be solved by a model with simple boundary conditions.We obtain the solutions for the stress and displacement fields of an infinite body caused by arbitrary surface tractions on the boundary of the coming tunnel(zone inside the tunnel before excavation) by integrating the extended Kelvin solution over the boundary.The obtained stress solution is used to solve the specific surface tractions,which can satisfy the boundary conditions of the second partial model,on the boundary of the coming tunnel in an infinite body.Then,the specific surface tractions are substituted into the obtained displacement solution to solve the displacement on the wall and face of the tunnel.Therefore,the LDP can also be calculated.The proposed solution is verified by both numerical simulation and the LDP functions recommended by other researchers.The major advantage of our analytical model is that it can consider the effects of the axial and horizontal lateral pressure coefficients.It is revealed that the horizontal lateral pressure coefficient majorly affects the LDP behind the tunnel face,while the axial lateral pressure coefficient dominates the LDP ahead of the tunnel face.Furthermore,the deformation characteristics of the LDPs ahead of the face and the unexcavated core are investigated.The axial displacements of the excavation face can be used to predict the crown displacements ahead of the face.     

杭州九沙大道人行通道基坑监测分析

结合杭州九沙大道1号人行通道基坑工程实例,介绍了基坑支护方式及基坑监测方案,并对基坑开挖过程中土体深层水平位移、地表沉降、地下水位变化等内容进行了现场监测结果分析,指出钻孔灌注桩结合高压旋喷桩的基坑围护方式保证了基坑支护结构的安全、基坑开挖施工的安全以及周边环境的安全。     

Effect of cross section on critical velocity in longitudinally ventilated tunnel fires

Numerical and theoretical work was conducted to investigate the effect of tunnel cross section on critical velocity for smoke control in longitudinally ventilated tunnel fires. The results show that for small fires, the critical velocity decreases with both the increasing tunnel height and tunnel width. For large fires, the critical velocity significantly increases with the increasing tunnel height but is independent of tunnel width. Different calculation models are compared with a focus on effect of tunnel cross section. A new correlation is proposed to account for the effect of tunnel width based on the previous model.     

浅埋暗挖热力隧道内固定支架处结构抗滑移设计

本文结合工作经验 ,探讨浅埋暗挖热力隧道内固定支架处结构抗滑移设计的方法。     

Excavation and support design of the Dicle–Kralkizi water tunnel: an overview

Tunneling projects have their uniqueness in terms of engineering problems. The expertise gained from analyzing these projects establishes a sound basis for future application. This paper conveys experiences gained during the construction and support of the design of the Dicle–Kralkizi water tunnel, Turkey. Tunnel stability problems including overbreaks and surface subsidence are evaluated. An analysis of the breakdowns, factors controlling advance rate and the overall performance of tunnel are covered. The accumulated information presented here is believed to be useful and reliable for a successful tunnel excavation in similar formations.     

开挖及支护方案对隧道围岩稳定性的影响

围绕开挖及施工方案对一般质量岩石隧道稳定性的影响展开研究。考虑隧道施工过程中有无支护安装与支护安装不同时机两个因素,制定施工方案。基于Hoek-Brown准则,进行隧道施工方案的FLAC3D数值模拟,探究基于收敛约束原理的隧道围岩稳定性分析。结果表明,考虑有无支护安装这一因素对隧道纵向特性曲线的形态及特征有重要影响。在考虑无支护安装的条件下,纵向特性曲线的形态及特征在不同开挖条件下的差异并不明显。考虑有无支护安装与支护安装不同时机,对围岩安全系数的影响并不大。     

Impact of location of jet fan on airflow structure in tunnel fire

Airflow structure and its magnitude are important for smoke management in longitudinally ventilated tunnels. This paper presents a sensitivity study by Computational Fluid Dynamics technique, which considers different dimensions, orientations and the natures of fire source. Its impact on the airflow velocity and temperature distribution is investigated with various locations of fan group activated. A theoretical correlation between the distance of active fan group from the fire source and the upstream velocity is proposed individually for pool fire and solid fire. It reveals that the nature of the fire source imposes adverse effect on the upstream air velocity and the airstream pattern over the entire tunnel. The upstream velocity remains fairly constant when the active fan group is located 200 m or beyond from a vehicle fire that occupies a significant cross-sectional area of tunnel.     

基础灌浆引起地层抬动的机理分析与控制方法

从控制好地层抬动是灌浆施工中避免造成破坏的关键入手,通过工程实例对各种原因产生的地层抬动机理进行了分析,提出了对地层抬动的控制方法,解决了地层抬动对施灌区域内的水工建筑物造成不同程度破坏的问题。     

Squeezing rock conditions at an igneous contact zone in the Taloun tunnels, Tehran-Shomal freeway, Iran: a case study

Squeezing rock conditions at the contact zone of an andesitic-basaltic body and tuff country rocks in the Taloun tunnels were investigated and analyzed. Evaluation of the rock mass properties illustrates the fact that they were significantly reduced at the contact zone, especially when wet. Detailed monitoring and measurements of tunnel-wall convergence at the contact zone in the Taloun service tunnel, during the 10 months following excavation and installation of initial support, prior to installation of heavy support, showed greater than 3% of the normalized tunnel closure. This confirms moderate squeezing conditions at the contact zone. The measured displacement was even higher than that of the fault zone in which deformation was decreased during the first month and eventually stabilized. Similarly, numerical modeling of the deformation at the contact zone not only confirmed a higher value of the tunnel convergence but also demonstrated the reduction of in situ stress and development of plastic zones across the contact zone. These data are also believed to account for the squeezing condition at the contact zone. It is expected that this condition will be significantly increased in the main road tunnels due to the fact that these tunnels are twice as wide as the service tunnel. Therefore, proper and timely support must be applied. Numerical analysis of the support at the contact zone showed that the stress due to bending moment is greater than that of the axial forces on the lining. This calls for certain support measures in the form of permanent lining and two layers of steel bars to compensate for the tensile stress exertion on the lining.     

Numerical 3D simulation of a longitudinal ventilation system: Memorial Tunnel case

In this work, a numerical 3D simulation of a longitudinal ventilation system (LVS) is developed to analyze the fire behaviour inside a road tunnel. The numerical modelling reproduces the Memorial Tunnel, a two-lane, 853 m long road tunnel, used for experimental purposes. On this tunnel, 98 full-scale fire ventilation tests with different ventilation systems were conducted, constituting the first significant experimental approach to analyze fire incidents inside road tunnels. A total number of 24 reversible jet fans were installed in groups of three, nearly equally spaced over the length of the tunnel, and cantilevered from the ceiling of the tunnel.

The validation of a numerical model is developed in the present paper. For that purpose, the behaviour of the smoke generated during a fire incident inside a road tunnel is predicted and compared with previous experimental data collected in the Memorial Tunnel Project. The smoke evolution and the performance of the LVS is simulated with a commercial code, FLUENT, which allows 3D unsteady simulations of the Navier–Stokes equations for multispecies mixtures of gases. A sufficient mesh density was introduced for the spatial discretization in order to obtain accurate results in a reasonable CPU time. Hence, typical ratios between total number of cells and the overall tunnel length were employed in the modelling. As a result, good agreement was achieved in all the tested cases, defining an accurate methodology to predict the performance of a LVS in case of fire inside a tunnel.