Unexpected tunnelling volume losses in the Westmister area, London

Proceedings of the ICE - Geotechnical Engineering, 2005

Géotechnique, 2012

Recent studies on London Clay have identified a number of different units in the geological profile, and have highlighted the role of soil structure in mechanical behaviour. In fact, structure is the dominant factor determining the differences in the mechanical response of different units. In the paper, numerical analyses simulating the undrained excavation of a tunnel in St James's Park are presented. London Clay behaviour is characterised by a kinematic-hardening structured soil model incorporating structure and stiffness degradation. The parameters and initial conditions are based on a careful calibration that takes into account the presence of different units within the London Clay formation and the different degrees of soil structure. The analyses performed result in a very satisfactory reproduction of the magnitude and patterns of short-term surface and subsurface displacements, as well as pore pressures. The paper concludes with a discussion of the results in the context ...

CRC Press eBooks, 2023

In a land-scarce country like Singapore, it is inevitable that demands for new space has led to the creation of complex underground networks. As our underground network becomes increasingly built up, the relationship between underground infrastructures in the urban areas also becomes progressively intricate, which presents multifaceted challenges in underground tunnel construction where potential occurrence of ground settlement is the main drawback. With the volume loss induced by tunnel excavation as the main determinant of ground settlement, this paper presents the studies on the volume loss caused by bored tunnelling in different geological conditions in Singapore with a variation of tunnel boring machines (TBM) used in some of the recent Metro line projects such as Downtown Line (DTL), Thomson-East Coast Line (TEL) and Circle Line 6 (CCL6). Back analysis on trough width parameter from the available data is also discussed. The main findings of this study also provide references for impact assessment of bored tunnelling in future projects.

Quarterly Journal of Engineering Geology and Hydrogeology, 2012

In the design of major construction works, the better the ground conditions are known, the more control there is on the assessment of risks for construction, contract and personnel, and ultimately on final costs. Understanding of the ground conditions is usually expressed as a conceptual ground model that is informed by the results of desk study and of dedicated ground investigation. Using the GSI3D software, a 3D geological model (a model comprised of attributed solid volumes, rather than of surfaces) can be constructed that exactly honours geologists' interpretations of the data. The data is used in its true 3D position. The 3D model of faulted Lambeth Group (Palaeogene) strata in the area of the proposed new Crossrail Farringdon underground station, in central London, has several types of benefit. These include enabling optimum use of available GI data, including third party data, with confidence. The model provides an understanding of the local geological structure that had not been possible using other commonly-used methods: in particular, it shows the likely distribution of numerous water-bearing coarse deposits and their faulted offsets, which has potentially significant effects on groundwater control. The model can help to target ground investigation, constrain design, and control risk. The design of major construction works requires an understanding of the local ground conditions. In general, the better the ground conditions are known, the more control there is on final costs and schedules and the less uncertainty there is in assessing risk, safety, design and finance. This is especially true for tunnelling works, which may require relatively early commitment to large expenditure on construction equipment, such as tunnel boring machines. A new underground Farringdon Station (Fig. 1) is proposed in east-central London as part of the Crossrail project. This project is building an east-west rail system linking central London and Canary Wharf with the Channel Tunnel rail link, with Heathrow Airport, and with Berkshire, Essex and North Kent.

Geomechanics and Tunnelling, 2021

When tunnelling with a TBM (Tunnel Boring Machine) in rock and soil, mostly the machine is described and often reduced to a slogan. Such descriptions say little about geotechnical processes at the tunnel face that are key to the success of tunnel driving and must be considered when selecting a tunnelling system. In soil tunnels the tunnel face must be safely supported and extracting material must be possible. For a slurry shield the slurry must not escape and pressure must act on the face. In the literature mostly bentonite content is considered. With an Earth‐Pressure balance machine the soil has to have characteristics that it can be remoulded and transformed in a mass of adequate consistency with mechanical means, adding water and additives such that this mass can support the face and be extracted. Long‐term experience shows that the fine content and polymers are also important factors. Flow channels (pores) in open gravel may be clogged, and the face supported by seepage forces....

HAL (Le Centre pour la Communication Scientifique Directe), 2015

˜The œJournal of Engineering and Exact Sciences, 2024

The research described in this paper deals with the impact of shallow tunneling on surface settlements in urban areas. The study focuses on carrying out a numerical analysis and a parametric geotechnical study to investigate the effects of tunnel excavation on the surface ground, particularly with regard to distortion and potential damage to structures above the tunnel. To carry out the study, the researcher used a finite element method (FEM) software package called Plaxis. This software is commonly used for geotechnical analysis and allows simulating and analyzing the subsurface conditions in Algiers underground in the context of excavating a shallow tunnel. The New Austrian Tunnelling Method (NATM) excavation method was chosen for the study. The results of the numerical analysis are presented in terms of displacements. The results indicate that ground flow has a significant influence on ground movement, probably contributing to surface settlement. However, the effect of tunnel excavation on the lowering of the water table and Young's modulus (a measure of soil stiffness) is relatively small in comparison. The research provides valuable information on the potential impacts of shallow tunneling in urban areas and the factors that play a crucial role in determining the extent of ground movement and surface settlement. By using numerical analysis and conducting a parametric geotechnical study, and gives valuable insights into the potential impacts of shallow tunnelling in urban areas and the factors that play a crucial role in determining the extent of ground movements and surface settlements. By using numerical analysis and conducting a geotechnical parametric study, and contributes to a better understanding of the behavior of the ground during tunnelling operations in Algiers. The findings can be helpful in designing future tunnelling projects to mitigate potential risks to structures and infrastructure located above the tunnels.

2011

In this extended abstract the subsidence geometry d ue to tunnelling is described. Firstly, empirical expressions, based on the unit volume of subsidence and on the distance between the plane of symmetry of the tunnel and the inflection points of the theoretical curve of subsidence, are presented. Then, an analytical expression for e stimating the displacement field is discussed, considering the effects of ovalization and pure con traction of the tunnel. In order to analyze the influence of ground variabi l ty and its spatial correlation properties on the estimates of ground settlements caused by tunne lling, one has to resort to the Random Field Theory and to the statistical characterization of t he geotechnical parameters. The estimated values of statistical measures are then presented. Two software tools are developed to analyze the set tlements caused by tunnelling. The first one is based on the Monte Carlo method and on the analy tical expressions herein presented. It is applie...

Engineering Geology, 2015

A tunnel for the High Speed Train (HST) was constructed in Barcelona with an Earth Pressure balance (EPB) Tunnel Boring Machine (TBM). The tunnel crosses Barcelona and passes under some famous landmarks such as the Sagrada Familia and the Casa Milà. Both monuments are UNESCO world heritage sites and a committee appointed by the UNESCO acted as external observers during the construction. Concerns about soil settlements and the hydrogeological impacts of the construction were raised. These concerns were addressed during the design stage to forestall any unexpected events. The methodology consisted of 1) characterising the geology in detail, 2) predicting the impacts caused in the aquifer, 3) predicting the soil displacements due to water table oscillations produced by the construction, and 4) monitoring the evolution of groundwater and soil settlements. The main estimated impact on groundwater was a moderate barrier effect. The barrier effect, the magnitude of which matched the predictions, was detected during construction. The monitoring of soil settlements revealed short and long term movements. The latter movements matched the analytical predictions of soil displacements caused by the groundwater oscillations. This paper proposes a realistic procedure to estimate impacts on groundwater during tunnel construction with an EPB. Our methodology will considerably improve the construction of tunnels in urban areas.