Design of urban tunnels in soft ground using TBM

Yolanda Alberto Hernández, Elías Antolín Tavera Gutiérrez

In the proceedings of: GEO2011: 64th Canadian Geotechnical Conference, 14th Pan-American Conference on Soil Mechanics and Geotechnical Engineering, 5th Pan-American Conference on Teaching and Learning of Geotechnical Engineering

Session: Buried Structures & Subsurface Systems

ABSTRACT: This paper presents a state of the art of urban tunnel design using a tunnel boring machine with earth pressure balance focusing on the major issues concerning this subject. Analytical and numerical methods used to compute surface settlements, face-support pressures and lining loads are summarized. Parametric studies were conducted to define the influence of soil properties on the lining loads design. Appropriate observations about numerical design were done. Specific features regarding urban environment, ground conditions and TBM technology are summarized and appraised, such as overburden, behavior of structures due to tunnel induced subsidence, groundwater, soil properties and grouting stabilization. Relevant conclusions regarding planning, design and construction of tunnelling are pointed out.

RESUMEN: Este artículo presenta un estado del arte del diseño de túneles en ambiente urbano, construidos con máquina tuneladora y sistema EPB, enfocándose en los problemas más importantes de este tema. Se resumen los métodos analíticos y numéricos usados para calcular los asentamientos superficiales, las presiones de frente y las cargas en el revestimiento. Se realizaron estudios paramétricos para definir la influencia de las propiedades del suelo en el diseño de las cargas sobre el revestimiento. Se realizan observaciones importantes sobre el diseño numérico. Se resumen y analizan características específicas sobre el comportamiento urbano, las condiciones de suelo y la tecnología de la TBM, tales como sobrecarga, comportamiento de estructuras debido a los asentamientos provocados por el túnel, piezometrías, propiedades de los suelos y estabilización de la lecha. Finalmente, se señalan conclusiones relevantes sobre la planeación, el diseño y la construcción de túneles. INTRODUCTION Ground behaviour is one of the most important features in urban tunnelling, since stability and deformations may cause severe issues. When selecting the tunnelling system for soft soil conditions, the use of tunnel boring machines (TBM) with earth pressure balance (EPB) system, becomes a major advantage to overcome the main concerns regarding ground behaviour. There are special aspects to be considered when using a TBM system: a) shallow overburden due to cost and functionality, b) structures on ground surface, c) foreign objects in ground such as drainpipes, foundations, anchors, etc., d) alignment and constraints regarding material transport and TBM access. Appropriate planning and geotechnical exploration may help to prevail over these difficulties. Design of TBM tunnels must take into account the previous aspects; the main problems regarding design are summed up in the following points: 1) Measures to control ground behavior 2) Loads on the liner and structural design 3) Prediction of ground displacements The existing methods to assess these three focuses will be discussed in the next sections. In addition, geology, changing conditions in ground due to lenses, boulders, etc., and presence of groundwater must be considered for tunnel design in order to select the best construction method and reduce risk scenarios. Soft soils represent a particularly difficult condition for tunnel construction. In Mexico City, as in many other cities, soil is characterized by high water contents and high plasticity, since the city is located in the central part of the basin where a lacustrine environment prevails. Low shear strength, high compressibility, consolidation and creep, just to mention some issues, pose a major problem regarding this kind of soils and importance must be attached to them. Although there is a lack of major regulations regarding soft soil tunneling, a large amount of research has been conducted and provides a better insight into this problem. This paper presents a review of the main features of soft soil tunneling with TBM-EPB. 1 GROUND BEHAVIOUR When using a TBM with EPB, measures to control ground behaviour refers to tunnel heading stability and evaluation of face pressures. Equilibrium condition is reached when the ground in the working chamber of the EPBS, achieves the maximum density for the acting pressure and the volume of the

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