Tunnelling in difficult conditions

The scope of the research project is to address the following subjects, with reference to mechanised excavation:
 
 (1) Tunnelling in "swelling and/or squeezing conditions". The objectives of the study on the swelling behaviour in tunnels is devoted to verify the effectiveness of the new approach set up by the research group to simulate the swelling phenomenon which arises in a swelling ground, after stress release due to tunnelling. To this end, the results of the new method will be compared to available monitoring data and real scale tests. In particular, a research programme carried out by the Geotechnical Group at the University of Cambridge will provide real scale tests data of a small diameter tunnel excavated in a reconstituted swelling clay. Also data from real case studies will be used for comparison. The study will be carried out both by the experimental and the numerical point of view. Barla (1999) triaxial tests will be performed, by means of the experimental apparatuses available, in order to characterise the swelling behaviour of geo-materials. The aim is to assess the relationship between the pore overpressure developed during the shearing phase and the volumetric strain at the end of the drained phase. This law will be implemented into a commercial numerical code in order to simulate the swelling behaviour occurring at the tunnel contour.
 With reference to the study of the Chaotic Complex Tectonised Clay Shales (CCTCS), the research project is to be carried out both by the experimental and theoretical point of view. The availability of a new High Pressure Triaxial Apparatus (HPTA) will allow to perform new test on specimens obtained from drilling at great depth (about 150 m). Samples from the Osteria access adit (along the high speed railway line Bologna-Florence) will be tested in order to assess the influence of higher stresses and different geologic conditions. Special attention will be devoted to the influence of the material fabric and to the time-dependent behaviour. For mathematical modelling, the role played by the two components (swelling and squeezing) into the overall mechanical behaviour will be studied. The triggering conditions of swelling and squeezing behaviour do not imply the concurrent development of both phenomena. With this respect, great importance must be given to the boundary conditions which apply to the work carried out. Typical visco-elastic plastic and more complex models will be considered in order to assess the required complexity of the law which is able to represent the mechanical behaviour satisfactorily.
 
 (2) Tunnels in overstressed rock masses.
 The main intent is to analyse the response of TBM excavated tunnels in hard rocks under high in situ stresses, when the failure process is dominated by stress-induced fractures leading to spalling and/or strain bursts. The use of continuum, equivalent continuum and discontinuum models will be considered. Also to be studied, in the framework of discontinuum modelling, is the adoption of damage laws for the rock blocks and joint-laws for the discontinuities, to be implemented by using the Distinct Element Method (DEM). Reference will be made to case histories of tunnels excavated in the Ambin Formation (Gneiss and Michaschists), where laboratory and in situ data are available, in conjunction with TBM performance monitoring.
 
 (3) Tunnelling under "difficult hydrogeologic conditions".
 The aim of the work is to develop the discontinuum modelling methods for the study of the fluid flow in fractured rock masses, focusing on the Distinct Element Method (DEM). Considering that the equivalent continuum approach is neither appropriate or realistic for simulation of fluid flow in fractured rock masses (only for preliminary analysis in terms of average hydraulic behaviour), the interest is centred upon discontinuum modelling.
 Nonetheless the discontinuum modelling is not being used as extensively as continuum methods and is considered to be a relatively new and “not yet proven” numerical technique to apply for analysis and design in rock engineering projects.
 The case study, to be analysed with discontinuum modelling, is the San Pellegrino Tunnel (Frasnadello and Antea), in Brembana valley (San Pellegrino Terme - BG), which was excavated in a region with complex hydrogeological conditions also for the presence of valuable mineral water springs.

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Publications

2009
  1. The Mechanical Behaviour of Clay Shales and implications on the Design of Tunnels
    Article

    M. BONINI; D. DEBERNARDI; BARLA M.; G. BARLA
    ROCK MECHANICS AND ROCK ENGINEERING
    Vol.42(2) pp.28 (pp.361-388) ISSN:0723-2632 DOI:10.1007/s00603-007-0147-6

2008
  1. Metodi innovativi per la costruzione di gallerie in rocce spingenti
    Article

    BARLA G.; BARLA M
    INGEGNERIA FERROVIARIA
    Vol.12 (pp.1-15) ISSN:0020-0956

  2. Numerical simulation of the swelling behaviour around tunnels based on special triaxial tests
    Article

    BARLA M.
    TUNNELLING AND UNDERGROUND SPACE TECHNOLOGY
    Vol.23 pp.14 (pp.508-521) ISSN:0886-7798 DOI:10.1016/j.tust.2007.09.002

2004
  1. Characterisation of Italian clay shales for tunnel design
    Article

    BARLA G; BARLA M.; BONINI M
    INTERNATIONAL JOURNAL OF ROCK MECHANICS AND MINING SCIENCES
    Elsevier
    Vol.41 pp.1 ISSN:1365-1609 DOI:10.1016/j.ijrmms.2003.01.001

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