Time dependent deformations during tunnelling and stability of tunnel faces in fine-grained soils under groundwater |
| |
Authors: | Roger Höfle Jochen Fillibeck Norbert Vogt |
| |
Institution: | 1. Zentrum Geotechnik, Technische Universit?t München, Baumbachstr. 7, 81245, Munich, Germany
|
| |
Abstract: | The measures required for driving a tunnel below the groundwater table depend on the permeability of the soil. In coarse-grained,
highly permeable soils additional measures, for example compressed-air support combined with a reduction of the permeability
of the soil, e.g. induced by grouting, are necessary. Compared to this, it is possible to do without such measures in fine-grained,
cohesive soils because of the increased short-term stability of the tunnel face under undrained conditions. In this publication
the results of 3-dimensional finite-element calculations are presented to show the influence of the permeability of the soil
and also the rate of the tunnel driving on the deformations around the tunnel as well as on the ground surface. The calculated
deformations can furthermore be considered as an indicator for the time dependent stability of the tunnel face due to a higher
redistribution of stresses and by that an enlargement of the plasticized zone. Usually the stability of the tunnel face is
reduced by the presence of water because of the flow of water towards the tunnel. In low permeable soils undrained conditions
prevail immediately after an excavation step. In this case relatively high stability-ratios may occur. The stability of the
tunnel face will be reduced with increasing time until reaching the lower boundary of possible values, possibly leading to
failure. If calculations are done under the assumption of drained conditions, the real stability of the tunnel face during
construction may substantially exceed that of the calculated one. On the other hand, if calculations are done for undrained
conditions, the effective stability may lie on the unsafe side 10]. There is therefore a big demand to optimize the method of investigating deformations around the tunnel, so as to ensure
a safe tunnel excavation on the one hand and to guarantee a cost-effective process on the other. In this paper the tunnelling
process is modelled by a step-by-step excavation under atmospheric conditions. The soil is described by a material model which
distinguishes between primary and unload-reload stress paths and also accounts for stress-dependent stiffness parameters.
The failure criterion is described by the Mohr-Coulomb criterion that considers cohesion, friction angle and angle of dilatancy. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|