39 research outputs found
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Twin-tunnelling-induced ground movements in clay
Modern tunnelling methods aim to reduce ground movements arising from the construction process. In clay strata the usual method of construction is by tunnel boring machine, which allows close control of the tunnelling process; however, any movements have the potential to cause damage to existing structures at, and below, the ground surface. The construction of underground rail systems often comprises two tunnels running in opposite directions. Common practice for assessing construction-generated movements around these tunnels is to make predictions based upon individual tunnel construction and utilise superposition to generate a total deformation profile. This approach does not take into account the strain- or stress-dependent effects between tunnel constructions. A delay may result in unanticipated ground movements generated by the construction of the second tunnel. The effect of this delay on the ground movements arising between the first and the second tunnel construction process was investigated in a series of plane strain centrifuge tests. The ground movements at and below the surface were monitored and were assessed against superposition-based predictions for surface settlement with the outcomes highlighting some inconsistencies. A procedure for predicting both surface and subsurface vertical settlement profiles in the plane transverse to the advancing tunnels in clay is suggested
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Apparatus for centrifuge modelling of twin-tunnel construction
In urban areas it is common for pairs of tunnels to be used as a method for building rapid transit systems. Driven by
an increasing population and demand for services, tunnels are more widespread in their use than at any previous time. Construction of any form of tunnel causes ground movements which have the potential to damage existing surface and
sub-surface structures. Modern tunnelling practice aims to reduce these movements to a minimum but there is still a requirement for accurate assessments of possible damage to structures resulting from settlements. For tunnels driven in clay, superposition of settlement predictions made by considering a single tunnel is an accepted method used to estimate movements around pairs of tunnels. Previous research, particularly numerical studies, has indicated that this may not necessarily be sufficient. In this paper a series of centrifuge model tests designed to investigate settlements related to twin-tunnel construction are described. The development of the experimental apparatus for sequential twin-tunnel construction with variable centre-to-centre spacing and volume loss is described in detail
Time dependent deformations during tunnelling and stability of tunnel faces in fine-grained soils under groundwater
Numerical analysis of the support system in the transition zone of the Esfahan subway project
This paper presents the design and 3D numerical modeling of the temporary support system for the twin tunnels in the transition zone of the Esfahan subway project. Ground movements caused by tunneling beneath urban areas can have a significant impact on adjacent structures and therefore require consideration when choosing the excavation method and the type of support system. Due to the old buildings in the historical city of Esfahan, this research requires parametric studies for the use of simulation techniques. This paper focuses on 3D stability analysis and design of the support system required to control the critical strain and ground movement due to excavation of the transition area of the twin tunnels in the Esfahan subway project. A numerical model is developed to estimate the excavation effects on the critical strain and ground settlement and also the effect of reinforcement measures. In the 3D numerical model, a constitutive law characterized by the time-dependent stiffness and strength of the shotcrete is employed. Results show that the suggested support is sufficient to control the settlement and critical strain due to tunneling. Comparison between the 2D model prediction and the results of corresponding 3D model indicates that the conformity between 2D and 3D analysis results decreases in the transition region. One of the most useful methods to determine the induced seismic loads, the use of time-history dynamic analysis is usually done for major projects. In this paper, for the twin tunnels of subway, Fast Lagrangian Analysis of Continua (FLAC) software is used for this purpose. © 2014 Saudi Society for Geosciences