Abstract
Abstract The construction of shallow tunnels in urban areas requires a prior assessment of their effects on the existing structures. In the case of shield tunnel boring machines (TBM), the various construction stages carried out constitute a highly three-dimensional problem of soil/structure interaction and are not easy to represent in a complete numerical simulation. Consequently, the tunnelling- induced soil movements are quite difficult to evaluate. A 3D simulation procedure, using a finite differences code, namely FLAC3D, taking into account, in an explicit manner, the main sources of movements in the soil mass is proposed in this paper. It is illustrated by the particular case of Toulouse Subway Line B for which experimental data are available and where the soil is saturated and highly overconsolidated. A comparison made between the numerical simulation results and the insitu measurements shows that the 3D procedure of simulation proposed is relevant, in particular regarding the adopted representation of the different operations performed by the tunnel boring machine (excavation, confining pressure, shield advancement, installation of the tunnel lining, grouting of the annular void, etc). Furthermore, a parametric study enabled a better understanding of the singular behaviour origin observed on the ground surface and within the solid soil mass, till now not mentioned in the literature.
Highlights
During shield tunnelling, soil movements induced by tunnel boring machines (TBM) are the result of a complex sequence of operations: excavation, front support, shield advancement, grouting of the annular void, grout percolation along the shield and grout consolidation
A 3D simulation procedure was proposed to account for all the different operations carried out during shield tunnelling by an EPB’s TBM
The procedure was applied to a real case in order to reproduce, by back-analysis, the movements recorded on construction site and for which the experimental data collected show a singular behaviour, namely, movements of the ground surface heaving associated with continuous horizontal convergence at the springline level
Summary
Soil movements induced by tunnel boring machines (TBM) (deformations of surrounding tunnel ground and surface settlement) are the result of a complex sequence of operations: excavation, front support, shield advancement, grouting of the annular void, grout percolation along the shield and grout consolidation. This complexity makes the explicit numerical simulation of the shield tunnelling difficult and at a particular design phase, the movements should be evaluated by accurate numerical modelling. A parametric study has allowed us to partially understand the origin of the atypical ground behaviour observed and which till has not been mentioned in the literature
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