ABSTRACT
The effect of annular void grout injection pressure on soil deformation control is usually overlooked in confinement design studies. For projects using an Earth Pressure Ballance (EPB) TBM in full excavation chamber mode, the high viscosity of the confinement mixture does not allow for continuous confinement application along the shield without lateral bentonite injection. In such cases, using the beneficial effect of annular void grout injection pressure may become necessary to justify the acceptability of soil deformations. In their work, Aristaghes & Autuori (2001) defined the efficiency coefficients of the annular void grout injection pressure based on an elastic soil behavior. The purpose of this paper is to estimate the effect of soil plastification, which occurs during deconfinement along the shield, on the efficiency of the grouting pressure regarding soil deformation control. The analysis approach is mainly based on 2D modeling of soil unloading/reloading sequences with a confinement explicitly modelled under the effect of low confinement pressure along the shield during the tunnel excavation phase, as well as the application of annular void grout injection pressure behind the lining. The results will allow to define the maximum soil deconfinement ratio required for full grouting efficiency or to propose a correction factor for the grout injection pressure to account for the soil plastification. An example of the application of the results of this analysis approach is conducted for civil works contract 4 of the 3rd metro line project in Toulouse, currently being built by Horizon joint venture with Bouygues Travaux Publics as the mandatory partner. This project involves a tunnel with a total length of 4.1 km, excavated by an EPB TBM with a diameter of 9.67 m. The tunnel is mainly constructed in Toulouse molasses, a sandstone with several sublayers of varying mechanical resistance, with a risk of encountering sand lenses.
