Abstract:
As part of the Grand Paris Express project, the Pont de Sèvres station required the use of retaining structures
in the form of diaphragm walls. Forty-five meters long, they are anchored in the underlying Campanian
chalk. Base slab level, thirty-five meters below ground level, was reached using top-down construction.
Even with this method, control over the deformations of the diaphragm wall required reinforcing the
weathered chalk to improve passive soil pressure during both construction and final stages. Two processes
were implemented in different sectors of the structure: localized unreinforced concrete cross walls (using
diaphragm wall excavation technology); or wide-reaching soil reinforcement through Deep Soil Mixing.
The article explains how to model retaining structures and these passive soil pressure reinforcement
methods. Results of calculations using subgrade reaction coefficients are compared to those obtained by
finite-element modelling. Issues related to the verticality tolerances of Soil Mixing columns being accounted
for are also addressed: a computational approach enabling to consider possible gaps in soil treatment
generated by column deviation is put forward.