Tunnel Modelling in Analogical Soil: Comparison of Experimental and Computational Results Obtained with a Finite Difference Program

Abstract

The aim of this work is to obtain a better simulation of soil movements due to reconstruction of shallow tunnels, dug with pressurised shield tunnelling boring machine, inducing in the soil mass, successive deconfining, reconfining cycles.

The reduced scale experimentation is realised on a two-dimensional model with the analogical Taylor-Schneebeli material consisting of metallic rods of 3 to 5 mm diameter.

The experiments have been analysed with digital image techniques, and the complete displacement and strain fields were obtained within the entire soil mass. The numerical simulation is done with the explicit finite difference program, FLAC V3.30. by ITASCA. Two different constitutive laws for the analogical soil have been tried: a elastic-plastic law (Mohr-Coulomb) and a constitutive law developed by our laboratory using a non-linear, irreversible law before failure (Duncan type) and a Mohr-Coulomb flow rule after failure. These constitutive laws have also been written for a purely 2D material and numerical results and will be compared with classical results obtained with the 3D model using strain plane analysis. The law parameters were determined from biaxial and oedometer tests done with the analogical soil. Experimental and numerical displacement field within the entire mass as well as the settlement of the soil surface are compared.