Numerical Simulation of the Mechanical Response of the Tunnels in the Saturated Soils by Plaxis

The forecast of settlement and movements caused by tunneling represents a significant challenge of technology. The evaluation of these movements is indeed of primary importance in order to prevent them. The methods of calculation making it possible to evaluate displacements and deformations in the ground due to tunneling give only one approximation of the true amplitudes of the movements in the ground. It is one of the assets of the Finite Element Method (FEM) which makes it possible a priori to treat configurations more complex and closer to reality. Our objective in this study is to calculate numerically the various movements caused by the construction of a shallow tunnel using a shield using PLAXIS 2D, the behavior of the ground is described by a perfectly plastic elastic model based on the criterion of Mohr-Coulomb. A comparison between the various methods: empirical, analytical and numerical in terms of settlement on the surface was carried out. The validation of these results was made by using results drawn from literature. We have also carried out a parametric study in order to analyze the influence of various geometrical and geotechnical parameters on the behavior of grounds due to tunneling. Lastly, we have treated the same example by supposing the existence of structures near the tunnel in order to see the influence of the presence of other structures on the profile of the settlements caused by tunneling. Results of our work agreed with those in literature

Influence of the Hydric State and Lime Treatment on the Thermal Conductivity of a Calcareous Tufa

An experimental study was conducted to investigate changes of thermal conductivity of a raw and lime-treated calcareous tufa (north-west of Algeria) during drying process. Treated (with 4% of lime) and untreated samples were prepared by static compaction at the Standard Proctor Optimum (SPO), Modified Proctor Optimum (MPO) and at a constant stress level of 4 MPa. Transient Hot Wire (THW) method was used to measure the thermal conductivity and the water content and degree of saturation of samples were determined at various drying times. Results show that the drying process induces a decrease in thermal conductivity. This parameter seems to vary linearly with the water content and the degree of saturation. In addition, it was found that the lime treatment leads also to a decrease in the thermal conductivity. Thus, the drying process and the lime treatment will jointly contribute to the reduction of the thermal conductivity of the studied material in such a way that it is more insulating than some traditional building materials like concrete or fired bricks. Doi: 10.28991/cej-2021-03091663 Full Text: PD