Deformation and Failure Parameters of Cement-Modified Loess: Application to the Calculation of the Safety Factor of a Road Structure

Loess is a geological formation with poor geotechnical performances that covers up 10% of the world’s land surface area. To upgrade and allow optimal use of this kind of material in civil engineering, it is common to add few percent of hydraulic binders. This technique significantly increases their engineering and mechanical properties and has the advantage of minimizing environmental impact and reducing the cost of infrastructures. However, the real mechanical properties of those materials are seldom estimated and their performances are sharply downgraded during structure design processes. The deformation and failure parameters of six mixtures of cement-modified loess have been determined based on direct tensile stress testing, indirect tensile testing and unconfined compressive stress testing. Results have been used to determine the parameters of the Mohr-Coulomb failure criterion and the parameter of the Hoek-Brown failure criterion. The Hoek-Brown model clearly shows that results from indirect tensile stress measurement must be weighted to describe materials properly. Both models’ results were then used to calculate the safety factor of a road structure with cement-modified loess used as subgrade material using reduction techniques. Specifically, for the Hoek-Brown model, a new calculation adapted to structures with tensile stresses is proposed. Results vary by around 8.9 for the Mohr-coulomb model and around 3.2 for the Hoek-Brown model. These shows at the laboratory scale that resource-based economies could be expected if cement-modified loess mechanical parameters were considered in the design of structures. It also shows that the Hoek-Brown model is a promising tool to study tensile stressed structures made with cement-modified materials.