Simulation of the physical degradation of natural slopes of Jurassic marls when excavated and subjected to suctions changes

Abstract

Soft clayey rocks such as marls and argillites are very common in the Iberian Peninsula. Design provisions for engineering works such as slope excavation in these materials must consider their evolving behaviour. Evolution can be identified by physical degradation. In fact, volume changes, stiffness loss, and, quite often, loss of mass continuity due to the development of fissures can cause instability phenomena of finite volumes of rock (Alonso et al., 2010). Abadia marls from Arruda dos Vinhos, in Portugal, are an example of soft rocks exhibiting such type of evolving behaviour. These marls, Upper Jurassic in age, are characterized by relatively high in situ water content and low porosity. Clay minerals present are mainly chlorite, kaolinite and illite, which explain the relatively high plasticity of the material. Excavated slopes in this material exhibit strong degradation of its hydro-mechanical properties, as illustrated in Figure 1.a. Because this degradation is due to the exposition to atmospheric actions, the excavated slopes are often protected with a membrane. This was the procedure adopted in A10