Enrique Edgar Romero Morales

The role of structure in the chemically induced deformations of FEBEX bentonite

Abstract The paper presents the experimental results of an investigation aimed at understanding the role played by the soil structure in the evolution of chemo-mechanical-coupled processes in bentonite. The objective was pursued by subjecting samples with different structures to similar salinisation–desalinisation cycles. Samples were prepared at approximately the same void ratio by means of either static compaction at hygroscopic humidity or starting from slurries consolidated under mechanical loads. The investigation was carried out both from a macroscopic point of view (measuring the induced deformations) and from a microscopic point of view (ESEM analysis, mercury intrusion porosimetry). It is evidenced how the behaviour of the compacted samples differs from the one in the consolidated samples, especially as far as the evolution in time of the deformations is considered. An attempt to explain the differences by means of structural considerations is then provided.

Tracking degradation of argillaceous rocks using bender elements.

The results of a comprehensive experimental program focused on the study of progressive degradation processes on a low permeability argillaceous rock induced by hydraulic cycles is presented in the paper. Relative humidity cycles were applied with vapour transfer technique, and bender elements were used to evaluate the evolution of shear stiffness during the application of hydraulic paths. The characterisation of the material included the determination of the water retention properties (water retention curve), as well as the pore size distribution using mercury intrusion porosimetry, complemented with SEM micrographs and elemental analysis using X-ray spectroscopy to characterise micro-structural features and detect clayey and non-clayey constituents. Results showed cumulative and irreversible swelling of the samples with the application of relative humidity cycles. Regarding shear stiffness, an important reduction (around 80%) was observed at the end of the hydraulic paths applied. Evidence of rock degradation at macro-scale was linked to structural modifications at micro-level.

Studying collapse behaviour of sandy silt under generalised stress conditions

This paper presents preliminary results on the collapse response of an artificially prepared sand-silt mixture in a hollow cylinder apparatus. The wetting stage is performed under constant mean and deviatoric stresses but at different intermediate principal stresses (controlled through the principal stress parameter b = (s2- s3)/( s1- s3)). Properties of the mixture are first described to complement its hydro-mechanical information. The preliminary results seem to indicate that collapse is larger when the intermediate stress coincides with the minor one.

Microstructural evaluation of the water sensitivity of clayey rocks

The paper presents both macroscopic and microstructural evidence of the water sensitivity of a low porosity clayey rock from Northern Spain. Particular emphasis is focused on the effects of water sensitivity at micro level. Results obtained from Environmental Scanning Electron Microscopy (ESEM) using the common procedure of sample preparation show that this procedure of sample preparation is not enough to evaluate in a proper way the irreversible changes induced at micro level by hydraulic effects. An alternative procedure is described, which seems to improve the evaluation of rock degradation at micro scale.

Thermo-hydro-mechanical analysis for the simulation of rapid sliding process in a new and fast ring shear prototype

Vajont was a case of an extremely fast landslide and efforts to clarify the failure have been mainly concentrated in providing a consistent explanation taking into account this characteristic feature. Particularly in the case of Vajont landslide, attention has been essentially focused on the shearing properties of the sliding surface. An accepted explanation for the velocity reached is the thermo-hydraulic-mechanical coupling under saturated conditions, which induces thermal dilation and effective stress reduction due to pore pressure build-up. Nevertheless, lack of in situ and experimental information has become one of the main drawbacks when trying to explain these coupled processes. In situ information is difficult to obtain since temperature and pore pressure development during these fast processes are impossible of being measured. To overcome this limitation, a new fast sliding prototype -emulating a ring shear apparatus- has been recently developed at the Universitat Politecnica de Catalunya (Spain). This prototype can reach relatively high speeds along the sliding surface (up to 30 km/h) under relatively high total vertical stresses (up to 3 MPa). Temperature and pore pressure changes can be locally measured with miniature transducers located close to the shear band. The design of this complex prototype requires the use of simulation-aided techniques, to help with the interpretation of the coupled processes, as well as to estimate the maximum temperature and pore pressure changes. A thermo-hydro-mechanical formulation, applied to the ring shear test, is proposed in the paper to study pore water pressure build up and dissipation in a sliding surface being heated by the frictional work induced by the motion. Particularly, the proposed model is applied to simulate the evolution of the shear strength along the sliding surface during a fast sliding process.