Eduardo E. Alonso

Eduardo E. Alonso
Emeritus Professor, UPC, Barcelona

Eduardo Alonso is Emeritus Professor of Geotechnical Engineering at the Civil Engineering School of UPC, Barcelona. He is a past Dean of the School and a past Vice-Rector for research at UPC.
His main research interests include the stochastic analysis of soil heterogeneity, unsaturated soil mechanics, rockfill mechanics, dam engineering, coupled thermo-hydro-mechanical, analysis, landslide research and some chemo-mechanical interactions.
He is known for his contributions to develop unsaturated soil mechanics and his involvement in a variety of Geotechnical Engineering cases, particularly those involving catastrophic failures. He has acted as a geotechnical consultant in several countries.
He is member of the Royal Academy of Engineering of Spain and he is past Editor of ICE journal Géotechnique. Past honorary lectures include Coulomb, Buchanan, Sowers, Croce, Heim, Kezdi, Rocha, BGA Touring lectures, Rankine, Leonards, Ardaman-Wissa, Šuklje and Zeng Guoxi and Jiménez Salas.

The  3rd Blight Lecture

The positive history of an error. Modelling the heave of a nuclear power station

The presentation describes the sustained efforts to understand the swelling mechanisms and to develop a proper model to predict the long-term heave of a nuclear power station founded on an unsaturated claystone. A significant heave was noticed and it was measured soon after the end of construction, in 1976. Most relevant, in addition to high swelling pressures (> 2MPa), were the secondary strains measured in long term tests. In 1985, a swelling model was set-up by interpreting the claystone as a “double structure” material. A hypothesized local transfer of water between the “macro” and “micro” continua could reproduce laboratory swelling tests. A hydromechanical finite element code, incorporating this idea, could reproduce the field swelling records.

Years later (1992, 1999) these ideas helped to formulate the “Barcelona Expansive Model” for unsaturated swelling clays. The double structure approach facilitated the simulation of osmotic effects and chemical interactions, which were ascribed to the micro level.

In 2002, several tunnels and a large railway viaduct built on the same claystone geological formation, experienced severe expansions. The research conducted revealed the presence of anhydrite in the claystone. The primary reason for the observed long-term heave was the precipitation of gypsum crystals in discontinuities. This evidence led to a review of the power station case. An examination of the mineralogical composition of claystone cores indicated the presence of anhydrite in significant proportions. The original swelling model was reformulated as follows:

  • The long-term expansion did not require any reference to a double porosity description
  • Solid balance equations were formulated for air, water, soluble species (anhydrite and gypsum) and non-soluble minerals
  • Dissolution, transport and precipitation of soluble minerals was accounted for
  • Rock damage during initial excavation of the foundations, in particular the opening of discontinuities, favoured crystal precipitation

The new formulation, described in the lecture, explains the results of laboratory tests, it is consistent with field swelling records and provides an estimation of long-term heave experienced by the buildings of the power station. The original formulation did not represent properly the physics of the swelling mechanisms. Nevertheless, it provided a convenient framework to interpret the behaviour of a wide class of expansive clays and claystones.