Mechanical effects of chemical degradation of bonded geomaterials in boundary value problems

ABSTRACT The paper presents a constitutive approach to describe the effects of rock weathering processes in boundary value problems. The term rock weathering is used to refer to a number of chemical and physical phenomena that continuously transform a rock mass into a granular soil. From an engineering point of view rock weathering can be interpreted as a generalised decay of the mechanical properties of the original material. It acts at a constitutive level essentially by reducing the strength-of the bonds joining the grains together. Such a material degradation can occur in a time scale which is comparable to the average life of engineering structures. Weathering can induce subsidence on shallow foundations resting on soft rocks layers or it can be crucial for what concerns the stability of slopes or abandoned underground mines. In the first part of the paper, it is shown how the progressive destruction of the intergranular bonds due to weathering has been modelled satisfactorily by extending a strain hardening elastoplastic model. Such a model has been corroborated by means of special oedometer tests on soft rock specimens in which a progressive chemical debonding has been induced through the exposition of the rock to a uniform flow of an acid solution. In the second part of the work, three different boundary value problems in which weathering effects cannot be neglected are presented. The numerical analyses performed with the proposed constitutive model refer to: i) the weathering-induced subsidence of a circular foundation; ii) the stability of a slope subject to weathering from the ground surface; and, iii) the effects of the progressive collapse of pillars in an abandoned underground mine.