Experimental methodology for chemo-mechanical weathering of calcarenites

Calcarenite is a soft rock strongly affected by weathering processes that markedly reduce the mechanical rock properties with time. As a conse-quence, cliffs and underground cavities formed in calcaernites are frequently affected by intense erosion and instabilities. The field and laboratory experi-mental results mainly show three peculiarities of calcarenite mechanical be-havior: a) a marked and instantaneous reduction in strength, up to 60% of the dry initial value, when water fills the pores of the rock; b) a slow reduc-tion in strength after saturation; c) progressive weakening of the material during wetting and drying cycles. In the present work we concentrate on the long term effect of water on calcarenite. In this context, an experimental pro-cedure necessary for the calibration of a strain hardening-chemical softening elasto-plastic constitutive model is presented. Suitably designed tests under controlled “weathering” conditions were performed in order to define the critical variables that can physically explain the variety of phenomena occur-ring in the material

Modeling physico-chemical degradation of mechanical properties to assess resilience of geomaterials

International audienceIt is widely accepted that critical properties of geo-materials that play a key role in failure of earth-structures undergo often a substantial evolution induced by non-mechanical processes and variables. That includes: hydro-thermal fracture, thermal collapse, chemical mass removal or accretion (dissolution or precipitation), chemical shrinkage/swelling, drying shrinkage, capillary force evolution during pore water phase change. The properties affected are: strength in all its manifestation, compressibility, permeability, thermal conductivity, to mention just a few. The physical processes involved are either natural or engineered. Their phenomenology is per se a conundrum, as often they constitute a series of parallel or sequential processes. A review of several phenomena leading to geomaterial degradation, and methodology is presented to deal with multi-physical couplings in constitutive modeling. In plasticity, the central constitutive function is a hardening rule. Also in this case, phenomenological observations indicate a chemo-mechanical, two-way coupling. Other degradation phenomena discussed include drying—cracking, and or the role of suction induced hardening in unsaturated materials