Oedometric Tests on Artificially Weathered Carbonatic Soft Rocks

Abstract

Carbonatic rocks are subject to progressive degradation of their mechanical characteristics due to weathering. This phenomenon may have relevance for engineering since it can induce settlement of foundations, progressive failure of slopes or an increase of pressure on tunnel liners. To study weathering effects on a laboratory timescale, oedometric tests have been conducted on specimens of calcarenite and artificially cemented silica sand. Weathering was simulated by percolating an acid solution. Under constant load, the recorded progression of deformation over time ends with a horizontal asymptote when only bonds are destroyed (cemented sand), whereas it results in a steady increase when the grains are also degraded (calcarenite). To determine the variation in stress state induced by weathering, a special oedometer was designed. Allowing very small lateral deformation of the ring, its circumferential stretching was measured with strain gauges and correlated to the lateral pressure exerted by the specimen. In all cases considered, the horizontal stress increased remarkably during weathering at constant vertical load. Predictions of a chemoplastic constitutive model are then compared to experimental data, and then show good agreement, especially for cemented sand.