Abstract

Climatic actions are one of the factors controlling the evolution of slopes, this paper is devoted to a specific effect, relatively little studied, related to the effect of climate-driven temperature changes on rock massif deformation. The particularity of the study is to focus on permeable rocks and Temperatures varying in a range which discards freeze/thaw effects. Research has been carried out in relation with the analysis of the real case of a limestone cliff located in the Périgord region, the massif was highly instrumented, results show a slow cyclic accumulation of deformations with time, essentially synchronic with thermal cycles. An advanced constitutive model, specifically developed to capture rock degradation due to the differential expansion of the main minerals composing the rock, has been developed. It has been calibrated on experimental results obtained in the laboratory on block samples tested in a climatic chamber for a long series (several months) of daily thermal cycles. Deformation and shear wave velocity were monitored during the test. Model shows a good agreement with laboratory measurements.

Introduction

Under cyclic changes in temperature, rock massifs experience expansion/contraction cycles that cause continuous stress redistribution in the zone of propagation and retrieval of the heat front. Because the amplitudes of temperature changes under climatic actions are moderate and it is generally considered that their maximum and minimum values were already reached during rock slope history, stress changes are in most cases expected to produce recoverable deformations. Observations evidence however that slow rock degradation may occur during this process [1–3]. It is usually attributed to processes of decohesion and microcracking caused by increase of stress intensity at grain contacts, resulting from the differential thermal expansion between minerals constituting the rock. This mechanism is mostly influenced by grain arrangement and minerals thermal expansion coefficient [3,4]. It may be at the source of degradation of rock mechanical properties like elastic moduli, tensile strength or uniaxial compression strength [5, 6] and may culminate into the propagation of discontinuities into the rock by microcracks coalescence.

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