Contents lists available at ScienceDirect Computers and Geotechnics journal homepage: www.elsevier.com/locate/compgeo Research Paper Shallow chalk quarry stability using an original shear strength reduction approach F. Rafeh a, ⁎ , H. Mroueh b , S. Burlon c a Department of Civil Engineering and Constructions, Issam Fares Faculty of Technology, University of Balamand, Lebanon b Laboratory of Civil and Geo-Environmental Engineering (LGCgE), Polytech'Lille University Lille 1 Sciences and Technologies, Villeneuve d'Ascq 59655, France c Terrasol-Setec, 42-52 Quai de la Râpée, 75012 Paris, France ARTICLE INFO Keywords: Failure mechanisms Joints Chalk Numerical modelling Degradation approach Shear strength reduction ABSTRACT Unexploited underground quarries may represent a potential hazard for the surrounding urban environment. In this context, this work presents a stability study of quarries in North France. A shear non-uniform non-homo- geneous degradation approach is proposed for the stability study. The presence of joints in the chalk continuum is considered by using an anisotropic plasticity model accounting for the accumulation of permanent strains along these joints. Stability analysis using proposed degradation approach is performed and compared with the conventional shear strength reduction approach. The comparison shows that the proposed degradation approach might be an alternative to conventional shear strength reduction approach. 1. Introduction With the increasing role of numerical methods, the most common approach used for the stability analysis of geotechnical structures is based on the conventional shear strength reduction approach [23]. This approach is performed by reducing the shear strength properties of the ground incrementally by using a reduction factor R f that is increased until the numerical instability is detected. The fnal value of the re- duction factor R f can be considered as the safety factor F that indicates the stability state: F > 1 means stable. This approach has been im- plemented, in combination with the limit equilibrium methods some- times, in numerical models for the stability study of slopes and other geotechnical applications [5,12,9,6,3,16,10], etc.). This method is based on a uniform decrease of the shear resistance properties and thus does not account for any physical mechanisms such as degradation or time efects. Consequently, the conventional shear strength reduction method might not always provide the most appropriate failure me- chanism. For example, in the region of North France, underground chalk quarries have been excavated decades ago and the stability analysis is expected to account for the degradation efects that are ac- cumulated with time. Such efects lead to a decrease in the mechanical strength of the chalk and thus afect the overall stability of the quarries. In this framework, this paper aims to develop an alternative pro- cedure of shear strength reduction considering the degradation efects which are revealed with time. This procedure is presented and compared to the stability analysis of the same quarry using the con- ventional shear strength reduction approach. Accounting for degrada- tion efects in the study of stability problems may provide some ele- ments for a better understanding of the strain and failure mechanisms. Nevertheless, a time dependent stability analysis remains complex and requires the development of specifc numerical procedures. In general, the degradation and time efects are studied by considering several approaches such as weathering, ageing, and creep. This includes var- ious phenomena responsible for the evolution of strains and displace- ments. For example, the efect of weathering can be illustrated by the degradation of the internal mechanical properties of the intact material [15] and [2]. Weathering is integrated using an elastoplastic strain hardening model in which the hardening law depends on plastic strains and a degradation parameter of chemical origin. Other approaches ([4,13,14,21,1]) account for the infuence of time by studying ageing and creep efects associated to the stress-strain evolution in the mate- rial. Classical models attribute the creep deformation to the viscous properties and the time-dependent deformation is thus entirely de- scribed by viscoelastic and viscoplastic theories [19,20] and [17]. However, creep can be also described in terms of microstructural evo- lution that integrates a progressive degradation in the material [15]. In this framework, a numerical approach based on the development of a degradation function is proposed in this paper. This degradation function is applied uniformly on the ground in place at the initial state and is based on a hardening function that integrates deviatoric plastic https://doi.org/10.1016/j.compgeo.2019.04.004 Received 14 March 2018; Received in revised form 3 January 2019; Accepted 3 April 2019 ⁎ Corresponding author. E-mail addresses: faten.rafeh@balamand.edu.lb (F. Rafeh), hussein.mroueh@polytech-lille.fr (H. Mroueh), sebastien.burlon@setec.com (S. Burlon). Computers and Geotechnics 112 (2019) 60–71 0266-352X/ © 2019 Published by Elsevier Ltd. T