Mechanical characterization of dry-stone walls for terraced slope stability assessment

Historically, many Mediterranean mountain environments were terraced through dry-stone walls for exploiting unfavorable areas for human activities and agricultural development. However, terraced slopes are often affected by instability phenomena. The objective of the study was the development of a rigorous and effi-cient methodology to parametrize the mechanical characteristics of dry-stone walls for the stability analysis of terraced slopes. As study area a terraced slope used for agri-cultural purposes (viticulture), located in the Troodos Mountains (Cyprus), was iden-tified. The dry-stone walls were characterized as a fractured rock mass, as to apply a spe-cifically adapted version of the Geological Strength Index Classification System (GSI), focusing on structure of the rock mass (i.e., the dry-stone wall) and conditions of the discontinuity surfaces (i.e., stones surfaces). For the structure the degree of interlocking between stones (apertures, contact area) and the homogeneity of the struc-ture (arrangement of blocks, variability of the dimensions of the blocks, prevailing angular-rounded shape) were quantified. To derive the surface conditions, the Joint Roughness Coefficient (JRC), weathering, presence of infilling material and Joint Wall Compressive Strength (JCS) were analysed, following the standard procedures for geomechanical surveys suggested by International Society for Rock Mechanics (ISRM). The GSI values were converted into cohesion and friction angle values through correlation curves available in the literature. To complete the conceptual model, soils constituting the backfill of the dry-stone walls were characterized through laboratory analysis, including texture and bulk density analysis, and shear strength tests. In the field, three well-maintained and three poorly maintained dry-stone walls were selected. The geomechanical characterization showed that well-maintained walls had better mean properties than poorly maintained walls regarding both structure and surface conditions. In particular, the JCS mean value of well-maintained walls was 151 MPa, while that of poorly-maintained wall was 142 MPa. Similarly, the exposed surfaces of single stones constituting well-maintained walls had an average area of 313 cm2 while the same parameter for poorly-maintained walls was 187 cm2. To con-firm the predisposition of these walls to instabilities numerical analyses are ongoing.