Engineering geological characterisation of the rock masses at Tannur Dam site,South Jordan

This paper highlights the geomechanical characterisation of the rock masses exposed at the dam abutments and reservoir area at the Tannur Dam site, South Jordan. The right abutment rock masses are characterised by closely to widely spaced joints. The rock-mass qualities were assigned using the rock-mass rating (RMR) and Q-tunnelling index. Both systems assigned a poor quality for foundation rocks because of the presence of weak rocks. The rock masses constituting the dam abutments exhibit fair quality. The results of packer tests indicate that the hydraulic conductivity of the rock masses of Fuheis-Hummar-Shueib (FHS) and Wadi es Sir (A7) formations range from 10 to 150 Lugeon units (LU). The FHS was characterised by lower LU values compared with A7; this reflects the fracturing characteristics of A7. However, the A7 should be grouted especially the right abutment. However, the FHS needs less grouting because the spacing between joints seems to be tight. The estimated shear strength envelopes relevant to the rock masses of both abutments as well as the foundation rocks were quite similar and, therefore, present similar shear strength characteristics. The shear strength for jointed rock masses showed curvilinear failure planes with average cohesion values of 0.67 and 0.64 MPa and friction angles of 36.5 and 35.5° for dam abutments and the foundation area, respectively.