Evaluation of Carbonate and Heterogenous Rock Masses for the Dam Foundation: A Case Study at Kanarwe River Basin, Sulaimaniyah, NE Iraq

Abstract

Evaluating rock masses for dam foundations, especially heterogeneous rock (flysch), becomes imperative and requires accurate geomechanical classifications. The rocks at the Kanarwe river basin, especially at a proposed dam site (Goma-Qazan near Khewata, Sura Qalat villages), mainly consist of interlaying massive carbonate rocks of the Aqra Formation with flysch rocks of Tanjero Formation. Therefore, selecting appropriate dam types is challenging and very risky. This study conducted a detailed study of lithology, discontinuity condition, rock sampling and laboratory tests to determine the site suitable for dam construction using the quantitative GSI, Rock Mass Rating, and Dam Mass Rating geomechanical classification systems. A new procedure was suggested for calculating stress relaxation and damage level (disturbance factor D) in rock masses. The Dam mass rating related to the foundation stability shows a good stability indication ranging from 43.7–82.9, indicating foundation suitability for all dam types. The foundation excavation desirability and consolidation grouting were evaluated based on dry basic rock mass rating, which shows that the site is suitable for earth fill and hardfill dams. However, the rock mass units require spot and systematic grouting for gravity and Arch dams, respectively. Ec/Em (deformation modulus of the dam/deformation modulus of foundation rocks) values for massive carbonate rock range from 0.18–0.93; they indicate site suitability for arch, gravity dam, earth fill and hardfill dams. While the Ec/Em values for flysch rock mass units range from 1–6.4, they indicate some units have a serious problem situation and need treatment based on the types of dams.