Petrographic and structural controls on geotechnical feasibility of dam sites: implications from investigation at Sher D
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ORIGINAL PAPER
Petrographic and structural controls on geotechnical feasibility of dam sites: implications from investigation at Sher Dara area (Swabi), north-western Pakistan Yasir Shaheen Khalil & Mohammad Arif & Hasnain Ali Bangash & Muhammad Sajid & Noor Muhammad Received: 9 February 2014 / Accepted: 11 June 2014 # Saudi Society for Geosciences 2014
Abstract The study area constitutes the south-eastern extension of the Ambela granitic complex and consists of three petrographically distinct rock groups, i.e. alkali granite, granite and micro-porphyritic granite. The strength and physical properties including unconfined compressive strength, unconfined tensile strength, specific gravity, water absorption capacity and effective porosity of the rocks show significant variation largely because of notable differences in petrographic characteristics. In addition to quartz to feldspar ratio and grain size and shape, amount of flaky minerals and presence, type, extent and abundance of features of ductile and brittle deformation are also important in determining the rock strength. Despite displaying variation in mechanical and physical properties, the Sher Dara rocks are sufficiently resistant and hence suitable to serve as foundation and abutments for a dam structure. The area is devoid of any major shear zone but pervaded by intimately spaced joints. However, proper grouting will improve the rock further so as to provide a strong and durable support to the proposed dam structure. Keywords Petrography . Mechanical and physical properties . Structural geology . Sher Dara dam site . Pakistan
Introduction The Sher Dara area (34° 21′ 23.28″ N–34° 14′ 42.32″ N; 72° 23′ 13.49″ E–72° 23′ 55.64″ E) lies about 11 km north-west of Swabi town, north-western Pakistan. It is a potential dam site and represents the south-eastern extension of the Ambela granitic complex (AGC). The latter itself constitutes a major bulk of the eastern part of the Peshawar Plain Alkaline Igneous Province (PPAIP). The AGC is locally intersected by thrust and strike-slip faults which have at places resulted in the development of sheared granites. According to Rafiq (1987), the faults are more common in the north-eastern part of the complex. Besides, discontinuous shear zones commonly occur in the area. The reported presence of these features casts doubts on the suitability and potentials of the region for the construction of a major engineering structure. The focus of the present study is to assess the feasibility of the Sher Dara site for the construction of a dam through a detailed geological investigation including field observations, geological mapping, petrographic examination and determination of strength and physical properties of the constituent rocks.
Geology and tectonics Y. S. Khalil National Center of Excellence in Geology, University of Peshawar, Peshawar 25120, Pakistan M. Arif : H. A. Bangash : M. Sajid Department of Geology, University of Peshawar, Peshawar 25120, Pakistan M. Arif (*) Department of Earth Sciences, CIIT, Abbottabad 2206
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