Feasibility Level Geological And Geotechnical Assessment Of Baz Ali Dam At Lower Kurram, Khyber Pakhtunkhwa, Pakistan

Abstract

A comprehensive research work was accompanied to the intended area i.e. District Lower Kurram, Baz Ali dam. The key subject of the research work was to study the area geologically and geotechnically and to guarantee that the area is feasible for dam construction. From fieldwork and over-all laboratory tests on different samples taken from outcrop, boreholes and test pits were analyzed and thus it was confirmed that the study area is comprised of major rocks units of mélange zone of Late-Cretaceous age thrusting over the east trending folded rocks of Jurassic, Cretaceous and Paleocene rocks. According to the geomorphology and geological conditions and economic reason, the dam has been designed as an earth dam with a clay core that can help the dam to be less permeable that is the reason the dam foundation is comprised of a sequence of limestone, shale and sand of the Jurassic age. Stratigraphically it is found that the formation on both abutments is Samana Suk Formation with Limestone and sand, shale beds. The diverse geotechnical studies were conceded out on the samples (disturbed and undisturbed) from the location, to determine the competency of the rocks and soil. From field tests and lab tests it is concluded that the Unconfined Compressive Strength, Point Load Strength Tests and Petrographic Analyses on samples shows high mechanical strength of rocks. Grain size outcome displays the existence of gravelly strata as major material encountered at minimal depth i.e. 1m to 5m on site. The bedrocks encountered at maximum depth >25m. The samples taken from the outcrop section and borehole that is the bedrock for dam foundation. Petrographic analyses shows a high percentage of ooids and pesoids (60% to 80%) and the process of micritization. The Atterberg’s result displays the state of plasticity of the soils ranges from 5% to 10% (Plastic Index) and 25% to 30% (Liquid Limit) that is ‘Slight- Low-Medium’ which also corresponds to the Casagrande’s arrangement which shows that most of the soils are Inorganic soils with Low plasticity. The permeability of soil samples that is ranging from 1.1178 × 10-4 cm/sec to 2.088 × 10-5 cm/sec which demarcates very low permeability with very slow class classifies the samples as impervious soils, which is an important parameter for the appropriateness of dam structure. The shear strength of the soils displays uniformity of the samples as ‘very hard’. Test pits samples collected, in order to check the availability of construction materials nearby has shown the presence of A-4 material. As per AASHTO classification which can be used as construction material.