EXCAVATIBILTY ASSESSMENT OF ROCK MASSES USING POINT LOAD INDEX AND UNI-AXIAL COMPRESSIVE STRENGTH, NIZAMPUR, MANKI SHARIF

Abstract

This study examines the empirical characterization of rock masses along the Nizampur-Manki Sharif road in Nowshera District, Khyber Pakhtunkhwa, Pakistan. The new road's fresh cuttings provided an ideal setting for geological investigations, including sample collection and documentation of fractures and joints within rock formations. These formations, primarily sedimentary, consist of clastic and chemical sedimentary rocks ranging from Precambrian to Cretaceous. The formations analyzed include the Dakhnair Formation (sandstone), Lockart Formation (limestone), Kawagarh Formation (limestone), and Lumshiwal Formation (quartzose sandstone). A geological survey captured joint characteristics including number, spacing, orientation, aperture, weathering degree, and fracture infillings, predominantly calcite. Due to the highly fractured nature of samples, engineering properties were calculated using equations proposed by Hawkins and Olver (1986) rather than laboratory testing. Discontinuities, including bedding planes, joints, shear zones, and faults, were recorded following International Society for Rock Mechanics (ISRM, 1978) standards, assessing parameters such as persistence, aperture, spacing, roughness, alteration, unconfined compressive strength (UCS), and orientation. Rock mass classification used established systems, including the Intact Rock Strength Classification and Discontinuity Spacing Classification (ISRM, 1981), Pettifer and Fookes (1994), and Hoek (1994). This enabled assessment of excavatibility for the studied formations. Results show variations in geomechanical properties among formations, influencing excavation techniques. The Dakhnair Formation, categorized as medium-strong, and the Kawagarh Formation, classified as strong, was found suitable for hard ripping. The Lockart Formation, identified as very strong, requires hard ripping or blasting, while the fractured Lumshiwal Formation allows easier ripping or digging. These classifications align with their Geological Strength Index (GSI) values and guide excavation method selection. This study highlights limitations of equipment-centric classification systems, such as those by the National Highway Authority (NHA), in addressing varied geological contexts.