PETROPHYSICAL AND MECHANICAL PROPERTIES OF ROCKS OF HIMACHAL AND GARHWAL HIMALAYAS

Abstract

Performance prediction in mining and civil engineering projects entails the characterization of rocks. The physical and mechanical properties of rocks are fundamental information for engineering purposes. These properties play a crucial role in categorizing and anticipating the behavior of rock mass with a view to the planning and execution of any geotechnical project such as underground structures, foundations on rocks, infrastructure works, tunnels, and dams. The Himalaya is a classic model of the structurally and tectonically complicated geo-environment and serve as a natural laboratory to examine diverse rock types and geological structures. Understanding these rocks is critical due to impending large-scale infrastructure developments in the Himalayas. However, examining the petrophysical and mechanical properties of rocks in a lab is difficult, expensive, laborious, and requires high-quality rock specimens. Consequently, indirect methods are promising for identifying these attributes. The petrographic parameters such as mineralogical composition and textural properties, intrinsically influence the physico-mechanical properties of rocks. This study aims to assess the physical and mechanical properties of Himalayan rocks and investigate the mutual dependence between these properties and the petrographic characteristics. Additionally, it examines the influence of seismic wave velocities on these parameters obtained through both in-situ and laboratory methods. The integrated analysis aims to comprehensively assess the impact of petrographic parameters and seismic wave velocities on the physico-mechanical properties of the studied rocks and to identify the dominant factors that affect them. Three sets of laboratory experiments were performed on the siliciclastic and carbonate samples collected from the study area. First, the petrographic test determined the mineral composition and textural characteristics of rocks. Second, the physical properties, including density, water content, porosity, and seismic wave velocities, were determined. Finally, unconfined compressive strength, Brazilian tensile strength test, and point load index test were done to evaluate their mechanical characteristics. Sandstone samples with varying textural characteristics and compositions were sampled from Himachal Himalaya and Garhwal Himalaya. Sandstone is one of the most abundant rock types found in nature and incorporates a wide range of rock types with varied mechanical, petrographic, and mineralogy characteristics. The substantial discrepancy in the petrographic and mechanical properties of sandstones is due to the inherent variability in mineral composition, grain size, shape variation, and non-uniform distribution of defects such as pores and microstructures.