Macro-mechnical charakteristics and their control on the strenght of sandstones of western Indo-Burmese Rangers, NE India

Abstract

Mechanically strong sandstones consider as a potential construction material which can withstand modest load and not associated with any geologic fractures. This work is about understanding the macro-mechanical properties of sandstones by studying several petrographic parameters, which could provide evidence of their influence on mechanical strength. Here the authors were considered the Bhuban sandstones of western Indo-Burmese Ranges (IBR) of north-eastern India to investigate the above criteria. The result shows that sandstones have a mean grain size between 108 to 208 μm. Moderate to poorly sorted (phi scale ranges 0.56–1.5) grains show greater content of rounded constituents (43–68 %) with sphericity between 0.65–0.85; along with moderate packing properties (packing density 54–77 %; packing proximity 32–70 %). The grains join by mostly straight (20–54 %) and concavo-convex (13–45 %) contacts; with lesser point (5–13 %) and sutured contacts (8-44 %). Schmidt Hammer rebound values (R-values) were used to calculate and analyse the uniaxial confined stress (UCS); which again validated with UCS testing of core samples. The comparison between macro-mechanical parameters and the UCS shows interrelationship among rock constituents which hold the key to the mechanical strength of the rock. The presence of angular grains and semi-angular spherical grains diminish the macro-mechanical strength to some extent. Moreover, FETEM-EDX analysis confirms the micro-weathering of the angular grains, which have a deformed lattice setting. These findings show that macro-mechanical and micro-nano scale properties of sandstones influence the rock strength.