Dynamic Compressive Strength of Thermally Treated Barakar Sandstone

Assessing the thermal influence on the dynamic mechanical properties of Barakar sandstone is crucial, notably in the examination of subsidence phenomena induced by underground coalmine fires in tandem with blast-induced loading. The Jharia region had been affected by underground coalmine fires, resulting in surface fracturing on both small and large scales. So, the objective of the study is to examine the impact of high temperature on the dynamic compressive strength of colliery sandstone subsurface samples, and its correlation with the mineralogical properties. To accomplish this objective, samples were subjected to a 24-hour heat treatment in a furnace at a controlled heating rate of 5°C/min, followed by natural cooling within the furnace. The samples were divided into five groups, each undergoing different thermal treatments at temperatures of 25°C, 200°C, 400°C, 600°C, and 800°C. The dynamic compressive strength was obtained by performing the dynamic compression tests on Split Hopkinson Pressure Bar setup. The results clearly indicate that up to a critical temperature i.e. 400°C, both quasi-static and dynamic compressive strength showing the minor strengthening effect. However, beyond this critical temperature, there is a significant decrease in strength, particularly up to 800°C. Additionally, for each temperature, the dynamic strength also exhibits an increasing trend with increase in strain rate. The study investigated the applicability of the Kimberley Theoretical Universal Scaling Law in predicting the dynamic compressive strength of thermally treated sandstone across different strain rates. Furthermore, it pinpointed the characteristic strain rate at which the dynamic compressive strength of thermally treated sandstone doubled in comparison to its quasi-static compressive strength.