Weathering effects on the strength and deformational behaviour of crystalline rocks under uniaxial compression state

Uniaxial compression tests were performed on different categories of weathe ring of three lithological units: Malanjkhand granite; Nagpur basalt; and D elhi quartzite, occurring in central and northern parts of India. The defor mational behaviour is studied in terms of variation in tangent modulus (E-t 50) and initial modulus (E-i) due to weathering. The power relationship bet ween uniaxial compressive strength (sigma(c)) and E-t50 shows strong corres pondence for weathering sequence of common rock types. This relationship ha s been established by regression analysis and significant correlation param eter (coefficient of determination, r(2)=0.87) for crystalline rocks. It is shown that there is a systematic decrease in stiffness ratio, that is, rat io of tangent modulus and uniaxial compressive strength with increased weat hering state. Comparison of E-t50 and E-i values has shown that E-t50 decre ases more gradually than E-i, and reduction is more drastic for E-i values with an increased degree of weathering in all the three rock types. The mod e of failure has been found to be influenced by weathering extent in rocks. A brief account is given of the intrinsic characteristics of fresh and wea thered rocks and mineralogical changes produced by weathering investigated quantitatively. Correlation drawn between the petrographical and mechanical indices has shown that mechanical properties are apparently dependent on t he intrinsic characteristics of weathered rocks. (C) 2000 Elsevier Science B.V. All rights reserved.