Paper Title
Time-dependent Compressive Strength of Gypsum

Abstract
Uniaxial and triaxial compression tests have been performed to assess the influence of loading rate on the compressive strength and deformability of gypsum. The rock specimens have been prepared to obtain 54 mm in diameter and 108 mm in length with two different bedding plane orientations of 0 and 90 degrees. The constant confining pressure are applied by Hoek cell with confining pressures from 0, 3, 5, 7 12 to 15 MPa. The constant axial loading rates vary from 0.001, 0.01, 0.1 to 1 MPa/s. Rock specimens under high loading rate show a higher strength than those under low loading rate. The ratio of elastic moduli parallel-to-normal of the strike of bedding planes tend to be increases with increasing loading rate, and increase with confining pressures. The strength-time curves indicate that the long-term strengths of gypsum are clearly lower than those obtained under laboratory test condition where the failure is induced in the specimens within few minutes. The result should be used in the design and analysis of the rock under in-situ condition. Keywords - Loading rate, Deformability, Compression test, Bedding plane