Strength and Stiffness of Claystone Specimens Tested with Neoprene Capping

Abstract

Cylindrical core specimens of Maha Sarakham claystone were uniaxially loaded to failure under various length-to-diameter ratios (L/D).  Compressive strength of the specimens tested without neoprene capping decreases from 50.6 MPa for L/D = 0.5 to 36.5 MPa for
L/D = 3.0.  This end effect is caused by friction at the rock-steel platen interfaces, creating shear stresses near both ends of the specimen, as evidenced by the results of finite difference analyses that the shear zones in rock near the loading ends become predominant for specimens with a low L/D ratio.  The claystone strengths obtained from neoprene capped specimens with different L/D ratios show a lower intrinsic variation and tend to be consistent at 32.4 MPa.  For the specimen with L/D ratio less than 2.0, the strengths from neoprene capped specimens may be more representative than those with
shape-correction from the uncapped specimens.  Elastic modulus values measured from both capped and uncapped specimens tend to increase with L/D ratio.