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Achieving Higher Normal Stress Levels in the Prismatic Wedge Shear Test T. Mirata A. Gökalp M. Sakar |
ABSTRACT The prismatic wedge shear test (priswest) is a relatively new technique of measuring the shear strength of gravels and gravelly clays using a portable frame and a right prismatic box (test mould) consisting of two identical halves separated by 5 mm to 12 mm high spacers which, when removed, leave the plane of shear, measuring 300 mm x 300 mm and inclined at an angle usually between 30o and 45o to the main load P, free for testing. P is applied through two grooved plates with a ball cage holding sixty-four 12-mm dia. steel balls in between; a relatively small lateral load Q has a similar effect as the cell pressure in the triaxial test in increasing the average principal stress in the test. It has previously been demonstrated that for a given Q, the normal stress in the priswest increases with the sum of the angle of internal friction of the soil and the angle between P and the shear plane. The results of priswests on well graded < 40 mm gravel using test moulds providing 30o to 40o for the latter angle have already been published. Presented in this paper, are the results of priswests on the same material using a 45-degree test mould, and those on clayey gravels, exhibiting a lower angle of internal friction, using an originally 40-degree mould which, with minor modifications, could be used as a 50-degree one when desired. Static compaction has been used for the compaction of the latter material in the priswest mould, using the same loading frame and hydraulic jack as used during shear. It has been demonstrated that normal stresses of the order of 1000 kPa can be achieved in the priswest both in clean gravels and in gravels containing up to 20 % of fines.
KEYWORDS: clay, gravel, degree of compaction, laboratory equipment, shear test, static compaction, triaxial test, wedge shear test.
