Development of high capacity torsional shear apparatus for the measurement of small strain deformation properties of soils

Abstract

Recently developed medium-sized torsional shear apparatus at Institute of Industrial Science. University of Tokyo, Japan and results from tests on dry Toyoura sand using a modified version of pin-typed local deformation transducer (PLDT) system with other conventional strain measurement techniques are presented. Loading system of this apparatus consists of servo motors coupled with reduction gear systems for controlling both vertical and torsional loadings precisely. This apparatus is capable of controlling both vertical and torsional cyclic loading either by stress amplitude or strain amplitude. Cell pressure can be controlled by an electro-pneumatic transducer. The three stress components (axial, torsional and confining stress) can be controlled independently by using a personal computer. High loading capacity of the apparatus and its capability of testing specimens of various sizes up to 20 em in outer diameter, 12 em in inner diameter and 30 cm in height arc helpful in understanding the properties ofgeomaterials with large particle sizes such as gravel. Axial and torsional loads are measured precisely with a twocomponent load cell, which has a negligible coupling effect. Cell pressure is measured by using a high capacity differential pressure transducer. In order to measure thc local strains, two sets of PLDT's arranged in a triangular form using separate hinges are used at opposite sides of a diameter of the specimen. Based on cyclic torsional shear and triaxial tests on dry Toyoura sand using this apparatus, it was confirmed that quasi-elastic deformation properties such as Young's modulus and shear modulus can be measured at various stress states by conducting small amplitude cyclic loading in axial and torsional directions. In addition, it was verified that this apparatus is capable of conducting large cyclic drained and undrained loadings and hence liquefaction behavior of sand can be investigated.