A versatile apparatus for assessing the shear behaviour of geotechnical interfaces coupled with imaging and acoustic capabilities

This paper presents a versatile interface direct shear test apparatus developed for systematically investigating the shear behaviour of geotechnical interfaces. The apparatus can support the testing of several particle–continuum as well as continuum–continuum interfaces and can also accommodate different configurations of testing, viz. conventional and fixed-box interface shear testing, by a simple rearrangement of the different components. The apparatus facilitates the visualisation and measurement of the deformation of geotextiles under pull-out loading, particle kinematics and the acoustic behaviour of soil–continuum interfaces by accommodating advanced deformation-measurement devices like digital cameras for digital image correlation (DIC) and sensors for acoustic emission (AE). The paper describes the design of all the components of the apparatus and the results of the interface shear tests of different particle–continuum and continuum–continuum interfaces. The repeatability of the test results is verified through multiple tests on the same interface. Results of the interface shear tests indicating the sensitivity of the apparatus for the different modes of testing are also presented. The provisions such as the shear box with a transparent side wall, the moving platform with an interchangeable transparent bottom and the capability to accommodate AE studies facilitated a detailed understanding of various types of interfaces. The DIC results provided insights into the shear zone formation at the dilative interfaces and the deformation of a geotextile under a pull-out load. The AE studies provided a new perspective on the response of particle–continuum interfaces.