Volume 31, Issue 6 (November 2008)
An Apparatus for Direct Shear, Pullout, and Uniaxial Testing of Geogrids
In this paper, design and calibration procedures for a new large-scale testing apparatus for testing geosynthetic-soil systems are described. The multiple functionalities of the apparatus are implemented through the use of a single loading frame, driving mechanism, instrumentation, and data acquisition system for three distinct modes of loading: pullout, direct shear, and uniaxial loading. The design is similar to a conventional pullout device, but also includes key modifications and additional modules to adapt it for additional types of experiments. For example, in the uniaxial tension configuration, extension rods are used to transfer the load from the driving mechanism to the mounted specimen. In the direct shear configuration, the bottom half of the shear box is allowed to slide horizontally on low friction roller bearings while connected to the driving mechanism, whereas the top half of the box is fixed. Hydraulic jacks and a steel plate are used to apply the normal pressure in the pullout and direct shear configuration. A series of pullout experiments were performed to validate the functionality of the apparatus and to examine the relationship between the geometry of the geogrid opening and its pullout resistance.