Investigation of force transmission during indirect activation of a geogrid in transparent soil

Abstract

The composite material geogrid reinforced soil has a wide range of applications. In most cases the geogrid reinforcement is indirectly activated by an applied load via the surrounding soil, for example in base layers of embankments, foundation pads and fill structures. Within these geogrid reinforced structures, different areas can occur in which the direction of force transmission might differ from soil to geogrid and vice versa. In particular, the force transmission in the soil-geogrid-interface involves a fundamental need for research. Therefore, this paper firstly introduces a conceptional model for indirect geogrid activation, secondly presents a test rig in which the interaction mechanisms can be investigated on micro scale and thirdly determines various areas with different directions of force transmission. For this purpose, transparent geogrid reinforced specimens are biaxially loaded, whereby an area-wide and undisturbed insight into the soil-geogrid-interface is enabled. The transparent soil is created as a two-phase medium consisting of a crushed fused quartz and a white oil with a corresponding refractive index. The displacement fields of the geogrid and the surrounding transparent soil were determined using a digital image correlation (DIC) method based on images taken continuously during the test. Then, strain profiles were derived for the longitudinal tensile members, which were converted into a force distribution along the geogrid. As a result, the conceptional model can be verified.