Experimental study on the seismic behaviour of geosynthetic-reinforced pile-foundation system

Abstract

ABSTRACT: The use of geosynthetic reinforcement in earth structures has increased significantly over the last two decades. The advantages associated with the use of geosynthetics have been well documented. Some of the typical applications include slope stabilisation, improvement of embankment foundations, mechanical stabilisation of retaining structures and subgrade improvement of roads. Certain subsurface conditions may dictate special foundation solutions such as piled foundations. Such foundations are widely used in seismically active areas, where they are expected to resist significant lateral loads. However, the weak subsurface conditions that dictate the use of pile foundation systems result in low lateral foundation resistance. The objective of this paper is to introduce an innovative use of geosynthetics as part of a novel foundation concept called geosynthetic-reinforced pile foundations, where polymer strips are used to enhance the lateral resistance of the pile foundations. The seismic pile–soil–geosynthetic interaction of this system was evaluated using a series of reduced scale physical model tests performed on a shaking table in 1g environment. A uni-directional laminar shear box containing a three-layer soil stratigraphy, which included a layer of synthetic clay known as Modified Glyben sandwiched between lower and upper layers of granular materials, was used in the physical model tests. The model pile-cap system that supported a single degree of freedom structure was installed and a series of tests were performed using dynamic loading in the form of sine sweep, harmonic and scaled earthquake signals in order to identify the amplification and resonance conditions of the foundation system and to evaluate various aspects of the pile–soil–geosynthetic interaction. The results revealed that introducing the model geosynthetic mesh attenuated the acceleration and displacement response of the low frequency single degree of freedom structure and its pile cap when subjected to a strong sine sweep signal. On the other hand, for weak shaking signals with high frequency single degree of freedom structure introducing the model geosynthetic mesh into the granular backfill did not demonstrate the same favourable effect because of the low soil strain associated with weak signals. These results demonstrate that the use of the geosynthetic mesh will be effective for strong earthquake events.