Behaviour of geogrid-reinforced load transfer platforms for embankment on rammed aggregate piers

Abstract

A test embankment was constructed over soft ground to evaluate the performance of different types of load transfer platform (LTP) supported on rammed aggregate piers (called ‘geopiers’). Three types of LTP were constructed in accordance with the recommended design for each: a geosynthetic-reinforced LTP with two layers of geogrid (catenary LTP), a geosynthetic-reinforced LTP with three or more layers of geogrid (beam LTP), and a reinforced concrete LTP. The results indicate that the differential settlement between the geopiers and the matrix soil is relatively small in all LTP sections, with the smallest in the beam LTP. The tensile strain in the geogrid was approximately 60% of the allowable design strain of 5% in the beam LTP. In the catenary LTP, the tensile strain in the geogrid was approximately 20% of the allowable design strain of 6%, although the differential settlement was larger than the beam LTP. The total and differential settlements observed indicate that the use of less stiff geopier columns together with LTPs provides an attractive option for supporting low embankments on soft ground with tolerable total and differential settlements. The presence of LTPs and the supporting columns also tend to reduce the lateral movement of the foundation soil. The cost analysis of the different LTPs indicates that construction costs for geosynthetic-reinforced LTPs are likely to vary with locality; however, it appears that beam LTPs offer a less costly approach, with enhanced performance.