Performance Study of Rammed Aggregate Pier as a Ground Improvement Technique in Soft Ground

Abstract

The development of modern foundation practices, namely ground improvement techniques, has been proved to be viable both the technically and economically for the improvement of marginal sites and to overcome the limitations of conventional foundation systems. Amongst the various ground improvement techniques for improving soft ground conditions, Rammed Aggregate Pier (RAP) such as Geopier is considered as one of the most versatile and innovative ground improvement method than the other methods. The performance of Rammed Aggregate Pier has yet not been examined in soft ground condition of Bangladesh at field level. This study is concerned with the performance of Rammed Aggregate Pier in soft ground at a selected site of South-West region of Bangladesh i.e. KUET (Khulna University of Engineering & Technology) campus. The ground at the site consists of soft fine-grained soil up to great depth with a layer of organic soils at 4.5 to 9m depth from the existing ground surface. The Rammed Aggregate Piers were installed by rammed method with locally fabricated equipments. This installation method is easier and cost effective than other counterpart. Rammed Aggregate Pier of cylindrical shape having 0.75m diameter and 3.4m length were installed manually in three arrangements as single, double and group. A uniform mixture of local sand and brick aggregates at the proportion of 1:2 was used as the granular materials maintaining saturated surface dry condition. The granular materials were poured into the excavated hole in layers and hence compacted adequately by using a hammer of 108kg and a free fall height of 600mm. Load tests on full-size isolated square footing of 1.68x1.68m resting at a depth of 0.75m from the existing ground surface were conducted on both the natural and improved ground by using the method similar to pile load test. The field measurement shows that the ultimate bearing capacity of footing resting on single, double and group RAP treated ground can be increased by 1.5, 1.8 and 1.96 times, respectively, comparing to that of natural ground. Field investigation reveals that the RAP made-up of locally available granular materials and the employed installation technique can be used successfully as a suitable ground improvement method to improve the bearing capacity of such soft ground.