Study on the Field Performance of Granular Pile as a Ground Improvement Technique

Abstract

Ground improvement by granular piles is considered as one of the versatile and cost effective ground improvement method. Installation of granular piles transforms the soils into a stiffer composite mass with intervening native soil proving lower overall compressibility and higher shear strength. In the recent years this technique has also been adopted in Bangladesh in various projects to improve the marginal sites. The installation technique has the big influence on the performance of this ground improvement method. There is a record of successful application of rammed-displacement method in the installation of granular piles in the soft ground of Bangladesh. This study concerns on the field performance of granular pile installed in soft ground of Bangladesh. For this investigation a typical soft ground site at KUET campus, Khulna is considered. The sub-soil of KUET campus consists of fine-grained soil of very soft to soft consistency up to the great depth. The more one sand pile installation in this study, sylhet sand. Granular piles of 300 mm diameter and 8.25 in length were installed in single. Load tests were conducted on 0.30m diameter plate resting at a depth of 0.91m from the existing ground surface on both the natural and improved ground. The plate load test were conducted on the natural ground and on the top of sand piles after one month and one year of installation of granular piles. Standard penetration tests were also conducted to observe the change of soil stiffness due to the installation of sand pile. The test results reveal that the bearing capacity of the normal ground was increased by the installation of granular piles. Comparing to the natural ground, the bearing capacity of improved ground was increased by 200% to 250%. The cost of mat and pre-cast pile foundation increased approximately 114% and 154% respectively while compared with sand pile. Field investigation reveals that the granular pile made-up of locally available granular materials and employed installation technique can be used successfully as a suitable ground improvement method to improve the bearing capacity of such soft ground.