Foundation Soil Improvement Using Vibro Compaction Combined with Geo Grids

This paper presents the approach and results achieved through using an innovative idea of integrating the principles of vibro-compaction (stone columns) with geo-grids to improve the soil properties and ensure a uniform geo-technical behavior of the foundation soil of a group of 6 No. 10 MIG steel water reservoirs constructed in the same area in Abu Dhabi in the United Arab Emirates. Tests performed on the soil at site proved that the soil is loosely compacted cohesion-less silty sand (SM) with a bearing capacity less than 100kpa. Depth to firmer strata ranged from 10m to 15m. The 60m diameter reservoir produced a bearing pressure of 200kPa. The solution of piles extending to firm strata was overruled in favor of the more economic solution of vibro-compaction. Vibro-compaction using stone columns provided the optimal solution for improving the upper loosely compacted soil to accommodate the bearing stresses of the reservoirs, while a system of uniaxial and biaxial geogrids ensured a uniform bearing capacity and settlement behavior of the improved soil. The paper presents the case history illustrating the design principles, parameters and the approach adopted to provide the soil improvement solution. The bearing capacity achieved through the adopted solution is 300kPa with a maximum recorded total settlement of 22mm and a maximum recorded differential settlement of 9mm for all 6 fully loaded reservoirs. In addition the economic advantage of using this solution amounted to 20% cost saving and 25% construction time saving.