Ground Improvement of a Liquefiable Soil by Granular Piles

Liquefaction is a physical process by which soil sediments below the groundwater table temporarily loose strength and stiffness, and initiate to behave as a viscous liquid rather than a solid. In addition to earthquake and rapid application of large loads, a soil may liquefy due to construction activities like blasting and during ground improvement by vibro-flotation and dynamic compaction. Liquefaction phenomenon may cause unrecoverable damage to a building and other civil structures. Hence, it is very important to know about the liquefaction potential of a construction site so that suitable protection measures can be adopted before construction. Granular piles are one of the popular treatment methods to make the soil less prone to liquefaction. In this study, liquefaction potential of a project site at Darbhanga in Bihar has been evaluated (by method developed by Youd et al. 2001) from the borehole data where groundwater table is at a shallow depth. Once the liquefiable depths in substrata are identified, granular piles along with the shallow foundation have been selected as the best viable foundation solution based on the soil characteristics determined. The design of granular piles consists of certain parameters, such as their diameter, total length, number of piles and their arrangement at site. Use of granular piles will not only improve soil strength significantly but also will provide drainage option for  the risen groundwater at high pore water pressure which may be generated during an earthquake event. To present the benefit of granular piles over conventional RCC piles, a comparative design and cost assessments of granular piles with RCC piles were also performed. It has been observed that a significant reduction of construction cost and settlement control may be achieved by granular piles over RCC piles. This kind of study will help in selecting an appropriate liquefaction measure and its design, leading to safer construction of the civil structures.