NUMERICAL ANALYSIS OF SAND-FIBER MIXED GRANULAR PILES

Abstract

Ground improvement technique is a methodology to treat and improve the foundation performance on poor ground so that the ground properties are improved and the effects of heterogeneity are reduced. Stone column or granular pile is one of the techniques of ground improvement. The installation stiffens the soil, reduces settlement, improves load carrying capacity and accelerates consolidation. Further, the addition of random fibers in the granular pile/ column matrix increases the stiffness. The response of granular pile due to random sand-fiber mix has been studied in detail by Basu (2009) by carrying out extensive short term model tests in the laboratory by varying fiber content, fiber length and depth of fibers in the granular piles. A considerable improvement in the performance of granular piles in terms of load carrying capacity, stiffness and reduction in bulging of the granular pile on addition of random fiber mixed and sand pad thickness has been reported by Basu (2009). The present work deals with the development and analysis of a numerical model of sand fiber mixed granular pile and thereby comparing the results with the experimental investigation results (Basu, 2009). For this purpose, a three-dimensional explicit finite-difference program i.e., FLAC3D has been used. FLAC3D is a numerical modeling code for advanced geotechnical analysis of soil, rock, and structural support in three dimensions. The present numerical study suggests that load carrying capacity of granular pile (GP) increases with increasing percent fiber content, fiber length, fiber depth, footing diameter, granular pile diameter and sand pad thickness. The optimum fiber depth with respect to the improvement in load carrying capacity has been found to be three times the diameter of GP (3.0d) for random fiber mix of 0.5% fiber content and fiber length of 30 mm. The improvement in load carrying capacity of GP with rigid footing diameter equal to diameter of granular pile (D = d case) has been found to be more than that of GP with rigid footing diameter twice the GP diameter (D = 2d case). The maximum bulging diameter of the GP decreases with increase in random fiber mix and sand pad thickness. But both the depth of occurrence of maximum bulging and total depth of bulging of the granular piles increases with increase in random fiber mix and sand pad thickness. This implies that the load has been transferred to a greater depth through the granular pile. The settlements at various depths of GP increases with increasing random fiber mix and sand pad thickness. Hence, these findings fairly authenticate the experimental study (Basu, 2009).