SCC for under-reamed piles

Self Compacting Concrete (SCC) is an ideal choice for cast in-situ piles where compaction is infeasible. An experimental study conducted at the Structural Engineering Research Centre, Chennai, clearly demonstrated the control on geometry of self compacting concrete under-reamed piles when cast against soil form work. Six double under-reamed piles of 250 mm diameter and 4 m length, three made of SCC and three of Conventionally Vibrated Concrete (CVC) having similar strengths, were cast and tested to evaluate their dynamic and static behaviour (axial compression and tension (pull out). Later, all the piles were exhumed using suitable machinery to examine the as-cast characteristics of pile shaft and bulbs. Ultrasonic pulse velocity measurements taken along the length of the exhumed piles evaluated the integrity of the concrete. Concrete cores of 75 mm diameter and 150 mm height taken from the pile shaft were evaluated for mechanical and durability related properties. The pile shaft and bulbs were observed to be well formed in SCC piles. The homogeneity of concrete was excellent. Hence, SCC is recommended for use in under-reamed piles as uniformity of concrete both in the shaft and bulbs are assured, leading to enhanced life expectancy of piles. The variation in surface characteristics of the SCC and CVC piles, the former being far smoother, has not led to any deterioration in bond properties between soil and the pile. This has resulted in similar performance of SCC and CVC piles under dynamic action. The CVC group of piles had shown pronounced non-linearity in the static tests, because of imperfections as well as due to deformation gradient effects affecting the performance of the compression pile.