Load settlement characteristics of a piled raft in sand
Seet, Kelvin Chee Kiong.
Date of Issue2010
School of Civil and Environmental Engineering
Raft foundations have been commonly employed as foundations to overcome differential settlements due to erratic soil conditions and close proximity of pile caps. The bearing capacity requirement is usually fulfilled due to the large area coverage by the raft foundation. However raft foundations may settle excessively in weak or compressible soils and the most cost effective method to reduce settlement is to introduce piles. Piles as settlement reducers were first proposed by Burland (1977). The traditional design approach is to ignore the bearing capacity of the raft and assume all structural loads to be carried by the piles. This unduly conservative approach ignores the load sharing effect between the raft and the piles and thus the design is extremely cost ineffective. If the bearing capacity of the raft-soil system is already adequate, the settlement of the raft should be reduced by introducing a minimum amount of piles. The objective of this project is to investigate the load settlement characteristics of a piled raft in sand with and without piles when subjected to vertical axial loading. Factors such as raft rigidity, pile length, pile numbers and pile spacing which have a significant impact on the load settlement characteristics were also being looked into. Model tests of rigid piled rafts were conducted in medium dense sand of relatively similar density. A ‘unit cell’ approach of ‘dividing’ the piled raft into individual units is employed to simplify the complexity of piled raft and to provide an alternate source of understanding. Experimental results have shown that increasing the number of piles, lengthening the piles and increasing the pile spacing in a piled raft will lower its settlement. However, it is observed that there is a pile-raft-soil interaction effect in the piled raft that has a significant impact on the settlement of piled raft. The piled rafts can be correlated with the unit cell to verify the effect of the pile-raft-interaction on the settlement of piled rafts.
Final Year Project (FYP)
Nanyang Technological University