Excavation of bored piles is usually implemented by a hammer grab. The steel casing will be extended by welding or bolting on additional casing and is installed by hydraulic oscillator.
Water is pumped into the casing during excavation and excess water head is required to be maintained to prevent any ingress of material at the bottom of casing. Moreover, for excavation below pile casing, the provision of excess water head is essential to maintain bore stability.
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This question is taken from book named – A Closer Look at Prevailing Civil Engineering Practice – What, Why and How by Vincent T. H. CHU.
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