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Piles Engineering

In deep excavation, adjacent ground water table is drawn down which may affect the settlement of nearby buildings. What is the remedial proposal to rectify the situation?

One of the methods to control settlement of nearby buildings due to excavation work is by recharging. Water collected in wells in deep excavation is put back to the top of excavation in order to raise the drawn-down water table.

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What are the problems associated with prestressed concrete piles (Daido)?

The origin of Daido piles comes from Japan where these prestressed concrete piles are used as replacement plies. Holes are pre-formed in the ground and Daido piles are placed inside these pre-formed holes with subsequent grouting of void space between the piles and adjacent ground. However, in Hong Kong Daido piles are constructed by driving into ground by hammers instead of the originally designed replacement method.
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Should compaction be carried out to freshly-placed concrete piles?

In normal practice, reliance is placed on the self-compaction of specially designed concrete mixes to achieve adequate compaction. The use of vibrating devices like poker vibrators is seldom adopted for the compaction of concrete piles.

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Is the quality of concrete impaired by free-falling concrete placement method in bored piles?

Based on the research by STS Consultants Ltd., it was found that concrete placed by free falling below 120 feet would not suffer from the problem of segregation and the strength of concrete would not be detrimentally impaired provided that the piles’ bore and base are dry and free of debris. Moreover, it is presumed in the past that during free falling of fresh concrete into the pile bores the hitting of falling concrete in the reinforcement cage causes segregation. However, in accordance with the experimental results of STS Consultants Ltd., the striking of reinforcement cage by fresh concrete does not have significant effect on the strength of concrete
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Is pile tip cover necessary for rock-socketed H-piles?

In current practice concrete cover is usually provided at the pile tips of pre-bored H-piles socketed in rock. The purpose of such arrangement is to avoid the potential occurrence of corrosion to H-piles in case concrete cover is not designed at pile tips. However, recent field and laboratory observations had reservation of this viewpoint.

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