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Piles Engineering

Why is sleeving applied in piles constructed on slopes?

For high-rise buildings constructed on steep cut slopes, these buildings are usually supported by large diameter piles. Though the piles are founded at some depth below the slopes, lateral load arising from wind on buildings may induce loads on the slop and causes slope failures. For shallow depths of slope which is marginally stable, it is more vulnerable to slope failure.
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What is the purpose of shaft grouting of deep foundations?

In shaft grouting operation, tube-a-manchette pipes are fixed at regular spacing to the reinforcement cage. After concreting barrettes/bored piles, a small volume of water is injected under high pressure into these pipes to crack the concrete.
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Can down the hole hammer function below water table?

Down the hole hammer has been used extensively to form pre-bored holes as rock sockets for mini piles and pre-bored H piles. The hammer functions by driving repeatedly a drill bit using compressed air on the rock. However, the use of down the hole hammer is normally limited to hole diameter of 600mm.
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Why can’t normal Reversed Circulation Drills function in shallow rock conditions?

Reversed Circulation Drill (RCD) is normally used for forming large diameter rock socket. The method involves the exertion of a download force of roller cutter bits on rock, together with the action of rotation and grinding of bits on rock. The cuttings are then removed by reverse circulation. The water and cuttings are airlifted through a central drill pipe, which is also used for rotating the drill bits.
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Should bentonite be added to improve the stability of grout?

For unstable grout, particles will come out of the grout suspension leading to incomplete grouting and clogging of pipes. The stability of grout can be improved by adding additives such as bentonite. However, bentonite should not be used with very fine cements because its grain size is bigger than that of fine cements. Tests conducted previously confirm that a grout with bentonite is less stable under pressure.
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What are the reasons in observed settlements in rockfill foundation?

Compression of rockfill is normally caused by a reduction in dimension of fill and by rearrangement of particles into closer packing.

When the rockfill are saturated, the strength of rock would be reduced accordingly. In fact, wetting of rock surfaces does not reduce the coefficient of sliding friction between rockfills. Considerable settlement may result not from the lubricating effect of water but from a reduction of rock strength at its point of contact. The contact points would then be crushed under intergranular force and the contact area increases until contact pressure is less than the strength of rockfill.
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In seismic liquefaction, what is the difference of pile failures mechanism between lateral spreading and buckling?

Most of design codes assume that pile fails during strong earthquake by lateral spreading. Lateral spreading is based on bending mechanism where the inertia and slope movement causes bending in piles. In essence, piles are considered as beams which are subjected to lateral loads such as slope movement leading to pile failure.
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When are prestressed tiebacks used in sheet piling works?

The use of prestressed tiebacks gets rid of the need of interior bracing. Prestressed tiebacks are anchored into rock or granular soils and excavation can be conducted by using powerful shovel instead of using hand excavation or other small excavators. It provides less restraint and allows free movement for excavation.
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What is the significance of quality of bentonite slurry in the construction of diaphragm walls?

The quality of slurry plays an important role in the quality of diaphragm walls. Firstly, if a thick slurry cake is formed in the interface between slurry and in-situ soil, it has a tendency to fall off during concreting works and it mixes with freshly placed concrete. Moreover, large thickness of slurry cake would reduce the concrete cover and affect the future durability performance of diaphragm walls.
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During concreting of diaphragm walls, three tremie pipes are used in one time. However, only one concrete truck is available. How should the concreting works be carried out?

The most ideal situation is to supply each tremie pipe with a single concrete truck. However, if only one concrete truck is available, all the fresh concrete in the truck should not be placed in one single tremie pipe.

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