bored pile

METHOD STATEMENT for the construction of

BORED PILES (General Use)

Method Statement for Bored Pile

METHOD STATEMENT FOR THE CONSTRUCTION OF BORED PILES A.

Excavation of pile shaft

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Before excavation of each bored pile, identify any possible obstruction and confirming founding level by site inspection.

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Set out the correct position of the bored pile on site. See Photo 1.

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Set up the vibrator in lifted with a crane.

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Install the bottom section of permanent or temporary casing into the ground by vibrating motion exerted by the vibrator.

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Excavate in soil using augering method. The auger is lowered down by a telescopic boom to excavate soil and retrieve the auger to the top after excavation.

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Move the auger with soil in it away from the excavated hole by swinging the machine. Rotate the auger in the opposite direction to remove the soil from the auger.

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The augering process is repeated until the required depth is reached or hard layer or rock is reached.

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If necessary, use a bucket to clean the bored hole with the process similar to the auger. However, for dumping of soil/spoils, the bucket needs to be released by pulling a pin manually.

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For hard soils and solid rock, if necessary, rock auger head can be employed to grind into hard soils and rock and subsequent removal of fragments by bucket.

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Extension of the steel casing can be done by welding on additional casing during excavation. A sample is shown in Fig.1. However, the method may vary from site-to-site, depending on the soil condition. If the soil is soft, simple full welding is sufficient.

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Verticality of the casing will be monitored by means of spirit level.

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Continue the above procedure until the tentative completed level / sound rock level has reached. Soil samples & rock fragments will be collected for inspection.



Figure 1 : Details for Connection of Casing

B.

Cleaning of Pile Shaft

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The pile shaft shall be cleaned by the bucket if there are suspected loose material at the toe. The presence of water in the shaft (if any) is OK, provided there are no collapse of soil in the hole.

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This can be checked with when the withdrawal of bucket, there shall be no debris, soils or rock fragments in the bucket after cleaning .

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The depth of the pile is checked using a weighted measuring tape.

C.

Preparation of Reinforcement Bars

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The reinforcement and links cage is prepared, prefabricated prior to the completion of the bore pile.

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The links shall be prepared first and subsequently tie the required amount of reinforcement, spaced equally onto the link.

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Place circular spacers onto the spiral link at intervals required by the design.


D.

Installation of Reinforcement Bars

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When the reinforcement cages are ready, they can be installed into the pile.

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The weight of the prefabricated cage can be calculated in order to select a suitable crane for lifting. If a mechanical bored pile machine is used, the bore pile machine engine shall be detached and the mounted crane can be used for lifting.

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The prefabricated cage shall be lowered down into the hole, segment by segment by lifting the entire cage using a suitable crane. The top of the cage will be welded with a suitable hook for lifting of the cage.

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Shall lapping of reinforcement is needed, a lap length of 40D shall be used. The laps shall be done using welding, or tied with tie wires or U-bolts.

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Repeat the step above until required depth is reached.

Photo 2: Installing the prefabricated rebar cage into the bored hole.


E.

Concreting (Direct Pour or Tremie Method)

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Set up a working platform to the top of the temporary casing if the ground is soft using steel plates.

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If there is less than 1m of water present in the hole (can use a tape measure and a piece of timber/wood tied at the bottom), the hole is deemed to be dry and direct pour method can be used.

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Otherwise, if the pile is flooded with water (>1m), the pile shaft shall be concreted by “Tremie Technique". The tremie pipe sections will be inserted and be jointed until it reaches the bottom of the pile shaft.

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Concrete will be poured into the tremie pipe by using a concrete skip. Concreting will be carried out in one continuous operation to a stop-off level ( above the cutoff level ) agreed with the Client. (See Photo 3).

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As concreting proceeds, the level of the concrete relative to the ground level can be monitored by measuring with weighted tape after each skip of concrete is placed.

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The tremie pipe can then be extracted piece by piece as the concreting goes on.

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The temporary casing can either be extracted simultaneously by the vibrator in course of concreting, or after completion of concreting. A head of about 2 m (minimum) is always maintained between the top of concrete and the bottom of steel casing.

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If a length of permanent casing is required, the extraction of casing shall be stopped after the bottom of casing reaches the required level.

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If the length of the permanent casing is already installed to depth, leave the casing intact after concreting.


Photo 3 : Concreting using a tremie pipe.


bored pile

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