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Piles Engineering

What is the purpose of setting maximum spacing of piles?

One of the factors that affect the distribution of loads from the structures to each pile is the assumption of flexibility of the pile caps in design. A pile cap can be modeled as a flexible or a rigid element based on their relative stiffness.

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What is the difference between capping beams and ground beams for piles?

Capping beams for piles aim at transferring loads from closely spaced columns or walls into a row of piles. On the other hand, ground beams are beams provided between adjacent pile caps and they perform as compression struts or ties in an attempt to prevent lateral displacement or buckling of piles under uneven distribution of loads on pile caps. Both of them have to be specially designed to cater for differential settlement of piles.

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What are the differences in function between rock anchors and rock sockets?

Rock anchors are used primarily for resisting uplift forces. On the contrary, rock sockets serve three main purposes:

(i) Rock socket friction and end bearing to resist vertical load.

(ii) Passive resistance of rock sockets contribute to resistance of lateral load.
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What are the limitations of Plate Load Test?

Plate load test is carried out to check the bearing capacity of foundation soils.

The limitations of plate load test are:

(i) It has limited depth of influence. It could only give the bearing capacity of soils with depth up to two times the diameter of plate.

(ii) It may not provide information on the potential for long term consolidation of foundation soils.
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Can both Pile Drive Analyser PDA and Pile Integrity Test PIT be used for checking pile capacity?

Pile Drive Analyser is a high-strain dynamic test to determine the force and velocity response of a pile to an impact force applied axially by a driving hammer at the pile top. It is applicable to driven piles or small diameter bored piles. The operation measures the elastic deformation of a pile after a hammer blow and is mainly used to check the ultimate capacity of piles. However, it may also be adopted to detect damages in pile body and obtain the friction profile along the pile shaft.

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What are the meanings of the mathematical terms in failure criteria pile load test?

Load tests are conducted to verify the design assumptions and parameters such as pile friction in soils and sock socket capacity. There are various failure criteria in current construction industry to determine ultimate load resistance of piles in pile load test. For instance in 90% criterion of Brinch Hansen, it is based on the laboratory measured stress-strain relations of soils and a point is identified in which soil fails. This essentially aims at looking for the ultimate bearing capacity and hence the ultimate loads. In fact, this is not intended originally for piles.

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What is the purpose of conducting load test for piling works?

Pile load test provides information on ultimate bearing capacity but not settlement behavior. In essence, it can determine if the load is taken up by the stratum designed or if the centre of resistance is at the design location in piles as suggested by Robert D. Chellis (1961).

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There is an old rule that the area of a follower should be one-fifth of precast concrete pile. Why?

The rules of wave mechanics suggested that to avoid reflection of stress wave caused by different impedance values, acoustic impedance should be the same for the follower and precast concrete piles. As such, it enhances smoothest driving and prevent follower from bouncing on the head of piles which is undesirable as it may damage the piles and lowers the efficiency of driving.

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In the installation of strain gages in driven H-piles to measure loads, why should they be normally used in pairs?

Strain gages are often installed in driven piles to measure the load distribution along the piles. They have to be protected from being removed as the pile is driven into the ground. Protection of strain gages is achieved by welding channels or angles for enclosure of stain gages.

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How can piles be driven through steeply dipping karst surfaces?

The steep dipping and variable nature of karst surfaces poses problems for installation of driven piles. Very often, the consequences of hard driving piles over steeply-inclined karst are slipping and buckling of piles. To tackle these problems, the following two options are mostly adopted:

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