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. For the pile cap to be assumed as rigid the stiffness of pile cap is infinite relative to that of pile/soil system and the deformations within the cap are not considered owing to its rigidity. On the other hand, for the pile cap to be designed as flexible, internal deformations of pile cap would occur.

In some design guidelines, maximum spacing of piles is specified to limit the length between adjacent piles so that the assumption of rigid pile cap can be justified.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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.

Capping beam performs the same functions as pile caps. However, ground beams are structural elements to connect adjacent pile caps to improve the stability of foundation.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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.

(iii) Socket shaft friction is also used for resisting uplifting forces. But only 70% of this capacity should be used because of the effect of negative Poisson ratio.

Note: Rock anchors, which may consist of a high tensile bar or a stranded cable, are provided for tension piles when there are insufficient soil covers to develop the required uplifting resistance.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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.

(iii) There is scale effect as the size of test plate is smaller than actual foundation.

(iv) To gain access to test position, excavation is carried out which causes significant ground disturbance. The change in ground stress leads to the change of soil properties which the test is planned to investigate.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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.

Pile Integrity Test is a low-strain dynamic test which involves the use of a small vibrator or a light hammer. It is applicable to small diameter driven concrete piles and large diameter bored piles. It can be used to check the following properties:

(i) Quality of concrete (e.g. honeycombing)
(ii) Location and type of damages
(iii) Estimation of pile length

However, it is mainly used to check the integrity of piles only and it may be used to deduce the pile capacity.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.