Loads from columns transferring to pile cap induce tensile forces at the bottom of the cap. For instance, by using truss analogy to analyze a pile cap sitting on two piles with a column at the centre of the pile cap, the
tensile force at the bottom is proportional to the pile spacing and is inversely proportional to depth of pile cap. The bottom reinforcement is designed to resist the tensile stressed generated from loads in columns.

Side reinforcement may not be necessary in pile cap (L.A. Clark (1983)). In fact, the primary aim of the side reinforcement is to control cracking. However, as most pile caps are hidden from view and it is considered not necessary to provide side reinforcement to pile caps based on aesthetic reason.

Sometimes, reinforcement may be designed at the top of pile caps which serve as compression reinforcement. This type of reinforcement is required in case there is a limitation on the depth of pile caps. Similarly shear reinforcement is introduced to the pile caps in case there is a restriction to the depth of pile caps.

L. A. Clark (1983) Concrete Bridge Design to BS5400 Construction Press, Longman Group Limited pp.94

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.

The construction of piles by driving method causes an increase in density of the surrounding soils. Hence, for loose soils this results in improved compaction of soils between the piles. The sum of the capacities of all piles
as a whole is generally greater than the sum of individual pile capacities provided that the effect of pile spacing is not taken into account. However, for bored piles the boring operation induces considerable stress relief and
this causes a substantial reduction in shear strength of soils.

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.

When the piles are progressively driven into the ground, the pile section above the ground declines. As a result, the degree of damping on the piles increases. Moreover, the area of exposure of piling surface reduces, thereby reducing the area generating noise form piles. Hence towards the end of pile driving operation, the noise level shall be reduced accordingly.

Noise screen shall be installed to tackle the noise problem. Noise screen made of plywood might not be sufficient because it tends to reflect the noise back to the site and increase the reverberation of the site. Instead for the face of noise screen facing the piling operation shall be lined with a layer of sound-absorbing material such as glass fibre. Moreover, openings on noise screen should be avoided because it can substantially reduce the performance of noise screen.

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.

In some design lateral loads are assumed to be resisted by earth pressure exerted against the side of pile caps only. However, it is demonstrated that the soil resistance of pile lengths do contribute a substantial part of lateral resistance. Therefore, in designing lateral resistance of piles, earth pressure exerted on piles should also be taken into consideration.

In analysis of lateral resistance provided by soils, a series of soil springs are adopted with modulus of reaction kept constant or varying with depth. The normal practice of using a constant modulus of reaction for soils is
incorrect because it overestimates the maximum reaction force and underestimates the maximum bending moment. To obtain the profile of modulus of subgrade reaction, pressuremeter tests shall be conducted in
boreholes in site investigation. Reference is made to Bryan Leach (1980).

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.

The choice of a large diameter pile suffers from the disadvantage that serious consequences would occur in case there is setting out error of the pile. Moreover, in terms of cost consideration, for the same load capacity the cost of a group of small diameter piles is generally lower than that of a large diameter pile. On the other hand, for small diameter piles i.e. mini-piles, they are advantageous in site locations with limited headroom and space. In addition, in some structures with only a few piles, it is uneconomic because of its high mobilization cost. Reference is made to Dr. Edmund C Hambly (1979).

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.