Chapter 8

8.1 General

Piles find application in foundations to transfer loads from a structure to competent subsurface strata having adequate load-bearing capacity. The load transfer mechanism from a pile to the surrounding ground is complicated and is not yet fully understood, although application of piled foundations is in practice over many decades. Broadly, piles transfer axial loads either substantially by friction along its shaft and/or by end bearing. Piles are used where either of the above load transfer mechanism is possible depending upon the subsoil stratification at a particular site. Construction of pile foundations require a careful choice of piling system depending upon the subsoil conditions, the load characteristics of a structure and the limitations of total settlement, differential settlement and any other special requirement of a project.

8.2.1 Concrete

Consistency of concrete to be used shall be consistent with the method of installation of piles. Concrete shall be so designed or chosen as to have a homogeneous mix having a slump/workability consistent with the method of concreting under the given conditions of pile installation.

The slump should be 150 to $180\mathrm{mm}$ at the time of pouring.

The minimum grade of concrete to be used for bored piling shall be M 25. For sub-aqueous concrete, the requirements specified in Part 6 ‘Structural Design, Section 5 Concrete, Subsection 5A Plain and Reinforced Concrete’ of the Code shall be followed. The minimum cement content shall be 400 kg/m $^{3}$ . However, with proper mix design and use of proper admixture the cement content may be reduced but in no case the cement content shall be less than 350 kg/m $^{3}$ [see also Table 5 (and Notes thereunder) of Part 6 ‘Structural Design, Section 5 Concrete, Subsection 5A Plain and Reinforced Concrete’ of the Code].

For the concrete, water and aggregates, specifications laid down in Part 6 ‘Structural Design, Section 5 Concrete, Subsection 5A Plain and Reinforced Concrete’ of the Code shall be followed in general.

The average compressive stress under working load should not exceed 25 percent of the specified works cube strength at 28 days calculated on the total cross-sectional area of the pile. Where the casing of the pile is permanent, of adequate thickness and of suitable shape, the allowable compressive stress may be increased.

8.2.2 Steel Reinforcement

Steel reinforcement shall conform to any one of the types of steel specified in Part 6 ‘Structural Design, Section 5 Concrete, Subsection 5A Plain and Reinforced Concrete’ of the Code.