12.1 General
Timber piles find extensive use for compaction of soils and also for supporting as well as protecting waterfront structures. The choice for using a timber pile shall be mainly governed by the site conditions, particularly the water-table conditions. Use of treated or untreated piles will depend upon the site conditions and upon whether the work is permanent or of temporary nature. The timber pile installed shall have its entire length embedded under water so that the pile may not get deteriorated. They have the advantages of being comparatively light for their strength and are easily handled. However, they will not withstand as hard driving as steel or concrete piles. Timber has to be selected carefully and treated where necessary for use as piles, as the durability and performance would considerably depend upon the quality of the material and relative freedom from natural defects. In coastal areas such as Kochi, Coconut/Palmyra tree trunks have been used as timber piles.
12.2 Materials
12.2.1 Timber
The timber shall have the following characteristics:
a) Only structural timber shall be used for piles (see Part 6 'Structural Design, Section 3 Timber and Bamboo, 3A Timber' of the Code);
b) The length of an individual pile shall be,
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the specified length ± 300 mm for piles up to and including 12 m in length, and
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the specified length for piles above in length.
c) The ratio of heartwood diameter to the pile butt diameter shall be not less than 0.8; and
d) Piles to be used untreated shall have as little sapwood as possible.
12.3 Design Considerations
12.3.1 General
Timber piles shall be designed in such a way that the load from the structure can be transmitted to the subsurface with adequate factor of safety against shear failure of subsurface and without causing such settlement (differential or total), which may result in structural damage and/or functional distress under permanent/transient loading. The pile shaft should have adequate structural capacity to withstand all loads
(vertical, axial or otherwise) and moments which are to be transmitted to the subsoil and shall be designed according to Part 6 ‘Structural Design, Section 3 Timber and Bamboo, Subsection 3A Timber’ of the Code.
12.3.2 Adjacent Structures
When working near existing structures, care shall be taken to avoid damage to such structures. In case of deep excavations adjacent to piles, proper shoring or other suitable arrangement shall be made to guard against undesired lateral movement of soil.
12.3.3 Pile Capacity
See 8.3.3.
12.3.4 Structural Capacity
The pile shall have the necessary structural strength to transmit the load imposed on it to the soil. Load tests shall be conducted on a single pile or preferably on a group of piles. For compaction piles, test should be done on a group of piles with their caps resting on the ground as good practice [6-2(19)]. If such test data is not available, the load carried by the pile shall be determined by the Engineering News formula (see Note).
NOTE — For timber piles, the load carried shall be determined by the Engineering News formula given below. Care shall be taken that while counting the number of blows, the head of the timber pile is not broomed or brushed and in case of interrupted driving, counting shall be done after 300 mm of driving.
For piles driven with drop hammer: