Timber piles are used extensively for compaction of soils and for supporting and protecting waterfront structures. The choice of use of timber piles is mainly governed by the site conditions, particularly water table conditions.
Timber piles are comparatively light for their strength and are easily handled. However, they cannot withstand hard-driving as concrete or steel piles can. Therefore, timber must be selected and treated carefully as durability and performance depend upon the quality of the material and absence of natural defects.
Class of Piles
Based on the nature of use, piles are classified as Class-A and Class-B.
The Class-A piles are used for railway and highway bridges, trestles, docks, and warehouses. The butt diameter or sides of the square shall not be less than 30cm.
The Class-B piles are used for foundation work other than specified in Class-A and temporary work. Piles used for compaction of ground shall not be less than 100mm in diameter or side in square piles.
Timber Piles Specfication
- The length of the individual pile shall be specified length ±30cm for long and ± 60cm for lengths above 12m.
- In the case of round piles, the ratio of heartwood diameter to the pile butt diameter shall not be less than 0.8.
- Both the ends shall be sawn at right angles to the length of the pile, and the knots and limbs shall be trimmed to make the surface.
Driving Timber Piles into Ground
- The piles in each bent of a pile shall be selected for uniformity in size to facilitate the placing of bracing members.
- The pile tip shall be pointed (unless driving in wholly soft strata) in the form of a truncated cone or a pyramid having the end 25 cm2 to 40 cm2 in area, and the length shall be 1 ½ to 2 times the diameter or side of a square.
- If the driving is to be done in a hard material such as stiff clay, gravels, etc., metal shoes of approved design shall be attached to the tip.
- The head of the pile should be hooped with a suitable ring or wrapped with wires to prevent splitting and reduce brooming.
- The heads of piles shall be further protected by the provision of cushion blocks.
- If the piles are required to be formed from two or more lengths, the butting surfaces shall be cut square to ensure contact over the whole cross-section of the pile.
- A thin steel plate placed between the butting surfaces will reduce the tendency to brooming.
- The pieces should also be secured with steel tubes or steel flats. Splices in the middle of the pile should be avoided.
- If it is necessary to obtain an increase in size and length of the pile by building up sections, the joints should be staggered, and the timber members connected by means of bolts or screws.
- In a pile group, the sequence of installation of piles shall normally be from center to periphery of the group or from one side to the other. Adjacent piles shall not be damaged when driving a pile; the danger is greater in compact soils than in loose soils.
- Driving piles in loose sand tends to compact the sand, which in turn increases the skin friction for friction piles. Therefore the order of installing such a pile group should avoid creating a compact block of sandpile into which further piles cannot be driven.
- In the case of very soft soils, driving may have to proceed from outside to inside, so that soil is retained from flowing and during operation.
- Jetting of cases by means of water shall be carried out if required in such a manner as not to impair the bearing capacity of piles already in place, the stability of the soil, or the safety or any adjacent buildings.
- Defective piles shall either be removed or left in place as is convenient without affecting the performance of the adjacent piles or the cap as a whole.
- Any sudden change in the rate of penetration, which cannot be ascribed to the nature of the ground, shall be noted, and its cause ascertained, if possible before driving is continued.
Handling of Timber Piles
- Proper care shall be taken to see that the piles are properly located to prevent damage due to excessive bending.
- Treated piles shall be handled with manila rope slings or hemp or other means of support that will not damage the surface of the wood.
- Dropping, brushing, breaking of fibers, and penetrating the surface shall be avoided.
- Sharp pointed tools must not be used for handling or turning timber piles.
- Minor abrasions of the surface of treated piles below the cut-off level in the portions, which are to be remaining permanently underwater, shall be permitted.
- Surface of treated piles below cut-off shall not be disturbed by boring holes or driving nails to support temporary material or staging.
FAQs on Driving of Timber Piles
Timber piles are used extensively for compaction of soils and also for supporting as well as protecting waterfront structures.
The class-A piles are used for railway and highway bridges, trestles, docks, and warehouses. The butt diameter or sides of the square shall not be less than 30 cm.
The class-B piles are used for foundation work other than specified in Class-A and temporary work. Piles used for compaction of ground shall not be less than 100 mm in diameter or side in the case of square piles.
1. The length of the individual pile shall be specified length ±30 cm for long and ± 60 cm for lengths above 12 m.
2. In the case of round piles, the ratio of heartwood diameter to the pile butt diameter shall not be less than 0.8.
3. Both the ends shall be sawn at right angles to the length of the pile, and trimming the knots and limbs shall make surface.