Types of Piles

The principal use of piles is for the support of bridges, buildings, wharves, docks and other structures, and in temporary construction. A pile transfers the load into an underlying bearing stratum by either of the following:

1. Friction along the embedded length of the pile

2. Point bearing plus any bearing from the taper of the pile

A pile maybe classified roughly as friction or end bearing, according to the manner in which they develop support. The load must be carried ultimately by the soil layers around and below the points of the piles, and accurate knowledge of the compressibility of these soil layers is of utmost importance.

Some of the common terms used with piles are as follows:

1. Piles. A pile is a load-bearing member made of timber, steel, concrete, or a combination of these materials, usually forced into the ground to transfer the load to underlying soil or rock layers when the surface soils at a proposed site are too weak or compressible to provide enough support.

2. Pile foundation. A pile foundation is a group of piles that supports a superstructure or a number of piles distributed over a large area to support a mat foundation.

3. Bearing piles. Piles that are driven vertically and used for the direct support of vertical loads are called bearing piles. Bearing piles transfer the load through a soft soil to an underlying firm stratum. They also distribute the load through relatively soft soils that are not capable of supporting concentrated loads.

4. End-bearing piles. Typical end-bearing piles are driven through very soft soil, such as a loose silt-bearing stratum underlain by compressible strata. Remember this factor when determining the load the piles can support safely.

5. Friction piles. When a pile is driven into soil of fairly uniform consistency and the tip is not seated in a hard layer, the load-carrying capacity of the pile is developed by skin friction. The load is transferred to the adjoining soil by friction between the pile and the surrounding soil. The load is transferred downward and laterally to the soil.

6. Combination end-bearing and friction piles. Many piles carry loads by a combination of friction and end bearing. For example, a pile may pass through a

Figure 12-74.-Types of bearing piles.

fairly soft soil that provides frictional resistance and then into a form layer which develops a load-carrying capacity by both end bearing and friction over a rather short length of embedment (fig. 12-74).

7. Batter piles. Piles driven at an angle with the vertical are called batter piles. They resist lateral or incline loads when such loads are huge or when the foundation material immediately beneath the structure fails to resist the lateral movement of vertical piles. They also may be used if piles are driven into a compressible soil to spread vertical loads over a large area thereby reducing final settlement. They may be used alone (battered in opposite directions) or with vertical piles.

8. Anchor piles. An anchor pile may be used to anchor bulkheads, retaining walls, and guy wires. They resist tension or uplift loads (fig. 12-75).

^{9. Dolphin piles.} As shown in figure 12-75, dolphin piles are a group of piles driven close together in water and tied together so that the group will withstand lateral forces, such as boats and other floating objects.

10. Fender piles. As shown in figure 12-75, fender piles are driven in front of a structure to protect it from damage.

11. Foot of pile. As shown in figure 12-75, the foot of a pile is the lower end of a driven pile, which is the smaller end.

12. Guide piles. Piles used as a guide for driving other piles or serving as a support as a wale for sheetpiling.

13. Pile bent. Two or more piles driven in a row transverse to the long dimension of the structure and are fastened together by capping and (sometimes) bracing.

14. Pile foundation. A group of piles used to support a column or pier, a row of piles under a wall, or a number of piles distributed over a large area to support a mat foundation.

15. Pile group. A number of bearing piles driven close together to form a pile foundation.

16. Test piles. A pile driven to determine driving conditions and probable required lengths; one on which a loading test may also be made to find its load settlement properties and the carrying capacity of the soil and as a guide in designing pile foundations.

^{17. Timber piles.} Common timber piles are usually straight tree trunks cut off aboveground swell, trimmed of branches, and the bark removed. A good timber pile has the following characteristics:

It is free of sharp bends, large or loose knots, splits or decay.

It has a straight line between centers of the butt and tip and lies within the body of the pile.

It has a uniform taper from butt to tip.

Figure 12-75.-Typical uses of piles driven in a waterfront structure.

18. Treated timber pile. A timber pile impregnated with a preservative material that retards or prevents deterioration due to organisms.

WARNING

When you are working with treated piles, protective clothing, such as long sleeves, gloves, and safety goggles, must be worn. The preservative used in treated piles can irritate the eyes and skin.

19. Concrete piles. Two types of concrete piles are precast and cast-in-place. Factors contributing to their use are the availability of the materials from which concrete is made.

l Precast concrete piles are steel reinforced sections that are square or octagonal in shape except near the tip. They vary in length up to 50 or 60 feet.

Because of their great weight, greater lengths are generally not feasible. They require time for setting and curing and storage space. Precast concrete piles are frequently driven with the aid of water jetting (fig. 12-76). Water is forced through and out the pile tip through jetting pipes constructed into the piles while the pile is driven.

Figure 12-76.-Water jetting precast concrete pile.

. Cast-in-place concrete piles may be used when conditions are favorable. They are made by pouring concrete into a tapered hole or cylindrical form previously driven into the ground or into a hole in the ground from which a driven mandrel has been withdrawn. The left-in-place form may be a steel shell heavy enough to be driven without a mandrel, or it may be a steel form designed for driving with a mandrel that is removed on completion of driving (fig. 12-77).

20. Composite piles. Composite piles are formed of one material in the lower section and another material in the upper section (fig. 12-78). A composite pile that is constructed of wood and concrete is used to support ^{loads of 20 to 30 tons.} A composite pile that is constructed of steel and concrete is used to support loads up to 50 tons. As shown in figure 12-78, the first section of wood or steel is driven first, then a mandrel and steel casing are driven on top of the first section. The mandrel is removed and the casing is filled with concrete.

^{21. Sheet piles.} Sheet piles are special shapes of interlocking piles that are made of steel, wood, or formed concrete which are used to forma continuous wall to resist horizontal pressures, resulting from earth or water loads.

Figure 12-77.-Cast-in-place concrete piles.

Figure 12-78.-Composite piles.

Figure 12-79.-Types of steel sheetpiling.

The most common types of sheet piles are straight-web, shallow-arch, and deep-arch (fig. 12-79).

The straight-web section is designed for maximum flexibility and tensile strength, particularly adapted to cellular cofferdam and retaining wall construction. The shallow-arch and deep-arch sections are multipurpose sections having some resistance to bending.