TYPES OF PILES AND INSTALLATION
Piles are made from concrete, steel, timber (Figure ), plastic, or composites. The selection of the type of pile required for a project depends on what type is readily available, the magnitude of the loading, the soil type, and the environment in which the pile will be installed, for example, a corrosive environment or a marine environment.
There are several types of concrete piles that are commonly used. These include cast-in-place concrete piles, precast concrete piles, drilled shafts, and barrette piles. Cast-in-place concrete piles are formed by driving a cylindrical steel shell into the ground to the desired depth and then fi lling the cavity of the shell with fluid concrete. They are called displacement piles. The steel shell is for construction convenience and does not contribute to the load transfer capacity of the pile. Its purpose is to open a hole in the ground and keep it open to facilitate the construction of the concrete pile. Plain concrete is used when the structural load is only compressive. If moments and lateral loads are to be transferred, then a steel reinforcement cage is used in the upper part of the pile. Vigilant quality control and good construction practice are necessary to ensure the integrity of cast-in-place piles.
Precast concrete piles usually have square or circular or octagonal cross sections and are fabricated in a construction yard or a factory from reinforced or prestressed concrete. They are preferred when the pile length is known in advance. The disadvantages of precast piles are problems in transporting long piles, cutting, and lengthening. A very popular type of precast concrete pile is the Raymond cylindrical prestressed pile. This pile comes in sections, and lengths up to 70 m can be obtained by stacking the sections. Typical design loads are greater than 2 MN. Micropiles (also called minipiles, pin piles, needle piles, or root piles) are small-diameter (50 mm to 340 mm) pipe piles (pushed or driven) or grouted (jet or post or pressure) piles. They are particularly useful for (1) sites with low headroom, congested areas, sites with restricted access, and foundation repair or strengthening.
Steel piles come in various shapes and sizes and include cylindrical, tapered, and H-piles. Steel H-piles are rolled steel sections. They are nondisplacement piles. Steel pipe piles are seamless pipes that can be welded to yield lengths up to 70 m. They are usually driven with open ends into the soil. A conical tip is used where the piles have to penetrate boulders and rocks. To increase the load capacity of steel pipe piles, the soil plug (Figure is excavated and replaced by concrete. These piles are called concrete-fi lled steel piles. The soil plug may adhere to the pile surface and moves down with it during driving. This is called plugging.