Piles can be made of metal, concrete, or timber. Concrete pile are precast, which can be found at the construction site or at a manufacturing point. The piles are driven into the ground vertically or at a predetermined angle to the vertical when laying the pile foundations. A pile hammer is used to drive the piles into the ground displacing the soil in equal volume to the mass of the pile.
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The soil around the piles becomes compact as the dislodged soil particles are forced into the adjacent spaces in the mass of soil resulting in the densification of the surrounding mass of soil. The pile used for compacting the adjoining soil is known as a compaction pile. The bearing capacity of a precast pile increase due to the pressure generated by the surrounding mass of compacted soil.
Source : civilblog.org
The poor drainage qualities of saturated, cohesive or silty soil make it impossible for the soil to densify around the pile when it is driven into such ground. The water in the pores makes it hard for the displaced soil particles to enter the void spaces. This action generates stresses in the mass of soil next to the pile when it is driven into the ground, and the stresses are an outcome solely created by the water in the pores. As a result, the pore water pressure decreases the bearing capacity of the soil surrounding the pile.
Source : dailycivil.com
The soil around the piles is remolded and will lose some substantial structural strength. In effect, the result of driving a pile in silty, cohesive, or saturated soils is a decrease in the bearing strength. But with time, the remolded soil will regain the lost strength as the disturbed soil particles are reoriented (what’s known as thixotropy), which arises from the consolidation of the mass.
The Advantages Of Using Piles
- They can be precast to specifications.
- They can be pre-made into any length, shape, and size and used on site thus reducing the completion time.
- A screw pile foundations bearing capacity increase when it is driven into the granular soil because the adjacent mass of soil is compacted around the pile.
- The piles give a clean and neat presentation thus requiring minimum supervision and less storage space.
- The piles can be used in places that do not allow drilling of holes because of borrowing and finding pressurized underground water tables.
- They are a great choice when working over water as is the case with piles in jetties and wharf structures.
The Disadvantages Of Using Pile
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- Adequate reinforcement of the precast concrete piles is necessary as this helps to make them bear stresses of being transported to location and when driven into the ground.
- Adequate pre-planning is essential for the proper handling of the pile when driven into the ground.
- The process of driving the piles requires heavy equipment.
- It is hard to determine the required length of the pile in advance; therefore, the process will involve the addition of more lengths or cutting off of the excess, and this increases the project cost.
- The piles are not suitable for soils with poor drainage. It the driving is on arranged and phase properly, heaving of the soil or an already driven pile popping up when the new one is pushed in may occur.
- Driving the piles generates vibrations that can affect the integrity of the foundations of neighboring structures.