Pile driving is a process for installing pile foundations. It’s a specialist activity that calls for considerable experience and knowledge of operating hammers and handling piles to achieve placement within specified tolerance levels and positioning.
The installation process of pile foundations is just as essential as the design process. To avoid damaging the piles, use the selected installation equipment and methods carefully.
The type of pile foundations used depends on various considerations, including cost, water level, available resources, soil conditions, timeframe of the project, noise and vibrations sensitivity, and total load from the superstructure.
The pile driving process consists of various steps:
1. Site Investigation
One of the most important steps in the pile driving process is the site investigation. Assess nearby structures as they could cause problems for the proposed project in the long run. To avoid time-consuming and costly mishaps, identifying these issues at the beginning stages of the process is recommended.
Note the distance from nearby apartment complexes, schools, buildings, and hospitals. If a school or hospital is close to the site, pile driving may not be feasible. However, in such situations, noise can be prevented or reduced by jacking piles.
If the proposed design of the building features a basement, underpinning nearby buildings is necessary for excavation. You can also use heavy bracing and secant pile walls. If a site has compressible soil, a new building may result in consolidation. For nearby structures piles, this will generate negative friction.
A piled foundation has a depth three times its breadth. Soil displacement as a result of pile driving can damage nearby buildings, but you can avoid it with proper site investigation.
2. Using Displacement Piles
You can design displacement piles for installation without having to remove soil from the ground. Laterally displace the soil and compact it into the surrounding terrain using special equipment. Although displacement piles are not for every situation, in some cases, they can support higher capacities compared to the alternative bored or helical piles since most of the load’s weight is transferred on the ground and distributed evenly into the earth.
Over time, commercial construction engineers have come up with a variety of displacement pile styles, which mainly fall under cast-in-place or pre-cast categories. Most are screwed, drilled, or driven into the ground. Solar pile drivers are commonly used during this process, allowing displacement piles to be managed efficiently.
3. Using Replacement Piles
Put piles into holes dug out of the earth. The steel or concrete replaces the clay or the excavated material. Replacement piles are often known as bored piles because removing the soil to form a hole for the pile involves the boring technique. You can use them to form pile foundations near existing buildings to allow limited noise and vibration, or in cohesive subsoils to help with the formation of friction piles.
4. Pile Driving Using Vibrations
You can use vibratory hammers to drive piles. They can either be hydraulically or electrically powered and feature contra-rotating eccentric masses placed in a housing attached to the pile head. The vibrations have enough amplitude to eliminate the skin friction present on the sides of piles. Vibratory methods are great for gravelly or sandy soil.
You can use water jetting to assist with the penetration of piles into sandy gravel or sand. However, in firm to stiff clay, or soil with significant boulders, cobbles, or coarse gravel, this method may not be effective.
5. Pile Driving Using Drop Hammer
This technique involves using a hammer with approximately the same weight as the pile, which is hoisted to a suitable height and then released onto the pile head.
There are two drop hammers: compressed or single-acting steam air, or double-acting pile, hammers. The single-acting steam or compressed air hammer features a massive cylinder-shaped weight. Compressed air or steam pushes up the fixed piston rod. Upon reaching the top, the operator cuts off the steam to let the cylinder fall freely on the pile helmet.
You can drive double-acting pile hammers using compressed air or steam, which does not require a piling frame. It can be attached to the top using leg guides. You can use double-acting hammers for sheet pile driving.
6. Pile Integrity Testing
The two main categories for pile integrity testing are low-strain methods and high-strain methods. The low-strain methods use a handheld hammer to strike the pile to generate two types of waves: shear and longitudinal waves. The waves travel along with the pile and return.
A sensor relays the information to the operator, who makes computations and provides necessary information concerning the integrity of the pile. Both waves should return fast if a pile is working well, but a broken section can delay the signal. Some sensors can record stress relief, strain, and the load on the pile.
For a high-strain method, you can use a pile-driving hammer instead of a handheld hammer. Together with pile integrity, this method provides the operator with the bearing capacity of the soil.