A "full displacement auger" or "full displacement pile" is a specialized type of auger and piling system used in foundation construction. This method is employed to create piles or deep foundation elements by displacing soil rather than removing it. Full displacement auger systems are commonly used when constructing piles in cohesive soils (clays) or mixed soil conditions.
Here's how a full displacement auger for displacement piling typically works:
Auger Design: The full displacement auger consists of a hollow cylindrical tube with a cutting head at the bottom, similar to a traditional auger. However, it also features a central steel core or mandrel that extends through the entire length of the auger.
The full displacement auger is attached to a drilling rig equipped with a rotary drive system.
The auger is inserted into the ground at the desired location.
As the auger is rotated clockwise, the cutting head at the bottom of the auger begins to cut into the soil.
Simultaneously, the central steel mandrel pushes downward, creating a void within the soil, effectively displacing it outward and upward.
Pile Construction: As the auger advances deeper into the ground, it continues to displace soil and create a cylindrical void. The displaced soil is compacted against the surrounding soil, improving the load-bearing capacity of the pile.
Reinforcement: In some cases, reinforcement material, such as steel reinforcing bars (rebar) or concrete, may be added to the central mandrel to enhance the structural capacity of the pile.
Withdrawal and casing (Optional): Once the desired depth or pile length is achieved, the full displacement auger is carefully extracted from the ground. In some applications, a steel casing or temporary casing may be used to maintain the integrity of the hole during drilling and prevent soil collapse.
Concrete Grout Injection (Optional): In certain displacement piling methods, after the auger is withdrawn, concrete grout is injected through the central mandrel to fill the void created by the displacement process. This reinforces the pile.
Full displacement auger methods are particularly useful in cohesive soils because they minimize the risk of soil caving and provide excellent pile integrity. These methods are often used in situations where high-capacity, deep foundation elements are required for supporting buildings, bridges, and other structures.
It's important to note that specific equipment and procedures for full displacement auger piling may vary depending on the manufacturer and project requirements. Engineers and contractors typically choose this method based on soil conditions, load-bearing requirements, and construction specifications. Proper installation and quality control are critical to ensure the reliability and load-bearing capacity of piles constructed using full displacement augers.