Open bore piling, also known as auger drilling or continuous flight auger (CFA) piling, is a common technique used in construction for creating deep, stable foundations for buildings, bridges, and other structures. This type of pile installation method involves drilling a cylindrical borehole into the ground and then filling it with concrete or grout while withdrawing the auger.

What’s the Process?

The process of open bore piling involves several key steps. Here’s a general outline of the typical procedure:

Site Preparation: The construction site needs to be prepared before starting the piling process. This includes clearing the area, removing any obstructions, and ensuring a stable working platform for the piling equipment.

Equipment Setup: Specialized piling equipment, such as a piling rig or crawler crane with an auger attachment, is brought to the site. The equipment is positioned in a suitable location, considering access, stability, and proximity to the piling locations.

Borehole Drilling: The drilling begins by inserting the continuous flight auger into the ground. The auger is rotated and gradually advanced into the soil, creating a cylindrical borehole. As the auger rotates, the soil is displaced upwards along the flights of the auger.

Soil Removal: As the auger progresses, the displaced soil is typically removed from the site using methods like a conveyor belt, trucks, or other suitable means. The removed soil may be temporarily stockpiled for later use or disposal.

Concrete or Grout Placement: Once the desired depth is reached, the auger is gradually withdrawn while simultaneously pumping concrete or grout through the hollow centre of the auger. The concrete or grout fills the void left by the auger, forming a continuous pile.

Reinforcement Placement (if required): For reinforced piles, reinforcement cages may be inserted into the borehole before or after the concrete or grout placement. The reinforcement cages provide additional strength and stability to the pile.

Trimming and Capping: After placing the concrete or grout, the pile may be trimmed or levelled to the required height. A pile cap or head plate is typically added to distribute the load from the structure above to the pile.

Quality Control and Testing: Various quality control measures are carried out to ensure the integrity of the piles. These may include load tests, integrity tests, or other assessments to verify the strength and performance of the installed piles.

Repeat for Additional Piles: Depending on the project requirements, the above steps are repeated to install additional piles at designated locations on the site.

Types of Open Bore Piling

Open bore piling, also known as auger drilling or continuous flight auger (CFA) piling, encompasses various types based on a construction project’s specific requirements and conditions. Here are some common types of open bore piling:

Standard Open Bore Piles

These are the typical open bore piles created by drilling a cylindrical borehole using a continuous flight auger and filling it with concrete or grout. Standard open bore piles are widely used in various construction projects due to their versatility and reliability.

Open Bore Piles with Reinforcement

In some cases, reinforcement is added to the open bore piles to enhance their load-carrying capacity and structural strength. Reinforcement cages made of steel bars or other materials are inserted into the borehole before or after the concrete or grout placement.

These reinforced open bore piles are commonly used when the structure requires additional support or when the soil conditions warrant reinforcement.

Secant Piles

Secant piles are a type of open bore pile where multiple overlapping piles are constructed to form a continuous wall. The primary purpose of secant piles is to create a watertight barrier or to provide structural support in situations where soil or water needs to be retained. The interlocking arrangement of the piles helps to prevent seepage and improve stability.

Contiguous Piles

Contiguous piles are similar to secant piles but have different arrangements. In contig wall piling, the piles are constructed adjacent to each other without overlapping. These piles are commonly used when excavation needs to be supported. Soil movement or water infiltration needs to be minimized.

Soil Mixed Piles

Soil mixed piles, also known as soilcrete or soil-cement columns, are created by mixing the in-situ soil with cement or other binders during the drilling process. The mixture is injected into the borehole through the auger while being withdrawn. Soil mixed piles improve the soil’s load-bearing capacity, enhance stability, and control settlement in weak or loose soil conditions.