Bored Piling Rigs: High‑Efficiency, Durable Drilling for Challenging Soft Ground Conditions

To support structures subject to immense static and dynamic loads, a strong and stable foundation is required. The biggest problem for engineers and site workers is soft ground conditions. In such a construction site, the problems of waterlogged clays, loose silts, or shifting sands do not have the shear strength required to support the weight of the construction or provide a stable foundation to ensure the loads of massive structures can be supported. The only solution for the soft ground conditions is to bypass the weak layer on the surface and transfer the load to a much more stable soil deeper in the ground.

To lay a foundation deep in the ground, piles are laid for a strong foundation. There are several methods to install those piles deep in the ground, and amongst those methods employed by the contractors is the Bored Pile Drilling Rig. In this article, we will be exploring everything about the Bored Piling Rigs, their components, uses, advantages, operation, site preparations, and the support equipment required to ensure a strong and stable foundation is achieved for the construction project.

What is a Bored Piling Rig?

For a strong foundation, piling is done deep in the ground where the soil is a lot stable. There are multiple methods to do piling deep in the ground, and amongst those methods is the Bored Piling Rig. Unlike other methods that utilize force to drive premade piles in the ground, a Bored Piling Rig, on the other hand,  drills a vertical hole in the ground to cast the piles.

A Bored Piling Rig digs down a vertical hole for the required diameter of the piles, which is then supported with a steel cage to prevent, after which liquid concrete is poured. Once the concrete has dried out, piles are made, providing a strong and stable foundation for large-scale construction projects.  Bored piling drilling rigs are becoming increasingly popular for construction projects where following strict vibration codes is highly crucial, and with applications that involve casting out piles with large diameters and extreme depths, where a traditional piling rig fails.  

Components and Their Uses

For a piling rig to successfully dig vertically down, there are multiple components that work simultaneously to ensure the process is efficient, smooth, and without any problems. These components also ensure the long term reliabilty and durability of the machine to prevent it from failing.

● Undercarriage and Base Carrier: When setting up machinery in soft ground, the main problem comes with ensuring stability. To ensure stability in the Bored Piling Rig, they come with wide crawler tracks to ensure that the machine's weight is distributed, which ensures smooth and stable operations during heavy lifting and torque application.

● Mast (Leader): On a bored piling drilling rig, there is a tall, vertical, rigid structure called Mast. Its main purpose is to guide the drilling mechanism vertically on the ground. It also supports the hydraulic cylinders that provide crowd force.

● Rotary Drive (Rotary Head): In a Bored Piling Rig, a rotary drive is responsible for providing the rotational torque and power to the drill to and down the mast to allow the drill to cut through soil, clay, and rock.

● Kelly Bar: It is an extendable piece of equipment that is responsible for transferring torque from the rotary drive to the drilling tool. Because it can extend, it allows the drilling tool to dig deeper than the height of the mast.

● Drilling Tools: These drilling tools are attached to the bottom of the kelly bar and are responsible for digging the hole. There are different types of drilling tools that can be attached to a Bored Piling Rig depending upon the soil conditions and required depth.  

Common Drilling Tools for Soft Ground

As we have mentioned above, different types of drilling tools are interchangeable. Below, in the table, we have mentioned those types, with their design features and applications, to help you better understand what type of drilling tool would be best suited for your construction needs.

The Operational Process

When digging a vertical hole for casting out piles, there are multiple operational processes essential for the drilling process to complete smoothly while also ensuring the soft soil walls don’t collapse during the digging process. These operational processes in bore pile rig consist of different phases mentioned below:

1. Excavation and Drilling: The first step is excavating or drilling the vertical hole. A rotary drive is used to provide rotational torque to the drilling tool through the kelly bar. The rotary drive spins the drilling bucket into the earth, and once it is full, it is brought back to the surface to remove the debris.  

2. Borehole Stabilization: With vertical drilling, the biggest challenge is the borehole collapsing if left unsupported. To ensure this doesn’t happen, a steel casing is used in the upper part of the hole for improved stability. For further stabilization, a drilling fluid like bentonite slurry is pumped into the shaft to exert hydrostatic pressure against the walls, which further stabilizes and prevents the soft soil from collapsing. It creates a filter cake on the bore wall.

3. Desanding and Cleaning: Once a required diameter hole is drilled to the depth required, the bottom of the hole requires cleaning and any debris removal to ensure a strong base for the concrete can be made.

4. Reinforcement Placement: Before the pouring of concrete, the reinforcement bar cage is placed in the hole to ensure stability when pouring concrete.

5. Concreting: The last piling steps involve pouring concrete. A tremie pipe is used, which reaches the bottom of the hole. It should remain submerged in the fresh concrete at all times to prevent soil or slurry contamination of the pile. Once the concrete starts to flow, it displaces the lighter bentonite slurry, which is usually pumped from the top. Finally, the temporary steel casings are removed before the concrete solidifies, and the concrete is let to dry out to achieve the structural strength.

Key Advantages

There are some of the key advantages offered by the board pile drilling rig over other methods, which makes them a preferred choice for piling for construction needs.

● Low Noise and Vibration: Urban areas or city centers have strict codes for noise and vibrations during construction, which makes using a Bored Piling Rig a great option. The drilling process is a lot smoother and quieter, great for following the city construction codes and protecting infrastructure around the site from vibrational damage.

● Adaptability to Soil Variations: There are multiple types of drilling tools that can be installed on a bored pile drilling rig, depending upon the soil variations and piling requirements.  

● Deep Reach: Bored pile drilling can be used for deep installations reaching drilling depths of 60 to 100 meters while also accommodating diameters of piles ranging from 2500mm to over 3000mm.

● No Heave: In the drilling process to make holes, the soil is removed rather than being compressed. This prevents the risk of the ground bulging upwards or disturbing nearby pilings.

Support Equipment

One of the challenges in construction sites where these boring piling rigs operate is the hundred of cubic meters of soil removed from the ground. To ensure the site remains clean and the operations remain smooth, support equipment such as a dump truck is required to remove the unused debris to keep the site clean and ensure a smooth flow of work.

Dumper Truck

On any construction site, the presence of a dumper truck is a must. The main purpose of a dumper truck is to remove the excess soil that is dug out during the piling process, and, depending upon the requirements, bring in raw materials like sand, gravel, and concrete components. The main purpose of a dumper truck is to prevent the accumulation of useless debris hindering the piling process.

Conclusion

A Bored Piling Rig is a great option when it comes to the challenging soft soil conditions at construction sites. Instead of driving piles, which come with lots of limitations like noise, vibrations, limited depth, and soil heaving, with a bored pile drilling rig, where a hole is dug, and a pile is cast, all those problems are solved. For an effective drilling and piling process, it is important to use the right type of drilling tool, and for a stable and strong foundation of piling to be laid, follow the operational processes.

So if you are an engineering firm or a contractor who is looking to get a bored pile drilling rig, it's highly crucial for you to ensure a manufacturer is trusted and known to manufacture equipment according to the industry standards. To explore a wide range of durable construction machinery that includes state-of-the-art piling solutions and site transport equipment designed to face your most challenging soft ground projects, visit T-Works today.

Frequently Asked Questions (FAQs)

Q. How does a Bored Pile Drilling Rig differ from a pile driver?

The major difference lies in the piling process. In a Bored Piling Rig, a vertical hole is made, after which concrete is poured to cast pilings. On the other hand, a pile driver drives piles in the ground using either static or impact forces.

Q. When should I use a crawler dumper truck instead of a standard Dumper Truck?

The purpose of a dumper truck is to remove excess debris from the construction site. If the soil is soft, muddy, or the ground is uneven, a crawler dumper truck can easily maneuver and won't get stuck in such conditions. A standard dumper truck is considered great if the main priority is speed. They can be used where the ground is a lot more stable and a proper pathway or road is built.

Q. How does the rig prevent soft soil from caving in during excavation?

During the drilling process for making holes for piling, holding off the soft soil from breaking and covering the hole is a challenge. To ensure it doesn’t happen, steel casings are used at the top of the hole, and for deeper applications, bentonite slurry is used to keep the walls intact.   

Q. Can a Bored Pile Drilling Rig cut through rock?

Yes, but it all depends on what type of drilling bit you are using. Although bored pile drilling rigs are known to be great against soft soil applications, if paired with heavy-duty core barrels equipped with tungsten carbide or roller bits, they can be capable of cutting through hard rocks and boulders without failing.