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Bored Piles | Uses | Construction Process

all about of Bored Piles

What Are Bored Piles?

Bored Pile is a Technology that has been in use since the beginning of the previous century.

Bored piles are foundation structures that are built by the excavation of the ground with the help of rotary drilling equipment. The construction process includes the drilling and removal of soil completely, from the intended area and the casting of concrete into the borehole.

The Bored piles are basically cylindrical shape body which is made from concrete with or without insertion of the reinforcement that is installed into the ground by a variety of techniques.

The shape and the length, material, and diameter of the bored piles vary according to their use. The main purpose of the construction of the Bored pile is to support the heavy vertical loads.

The defining feature of bored piles is their cylindrical form that usually measures more than 600 millimetres. Bored piers are modelled by engineers so that axial compressive loads can be resisted.

It is a technology that is gaining popularity owing to the availability of more and more powerful equipment and also the support of bentonite or polymer slurry for borehole walls.

Bored Piles Construction Process

The construction of the Bored Pile takes place mainly in two steps:

1. Drilling Phase:

The phase where demolition or digging takes place, followed by removal of dirt, and then stabilization is initiated.

2. Construction Phase:

The phase where reinforcing cages are put into place according to the need of foundation, casting of the concrete takes place, and then curing is initiated.

Following are the steps in the construction of the Bored pile which are as follows

Stages included in the construction of the Bored Pile are as follows

  • Drilling 
  • Insertion of Reinforcement 
  • Casting of Concrete 
  • Finished pile

A. Inserting the reinforcement cage:

The process of insertion of steel reinforcement cages is enacted with the help of service cranes which need to be of suitable capacity.

In the process of lowering the reinforcement cage, spacers, either made of plastic or concrete, have to be utilized to avoid the deforming of the design planned for the concrete cover.

B. Casting the concrete:

This is the stage where the borehole is supplied with concrete after the reinforcement cage has been implanted in its designated place successfully.

This process is initiated with the input of a string of thin pipes made of steel. These steel pipes need to be at least 250 mm in diameter and have to be inserted at the center of the shaft.

A factory-grade funnel is placed at the topmost tip of the string. Concreate is then streamed down the funnel. When the concrete reaches the pit, it begins to fill the borehole.

Owing to the extensive density difference that is present between the concrete and the drilling slurry, both fluids do not intermix with each other. The drilling slurry is pushed upwards to the surface and then collected in special pits dug up for the slurry. This slurry can then be used again in construction processes.

The streaming of concrete down the funnel is halted once the level of concrete reaches the elevation required for the design of the construction of the specific boring pile.

C. Curing:

The concrete needs curing time, and once that time has passed mining and digging are done around the boundary of the foundation pile mass. Only reinforcement bars are left remaining after the pile heads are trimmed.

Also Read: What Is Pile Foundation? | Uses of Pile Foundations | Types of Pile Foundations |

Types of Construction Methods of Bored Piles

The various types of construction methods that are used for the bored piles are as follows:-

1. Dry Bored Pile Construction:

This approach is used when the ground where construction of the bored pile is to be executed is stable and thus the construction process can be enacted without the implementation of stabilization operations.

While drilling, the loosened soil is eliminated from the boring hole and the reinforcement cage is allocated in place. This is followed by the stage of concreting the shaft.

2. Wet Bored Pile Construction:

In this approach, the borehole is filled with drilling mud for the prevention of the collapse of borehole walls. Drilling mud, also called drilling fluid, constitutes Bentonite and Polymer slurries.

This approach is used when the ground where construction of bored pile is to be enacted, is made of loose soil or very soft clay and is below the water table. While drilling, special drilling fluid is employed for the purpose of stabilization of dug-up borehole walls.

These drilling fluids have a greater specific weight than water. This helps to establish a waterproof layer over the surface of the borehole walls. When the drilling fluids cover the walls for more than about a meter above the water table, it impacts in making the shaft watertight and initiates the prevention of the collapse of borehole walls.

The sustained supply of drilling fluids is crucial at this construction stage. Problems such as a sudden drop of fluid level, the discovery of underground cavities, or the discovery of extremely loose soil can arise unannounced.

This is why the production of these fluids, either bentonite-based or polymer-based, takes place on-site with the use of some high turbulence mixing plants.

The fluid needs to have certain rheological characteristics for it to serve the purpose of stabilization of borehole walls effectively. For this reason, the density, viscosity, sand content, etc. is checked from time to time during the duration of construction.

On completion of the drilling procedure, cleaning of the borehole’s pits takes place with the help of special tools as well as the desanding of slurry in the borehole with the help of desander equipment.

The aim of this stage is to maintain the level of slurry in the borehole. Next, the reinforcement cage is allocated in place. This is followed by the stage of concreting the shaft.

Also Read: What Is Well Foundation? | Shapes of Well Foundation | Component of Well Foundation | Advantages &Disadvantages of Well Foundations

3. Cased Bored Pile Construction:

In this approach, temporary casings are enacted in place while drilling, so that the borehole remains open while concrete is cast for construction.

The execution of this approach is adopted when the use of drilling fluids is not applicable to the construction process.

The use of segmental casing can be for temporary or permanent support in the process of construction of a bored piling system. This is enacted when the ground for construction has deep or unstable soil conditions like when the ground has rocks or boulders that can deviate from the work of the drilling axel.

In case of such an instance, the apparatus can withhold serious damage. The application of segmental casing is put into effect to foundation piles, contiguous walls to be retained, etc. Utilizing casing support enacted at the drilling stage is important. A drilling apparatus or an oscillator fixed to an apparatus or service crane has to be implemented for the installation and extraction of the casings.

The rotary head of the drilling apparatus, or a hammer that works through vibrations and is connected to a service crane, can be used to put the temporary casings in place into the ground.

Casings can be of two variations. They can be temporary or permanent.

1. Temporary Casings:

When the sides of the borehole need to be retained only till the fluid concrete is put in place, the application of temporary casings is required. These temporary casings need to be in a place where they are utilized until the placement of the fluid concrete up to a level enough to withstand the pressures of the ground as well as the groundwater. When the purpose of such casings is fulfilled, they are extracted out.

2. Permanent Casings:

When the casings installed during construction of pile boreholes go on to become a permanent component of the foundation of the construction site, they are known as permanent casings.

The applications of these casings can be described for construction processes, for instance, when the installation of a drill shaft takes place through the water. The parts of the casings which are extruding from the ground are used as a form in construction sites using this method.

It has to be remembered when applying this approach to construction that these temporary casings are able to be driven only when the use of special hydraulic equipment named the casing oscillator is available for use. This is followed by the stage of concreting the shaft.

The support casings are disengaged in segments during the stage of concreting and need to be extracted using the oscillator or piling apparatus.

Also Read: What Is Spread Footing? | Types of Spread Foundation | Design of Spread Footing

Equipment Required for the Construction of Bored Piles

A standard construction site that implements the use of slurries to build bored piles uses the following equipment:

  • A hydraulic drilling apparatus
  • A high turbulence mixing plant for the production of drilling fluid.
  • Special machinery that works towards desanding the slurry.
  • A service crane apparatus is used for positioning the steel reinforcement cages into the borehole and to maintain the position of the string of steel pipes that are cast in the concrete.
  • A backhoe excavation tool or a shovel for the process of transporting the dirt and gravel that is dug out, away from the area of construction.

Drilling Tools Used in Bored Piles

Drilling Tools Used in Bored Piles (1)

The various Drilling tools that are used are as follows

1. Auger:

This tool is most suitable when the soil at the construction site where excavation needs to be taken place is clayey, dry, or cohesionless.

This tool is made up of a central shaft which is surrounded by a spiral-shaped flange. The sharp edges of the helical flange are designed to seem like wedge-shaped teeth.

2. Bucket:

This tool is most suitable when the soil at the construction site where excavation needs to be taken place is loose, cohesionless, or soft and is below the water table.

This tool is made up of a hollow and cylindrical part that has a hatch on the bottom. This hatch is designed with a slit that attaches to one extremity of the cylinder with the use of a hinge. The edge of the slit is designed to seem like cutting teeth.

These aid in the loading of soil into the cylindrical bucket as well as counter the soil from spilling down when the tool is retracted. When the drilling tool reaches the surface, the hatch is unhinged from the bucket and the soil falls down to the ground.

 3. Rock Auger:

This tool is most suitable when the soil at the construction site where excavation needs to be taken place is highly compacted, clayey, soft, or has extremely weathered rocks. This tool is made up of a central shaft which is surrounded by a spiral-shaped flange.

The cutting teeth of a rock auger are distinct from a traditional auger. A rock auger does not have wedge-shaped teeth but rather has conical teeth.

Their design resembles the stream-lined tip of a bullet. Hence, they are sometimes also referred to as bullet teeth. At the top of the bullet teeth, a heavy-duty metal element is used. This along with their structure-based with supports that help in rotating around the axel keeps the wearing of the rock augers cutting tip uniform.

4. Core Barrel:

This tool is most suitable when the soil at the construction site where excavation needs to be taken place is made up of extremely hard rock and stone formations.

This tool is made up of a hollow and cylindrical part just like a bucket but the hatch on the bottom is excluded. The core barrel is designed to have cutting teeth placed along the full length of the lower edge.

When the dug-out rock core enters the inner cylindrical assembly of the core barrel, it stays put while being retracted. This is because of the distinctive configuration and arrangement of its teeth.

Also Read: What Is Residential Building? | Types of Residential Buildings | Site Selection for Residential Buildings

Construction Challenges of Bore Piling

There are various challenges which are faced during the construction of the bored piles are as follows

  1. The operations that are performed for the construction of bored pilings need the usage of rotary drill apparatus which are cut out for the specific operation. Various factors need to be taken into perspective for this, such as diameter, depth, soil conditions, method of construction, etc.
  2. Due to varying soil and site conditions, stabilization of boreholes needs to be done with the application of a temporary casing.
  3. Even after extensive planning, the actual soil conditions found on the construction site will lead to the determination of the length of the casing.
  4. The contractor should perform an investigation of the soil to understand the engineering properties of the soil. The type of drilling method depends upon the type of soil which has to be used in the construction of the bored piles.
  5. Every pile position has to be surveyed individually and then it has to be assured that no disturbance is created at that site until the construction of the boring pile has begun.
  6. The piling contractor completely depends upon the past reports of the soil investigation in order to choose the method which causes less disturbance.
  7. The drilling of the hole and the pile construction on the cohesionless soil is a very difficult and complex process.
  8. When the depth of the drilling reaches more than the water table then it is necessary to provide the additional support with the help of the steel cage and the main challenge is faced with the cohesionless soils.

Also Read: What Is Standard Proctor Test? | Uses of Standard Proctor Test | Standard Proctor Compaction Test Apparatus | Procedure of Standard Proctor Test | Advantages & Disadvantages of Standard Proctor Test

Advantages of Bored Piles

Advantages of Bored Piles

There are various advantages of the construction of the bored pile are as follows

  1. Foundation piles of diameter up to 4 meters and depth 100 meters can be drilled and constructed using Bored Piling.
  2. The slurry manufactured on the construction site using high turbulence mixing plants can be recycled.
  3. Bored piles constructed with a protective shell are environmentally friendly, corrosion-resistant, water-resistant, and provide optimal distribution of load-bearing for the entire length of the shell.
  4. Bored piles are designed so that they are able to bear the heavier load and also able to transfer the load to the ground.
  5. The Bored piles are facilitated the easy movement of the piles at the variable depth.
  6. Bored piles are best suitable for soft, compressible, and swelling soils.
  7. The Bored piles can be extended to the depth below the seasonal moisture variation.
  8. Bored piles offer higher bearing capacity as compared to the Driven piles.

Disadvantages of Bored Piles

Disadvantages of Bored Piles

There are also some disadvantages of Bored piles foundation that is as follows

  1. Construction sites where Bored Piling methods are used need the presence of high turbulence mixing plants. These plants require a lot of work and specifications.
  2. All of the concrete that has to be utilized for the construction process has to undergo compressive testing and sampling as per the instructions of the engineer or the engineer’s representative.
  3. The quality of the concrete cannot be controlled in the case of the bored piles.

Also Read: What is Mat Foundation? | What Is Mat Foundation Used For? |Types of Mat Foundation | Construction of Mat Foundations |

Applications of Bored Piles

There are various applications of Bored piles in the construction that are as follows

  1. Bored piles are used in the construction of High rise industrial and commercial buildings.
  2. It is used where the bearing capacity of the soil is low.
  3. Bored piles are also used in the construction of the caissons.

Conclusion

A bored pile is a favorable piling process as time and material can be managed economically. Boring piles can be cast into exact lengths, saving from wastage.

Bored piles are designed so that they are able to bear the heavier load and also able to transfer the load to the ground because they can be cast far and are deep-seated into the ground. Thus, the increasing use of Bored Piling is justified in the engineering and construction business.


Frequently Asked Questions(FAQ)

How Are Bored Piles Constructed?

Bored piles are foundation structures that are built by the excavation of the ground with the help of rotary drilling equipment. The construction process includes the drilling and removal of soil completely, from the intended area and the casting of concrete into the borehole.

What Is the Difference Between Cfa Piles and Bored Piles?

Rotary bored piles are often larger in diameter than conventional continuous flight auger (CFA) piles. They are used to support greater loads, overcome underground obstructions, and penetrate ground too hard to bore using continuous flight auger techniques.

What Is Diameter of Bored Piles?

The shape and the length, material, and diameter of the bored piles vary according to their use. The main purpose of the construction of the Bored pile is to support the heavy vertical loads. The defining feature of bored piles is their cylindrical form that usually measures more than 600 millimeters. Bored piers are modeled by engineers so that axial compressive loads can be resisted.

How Deep Can Bored Piles Go?

Bored piles can usually be drilled to a depth of more than 60 m and the diameter can be up to 2.4 m.

What Do Bored Piles Do?

Bored piles are cylindrical foundation elements made of concrete, which are installed in the ground by a variety of methods. They transmit high structural loads into lower, load-bearing soils.

What Are Bored Piers Used For?

Bored piers are typically used as foundation piles to limit settlement of the structures they support, however, the technique may also be applied to the construction of soldier piles for retaining walls. The bored pier installation process involves minimal noise and vibration in comparison to driven pile techniques.

Why Bored Piles Are Used in Clay?

Driving piles into clays alters the physical characteristics of the soil. In soft clays, driving piles results in an increase in pore water pressure, causing a reduction in effective stress. As the pore water pressure dissipates with time and the ground subsides, the effective stress in the soil will increase.

What Is Bored Construction?

In the context of the construction industry, boring involves the drilling of holes into the ground for various purposes, such as determining whether or not the ground at a project site is safe to build on.

What Is Permanent Casing for Bored Piles?

Piles through water and soft upper soil layers shall be provided with a permanent steel casing if shown on the Drawings. The pile boring shall be carried out using a temporary steel casing bored to the pile toe or to a level approved by the Engineer. The temporary casing shall be withdrawn.

What Is Rotary Bored Piling?

Rotary bored piling (RBP) uses a machine, called a piling rig, with specially designed drilling tools including buckets and augers to remove soil and rock. These tools are used to bore into the ground repeatedly, removing spoil as the pile is progressed, until the design depth is reached.

What Is Large Diameter Bored Pile?

Large Diameter Bored piles are constructed using powerful hydraulic piling rigs which can use interchangeable attachments such as augers, buckets, or core barrels. These tools can cope with all types of granular or cohesive soils including rock up to a strength of 100MPa.


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