Types of Drilling for Deep Foundations

Types of Drilling for Deep Foundations

In any construction project, the strength of the building is almost entirely dependant on its foundations, making laying them the single most important part of the construction.

They provide a building with much of its structural integrity, ensure that moisture at ground level doesn’t cause any gradual damage to the structure itself, and ensures that the building, no matter what size, can be occupied and used safely, without any risk of its structure giving way and possibly causing injuries or even deaths.

There are a number of approaches to laying foundations for a construction project, with some being more suited to certain scaled projects than others.

Deciding which approach takes an understanding of the type of terrain that the site is being built on, the dimensions and architectural challenges faced by the design of the building itself, and, of course, how the building is intended to be used.

In this article, we will explore how these foundations are laid using drilling services that are designed to provide buildings with the highest possible levels of strength and reliability; particularly where deep foundations are concerned, as opposed to shallow ones.

To do this, we will take a look at what deep and shallow foundations are, and will explore some of the most common and effective approaches to creating deep foundations. On top of that, we will help you find the best contractor for the job, by taking a look at various factors that you can use to determine the quality of their services.

So, let’s get started:

Types of Foundations

At their most general level, foundations can be divided into two different types, each a category for different other types. These two types of foundations are simply called shallow foundations, and deep foundations.

While this article will focus on the latter to explain certain drilling services, we will touch on the difference between these two here, and the types of foundations they include:

Shallow Foundations

Shallow foundations transfer a structure’s loads to the earth, ensuring that its loads are kept as near to the surface as possible.

Shallow foundations include individual and isolated footing, strip foundations, and raft or mat foundations:

Individual & Isolated Footing

These types of foundations transfer loads to the underground soil through a central or singular column. This demonstrates a key difference between the term foundation and the word footing.

Where ‘foundation’ describes the part of a substructure that makes actual contact with the earth to bear the load of the structure, ‘footing’ describes a unit on the actual foundation that can either be deep or shallow.

Strip Foundation

Strip foundations aim to spread the weight of a load-bearing wall so that the extended surface area goes across the entire wall, across a continuous level or even in steps.

Raft or Mat Foundation

Raft or mat foundations seek to reduce the amount of stress that a structure puts on the soil beneath it. It does this by using a slab that extends beneath the entire structure of a building to distribute its load more effectively when directing it to the ground.

The fact that it rests on the soil as opposed to being trenched into it, makes this a prime example of a shallow foundation.

Deep Foundations

The next major category of foundations and the one that will form the focus of our discussion in this article are deep foundations.

Deep foundations differ to shallow ones in that, while they also transfer the weight of a structure to the ground, they go far further down into the subsurface of the soil than shallow ones do.

Some of the most popular forms of deep foundations include pile foundations and drilled shafts or caissons.

Let’s take a closer look at each of these sub-categories of deep foundations:

Pile Foundation

Whenever the design of a structure means that it will have a weak shallow bearing stratum, there is a need for a foundation that goes deeper into the strata to improve on the support it offers the structure.

This is very often the case with high-rise buildings but isn’t mutually exclusive to them.

Pile foundations are driven deep into the earth to provide this additional load-bearing capacity.

These types of foundations transfer the load of the structure as far down as to reach the layers of high-density rock beneath the soil to provide enough of capacity for load-bearing to the building.

Drilled Shafts or Caissons

This type of foundation includes drilling deep shafts into the ground and filling them with concrete to create deep foundational solutions that can support structures with excessive axial and lateral loads that need to be supported.

Types of Drilling for Deep Foundations

Here we will explore the latter category, deep foundations, in a little more detail; with particular attention paid to the drilling services used to create them.

Drilling is an often-understated part of the piling process, with piling machines requiring cavities to first be prepared in the soil to allow the foundations to penetrate deeper into the earth.

There are a number of approaches to drilling that can be used to create deep foundations, including Kelly drilling, continuous flight auger drilling, double rotary drilling, full displacement drilling, grab drilling, air injection drilling and down-the-hole drilling.

Let’s explore each in a little more detail:

Kelly Drilling

This type of drilling service is widely regarded as one of the most common approaches to dry rotary drilling.

It is most commonly used for piles with a particularly large diameter and is well suited to just about any type of soil and terrain.

During the process of Kelly drilling, short rotary drilling tools and a drill rod (called a Kelly bar). Since these Kelly bars are designed to be telescopic to facilitate drilling at greater depths.

This approach offers improved drilling speed as its main benefit. It also offers a cost-effective approach when compared to other types of drilling.

Continuous Flight Auger Drilling

This is also a type of dry rotary drilling that is widely used for laying deep foundations in construction tasks. The characteristic feature of continuous flight auger drilling is that it makes use of auger flights to support the structure of the hole’s wall to prevent it from collapsing.

During this process, soil and rock are loosened and removed on a continual basis to gradually create the cavity in preparation for piling.

The top advantage of this type of drilling is that it can be conducted with comparatively less noise and vibration than with other methods. Additionally, assembly of the piles is relatively quick and does not require any temporary casing, even when used on unstable soil.

Double Rotary Drilling

Double rotary drilling takes the concepts used in auger drilling and includes the use of continuous casing.

Through the use of both the casing and a contained auger, this method provides a fairly efficient and effective approach to producing cast-in-place piles.

This approach is ideal where drilling needs to be done through heaving sands, gravel formations, boulders and cobbles, which can often present a challenge when using other approaches.

This ability to work with a versatile set of different types of soil, and the added convenience of efficiency, makes for the most prominent set of advantages offered by double rotary drilling.

Full Displacement Drilling

Full displacement drilling also takes a leaf out of the book of continuous flight auger drilling but changes it somewhat to only displace the surrounding soil, without conveying drill cuttings to the surface.

To do this, a smooth casing is used as opposed to a continuous auger, which is fitted to the displacement body using a casing at the lower end of the drilling rig.

This makes it exclusively suited for the production of cast-in-place piles above any other function.

This results in their top advantage being the minimal amount of spoil material, which makes this process best used with contaminated soils. This also results in enhanced manoeuvrability on-site, as far as the drilling rig is concerned.

Grab Drilling

Grab drilling represents one of the longest-used approaches to drilling. While there is evidence that grab drilling was done as long ago as 5000 years, the appropriate drill bit was officially invented in 1861; and is still widely used today.

Through this process, the soil is loosened by cutting or impact driving, depending on the type of tools used.

While it is often used for good drilling, it is also a popular approach to producing cast-in-place piles with a relatively large diameter.

Reverse Circulation Air Injection Drilling

This type of drilling is generally reserved for projects where holes of just over 3m in diameter need to be produced. It often requires a preparation process whereby grab drilling is first done, after which a hydraulic pump conveys the soil to the surface to flush the space between the hole and the drill rod, from where it rises inside the drill rod.

It is most typically used for drilling boreholes but can be used for piling.

This method of drilling offers a low-cost approach, improves the efficiency of penetration and offers greater accuracy during the drilling process.

Down the Hole Drilling

In this approach to drilling, a hammer is fitted to the lower end of the drill rod and is subsequently activated by applying compressed air to drive it into the ground, while also rotating and impacting it at the same time.

It then uses a flushing current to collect loosened cuttings and moves them upward towards the surface of the hole.

The top advantage of this mode of drilling is that it is particularly well suited to hard and rocky terrain that may present a challenge for other approaches.

This also offers a fairly energy-efficient approach to drilling, reducing the environmental impact of doing so.

Finding the Right Drilling Contractor

With all of this in mind, you should have a better understanding of what type of approach to drilling would best suit the needs of your current construction project, and the type of soil that the foundation needs to be laid into.

The next thing to do is to find a contractor who can provide you with the right drilling service to get it right, and of course, at the best possible cost and quality.

To ensure that the contractor you are looking at offers what you need, ask yourself the following questions when investigating their services:

How Experienced is the Company & Team?

In any facet of construction, the experience of the contractor counts for a lot, which is why it is the first thing you should scrutinise.

An experienced team will work with greater efficiency and accuracy and will save you money on costs associated with mistakes and wastage.

They may come at a bit more of a cost than inexperienced teams, but you can’t really put a price on high-quality work in this regard.

What Does their Fleet Look Like?

The next important thing to look at concerns the contractor’s equipment.

The condition and variety of their fleet will tell you a lot about the quality of their work, and what they are able to do. If the right tool makes for a better job, you should absolutely avoid any contractor who doesn’t have what is needed to complete it.

What are their Customers Saying?

These days, it is easy to find out what a contractor’s customers are saying by either Googling their name or taking a look at their social media profile if they have one.

While it is unlikely that you will find a contractor with consistently favourable reviews (some clients just cannot be satisfied), a company with a consistently low rating should be avoided.

Contact Gauteng Piling to Learn More

If you would like to know more about our offers on specialised drilling services for the creation of deep foundations in construction, be sure to get into contact with a representative from Gauteng Piling today, or visit our website for additional information on our offers and services.