The Break-Down: Understanding Different Types of Construction Excavation

The Break-Down: Understanding Different Types of Construction Excavation

Right now, all across the country, a lot of public and industrial construction projects are underway. These range from the building of new homes to the raising of new bridges, to the development of roads, new mines and even piping. Something all of these many and diverse construction projects have in common - regardless of end result - is that they all require thorough excavation prior to commencement - and there are a lot of types of excavation and not every type is required for every project. So, let’s break down some of the different types of excavation for construction work.

Excavation by Depth and Soil Type

Topsoil Excavation

This type of excavation is simply about removing the upper layer of soil, vegetation and other exposed parts of the landscape. During the process, the site is prepared for dealing with heavy machinery and tested for its viability to handle structural loads. The primary purposes of this are to prevent soil erosion, ensure a stable foundation, provide proper drainage and uncover any unseen obstructions that may lie just below the surface.

For this last point, core drilling is often utilised as this can be an effective test of the earth’s contents for several metres below the immediate surface. Almost every construction is required by law to perform topsoil excavation and core drilling prior to all other work as it is an essential step for ensuring the safety of the workers and any future occupants. This is also why core drilling in Sydney and other major areas is so common.

Muck Excavation

Working in wetlands or in areas with poor drainage can result in a combination of soil and water that is difficult to work with. This muck needs to be dried out and cleared before any other work can be done. In these circumstances, proper testing of the soil must be conducted to ensure that there aren’t further liquid caches just below the surface.

Earth Excavation

Although most buildings can be constructed with little more than a topsoil excavation, for some larger projects - especially those that enter into sub-basement levels - much more than just the topsoil needs to be removed. Earth, rock and other materials need to be excavated - often going deep enough to be of archaeological significance. If this is the case, it is worth checking in with the Australian Archaeological Association to ensure that your project is following the proper protocols as it can be against the law to excavate any site that might be of archaeological significance.

Excavation by Approach and Methodology

Cut and Fill Excavation

Also known as stripping, this is an approach to excavation intended to clear large areas of land to a shallow depth. This is most common amongst projects that only require topsoil excavations and can often be performed with one or two machines. This process does result in large land cuts that need to be filled in - resulting in the mounds of soil seen on many construction sites. Due to the disturbing of so much soil, it is very important that during the fill phase soil is heavily compacted. If not, soil can shift under future constructions causing cracked foundations, developing underground water caches, or simply leaving a lot of landfill that needs to be gotten rid of off-site.

Trench Excavation

When a long, deep channel is required, trench digging is preferred. It is most often used for laying wires or piping, but it can be required for other purposes as well. Although it is a relatively cheap option, trench digging comes with many limitations. It is normally limited in overall depth to no more than 1.5 metres - in fact, it is often prohibited in any circumstance where there is the risk of a person falling more than two metres. It is also often prohibited in circumstances where there is the risk of damaging pre-existing infrastructure such as other pipes or wires. Trench digging is often considered high risk and proper precautions should be taken wherever possible.

Basement Excavation

Basement excavation is the most complex form of excavation as it often requires going deep underground. As other forms of excavation are limited in overall depth, this type of excavation often requires special permits and permissions and normally runs into all issues that one might expect from earth excavations - including changing rock types, breaking into sites of archaeological significance, and even the risk of finding previously undetected underground caves. There are many types of basement excavation, with each approach depending greatly on the overall depth, earth type and needs of the project. However, in all of these core sampling and thorough testing of the earth is critical - there is a lot that can go wrong without proper surveying.

Dredging

The final type of excavation is dredging, which is specifically utilised in underwater constructions. Unlike other forms of construction, the water often cannot simply be moved out of the way and sentiment deposits, coral, and other forms of underwater debris can pose unique challenges and issues. Special machinery is utilised for this process ranging from simple tools like the bucket-line, all the way to more complex machinery like the clamshell dredge or hydraulic dredging.

All of these need to be capable of operating underwater where vision is often severely limited. Notably, this type of dredging has often revealed the existence of gold or tin that can cause complications in construction both due to their material value and the changing composition of the surface. As some forms of dredging are ill-equipped to remove such material deposits, it is important to properly survey the site in order to minimise future risk.

And there you have it. The most common types of excavation and a little of what you need to know in order to take the next steps in your project. It may seem daunting at first - especially with all the constant surveying, legislation and bureaucratic nonsense in the way - but every step is important and having clear information and working within the tight legislation is important - it’s tight for a reason and those reasons could be the difference between a successful and unsuccessful construction site.