When the shovel hits the ground for the first time – new house build.

When it comes to building your home, there’s a great deal of work that goes on behind the scenes before you can take the first steps towards constructing the building itself.

One important stage in the process and the very first step when it comes to the process of building is excavation.
If you’re building a new house, then you most likely included an expense like this in your budget. Excavation isn’t always easy, nor is it a particularly inexpensive step in the process, but it’s one that’s vitally important nonetheless –especially in Sydney Australia, where there’s an abundance of harsh compressed land. 

Before Excavation: A Surveyor & a GeoTech will be involved in the process of identifying a benchmark, building lines and foundation requirements dependant on the soil. This accomplishes two things; first of all, it enables us to help determine where the ideal building location will be. If the site won’t work or the cost of excavation is too high, our clients can terminate the deal during the inspection period of the transaction, minimizing additional expenses.

Based on the results of the soils test, we’ll receive one of the following from the GeoTech:

  • Approval to proceed in the desired site location, or
  • Conditional approval based on bringing the soils at the site up to an acceptable standard

In the case of conditional approval, the general course of action includes what’s known as an ‘over dig and backfill.’ With this approach, the excavator will over dig; beyond the actual size of the foundation. The scope of the over dig will be determined by the geologic engineer. In most cases, they may ask for a four-foot over dig, while less common, there may be a recommendation for the dig to be up to 3 metres. Ultimately the surveyor will finalise the site plan and placement, officially staking the property in order to produce an approved plan.

Excavation begins once we have an approved plan, excavation begins.
A professional excavator operator will come in and begin digging.
The excavator will use the approved plan in order to know where to dig.
The depth that they will dig depends on a number of factors, including the type of foundation, whether there will be a crawl space, and whether there will be a basement.
No matter what type of foundation you ultimately choose, it will most likely need to be placed on concrete piers. We can drill down to 3 metres with our auger drive using our 6T Excavator.

The type of foundation will be the deciding factor as to how deep the piers ultimately end up. Usually its to until we hit shale.

Let’s look at each of these foundation types and how they affect excavation and footer depth now;

Slab: This is the most basic of foundation types, as the name suggests it is a simple concrete slab. There is a wide range of options and variables that pertain to the slab foundation, enough for a complete article.

Basement: This is by far the most popular type of foundation as it provides a great foundation system with the added benefit of extra storage space or affordable finished living space. There are different types of basements as well; Full basement, Garden Level and Walk out. 
The basement excavation certainly costs more but when you weigh the cost against the other options and frost mitigation requirements, the basement turns out to give home owners the best bang for the buck.

Once the engineer signs off on the soils and condition of the excavation,  the process of pouring the foundation can begin.

How Long Does It Take?

Excavation for a foundation can range from 1 to 3 days, on up to 3 weeks for a basement.
Generally, a worst case scenario will involve a rock excavation which is generally charged at $150 per hour due to the wear that occurs to the cutting tools. Most occurrences of rock drilling or rock excavation occur in the north shore and the central business district of Sydney.

Once the dig is complete, we’ll then have it backfilled with non-expansive, or ‘structural fill soils,’ although in some cases, the engineer will allow the soil to be removed, conditioned (wetted down), compacted, and returned.

How Much Does It Cost?

The cost of excavation itself can vary considerably depending on the contractor that you use, as well as the extent of the job. For instance, excavating a patch of land that’s easily accessible and contains few trees is far cheaper than clearing a remote patch that contains large boulders that are stuck in clay. Generally, though, you can expect to spend between $3,000 to $60,000 on excavation costs in most areas. Be sure to obtain a few different estimates from excavation companies up front. Also, keep in mind that extra excavation, hauling away dirt, disposal fees, and bringing in new soil, can all add to the cost.

We hope this article was helpful to you – 6 Axis Pty Ltd – Excavation for Sydney.

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