Soils ain’t Soils
One of the important first steps in the construction of your new home is a soil test so the building foundations can be designed and certified. The soil test will give the soil a classification based on the NCC ( National Construction Code). Many of the sites where we have built have had a S or M rating. These classifications usually present no problems for the Surefoot stumping system that we often use.
Sites given an A or P rating can be more of a problem. These ratings are usually given because of rock being present or there are areas of loose fill on the site where the modules are to be placed. Usually your best views are from the tops of hills and usually the hills are hills because of the rock so there is no getting away from it.
Hence we have developed a few different foundation systems to deal with the different soil types. In most cases the foundation system will be consistent across the complete building but in some cases it may be a mixture.
Surefoot
These are an all steel footing system which uses a set of driven gal piles to engage with the soil. They are typically driven to a depth of 1.6m using standard equipment. They have a good flexibility in offering adjustment of the final stump height and position. They also have the advantage that they can be removed down to ground level easily, which allows the modules to be driven through the stumps for placement. The system uses no concrete and, because there is no excavation, there is very little impact on the site.
Rocky sites
Rocky sites can present problems in a number of ways. It can be an exposed fractured shale type material through to “floaters” which hide just below the surface where the foundation is to be made. The “floaters” (sometime called by their technical term “goolies”) may give you the impression that they are small, but, after 15 minutes of excavation, you find that it is just the tip of the iceberg. In some cases we can still use the surefoot system but we need to rock drill using an air drill to drill out each of the holes for the piles. This might only be necessary on a small percentage of the overall site.
If the rock is more extensive then heavier equipment may be needed to bore out suitably sized holes for concrete piles to be poured in place. Bolt cages are used in the concrete piles to give the footings for the steel stumps on which the house will sit.
Loose fill
The loose fill material cannot be used as a foundation material for the Surefoot system and hence it cannot be used. The problem is that the foundations need to penetrate through the loose fill material and into the suitable founding material below. This can either be done by boring through the loose material and into the natural ground below. These are then filled with concrete together with the bolt cages to form the complete concrete pile. Another option is to use a screw pile. These are bored down through the loose material and founded in the parent soil below. The force required to screw the pile in gives the operator an indication of how strong the foundation is so they can tell when they are through the softer loose fill and into the good material below. The screw pile does not need the concrete but will require some site disturbance because of the heavy equipment required.
So all soils aren’t the same and only the soil test will tell. Prominda will work through what is required and , together with our engineers, work out what is needed specific to your site.