In many Local Government Areas (LGAs), some form of geotechnical reporting is required by Council to support a Development Application (DA) or Construction Certificate (CC). This requirement may be the result of a geotechnical hazard zone or landslip/landslide risk category applying to the site, or as a result of the scope of works being proposed. For example, many Councils require a geotechnical report where excavation or filling is proposed.

Each Council has specific requirements for the requisite geotechnical reports. AscentGeo are experts at deciphering the often-complicated reporting and documentation requirements of the various Councils, thereby ensuring you will have all the necessary information required for your submission. 

While reports of this kind are designed to satisfy Council requirements, their primary aim is to provide technically accurate, site-specific information to inform appropriate structural design of footing and retention systems, as well as providing recommendations for appropriate excavation and construction methodology.

Contact AscentGeo for expert advice on your project’s DA/CC requirements.

A geotechnical investigation or ground testing is carried out to determine the geotechnical characteristics of a site in accordance with AS 1726. These investigations provide valuable data that are used to evaluate and interpret the ground conditions and ultimately inform structural design, manage risk, and provide recommendations on appropriate excavation and construction methodology.

The incorporation of factual ground information into the structural design or excavation/construction quoting can reduce your project cost by tens of thousands of dollars.

Ground testing can also be valuable where existing construction is damaged due to ground-related issues such as settlement or subsidence, ground water, etc. In these cases, an accurate determination of existing conditions, such as compaction of soils/clays, presence of water, or depth to bedrock can be crucial to the design of appropriate remedial works.

As it is impossible to see below the surface, it is necessary to use equipment that can help us interpret the subterranean conditions of your site. In most cases, testing is comprised of bore holes, utilising hand operated augers or mechanical core drilling, where coring through rock is required, and penetrometer testing. The combination of these test methods allows an inferred geotechnical model to be developed for your site.

Site classification is a systematic categorisation of the soils found on a site. Soil samples are taken to assess their distinguishing characteristics which in turn determines their ‘Class’. This information ultimately informs the correct footing design by the structural engineer.

The classification of the site is based on the expected reactivity or movement (shrink or swell) of the foundation soils.

Site classification assessments are undertaken are in accordance with the following Australian Standards:

• AS2870: “Residential Slabs and Footings”

• AS1726: “Geotechnical Site Investigations”.

Most residential sites will be classified as one of the following:

• Class A: Mostly sand and rock sites, with little or no ground movement expected.

• Class S: Slightly reactive sites. Only slight ground movement from moisture changes expected.

• Class M: Moderately reactive clay or silt sites which can experience moderate ground movement from moisture changes

• Class H: Highly reactive clay sites. Can experience high ground movement from moisture changes.

• Class E: Extremely reactive sites. Can experience extreme ground movement from moisture changes.

• Class P: A problem site. This can include soft soils, such as soft clay or silt, varying depths of fill, loose sands, landslips, mine subsidence, collapsing soils, soils subject to erosion, reactive sites subject to abnormal moisture conditions, or sites which cannot be classified otherwise.

Soil types M, H, and E may also have an added classification of ‘D’. This indicates deep seasonal moisture variation which can mean significant expansion and contraction.

These types of assessments are recommended for very steep sites, sites with a history of land movement, sites with cliffs or proximity to problematic land forms, or for sites where existing structures such as retaining walls are in need of some attention.

These assessments are often carried out with the property owner, or potential owner, in attendance in order to discuss specific concerns and site conditions.

A slope stability/general geotechnical assessment can be undertaken as visual assessment only, or include a letter report.