Do you have a piece of land you are looking to subdivide?
Council often require geotechnical input for subdivisions to ensure that there is a safe and stable building platform on each Lot as well as access to it. KGA can assist with geotechnical investigations for any size of subdivision, whether it be splitting a single Lot into two, a rural residential subdivision or developing a green field area into hundreds of new Lots.
An important aspect of the geotechnical investigation is to identify and potential geological hazards on the site, such as past landslides, fault traces or swampy ground. This can be achieved through a detailed walkover inspection and aerial photograph interpretation. The presence of these hazards may impact on future development and by identifying them, we can determine what remediation options are required. Subdivision formation works often transform the landscape via excavation and filling and it is important to ensure that the proposed earthworks do not adversely affect the existing stability of the land.
KGA works alongside surveyors, planners, civil and structural consultants to provide solutions for all geotechnical aspects while maximising subdivision design.
I have a piece of land I’m looking to subdivide. What will a geotechnical investigation include?
The scale of geotechnical investigation will vary based on the size of the subdivision and the amount of site formation works required.
For small scale residential subdivisions, with limited site formation works, an investigation will generally include a detailed site walkover inspection and the drilling of hand auger boreholes to explore the shallow soil conditions. If it is a sloping site, stability analyses will be undertaken to confirm that there is a safe and stable building platform. The report will be suitable for a Resource Consent application. We can also provide geotechnical recommendations for future development on the Lot.
For larger scale, multi-Lot subdivisions that require significant site formation works, we generally undertake the geotechnical investigation as a staged approached. The aim of the first stage is to identify potential constraints to the development and provide preliminary geotechnical recommendations for the site formation works. Hazard mapping and subsurface drilling is undertaken in the initial stage and will often include machine boreholes and CPT testing to explore the deep soil and rock conditions. This report can be used by the design team in the refinement of the subdivision design. From there, we can provide geotechnical input for the detailed design on the subdivision.
I’m in an Earthquake Prone Area. Are there any special requirements?
When in an earthquake prone area, the liquefaction potential of the soil must be assessed. If the land has alrready been given a Technical Category, then no additional testing is required to determine this. If no technical category has been provided, further ground testing and analysis will be required.
Can KGA undertake construction monitoring and provide a Geotechnical Completion Report?
Yes. KGA can undertake on-going monitoring of subdivision site formation works, such as expectation of prepared subgrade, testing of the fill placement, inspection of retaining wall pile holes etc. KGA can also organise testing such as shrink swell soil tests and nuclear densometer testing. At the completion of earthworks, KGA will prepare a Geotechnical Completion Report (GCR) which outlines what site formation works were undertaken and provides details on future development for each Lot.
What is the time frame and cost for a geotechnical investigation for a subdivision?
This will vary based on the size of the subdivision and the level of geotechnical investigation required. To discuss your project, give us a call to talk to one of our engineers (Auckland – 09 478 6655 or Christchurch – 03 343 5302). We will talk through the project with you and work out what is required for a Resource Consent submission. We will then prepare a fee proposal for you.