Geotechnical investigation in Canberra defines the essential first step for any project interacting with the region’s complex subsurface, characterised by deeply weathered Ordovician metasediments, the Canberra Formation, and highly reactive clay soils. A robust investigation program, guided by AS 1726, navigates these variable ground conditions to assess bearing capacity, shrink-swell potential, and slope stability. Deploying in-situ techniques like the CPT (Cone Penetration Test) provides continuous, high-resolution profiling of soil stratigraphy, an indispensable complement to traditional boreholes for accurate geotechnical characterisation.
This foundational work is critical for residential developments on reactive clays, multi-storey commercial basements, and infrastructure projects such as arterial road expansions. The data acquired informs precise foundation design and earthworks specifications, directly mitigating risks like differential settlement. Comprehensive investigations also integrate CPT testing with laboratory analysis to model groundwater conditions and excavation feasibility, forming the technical basis for safe, cost-effective construction across the ACT.
Prestressed strand systems for basement propping and retaining walls where immediate load transfer and minimal deflection are critical.
Bar or strand tendons for soil nails and rock bolts that engage through ground deformation, ideal for slope stabilisation and temporary excavations.
Performance and acceptance testing to AS 4678, including load-extension monitoring and residual load assessment on site.
Evaluation of groundwater chemistry and soil resistivity to specify the correct protection class for a 50 to 100-year design life.
AS 4678-2002, AS/NZS 1170.4:2007, AS 1726:2017, AS 3600:2018
For a standard scope covering the design of a single anchor row and on-site proof testing, project fees typically range from AU$1,620 to AU$5,800. The final cost depends on the number of anchors, the required corrosion protection class, and the complexity of the site geology.
An active anchor is prestressed and locked off against the structure immediately after installation, controlling movement from the start. A passive anchor, like a soil nail, is not tensioned; it develops its resisting force as the ground deforms. We specify active anchors where settlement-sensitive structures are adjacent to the excavation.
Local groundwater in areas like the Inner North can be slightly acidic and carry sulfates from weathering rock. Combined with the seasonal wet-dry cycles in the reactive clay profiles, this creates a moderately aggressive environment. A solid double-corrosion barrier prevents tendon degradation over the structure's design life.
We conduct proof testing in accordance with AS 4678. A sacrificial anchor is loaded incrementally to 1.5 times the design load while recording displacement at each step. The creep rate over a fixed time period is measured to confirm the anchor sits within acceptable geotechnical limits before locking off production anchors.
A targeted geotechnical investigation is essential. This includes boreholes with SPTs to define rock strength and weathering grades, combined with sampling for laboratory bond strength testing. The investigation must extend at least 3 metres beyond the proposed bond zone to ensure the anchor is founded in competent material.
We serve projects across Canberra and its metropolitan area.