Geotechnical Engineering & Engineering Geology
Ground investigation and design expertise for projects of every scale, from single house sites through to regionally significant infrastructure.
Understanding the Ground You’re Building On
Every project sits on ground that’s unique to it, and every client comes to that ground with different questions. Geotechnical engineering and engineering geology are usually where the answers start. These disciplines examine how soil and rock behave, and how structures like buildings, bridges and ground improvement works interact with the conditions beneath them.
This work tends to happen early. Before design gets locked in, before construction begins, and often in the aftermath of a landslide or natural disaster, when understanding what’s actually happening underground matters most. Get that foundation right, in every sense, and the rest of the project follows.
Earthtech has been providing geotechnical engineering and engineering geology services across New Zealand since 1989. Our engineers and geologists combine technical expertise, hands-on field experience and current design standards with efficient investigation techniques and design software. We work directly with homeowners, developers, contractors, drillers, planners, architects and councils, adjusting our approach to suit the scale and complexity of each site.
Applications & Services
Our team is involved at every stage of a project, from feasibility studies and site selection through to detailed design, remedial works, peer review and construction inspections. Senior engineers stay hands-on throughout, so you’re never handed off to someone unfamiliar with your project.
Design & Project Expertise
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Geotechnical slope assessments, landslide mapping and slope stabilisation design -
Identification of geohazards and assessment of adverse geological conditions
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Liquefaction assessment, mitigation and prevention works
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Ground improvement and remedial works
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Bridge and roading design, including pile design, retaining walls and MSE walls
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Foundation solutions for very weak ground, including wick drains and preloading
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Small to large subdivisions, including canal, waterways and retirement village developments
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Single house site stability, foundation design and on-site wastewater systems
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Commercial and industrial buildings and warehouses
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Quarry and landfill design and assessment
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Category 1 geotechnical checking and independent peer review
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Expert evidence at Council and Environmental Court hearings
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Detailed working knowledge of TS 1170.5, NZGS Modules 1–6, MBIE Guidelines and related standards
Field Investigation Expertise
Every investigation is tailored to the site, from a handful of hand augers to multi-day programmes coordinating teams of specialist subcontractors. Our field capability includes:
Geological mapping of landforms, geomorphology and exposures
Hand auger bores and shear vane testing
Scala penetrometer (dynamic cone penetrometer) testing
Test pit investigations
In-situ permeability (soakage) testing for wastewater and stormwater disposal
Coordination of CPT and seismic CPT testing, and machine-drilled boreholes, via specialist subcontractors
Why Choose Earthtech?
We take the time to properly understand your site, and your project, before we recommend anything. That grounding in your specific ground conditions is what lets us deliver solutions that actually work, not just ones that tick a box. It’s the same approach whether we’re advising on a single house site or a regionally significant piece of infrastructure, and it’s why clients come back to us project after project.
“Earthtech is a long-standing go-to geotechnical subconsultant for BBO bridge projects. I have found Michelle to be consistently helpful, insightful, and responsive.”
Pang Chong Heng – Director / Structural Engineering Manager
Bloxam Burnett & Olliver Ltd
Our Geotechnical Engineering Projects
Pukekohe Municipal Water Supply
Project Summary Recommissioning of the Pukekohe municipal supply which abstracted water from Hickey's Spring and two deep Kaawa aquifer bores. Services Provided Conceptual and numerical groundwater modelling of effects for 1,509,000m³/yr take for Watercare from three production bores. Quantitative streamflow analysis to determine flow available for abstraction and low flow requirements in the Whangapouri Stream, including statistical analysis of low flow recurrence intervals. Preparation of Assessment of Environmental Effects (AEE). Project Conclusion Successful consenting of the water take consent as part of Watercare's response to the 2020 drought conditions.
Franklin Deep Waitemata Aquifer Groundwater Availability Study
Project Summary Deriving the groundwater abstraction availability for the Franklin Deep Waitemata Aquifer in accordance with the Auckland Unitary Plan. Services Provided Development of a conceptual model for the aquifer; including groundwater flow paths, recharge and discharge zones, and aquifer boundaries. Review of existing management area boundaries. Calculation of groundwater availability for each management area. Project Conclusion The successful determination of aquifer abstraction availabilities for four separate groundwater management areas.
Ohinekaua Stream Bridge
Project Summary Earthtech has assisted with the bridge replacement by carrying out geotechnical design of the new Ohinekaua Stream Bridge. Ground conditions at the site were complex, including a thick layer of weak and compressible peat and clay, and deep liquefaction effects. Through specialist testing and analysis, and working closely with the project team, we were able to provide a practical solution which saved the project millions of dollars in foundation and ground improvement costs. Services Provided Organisation of sCPT testing to define ground conditions. Specialist liquefaction susceptibility analysis based on recent research and considering the requirements of current design standards. Specialist assessment of consolidation settlement effects. Bridge pile design including negative skin friction. Project Conclusion This project showcases how…
Groundwater Take Assessment for Kiwifruit Orchard Irrigation
Project Summary The development of a >500,000m³/yr groundwater take for irrigation, frost protection and spray use for a large kiwifruit orchard. The water is supplied from two boreholes tapping the deep confined fractured ignimbrite Mamaku aquifer. Services Provided Desktop study of hydrogeological/hyrological setting. Drilling liaison and pump testing. Assessment of Environmental Effects (AEE). Development of a numerical groundwater model to assess groundwater pumping effects on surface water. Council liaison and iwi consultation. Project Conclusion This project secured groundwater abstraction rights, demonstrating that the proposed take aligns with sustainable allocation limits and regulatory requirements.
Groundwater and Surface Water Take Assessment for Dairy Farm Irrigation Supply
Project Summary The development of a dairy irrigation supply consisting of a groundwater take of 406,800m³/yr, from two production bores >100m deep which tap the Awhitu Peninsula Kaawa aquifer, and a run-of-stream take of 465,700m³/yr. Services Provided Desktop study of hydrogeological/hydrological context. Drilling liaison and pump testing. In-stream flow monitoring with a weir. Assessment of Environmental Effects (AEE). Saline Intrusion monitoring. Project Conclusion This project secured groundwater and surface water abstraction rights, demonstrating that the proposed takes align with sustainable allocation limits and regulatory requirements.
Wairere Drive-Cobham Drive Intersection Grade Separation
Project Summary Earthtech carried out detailed geotechnical investigations for the four-lane bridge, associated on- and off-ramps, and road alignments. This included the design of deep soil mixing ground improvement to address liquefaction effects, retaining walls, earthworks, stability assessment adjacent to live roads and nearby gully, and dewatering for buried services construction. The scope of work included construction inspections and producer statement (PS4) signoffs. During the course of the project, we formed effective working relationships with the project team. Services Provided Detailed geotechnical investigations, including seismic testing. Geotechnical design of bridge foundations, retaining walls, ground improvement, slope stabilisation works, preloading to address ground settlement effects, dewatering and groundwater control works, and many more. Contractors' temporary works, including haul road formation. Specialist…
Ngaakooroa Stream Bridge Dewatering
Project Summary Elevated artesian groundwater pressures coupled with overhead power lines, created challenging conditions for bridge pile construction. Working with the project team, Earthtech provided a dewatering bore design solution to depressurise the artesian groundwater levels. Timeframes were very tight, meaning that the dewatering design, consenting and dewatering bore construction stages significantly overlapped. The project was delivered on time, and Earthtech assisted with real-time groundwater level control and monitoring during piling activities. Services Provided Groundwater analysis and design of a bore-field dewatering system. Preparation of the Assessment of Environmental Effects and consenting of the groundwater take (dewatering) and diversion activities. Ongoing involvement and contractor support during dewatering and piling activities, including assisting with the setup of groundwater level alert and…
Whitianga Waterways, Marden Cove Waterways and Pauanui Waterways Canal Subdivision Developments
Project Summary Earthtech has been assisting these clients with canal subdivision developments since the 1990s. Across these projects, we have supported the developer through the design and construction of multiple subdivision stages, including associated retirement villages, commercial buildings, and road access bridges. Services Provided Geotechnical investigations to define ground and groundwater conditions, including machine boreholes, CPT testing and hand augers. Geotechnical subdivision design, including the design of preloads to address consolidation ground settlement effects, ground improvement to manage liquefaction effects, slope and canal edge stability and stabilisation, and geohazard identification. Inspections, verification testing and general advice during construction. Preparation of Geotechnical Completion Reports and geotechnical producer statement sign-offs. Project Conclusion These projects stand as a testament to the long-standing care…
Talk to Our
Geotechnical Team
Whatever the scale of your project, you’ll be dealing directly with the person who understands your ground conditions. No call centres, no account managers standing between you and the answer.
