In Auckland, a robust geotechnical investigation is the essential first step for any construction or earthworks project, directly informing safe and economical design. The region's complex geology, shaped by its volcanic field and underlain by Waitematā Group sandstones and siltstones, combined with weathered residual soils, demands a thorough understanding of subsurface conditions. Our investigation services align with the requirements of the New Zealand Building Code (Clause B1) and are guided by NZGS guidelines and standards such as NZS 4402. We begin with targeted investigation planning, often commencing with exploratory test pits to visually assess shallow strata, which is critical for identifying fill, services, and root systems before advancing to deeper mechanical methods.
Our field methodology strictly adheres to New Zealand and international standards to ensure data of the highest integrity. We deploy a range of in-situ tests to characterise soil and rock properties directly within their natural environment. The Standard Penetration Test (SPT), performed in accordance with NZS 4402 Test 6.5.1, provides a direct measure of soil density and strength in boreholes. For a more refined stiffness and strength profile, particularly in sensitive Auckland clays, we utilise the Ménard pressuremeter test (PMT). These methods are complemented by other In-Situ techniques to capture a complete picture of geotechnical behaviour, moving beyond the limitations of point-source data.
Auckland's diverse project landscape, from large-scale greenfield subdivisions in Drury to complex commercial basements in the CBD and critical infrastructure upgrades, presents unique geotechnical challenges. For instance, assessing the compaction of structural fill for residential platforms commonly requires a field density test (sand cone method), a direct and reliable method we perform to NZS 4402 Test 5.1.1. On major brownfield sites, understanding the permeability of reworked soils is vital for dewatering design, which we evaluate through field permeability tests (Lefranc/Lugeon). These tests provide essential design parameters for retaining walls, foundations, and stormwater management systems, mitigating risks associated with groundwater and soil instability.
The investigation process culminates in a comprehensive factual and interpretative report, transforming raw field data into a clear geotechnical model. This is underpinned by the quality of our sampling; undisturbed sampling using a Shelby tube allows for accurate laboratory strength and compressibility testing of cohesive soils, a critical input for settlement analysis. Our deliverable provides you with a complete set of parameters—from bearing capacity to seismic subsoil class—in a format ready for your structural and civil designers. The ultimate value lies in de-risking your project from the ground up, ensuring compliance with Auckland Council consenting requirements and providing a foundation for optimised, cost-effective construction.