Methodology
The SPT procedure follows ASTM D1586-18, utilising a 63.5 kg hammer dropped 760 mm to drive a split-barrel sampler 450 mm into the soil. Blow counts (N-values) are recorded for each 150 mm interval, with the sum of the last two increments reported as the standard penetration resistance. Our team employs automatic trip hammers to ensure consistent energy transfer (typically 60–70% efficiency), reducing variability. Boreholes are advanced using rotary wash boring or hollow-stem augers to maintain borehole stability. SPT is performed at 1.5 m intervals or at every change of stratum, with continuous sampling in critical zones. For hard layers, refusal is defined as 50 blows for a 150 mm advance. Additional data such as soil recovery, moisture content, and granularity are logged. For complementary high-resolution profiling, we also offer Cone Penetration Test (CPT) services.
Reference Technical Parameters
| Parameter | Reference Value |
|---|---|
| Hammer Weight | 63.5 kg |
| Drop Height | 760 mm |
| Sampler Type | Split-barrel, 35 mm ID / 51 mm OD |
| Blow Count (N-value) Range | 0–50 blows/300 mm (refusal at 50) |
| Typical Depth Interval | 1.5 m (or at stratum change) |
Local Considerations — Australia
Australia’s seismic zones (AS 1170.4) and variable soil conditions demand tailored SPT approaches. In Adelaide, reactive clays and karstic limestone require shallow SPT to characterise shrink-swell potential. In Brisbane, deep residual soils and Brisbane tuff necessitate extended boring depths. In Perth, the sandy Swan Coastal Plain often yields low N-values requiring energy correction. Our team adapts equipment—using heavyweight hammers for dense gravels in Ballarat or portable rigs for confined sites in Melbourne—while maintaining ASTM D1586 compliance. For projects in specific regions, we provide detailed local knowledge; for instance, our Adelaide service incorporates site-specific protocols for the St Vincent Basin geology.
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Applicable Standards
- ASTM D1586-18 Standard Test Method for Standard Penetration Test (SPT)
- AS 1289.6.3.1-2004 Soil strength and consolidation tests – Determination of the penetration resistance of a soil – Standard penetration test
- AS 1170.4-2007 Structural design actions – Earthquake actions in Australia
- BS 5930:2015 Code of practice for ground investigations
Frequently Asked Questions
What is the standard procedure for SPT in Australia?
Our team follows ASTM D1586-18 and AS 1289.6.3.1-2004, using a 63.5 kg hammer dropped 760 mm. The split-barrel sampler is driven 450 mm, and N-values are recorded for each 150 mm interval. Testing is conducted at 1.5 m intervals or at stratum changes, with refusal defined as 50 blows per 150 mm.
How does SPT data inform foundation design?
SPT N-values correlate with relative density, friction angle, and undrained shear strength. These parameters are used to calculate bearing capacity (AS 2159-2009) and settlement. For seismic design (AS 1170.4), N-values help classify soil liquefaction potential using methods like Youd et al. (2001).
What is the typical turnaround time for SPT results?
Fieldwork is completed within 1–3 days for a standard borehole. Preliminary N-values are provided on-site, while final logs and laboratory correlations (e.g., grain size, moisture content) are delivered within 5–10 business days, depending on project scope and number of tests.
How much does Standard Penetration Test (SPT) cost in Australia?
The cost for SPT varies based on depth, accessibility, and number of tests. A typical SPT borehole (10 m depth with tests every 1.5 m) ranges from $840 to $1,170 (2026 reference). This includes mobilisation, drilling, and preliminary reporting. For an accurate quote, contact our team with project details.