The difference between building on the Urangan sand ridge versus the Pialba lowlands is massive. In Urangan, the dune sands are dense and well-drained, while closer to the Mary River the alluvial silts and soft clays dominate. That contrast makes vibrocompaction design in Hervey Bay a site-specific challenge every time. We've worked on projects where the target depth shifted 4 meters between adjacent lots due to paleochannels. Before specifying probe spacing, we always run a MASW survey to map the stiffness profile continuously, and then calibrate with a CPT cone for precise tip resistance.
In Hervey Bay's coastal sands, achieving 80% relative density at 8 meters depth requires probe spacing tighter than the textbook 3.0 m grid.
Service characteristics in Hervey Bay
Critical ground factors in Hervey Bay
A 10-tonne vibroprobe running at 30 Hz sinks into loose sand in seconds here, but the risk is not reaching the target depth because of an interbedded clay layer. We've seen cases in the Urraween estate where the probe refused at 5.5 meters on a stiff clay seam, leaving untreated loose sand below. That's why we always run a pre-treatment CPT to 1.5 times the design depth. Liquefaction potential under UHS 0.08 g (AS 1170.4) is moderate in the coastal strip, so the vibrocompaction design in Hervey Bay must target a minimum corrected SPT blow count of 18 blows/300 mm to mitigate cyclic softening.
Our services
Our team delivers three complementary services for vibrocompaction design in Hervey Bay, each tailored to the local soil profile:
Pre-treatment site investigation
CPT and SPT boreholes to map loose sand zones, clay seams, and groundwater conditions. We correlate with MASW profiles to optimize probe spacing before mobilizing the vibrator.
Vibrocompaction design report
Detailed specification of probe pattern, depth, energy input, and post-treatment verification criteria (cone resistance, relative density, settlement reduction). Includes liquefaction triggering analysis per NCEER 2001.
Post-treatment field verification
Follow-up CPT or SPT at 48-hour rest period to confirm density gain. We provide signed compliance certificates for AS 4678-2004 projects.
Frequently asked questions
How does vibrocompaction differ from dynamic compaction for Hervey Bay sands?
Vibrocompaction uses a vibrating probe inserted directly into loose sand, densifying it without impact energy. In Hervey Bay's saturated sands below 4 meters depth, vibrocompaction is more effective than dynamic compaction because it treats the full column without crater formation. Dynamic compaction works better on unsaturated fills above the water table.
What is the typical cost range for a vibrocompaction design in Hervey Bay?
For a standard residential project covering 500–1,500 m² with probe spacing at 2.5 m grid, the design and field verification package ranges between AU$2,390 and AU$7,700. The final cost depends on target depth, number of verification points, and whether CPT or SPT is used for post-treatment control. Contact our team for a site-specific quotation.
Can vibrocompaction treat loose sand under existing structures?
No. Vibrocompaction requires direct access to the ground surface because the probe is lowered vertically from a crane or excavator. For densification under existing slabs or footings in Hervey Bay, we typically recommend jet grouting or compaction grouting as retrofitting alternatives.
What verification tests do you use after vibrocompaction in coastal sands?
We rely on CPT cone resistance (qc) and SPT blow counts at 1-meter intervals across the treated grid. The acceptance criterion in Hervey Bay projects is a minimum qc of 8 MPa or SPT N-value of 18 blows/300 mm, whichever governs. We also run a seismic dilatometer test (SDMT) on deeper treatments to confirm vs30/" data-interlink="1">shear wave velocity gain.