BS EN 1997-2:2007 is not optional when designing ground improvement in Bournemouth. Much of the town sits on the Branksome Sand Formation, a notoriously loose, fine-to-medium sand that underlies large residential and commercial plots from Westbourne to Boscombe. Add the legacy of historic gravel pits and unmapped infill, and you get a soil profile that demands a precise vibrocompaction design. Our team works directly with the actual grain-size distribution and in-situ density data from each site. We quantify target relative density, spacing, and energy input for every grid point. For sites where the granular layer is thin or interrupted by silt lenses, we often combine the densification plan with a CPT testing programme to confirm pre- and post-treatment cone resistance. Bournemouth’s coastal groundwater, typically within 2 metres of ground level, adds another variable: we adjust the compaction sequence to avoid pore pressure build-up and loss of effective stress during vibration.
We design vibrocompaction grids that turn loose Branksome Sand into a dense bearing stratum, verified by CPT before and after every campaign.
Service characteristics in Bournemouth
Typical technical challenges in Bournemouth
The most expensive mistake we see in Bournemouth is treating vibrocompaction like a generic ground improvement item. Contractors order a rig, set a fixed spacing, and run the vibrator to refusal without a site-specific design. Then the post-treatment CPTs come back with patchy densification and the structural engineer refuses to sign off. Suddenly you are back to piling, with six weeks lost and a six-figure cost overrun. The root cause is almost always the same: no one mapped the lateral variability of the Branksome Sand, no one checked for buried organic layers from old stream channels, and no one adjusted the compaction energy to the actual fines content. A proper design document eliminates guesswork. It specifies the compaction grid, the step duration, the water-jetting pressure if needed, and the acceptance criterion tied to a minimum cone resistance or shear-wave velocity. In a town where the water table sits barely a metre below the terrace gravels, controlling pore pressure during compaction is not a detail; it is the difference between a successful campaign and a liquefied mess.
Our services
Our Bournemouth vibrocompaction design package covers the full workflow, from site characterisation to compaction specification and post-treatment verification:
Pre-treatment site characterisation
We review existing borelogs and run supplementary CPTs across the site to map layer boundaries, fines content, and initial cone resistance. The data feeds directly into the densification model.
Compaction specification and grid design
We produce a detailed method statement with probe spacing, depth, step duration, vibrator power, and backfill gradation. Every parameter is tied to a target post-treatment qc or Dr value.
Post-treatment verification testing
We execute a CPT programme on the same grid after compaction and compare qc profiles against the acceptance envelope. Results are reported with statistical confidence intervals.
Frequently asked questions
What does a vibrocompaction design cost in Bournemouth?
For a typical residential or light commercial site in Bournemouth, the design package ranges from £1,100 to £4,420. The fee depends on the treated area, the number of compaction points, and the extent of pre- and post-treatment CPT testing required.
How deep can vibrocompaction work in the Branksome Sand?
We routinely design treatments down to 20 metres in Bournemouth. The Branksome Sand extends well below that in many areas, so the limiting factor is usually the vibrator reach and the presence of any silt layers that would drain energy away from the sand matrix.
What is the minimum site size for vibrocompaction to be economical?
We have delivered designs for plots as small as 200 square metres in central Bournemouth. The key variable is access: if a standard 30-tonne rig can manoeuvre on site, vibrocompaction is viable. Below that footprint, alternative methods like rapid impact compaction may be more practical.
How long does the design and verification process take?
Pre-treatment CPTs and reporting take 3 to 5 working days. The compaction design itself is typically issued within 48 hours of receiving the ground investigation data. Post-treatment verification follows immediately after the rig finishes, and the final acceptance report is delivered within 3 working days.