Bournemouth’s expansion from a pine-forested heathland into a major coastal conurbation created some tricky drainage legacies. Victorian engineers often routed surface water into unconsolidated sands and gravels of the Branksome and Bournemouth formations, assuming natural infiltration would take care of the rest. Fast-forward to today and that assumption needs hard numbers to back it up. We run field permeability testing across the BCP area to measure hydraulic conductivity in situ, because lab remoulded samples simply cannot replicate the layered lenses of sand, silt, and iron-cemented pan that define the local geology. The constant-head Lefranc method gives reliable point measurements in boreholes through the unsaturated zone, while Lugeon packer tests quantify rock mass permeability in deeper chalk or sandstone strata. Both approaches feed directly into dewatering plans, soakaway sizing, and groundwater control for basements, foundations, and infrastructure drainage.
A five-metre change in borehole depth in Bournemouth can shift hydraulic conductivity by two orders of magnitude when you cross a cemented sand lens.
Service characteristics in Bournemouth
Typical technical challenges in Bournemouth
BS EN 1997-2 (Eurocode 7) explicitly requires that the design value of permeability for groundwater control be derived from field measurements, not just lab correlations. In Bournemouth, ignoring this is a direct route to construction delays. The Branksome Sand contains discontinuous iron-pan horizons that act as local aquitards; a borehole that hits one of these pans might suggest low permeability, while a metre laterally the conductivity is ten times higher. Underestimating inflow into a deep excavation in the town centre can quickly overwhelm sump pumps and destabilise adjacent footings. Our test records include at least three recent commercial projects where preliminary desk-study estimates had to be revised by over 200 percent once in-situ Lugeon data from the chalk interface was processed. The cost of a Lefranc or Lugeon test pales against a single day of emergency dewatering and temporary works redesign.
Our services
All field permeability testing in Bournemouth is run by drillers and geotechnical engineers with direct experience in the Wessex Basin sedimentary sequence. Each test programme is tailored to the specific aquifer geometry encountered on site.
Lefranc Borehole Permeability Testing
Constant-head and falling-head tests executed in cased boreholes through the unsaturated zone. We isolate the test section with a sand pack and bentonite seal, then log drawdown or recovery at intervals calibrated to BS 5930. Ideal for soakaway design, infiltration basins, and dewatering assessments in Bournemouth’s sands and gravels.
Lugeon Packer Testing in Rock
Multi-stage pressure tests in rotary-drilled boreholes using single or double packers. Each stage runs for a standard duration at increasing and decreasing pressure steps to identify flow regime (laminar, turbulent, dilation, washout). Applied to chalk and sandstone formations beneath Bournemouth for tunnelling, deep basements, and slope drainage design.
Frequently asked questions
How much does a field permeability test cost in Bournemouth?
For a single Lefranc test at one depth interval within a borehole, budget between £490 and £720 depending on access, depth, and whether the borehole is already drilled. A full Lugeon profile with five pressure stages in rock typically falls in the upper part of that range due to packer rig time and data interpretation. We provide a fixed-price quote once we review the site location and ground conditions.
When is a Lugeon test required instead of a Lefranc test?
Lugeon tests apply to rock masses, particularly fractured chalk, limestone, or sandstone where flow occurs through discontinuities rather than pore spaces. In Bournemouth, we switch to the Lugeon method once the borehole enters competent chalk below the superficial deposits, or when the client needs rock mass permeability for tunnel inflow estimates or grouting design.
How many test intervals do I need for a soakaway design?
BS 5930 and BRE Digest 365 recommend a minimum of three test intervals within the proposed infiltration depth, plus one test at the base. For a typical Bournemouth housing plot with a 2-metre deep soakaway, that means four Lefranc stages spaced roughly 0.5 m apart. We adjust the spacing on site if the driller encounters a change in material, such as a silt layer or iron pan, to ensure each distinct stratum is tested. More info.