MASW & VS30 Shear Wave Velocity Testing in Slough

Q: How much does a MASW survey cost for a typical Slough site?

For a single MASW line with processing and a signed report, you are looking at between £1,250 and £2,610 depending on the array length, access conditions, and whether we combine it with other testing on the same mobilisation. Sites on the Trading Estate with tight access or night-time working windows tend to sit at the upper end.

Q: What is the difference between MASW and a seismic refraction survey?

Seismic refraction gives you a P-wave velocity model and works well for mapping bedrock depth, but it struggles when you have a velocity inversion, which is common in the London Clay where a stiff crust overlies softer weathered material. MASW uses surface waves (Rayleigh waves) and is sensitive to shear-wave velocity, so it handles inversions cleanly and gives you the Vs30 value that Eurocode 8 actually needs.

Q: How long does a MASW test take on site?

A single 46-metre spread with a sledgehammer source typically takes about 45 to 60 minutes of active shooting once the geophones are planted. Setting out the line and levelling the array adds another 30 minutes. Most Slough sites we can complete a full line and demobilise within two hours, assuming reasonable weather and no buried services interrupting the spread.

Q: Do you need to drill boreholes alongside MASW, or can it replace them?

MASW cannot replace boreholes entirely because it does not give you a physical sample for logging, index testing, or contamination analysis. What it does exceptionally well is fill the stiffness gap between zero-depth geophysics and the first rotary core run. We typically recommend at least one borehole or CPT to ground-truth the Vs profile, especially where the Lambeth Group sands appear at depth and the velocity contrast can be subtle.

Slough sits on a patchwork of Quaternary gravels and the stiff, overconsolidated London Clay that defines the geology of the Thames Basin. With over 157,000 residents and a trading estate that covers roughly 600 acres, development pressure here never really lets up. The thing is, the clay can look perfectly competent in a trial pit but still hide a Class C or D seismic response that alters your foundation loads under Eurocode 8. We run the active MASW spread with 24-channel geophones, extracting a Vs profile down to 30 metres to lock in the VS30 value. It is the fastest way to get from a greenfield site to a defensible ground model without waiting for borehole lab turnaround, and we tie it back to the seismic microzonation requirements that insurers and warranty providers are starting to ask for in the Thames Valley.

VS30 is not just a number for a compliance box; it is the parameter that decides whether your structure sees 0.125g or 0.25g at the bedrock interface.

Our service areas

Scope of work

The superficial geology across the borough swings from Lynch Hill Gravel in the north to Boyn Hill Gravel and alluvium along the Jubilee River corridor, before hitting the London Clay Formation at depth. What we consistently see is a stiff to very stiff clay with undrained shear strengths above 100 kPa, yet shear wave velocities that barely scrape 200 m/s in the upper 5 metres when the clay is weathered. A single MASW line of 46 metres gives us a continuous Vs column without the disturbance you get from pushing a sampler. We process the dispersion curve through forward modelling, picking the fundamental mode and iterating until the misfit drops below 3%. The output feeds directly into BS EN 1998-1 site classification and the EC8 elastic response spectrum, which is often the difference between a straightforward shallow footing design and having to jump to a Type 2 spectrum with higher plateau accelerations. On sites near the M4 corridor or the Slough Trading Estate, where vibration sensitivity matters, we can also extract the small-strain shear modulus for dynamic settlement analysis.

MASW & VS30 Shear Wave Velocity Testing in Slough — Technical reference — Slough

Local geotechnical context

The contrast between the gravel-capped terraces north of the A4 and the alluvial clays down by the Jubilee River is sharper than most engineers expect until they see the borehole logs side by side. We worked on a warehouse extension near the Slough Heat & Power plant where the initial CPTs suggested competent gravel at 2 metres, but the Vs profile showed a velocity inversion at 8 metres that matched a lens of soft clay nobody had picked up. The original pad footing scheme assumed a ground type B; the measured VS30 pushed it to type C, adding 15% to the base shear. On the opposite end, a residential block off Bath Road sat on dense gravel with Vs above 400 m/s from 3 metres down, and the MASW data allowed the structural engineer to drop back to a type B spectrum and save on reinforcement. In Slough, the seismic site class can flip within a hundred metres, and guessing it from the geological map alone is a gamble that rarely pays off.

Need a geotechnical assessment?

Reply within 24h.

Email: contact@geotechnical-engineering1.com

Relevant standards

BS EN 1998-1:2004+A1:2013 (Eurocode 8), BS 5930:2015+A1:2020 (Code of practice for ground investigations), BRE Digest 523 (Seismic site classification practice in the UK)

Reference parameters

Parameter	Typical value
Survey depth (standard)	30 m below ground level
Geophone spread	24-channel, 1–2 m spacing
Source type	Sledgehammer on aluminium plate
Vs uncertainty (modelled)	< 10% for top 20 m
Data format	SEG-2, dispersion curves, 1D Vs profiles
Compliance standard	BS EN 1998-1 (EC8), BRE Digest 523
Report turnaround	3–5 working days with interpretation

Common questions

How much does a MASW survey cost for a typical Slough site?

For a single MASW line with processing and a signed report, you are looking at between £1,250 and £2,610 depending on the array length, access conditions, and whether we combine it with other testing on the same mobilisation. Sites on the Trading Estate with tight access or night-time working windows tend to sit at the upper end.

What is the difference between MASW and a seismic refraction survey?

Seismic refraction gives you a P-wave velocity model and works well for mapping bedrock depth, but it struggles when you have a velocity inversion, which is common in the London Clay where a stiff crust overlies softer weathered material. MASW uses surface waves (Rayleigh waves) and is sensitive to shear-wave velocity, so it handles inversions cleanly and gives you the Vs30 value that Eurocode 8 actually needs.

How long does a MASW test take on site?

A single 46-metre spread with a sledgehammer source typically takes about 45 to 60 minutes of active shooting once the geophones are planted. Setting out the line and levelling the array adds another 30 minutes. Most Slough sites we can complete a full line and demobilise within two hours, assuming reasonable weather and no buried services interrupting the spread.

Do you need to drill boreholes alongside MASW, or can it replace them?

MASW cannot replace boreholes entirely because it does not give you a physical sample for logging, index testing, or contamination analysis. What it does exceptionally well is fill the stiffness gap between zero-depth geophysics and the first rotary core run. We typically recommend at least one borehole or CPT to ground-truth the Vs profile, especially where the Lambeth Group sands appear at depth and the velocity contrast can be subtle.

Location and service area

We serve projects in Slough and surrounding areas.

View larger map