The geophone array sits in a straight line across the site, 24 channels picking up surface waves generated by a sledgehammer strike on an aluminium plate. In York, that plate often rests on a thin layer of made ground covering the York Moraine Member—glacial till that can look solid at the surface but hides variable stiffness at depth. The acquisition unit converts those vibrations into a dispersion curve, and from that curve the shear wave velocity profile emerges. It is the most practical way to get a VS30 value without mobilising a drilling rig into a tight city-centre plot off Micklegate or behind the Minster. When the team processes the data back in the office, they are looking for that critical 30-metre average that feeds directly into the seismic site classification under Eurocode 8 and will shape the foundation design. A single MASW line can reveal whether the stiff clay at 8 metres is sitting on something much softer—exactly the kind of transition that matters for a piled solution or a mat foundation where differential settlement could become an issue.
A VS30 of 168 m/s versus 210 m/s can shift a site from ground Type C to Type D, altering the entire seismic design basis for a York structure.
Process and scope
Local ground factors
A developer planned a five-storey residential block on a former industrial yard near Leeman Road, where the ground investigation logs showed 4 metres of sandy fill over soft alluvial clay. The structural engineer assumed a ground type based on a desk study and specified shallow pad footings. When the MASW survey was finally commissioned, the VS30 came back at 168 m/s—placing the site firmly in ground Type D, with a significantly higher seismic design acceleration than the Type C assumption that had been used. The foundation design had to be reworked, adding ground beams and deepening the footings into the till at 6 metres. The delay cost the project six weeks. York is not in a high-seismicity zone by global standards, but the UK National Annex to BS EN 1998-1 still requires seismic consideration for structures of consequence class CC2 and above, and the ground type is the single largest factor controlling the spectral shape. Getting the VS30 wrong does not just affect the structural frame—it cascades into the retaining wall design, the floor slab detailing, and the earthworks specification. A morning of MASW testing costs a fraction of the rework bill that comes from an incorrect site classification, yet too many projects still treat it as an afterthought.
Relevant standards
BS EN 1998-1:2004 + UK National Annex (seismic ground type via VS30), BS 5930:2015 + A1:2020 (Code of practice for ground investigations), BS EN 1997-1:2004 + UK National Annex (geotechnical design)
Other technical services
VS30 Site Classification
Single or multiple MASW lines processed to deliver the VS30 value and ground type classification per BS EN 1998-1, suitable for planning submissions and structural design briefs.
2D Shear Wave Velocity Profiling
Roll-along MASW acquisition creating a continuous cross-section of Vs values, used to map lateral changes across a site—particularly relevant where the alluvium-till boundary runs diagonally beneath the footprint.
Combined MASW and Borehole Calibration
MASW lines tied to existing or new borehole logs, using the borehole stratigraphy to constrain the inversion model and improve the reliability of the Vs profile at depth.
Small-Strain Stiffness for Settlement Analysis
Derivation of Gmax (small-strain shear modulus) from the Vs profile, feeding into advanced constitutive models for settlement prediction under sensitive structures on York's compressible alluvial soils.
Typical parameters
Quick answers
What does a MASW survey cost for a typical residential plot in York?
For a single-family plot or small residential development in York, a MASW survey with one or two lines and a VS30 report typically ranges from £1,210 to £2,610 depending on access, line length, and whether supplementary borehole data is available to constrain the inversion. Larger commercial sites requiring multiple lines or 2D profiling will fall toward the upper end or beyond.
How long does the fieldwork take, and what access is needed?
A single MASW line of 50 to 70 metres takes about 90 minutes to set up and acquire, including the time to lay the geophone cable, test the coupling, and record multiple hammer strikes at each offset. The crew needs a clear strip roughly 5 metres wide and as long as the array, which in York's tighter sites sometimes means working along a pavement or closing a lane briefly. Data processing and reporting add three to four working days.
Can MASW work on a site with a concrete slab or hardstanding?
Yes, but the geophone coupling changes. On hardstanding, the team uses base plates with adhesive or heavy sandbags to ensure the geophones are firmly coupled to the ground and not just vibrating with the slab. The sledgehammer source still works, though a heavier hammer or a weight drop may be needed to generate enough low-frequency energy to reach the full 30-metre depth. The dispersion curve will show whether the slab itself is introducing a high-velocity surface layer that needs to be accounted for in the inversion.