In Bognor Regis, seismic site assessment is a critical first step for any development on the coastal plain, where the underlying geology of Quaternary drift deposits overlying Cretaceous Chalk creates specific foundation challenges. Our service addresses the requirements of UK building regulations and Eurocode 8, focusing on ground motion characterisation for sites that may be influenced by the deep-seated Chichester Syncline and nearby tectonic features. A robust seismic evaluation always begins with a comprehensive ground investigation to define the stratigraphy, followed by targeted CPT testing to measure small-strain shear wave velocity in situ, a parameter essential for liquefaction assessment in the loose, saturated sands found in the Arun district.
Our methodology aligns strictly with BS EN 1998-1:2004 and the UK National Annex, employing a combination of geophysical and direct penetration techniques. We utilise the seismic cone penetration test (SCPT) to acquire continuous, high-resolution profiles of VS, allowing for accurate site classification to BS EN 1998-1 without the disturbance associated with traditional borehole geophysics. Data interpretation is calibrated and validated through our UKAS-accredited laboratory, where cyclic simple shear tests may be specified. For critical layers, we correlate field data with advanced laboratory tests such as grain size analysis and Atterberg limits to fully characterise soil behaviour under cyclic loading, confirming the potential for liquefaction or cyclic softening in fine-grained materials.
Typical projects in Bognor Regis demanding this level of seismic scrutiny range from coastal defence structures and marina developments to multi-storey residential blocks. The presence of soft alluvial clays and loose marine sands means even modest structures require a clear assessment of ground deformation risk, while major infrastructure must account for the long-period effects amplified by deep chalk basins. For foundation design, our foundation recommendations are directly informed by the seismic analysis, ensuring that options like deep piles socketed into the chalk are verified against lateral spreading and kinematic loading, a common concern where superficial deposits overlie a rockhead with a pronounced dip.
The process delivers a concise Seismic Site Assessment Report, providing the ground type (A through E), peak ground acceleration (PGA) for the 475-year return period, and explicit statements on liquefaction potential and slope stability under seismic action. We move beyond generic desktop studies by integrating direct measurements of dynamic soil properties, offering a clear value: regulatory compliance coupled with an optimised foundation concept that is not over-engineered. This targeted, data-led approach gives structural engineers in Bognor Regis the certainty needed to design resilient structures on a complex and variable coastal geology.