Geophysics in Cambridge provides a non-intrusive window into the ground, essential for understanding the complex and often variable subsurface conditions that define this historic city. From the gravel terraces of the River Cam to the Gault Clay and deep Chalk bedrock, the geological succession presents significant challenges for construction, environmental assessment, and archaeological investigation. Our geophysical surveys allow engineers, developers, and researchers to map these layers, identify buried obstacles, and assess ground stability without the need for extensive and disruptive excavation. This approach is particularly valuable in a city where the preservation of ancient college foundations, medieval street patterns, and sensitive ecological zones is a paramount concern.
The local geology is dominated by the Cretaceous West Melbury Marly Chalk and Zig Zag Chalk formations, which are often overlain by Quaternary river terrace deposits of sand and gravel. These superficial deposits can be highly heterogeneous, with lenses of soft alluvium and peat that pose a risk of differential settlement. A key geotechnical parameter in Cambridge is the shear wave velocity profile, which is used to calculate Vs30 values for seismic site classification. We determine this through MASW (Multichannel Analysis of Surface Waves), a technique that efficiently provides the stiffness data required for Eurocode 8 compliance, even on the challenging, soft soils found near the river.
Regulatory compliance in the UK is driven by the Building Regulations 2010 and the associated Approved Documents, particularly Document A (Structure), which mandates a thorough ground investigation. The execution of this investigation must follow BS 5930:2015+A1:2020, the code of practice for ground investigations. For seismic design, BS EN 1998-1:2004 (Eurocode 8) is the governing standard, requiring the determination of a ground type based on Vs30. Additionally, projects near the historic colleges or within conservation areas will be subject to strict planning conditions from Cambridge City Council, often requiring a detailed desk study and field investigation to protect both the built heritage and underlying archaeology before any ground is broken.
The applications for these services span a wide range of projects in and around Cambridge. Large-scale commercial developments on the science parks, new residential estates on the city fringes, and infrastructure upgrades like the Cambridge South railway station all require detailed ground models. Electrical resistivity surveys (VES) are routinely deployed to map the depth to bedrock, locate buried channels, and assess groundwater conditions, which is critical for designing effective dewatering strategies. For investigating the integrity of existing structures or mapping dissolution features in the chalk, seismic tomography (refraction/reflection) provides a high-resolution image of the subsurface, revealing anomalies that could compromise foundations or lead to sinkhole formation.
Geophysics provides continuous, non-intrusive subsurface profiles between boreholes, revealing lateral variations in ground conditions that point investigations can miss. In a historically sensitive city like Cambridge, this minimises disturbance to archaeology and structures, targets subsequent intrusive investigations precisely, reduces overall project costs, and provides critical data like Vs30 for seismic design across the entire site.
Vs30 is the average shear wave velocity in the top 30 metres of the ground. It is the primary parameter used in Eurocode 8 (BS EN 1998-1:2004) to classify a site’s ground type for seismic design. This classification dictates the seismic load a building must be designed to resist, making the measurement a fundamental requirement for the structural design of most significant buildings in the UK.
Yes, this is a common application, especially in Cambridge’s historic core. Methods like electrical resistivity and ground penetrating radar can detect buried walls, foundations, and infilled ditches by measuring contrasts in physical properties. This non-intrusive mapping is often required by planning authorities to inform mitigation strategies and ensure compliance with policies protecting heritage assets before development begins.
The effective depth of investigation depends heavily on the specific method and local geology. Electrical Resistivity Tomography (ERT) can reliably image to depths of 30-50 metres, while seismic refraction is typically effective to 20-30 metres. MASW for Vs30 profiling is designed specifically for the top 30 metres. These techniques are well-suited to mapping the interface between superficial deposits and the underlying chalk bedrock.