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Challenging Ground Conditions

Some of the most complicated challenges on any project can be dealing with constraints within the ground build-up. These can come in a range of forms, from weak soil strata to buried obstructions. At Davies Maguire, the team has extensive experience dealing with these challenges and developing innovative designs to provide efficient solutions.

The key to delivering the right geotechnical solution, is to first establish an in-depth understanding of the existing conditions. We do this through specifying ground investigations, soil testing and groundwater monitoring, tailoring our specifications to suit the project. For example, we focus on detailed surveys around buried obstructions to mitigate conservative assumptions in the design or allow for smaller testing equipment for existing buildings or constrained sites. On a recent project, we specified a month-long ground water monitoring programme during the high spring tide on a river side site, to establish the relationship between the groundwater table and the tide. This enabled us to determine the highest possible groundwater level which in turn informed the architectural ground levels and the safest open-cut excavation depths for temporary works.

The temptation with buried obstructions, can often be to specify their removal to simplify the foundation design, however, this can be time consuming and costly to carry out on site. We therefore endeavour to develop foundation schemes that can work around obstructions. A recent example of this was a historic gasworks site where we designed a transfer structure to bridge an existing buried gasholder foundation. The structure was 8m deep and located in contaminated soils, which would have been very costly to remove. We integrated survey results into our BIM model to accurately coordinate our design around the obstruction, saving time and money for the client, while also reducing risks of on-site clashes.

Our team has experience working in a variety of soil strata build-ups, from deep made ground and London Clay in Central London, to shallow chalks in rural areas. Each situation presents its own challenges, and we design our foundation solutions to suit each unique condition. Shallow foundations are often not possible where deep made ground is present. We therefore ensure we optimise our piled foundation designs by reviewing the ratio of load capacity to pile diameters and the associated volume of concrete, optimising the solution in terms of sustainability, cost, and site programme.