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Geotechnical Design

Laying the foundations

With nearly 40 years in the market, the “type” of proposed development could vary significantly ranging from low-rise or high-rise residential potentially including single/double basement to warehouse-type commercial or school structures, therefore close liaison with the Client and their Architect and/or Structural Engineer during the foundation design stage is essential, to ensure the drawings in-hand and loading data of the proposed are both accurate and reliable.

At Soils, we tend to believe that a key element for a safe and cost-effective foundation design lies at Preliminary Investigation Report (pre-works) stage, during which anticipated geology on site is identified and potential geo-hazards are revealed. Awareness regarding the risk of man-made or natural cavities, landslide instability, soils of volume change potential, high water table or poor ground conditions i.e Made/Worked Ground is essential and ensures the appropriate scope and method of investigation is adopted, ranging from rotary (open and core) and cable percussive drilling to windowless sampling and trial pitting.

A credible geological profile for the site is thus created, which is coupled with field (i.e. N60 SPT, DPSH or CPT) and geotechnical laboratory data (i.e. QUU, Grading Analysis, Atterberg) to allow our Engineers to confidently quantify the risk (if present) and undertake a site-specific assessment regarding the most suitable foundation option for the proposed development.

Equipped with modern in-house software and in full alignment with Code of practice for foundations BS 8004:2015 (or Eurocode-7 upon request) both shallow and deep foundation scenarios are evaluated first against safety and then cost, for the ground conditions encountered. Shallow foundations could include strip, pad or rafts and are typically adopted where relatively low to moderate loads are expected, with the depth of excavation not in excess of 3.0m, thus frequently more economic than deep foundations, such as driven or bored (i.e CFA) piles, which are preferred when either near-surface soils are “problematic” or anticipated loads are relatively high (or both).

Our geotechnical reports provide our Clients with detailed justification regarding the selection of the appropriate foundation solution, followed by the presentation of either allowable bearing capacities for various foundation depths for a given strip/pad/raft configuration or anticipated safe working loads with depth for various pile diameters.

Subject to size and complexity i.e. major (circa 10 hectares) residential schemes, a mixture of shallow or deep or occasionally less traditional i.e. ground improvement techniques, screw pile, micro-pile foundation solutions are adopted over separate zones of the development to assist the Client in their feasibility assessment.