Geotechnical Earthworks Specification and Validation – Lancashire

Background: E3P

E3P were instructed to prepare a Geotechnical Earthworks performance specification for construction of structural fills to support a proposed adopted highway and earth embankment retaining feature at a residential development in Lancashire, England. The performance specification detailed how site won materials were to be compacted as a structural fill and detailed the validation testing protocol necessary to demonstrate that the emplaced material had met with the specification stated within Lancashire County Council Highways Authority & the Highways Design Manual. The E3P performance specification also detailed the necessary exemptions required to ensure that the works were completed in strict accordance with Waste Management Regulations.

Findings

As part of the works, E3P completed a detailed site cut/fill model which identified that there would be excess cohesive material generated by the reduction in levels within the proposed development area. E3P established that due to the long term potential for settlement associated with even well compacted cohesive soils due to elevated pore water pressures, that it would be essential for the cut and fill process to be well controlled. Furthermore, E3P also established that as the filled material will form a structural fill to support a road and retaining embankment the cohesive fill must be re-engineered to conform to Class 7a material if it is to be deemed suitable for re-engineering using the appropriate method (7A) to achieve the required end product performance criteria.

Outcome

E3P, using knowledge of waste management legislation and geotechnics were able to divert a significant volume of material from landfill while also reducing the requirement of a significant import of engineered fill. The specification and monitoring and validation completed by E3P demonstrated that all the works met with the LCC Highways Design Manual Specification.