The latest NHBC Standards, effective from January 2024, include a new chapter (Chapter 4.6) on engineered fill, which Lithos Director Adam Gombocz contributed to. The chapter provides guidance for using engineered fill to support new build plots, external works and infrastructure.
One of the requirements of Chapter 4.6 is for engineered fill to be placed to a suitable Earthworks Specification.
Lithos are able to draft Earthworks Specifications, for various scenarios including:
- Construction of low-rise buildings which will derive direct support from engineered fill compacted in accordance with an End Product specification.
- Construction of low-rise buildings which do not derive direct support from engineered fill compacted in accordance with a Method Specification (foundation loads transferred to underlying competent strata by either trench fill or piled foundations).
- Construction of a highway embankment.
Lithos can prepare ‘simple’ foundation zoning plans and more detailed Foundation Schedules which take account of proposed final levels, trees, and ground conditions. Our Schedules typically include the following for each plot:
- Foundation type
- Founding strata
- Safe bearing capacity
- Founding depth (after consideration of tree influence)
- Foundation width
- Floor type
Analysis of ground movement as a result of an increase in load or change in pore pressure. This may be caused by a change in ground level, change in groundwater regime, or the construction of a foundation. Lithos utilises an array of mathematical techniques from classical mechanics to finite elemental analysis, using state of the art software.
Determination of soil shear strength to establish the safe bearing capacity of a soil, prior to foundation design.
Lithos are able to review ground investigation and topographic survey data and then use bespoke software to perform a limit equilibrium assessments for circular (Bishop) and non-circular (Janbu) failure mechanisms.
Analysis is usually undertaken based on a global Factor of Safety on shear strength and Serviceability Limit State partial factors. Where the slope will be permanent, the assessment will consider long-term stability using drained geotechnical parameters.
Analysis of earth pressures on gravity retaining walls, embedded retaining walls, crib walls, gabions and reinforced soil design.
The design of earthworks to provide enhanced engineering performance of the soil to support pavements and where possible building structures.
Often where piling or vibro is proposed, ground conditions require provision of a piling mat (working platform). Provided the proposed plant loadings and resulting pressures are known, and appropriate ground investigation has been completed, Lithos can undertake mat design in accordance with guidance provided in the 2004 BRE document, “BR 470: Working platforms for tracked plant”.
