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4.6.13 Reporting
A detailed Earthworks Verification Report shall be provided to the NHBC on completion of the earthworks filling and testing. Where appropriate, the contents shall be agreed with the NHBC prior to the work being done.
A comprehensive Earthworks Verification Report for the filling works should be provided to the NHBC as soon as practicable. It should provide an interpretation and assessment of the factual data contained within the report as well as a detailed summary of the works undertaken including testing. A site wide or phased reporting approach is acceptable.
Where reinforced strip foundations are proposed, the report should be produced by a third-party organisation separate from those undertaking the works, ie, by the overseeing supervising engineer, with all factual information made available. The report, where beam grillage or semi-raft foundations are proposed, can be produced solely by a suitably experienced earthworks contractor.
The content of the Earthworks Verification Report shall be defined within the earthworks specification. Guidance on the contents and structure of the detailed report may be based on information within DRMB CD 622, where it is termed a Geotechnical Feedback Report.
It is important that the report is in an appropriate format. Test results should be suitably summarised and presented to provide clear understanding using graphs and charts as necessary.
The Earthworks Verification Report should give details as appropriate of the following:
- The contractors and personnel responsible for the filling work including details of supervision and testing
- Preparation works prior to earthworks filling
- Reference to the earthwork specification and method statement(s)
- Sources of material used as engineered fill and their material classification
- Any treatment, reconditioning or remediation of proposed engineered fill
- Plant and methods used
- As built survey records including post topsoil strip level or formation level for the earthworks, reduced levels following earthworks cuttings, final as-built or post earthworks filling formation level, plan(s) and other drawings as appropriate that show the extent and depth of earthworks filling
- All test results and certificates
- Progress photographs and surveys
- Progress reports, site diaries, with details of weather/site conditions and any agreed variations or changes to the specification
- Graphical representation of the classification and compliance test data as show in Figure 7 below
- Changes and amendments to design and earthworks specification
- Records of remedial actions in areas of non-compliance
- Problems experienced and solutions and methods used to overcome the issues
- Confirmation that the works comply with the earthworks specification and are suitable to support the proposed foundation types, where applicable. All non-compliances or departures from the earthworks specification should be clearly identified and suitably assessed
- Drawings showing known obstructions and any relevant features under or within the engineered fill
- Graphical representation of the load-settlement tests, surcharge trials or post-completion monitoring over time with plots of settlement versus natural and log time presented to demonstrate that primary settlements are complete, with a clear trend of any remaining creep settlement projected to allow for a satisfactory building performance over a 60-year design life
- Information required by the builder to safely undertake follow-on works in the ground including any special precautions which should be undertaken or unusual constraints that exist, and any residual risks for example further measures may be required where upfilling or an increase in ground levels post-remediation are likely to be proposed
Notes
A – Indicates placed fill is of significantly higher density than achieved in the laboratory – the fill classification is likely not complying with the specification. Repeated results higher than the MDD indicates the laboratory testing was not on representative material or the method of laboratory compaction was too light.
B – Indicates placed fill has been compacted too dry of optimum and may therefore, where cohesive fill has been used, be liable to settlement when wetted.
C, D & E – Marginally outside of the compliance zone. As part of a large set of results that are otherwise compliant these marginal failures may be acceptable provided, they are not part of non-compliant clusters.
F – Indicates fill placed wet of optimum and may be liable to settlement under load or over time.
Results of type A, B & F should be assessed further, and explanation provided of remedial actions, further testing or reasons for acceptance.
Further guidance on acceptability testing of proposed source fills and compliance testing of placed engineered fill is provided in BS 6031:2009. In setting the compliance curve of dry density/moisture content relationship all tests should be presented/or made available such that the target basis of design (for each fill type) can be agreed with NHBC, noting the degree of interpretation and assessment including outliers. Updated targets may be appropriate in variable materials and should be detailed and agreed with the NHBC.
Compliance test results should be summarised and presented so that any non-compliances can be easily identified.
If the site has been filled some years before the intended construction works or for an alternative end use such as commercial buildings, then a retrospective validation may be appropriate. Assessment of historic fill within land reclamation schemes and marginal sites are generally outside the scope of this Chapter. Consult NHBC or consider using NHBC Land Quality Service for a bespoke consultation.
Last updated: 2nd January 2024