4.6.4 Desk study and ground investigation
A desk study and ground investigation shall be undertaken, and the findings used to inform the design of the filling and earthworks specification.
A desk study and sufficient ground investigations should have been undertaken to characterise the site and identify all the features and potential geotechnical and environmental ground hazards relevant to the earthworks, including classification of the fill material itself.
The ground investigation should take account of the findings of the desk study and relevant standards listed in clause 4.6.1. Further guidance is given within Chapter 4.1 ‘Land quality - managing ground conditions’.
The desk study and ground investigation should determine the following items listed in Table 2, as a minimum:
Table 2: Typical items to be covered by desk study and ground investigation.
| Item to be determined | Guidance |
|---|---|
| Site history and past usage (eg, agricultural, residential, commercial or industrial) | To aid in determining a ground model for the site and potential areas of concern |
| Known areas of made ground | As shown on BGS Geo-index, other geodata services, historical site investigations and their reports |
| The nature of the underlying geology | To determine the potential for soft, loose soils, instability, voids, or highly compressible soils and to allow an assessment of pre or post treatment of the existing ground |
| The proximity of any existing buildings, roads or services | To assess whether these could be affected by ground movement caused by filling |
| The strength/density, compressibility and stability of soils beneath the proposed fill and for the potential re-use for fill earthworks | To enable the level of risk to be determined including settlement of the underlying soils and whether unsuitable material needs to be removed or if any form of pre-treatment is required. To assess the acceptability of site derived fills |
| The nature (presence and extent) of any groundwater and surface watercourses | To assess whether groundwater (or surface water) may affect the existing made ground/ natural soils or newly placed fill – for example by causing inundation settlement or washout of ‘fines’ |
| The geotechnical properties of soils including sulphate content and pH | To determine the suitability of soils for use as engineered fill and for the design of buried concrete |
| The presence of any slopes, embankments, cuttings, quarry highwalls, buried batters or earth faces | To assess the potential negative effect of earthworks on existing ground stability and the potential effect of features on the performance of earthworks and foundations bearing upon the placed fill |
| The presence of any buried services, culverts, tunnels or other buried structures | To assess the effect of structural loading from earthworks and associated earthworks machinery and whether protection or mitigation measures are required |
| The presence of contaminated substances or materials suspected to be contaminated | To assess whether cut earthworks and placement of filling may cause, or increase, the release of contaminants such as leachate, hazardous ground gases, etc refer to Chapter 4.1 ‘Land quality - managing ground conditions’ |
| Geotechnical Risks | An initial geotechnical risk register to ensure that all known or anticipated natural or man-made geohazards are identified and can be investigated and considered within evolving stages of investigation, designs and earthworks execution |
Other items to consider in addition to Table 2, but not repeated here, are listed in Table 1 of Chapter 4.5 ‘Vibratory ground improvement techniques’ and in Chapter 4.2 ‘Building near trees’.
Where a ground investigation has been undertaken without considering the proposed earthworks, it may be necessary to carry out further supplementary investigation, sampling, testing, and/or monitoring to inform the earthworks design and earthworks specification.
Last updated: 2nd January 2024