Geotechnical and Geoenvironmental Consultancy

The HS2 Old Oak Common Enabling Works was undertaken over two years and comprised the remediation of former railway sidings to enable construction of the £1.3bn Old Oak Common Station Super Hub. CGL provided full-time, site and office-based consultancy services to the primary subcontractor, Erith Contractors Limited, and acted as Erith’s Remediation and Earthworks Consultants throughout the scheme.

Site services comprised a team of CGL engineers and senior engineers with full-time responsibility for works supervision across the three stages of the scheme. Site supervision included inspection, sampling and testing of excavations and stockpiled materials alongside the provision of a geoenvironmental and geotechnicalwatching brief and liaison with the client and main contractor.

Office-based consultancy services included geotechnical, geoenvironmental and waste characterisation of excavated materials and stockpiles, with a primary focus on maximising re-use of site won soils. Deliverables comprised stockpile reports, materials tracking and placement pro forma, risk assessments and technical notes, and preparation of interpretative reports for specific areas of the scheme.

CGL worked with a specialist sub-consultant, DustScan AQ, to provide air quality monitoring and occupational and environmental asbestos monitoring throughout the works. The monitoring included sampling of airborne asbestos fibres and airborne polyaromatic hydrocarbons in the dust, data from which were used to provide ongoing risk assessments.

As the site was almost 1km in length it was subdivided into 27 individual sub-areas to track and control material movements efficiently. In total, some 120,000m3 of material was excavated from the site and over 200 stockpiles generated. CGL assessed, and generated a report for, each individual stockpile detailing the chemical and geotechnical testing undertaken, and providing assessment of material acceptability and recommendations for either re-use or disposal off-site.

This approach enabled the client and contractor to assess the acceptability of materials for re-use on an individual stockpile/material type and mitigated delays by pre-assessing materials before being used within earthworks.

The majority of material was subsequently re- used within the scheme and placed as compacted fill in accordance with an Earthworks Specification for which CGL provided a geotechnical watching brief, assessment of material acceptability, earthworks testing and subsequent verification.

Geoenvironmental and Geotechnical Verification Reports for ten grouped sub-areas, detailing the works undertaken, supervision findings and final validation of the remediation and earthworks undertaken were produced on completion.