As part of the £8.5m prelims work, Osborne will deliver ecological mitigation work, site clearance, associated highways alterations and utilities work.
Osborne project director Chris Hudson said works include modifications to the Rollestone junction, safety improvements to the A303 east of Amesbury and water main installation.
Highways England also awarded Wessex Archaeology a record-breaking £35m contract for archaeological protection and excavation work.
Fieldwork will start in late spring 2021, should planning consent be granted for the scheme.
The 2-mile tunnelling project and 8-mile dual carriageway through the world heritage site is still awaiting its Development Consent with a decision due by 13 November.
Highways England is also currently progressing the procurement process for the main works contract.
Procurement chiefs are participating in dialogue with bidding consortia before they submit their final tenders.
The prestige project has attracted a European line up of firms from France, Germany, Spain, Italy and Austria, with Murphy the only UK contractor in the chase.
- BMJV – Bouygues Travaux Publics and J Murphy & Sons
- HDJV – Hochtief Infrastructure and Dragados
- MORE JV – FCC Construcción Salini Impregilo and BeMo Tunnelling UK
The preferred bidder is expected to be announced in late 2021.
Osborne said: “Osborne has significant experience working collaboratively with Highways England and local stakeholders on a wide variety of challenging projects.
“We are looking forward to undertaking this essential project safely and efficiently keeping inconvenience to neighbours and travelling public to a minimum.”