A303 Amesbury to Berwick Down (Stonehenge)

Tender description

The scheme is an integral part of National Highway's commitment to deliver a high-performing, high-quality route along the A303/A358 corridor between the South West and South East. It will also help to conserve, reconnect and enhance the Stonehenge world heritage site (WHS), making it easier to reach and explore, as well as improving biodiversity and providing a positive legacy for nearby communities. The scheme will be approximately 8 miles (13km) long and comprises the following key components: • a northern bypass of Winterbourne Stoke with a viaduct over the River Till valley; • a new junction between the A303 and A360 to the west of and outside the WHS, replacing the existing Longbarrow roundabout; • a twin-bore tunnel approximately 2 miles (3.3km) long through the WHS; and • a new junction between the A303 and A345 at the existing Countess roundabout. Lot 1: The requirements of the scheme that will be the responsibility of the successful applicant are principally captured in the following areas: 1. Design and construction of the new works; The scheme's new works includes the design and construction of the civil, mechanical, electrical and plumbing (MEP), technology and environmental components, key features of the new works are summarised below: • Tunnel: A twin-bore tunnel, approximately 2 miles (3.3 kilometers) long beneath the Stonehenge World Heritage Site, including tunnel portals and approach structures, tunnel service buildings and plant rooms, tunnel control system and mechanical, electrical and plumbing systems • Tunnel boring machine - design, manufacture, testing, shipping and on-site assembly • Carriageway works • Bridge works to form a viaduct over the River Till, an under bridge for the B3083, a flyover at the A345 Countess Roundabout, and 4 green bridges (Parsonage Down accommodation bridge, Winterbourne Stoke accommodation bridge, A360 Longbarrow Junction & green bridge No. 4) • Carriageway and tunnel technology • Landscaping and habitat creation • Extension of Parsonage Down National Nature Reserve • Protected species mitigation measures • Ensure rights of way and private means of access • Mainline earthworks • Utilities works 2. Refurbishment, replacement and modification of existing assets; There are works required on existing assets under the current ownership of both National Highways and Wiltshire Council. Continued engagement and consultation will be required with both parties throughout the design and construction phases for these elements including: • Existing A303 de-trunking works • Demolition works and site clearance works • Modification works to existing structures 3. Maintenance and operation during construction Maintenance and operation of the existing A303 within the site boundary will be required for the duration of the construction works. The appointed Contractor will be required to liaise with National Highways, its maintenance contractors and Wiltshire Council to coordinate activities. 4. Post construction maintenance period There is an extended maintenance period (minimum of 5 years, maximum of 7 years) after construction to 'prove' the tunnel performs as intended. Maintenance is included as part of this period and the Contractor will be responsible for all elements of the infrastructure associated with the tunnel and its approaches. The appointed Contractor will be required to liaise with National Highways, its maintenance contractors and Wiltshire Council to coordinate activities and tunnel operations. The appointed Contractor will be required to fulfil the duties of Principal Designer and Principal Contractor under the Construction (Design and Management) Regulations 2015.