Client-Esh Civils

Location-Border of South Tyneside/Sunderland City Council

Project Summary

The aim of the IAMP Northern Employment Area Phase 1 project was to deliver the essential highway and infrastructure work required to facilitate the continued expansion of the strategic area. This project involved the delivery of new highway infrastructure associated with drainage work, earthworks and supporting infrastructure which enabled future development within the Northern Employment Area. This approach provided a more practical and efficient construction solution while satisfying the relevant highway, drainage and site constraints.

Lynas Engineers was appointed by Esh Civils to provide civil and highway engineering design services. The original design resulted in relatively high finished road levels, significant earthworks, large swales and a deep pavement construction while the site also presented constraints associated with existing infrastructure and overhead high-voltage cables. The design package was progressively updated to address technical queries relating to drainage, pavement, earthworks, utilities, rising mains, kerbing, footways and adoption requirements. This approach allowed the design to respond effectively to construction-stage constraints and changing site conditions.

Following the design review Lynas Engineers developed the revised civil and highway design in accordance with the agreed design changes. The team also coordinated the associated design information and interfaces between the various engineering disciplines to ensure that the design was fully integrated and suitable for construction. The revised design provided a coordinated and practical engineering solution that supported the efficient delivery of the works on site. Working closely with Esh Civils and South Tyneside Council, Lynas Engineers developed an integrated highway, drainage, earthworks and pavement solutions.

Throughout the construction phase, Lynas Engineers provided continued technical design support and coordinated CAD and 3D information to facilitate setting out, earthworks and drainage operations. The team also reviewed and coordinated revisions to the rising main alignment. Following the identification of an opportunity to reduce the length of rising main within the carriageway, Lynas Engineers hydraulically assessed the proposed realignment and liaised with Retro Flo to confirm that the revised arrangement satisfied the required gradients, cover depths and operational criteria.

The revised highway design incorporated carriageway crossfall, which allowed the western swale and associated drainage kerbs to be removed. The eastern drainage system was simplified through the use of front-entry gullies discharging towards the swale. The swale configuration was also rationalised, with reduced depths and widths while retaining the required hydraulic capacity. The swales were interconnected by a carrier drain beneath the southern access. Revised highway levels reduced the overall excavation requirements and volume of imported fill, providing a more efficient earthworks solution.

Following the ground investigation and initial CBR testing, Lynas Engineers reviewed the proposed pavement build-up, which had originally been approximately 1,140mm deep. Where CBR values of 3% or greater were recorded, the value-engineered solution reduced the pavement depth to approximately 600mm, representing a reduction of 540mm, or approximately 47%. Further CBR testing undertaken during construction identified weaker formation conditions, with results ranging from approximately 1% to 2.5%. Lynas Engineers subsequently reassessed the pavement foundation requirements and evaluated alternative strengthening measures, including additional Type 1, capping and geogrid solutions. Specialist geosynthetic suppliers were consulted to establish appropriate treatment measures for the ground conditions encountered while maintaining the overall value-engineering objectives.

Challenges

• The original highway levels resulted in substantial earthworks, largely influenced by the surface water drainage requirements.
• Existing overhead high-voltage cables imposed level and clearance constraints that required careful consideration during the design development.
• The drainage network and swale configuration were complex and required simplification while retaining the necessary hydraulic capacity.
• The proposed pavement depth was reviewed and optimised to reflect the site-specific ground conditions.
• Low CBR values were identified during construction, which resulted in further pavement investigations and assessment.
• Highway geometry, utility interfaces and rising main requirements were continuously coordinated throughout the construction period.

Successes’

• An integrated value engineering approach was applied across the highway, drainage, earthworks and pavement design.
• Pavement construction depth was reduced by 47%, from 1,140mm to 600mm where CBR values were ≥3%.
• The drainage and swale layouts were simplified, eliminating unnecessary infrastructure while maintaining required performance.
• Road levels and earthworks were optimised while maintaining appropriate drainage gradients and safe electrical clearances.
• Coordinated 3D models and setting-out information were developed to support accurate construction delivery.
• Responsive design support and multidisciplinary coordination were provided throughout the construction stage.

The resulting design provided a coordinated and construction focused solution that simplified the original infrastructure by reducing pavement construction depths where ground conditions were permitted, removed unnecessary drainage infrastructure, addressed unforeseen ground and construction constraints through practical engineering solutions.