Benefits of a collaborative commercial model for specialist ground engineering-Paper

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The A1 Birtley to Coal House highway project in Northeast England required major ground improvement for approach embankments near the new Allerdene viaduct. Deep, soft glaciolacustrine soils were predicted to settle by up to 1.5 metres, threatening highway performance, nearby railway infrastructure and buried utilities. The solution comprised nearly 7,000 rigid inclusions, up to 36 metres long, designed to reduce settlement to around 250 millimetres and limit differential movement.<br /><br />Delivery was complicated by the package’s scale, intense competition for specialist labour and equipment, supply-chain disruption, inflation and tight programme constraints. Missing the Christmas rail possession needed to demolish the old bridge could have delayed project completion by a year. The teams also faced complex site conditions and sequencing challenges.<br /><br />Costain and specialist contractor Cementation Skanska engaged early to develop the design, programme, resourcing and commercial approach together. Rather than use a conventional lump-sum subcontract, they adopted an NEC4 Option E cost-reimbursable model. Direct costs and some overhead were guaranteed, while the remaining overhead and profit depended on jointly agreed performance indicators, primarily milestone and completion dates. This linked commercial rewards to shared project outcomes and reduced the focus on claims and change negotiations.<br /><br />Early resource commitments and an on-site concrete batching plant helped address capacity and supply risks. The plant provided reliable material supply, reduced lorry movements by more than 48,000 vehicle-miles and saved an estimated 73 tonnes of CO₂e.<br /><br />Although the work was initially forecast to take 48 weeks, it was completed in 37 weeks, meeting the critical deadline and saving approximately £2 million—around 13% of the anticipated package value. The case demonstrates how collaborative procurement can align specialist contractors and main contractors around safe, timely and cost-effective delivery.

Keywords

A1 Birtley to Coal House

Allerdene viaduct

ground improvement

rigid inclusions

soft glaciolacustrine soils

settlement reduction

NEC4 Option E

Costain

Cementation Skanska

collaborative procurement