How MARS increased a failing stone bridge’s weight from 7 to 40 tonnes without rebuilding it

Client: Sheffield County Council Highways. Main Contractor: Amey LG Limited. Location: Stocksbridge, Sheffield. Completed: 2017

The problem: a vital river crossing restricted to 7 Tonnes

Unsliven Old Bridge carries Smithy Moor Lane across the Little Don River, just below Underbank Reservoir – the water source for Stocksbridge and its steelworks. A local authority assessment restricted the bridge to a 7-tonne weight limit, spanning the river well above normal water level. The council faced two options: decommission the bridge or demolish and replace it with a new concrete structure.

Why the bridge had weakened

Much of the bridge’s lost capacity traced back to a previous electric cable installation. The stone arch had been cut into from above and channelled out to give the cable the necessary cover, weakening the arch barrel and compromising its load-bearing capacity.

Local pressure to preserve the historic bridge

Community opposition to demolition brought the project to Stress Goldhawk Division, who re-assessed the structure and proposed the MARS System as an alternative – strengthening the bridge to a full 40-tonne capacity rather than replacing it.

Access challenges: Pontoon and scaffolding over the river

Working height above the river required a crane-lowered access pontoon, assembled directly in the water, with a scaffolding staircase built to connect the road-level riverbank to the pontoon safely. Scaffolding towers were then erected on the pontoon itself to reach the underside of the arch at height.

The MARS system solution

The MARS System strengthened the arch from beneath, offering Sheffield County Council Highways a cost-effective, low-carbon alternative to
a full concrete rebuild.

Repairing the cable damage from above

Because the electric cable installation had also damaged the arch from above, additional work was needed at road level:

• The road surface was removed and fill carefully excavated to expose the top of the arch barrel
• Minor repairs and grouting were carried out from above
• The fill was replaced with ‘no-fines’ weak concrete to restore depth without adding excess load
• Tarmac was reinstated and the road reopened to all traffic.

The result

• Weight limit increased from 7 tonnes to 40 tonnes full highway loading restored
• Bridge replacement avoided, saving significant cost and carbon compared to a new concrete structure
• Minimal disruption to drivers and road users during the works
• Delivered on time and on budget for Sheffield County Council Highways and main contractor Amey LG Limited.