BEAR Scotland Case Studies
A90 Hatton Bends
1.0 Brief Description of the Works
This minor improvement project is located approximately 13km south of Peterhead on the A90 Perth to Fraserburgh Trunk Road. The works consisted of a new off-line section of single carriageway north of Hatton, west of Cruden Water to west of the Auchiries South Junction, an overall distance of around 1km. This improvement included lengths of new side roads, construction of a new bridge over the Cruden Water and a footway along the south side of the A90 Trunk Road, demolition of the existing Midmill Bridge, associated traffic signing, temporary fencing, diversion and renewals of public utility apparatus, including a piled bridging structure over a Shell Oil pipeline, drainage, landscaping and accommodation works.
2.0 Client for the Works
The Client for the works was Transport Scotland (Trunk Roads Network Management)
3.0 Value of Construction Phase
£5.65m
4.0 Name of Contractor
Balfour Beatty Civil Engineering
5.0 Commencement of Construction & Duration
Commencement – 21 November 2005
Completion – 6 February 2007
6.0 Design Brief
The objective of the scheme was to improve the alignment of the existing carriageway.
7.0 Innovation Including Trials and Monitoring
as part of this scheme was the replacement of Midmill Bridge, a reinforced concrete and masonry arch bridge carrying the road across Cruden Water. Early in the design process the approach adopted was to maximum durability by constructing the arch in discrete interlocking precast concrete voussoirs and thus eliminate reinforcement entirely from the arch structure.
The road crosses the river obliquely and to maintain the spandrels parallel to the road a skew of 35° on the arch was required. Skewed arches pose a challenge as the geometry of the coursing of the voussoirs is extremely complex.
3D CAD modelling was deployed at the design stage to obtain an economic and buildable voussoir block that could be set out and placed on the barrel falsework requiring no more than conventional site skills and resources.
A single block type was designed for the arch and in total 479 were cast to construct the majority of the arch barrel. The voussoirs are placed in the English or helicoidal arrangement.
The arch barrel is completed by the subsequent injection of non-shrinkage cementitious mortar compound to form the bedding joints.
8.0 Site Supervision Issues
The project supervision was undertaken by Jacobs managed by BEAR. Several difficulties during construction were overcome, primarily due to ground conditions at both the major structures.