COMTECT BIO ENGINEERING recently finished a year-long contract on the upgrading of the A19 in Teesside.
The firm, part of the design team for the DBFO joint venture of Amey, Sir Robert McAlpine and Taylor Woodrow, was initially contracted to build a series of reinforced soil retaining walls using its Textomur system on a section of the road north and south of the River Tees.
But as the project progressed, it was asked to construct a variety of different structures including temporary work to ease traffic management problems on the scheme.
'Design alternatives were sought wherever possible, doubling our workload,' said Comtec Bio Engineering senior design engineer Dave Woods.
For the vegetated retaining walls, 4500m2 of Textomur was used. The system comprises geotextile reinforcement inside patented steel formwork. It can be used either as a facing wall in front of steep slopes or as a retaining structure to embankments.
Textomur Green is vegetated to blend into the local environment and is generally built at angles of 60degrees or 70degrees. On this contract the retaining walls were up to 7.5m high and their steep slopes allowed widening of the road within existing boundaries.
Woods said that the vegetated finish and the system's ability to reuse the existing cohesive glacial till as a fill material were of prime concern in its selection.
One design alternative was on a new approach road to the A19 at Billingham Beck. Geolock concrete block faced reinforced soil was used for the wing walls to piled bridge abutments over a culvert. Ground conditions were poor, comprising peat and alluvial deposits with high seasonal flood levels.
'The use of reinforced soils reduced bearing pressures over the poor ground and gave a greater tolerance to any future differential settlement than many conventional structures offered,' Woods said.
To ease traffic management at the busy Mandale junction, two 9m high vertical temporary walls were built as stop ends to the new northern overbridge at two thirds width, allowing traffic to be re-routed before demolition of the existing structure and completion of the new bridge.
On the Mandale South overbridge, a 9m high permanent vertical structure was used to alleviate thrust loading to the back of an existing piled bridge abutment.
Woods said: 'This reduction in moments, together with the use of a lightweight PFA fill material and polystyrene fill over the abutment, enabled the existing piled foundation to be incorporated into the new widened overbridge.'