FP McCann’s FlexiArch System used in two bridge installations for Devonshire Estate.
Project: FlexiArch Bridge Installation at Devonshire Estate
Main Contractor: Dean and Dyball Civil Engineering
Consultant Engineers: Parsons Brinckenhoff
Products Supplied: 2 FlexiArch Systems; 16nr. 1050mm CFA Piles (4 per abutment) to 6.5m depth; and precast arch springing blocks.
Heavy rains and serious flooding from August to October 2008 brought about catastrophic failure of two brick arch bridges dating from the mid-19th Century in the grounds of Escott estate, Devon. Dramatic scouring of foundations caused the backs to break and bridges to fall inwards.
FlexiArch was chosen as the most ideal replacement bridge solution for this location which had a combination of construction restraints which include access, ecology and heritage.
Due to listed building and other planning consent issues, East Devonshire Conservation officers were committed to the replacement of arch bridges by arch bridges. In addition, the Environment Agency required river invasive works to be minimized.
The new foundations for installations were designed to be highly robust in order to provide scour protection to a depth of up to 750mm, with the perception that flood incidents are likely to continue with greater frequency in the future.
Working from the riverbanks within temporary cofferdams, 16nr, 1050mm CFA Piles were installed (4 per abutment) to 6.5m depth. Macrete’s precast arch springing blocks were fixed to the pile caps by twelve 32mm steel tensile bar dowels per block secured by high strength grout. Time for installation of the FlexiArches totaled 4 hours for each bridge.
The flat packed arch rings arrived on one transporter, while the precast side spandrels arrived on another. Each arch ring was craned directly from the transporter and lowered into place onto the springing blocks. As the flat lying arch ring was lifted its arch shape was formed and it fell naturally into the exact span and rise to make the primary arch formation of the bridge.
The site foreman guided the unit into place with hand instruction to the crane operator and two further workers assisted in the correct seating of the arch on the springing block.
Apart from a small flexible bund in the river to retain any chance item that might fall in the river to retain any chance item that might fall in, the river itself was untouched and undisturbed. Installation of each arch ring took about 15 minutes. Installation of the four quarter spandrels and tying them together laterally with supplied steel tie rods took a further 45 minutes per spandrel, with checking of line and level included.
The arches would then be back filled with poured concrete to road level in a series of pours to prevent, the occurrence of unbalanced loads on the arches. A layer of steel mesh was included in the top of the backfill as an anti-cracking measure. The roadway was completed with a blacktop surface.
The precast spandrels were clad with reclaimed brick and the parapets topped with a stone coping. A three-ringed mock arch header brick course mimics the style of the original bridges.
Embankment construction and reinstatement earthworks mark the final stages of this bridge replacement.
For further information on FP McCann’s Bridges Solutions Contact Our Toomebridge Depot at 028 7965 0471 or email sales@fpmccann.co.uk for a quote.
