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Borrobol Estate: Replace Estate Bridge

Location:

The estate is located adjacent to the A897, between Helmsdale and Kinbrace.

Map

Background:

Borrobol estate required to exact 20,000 tonnes of timber across an estate bridge crossing the river Helmsdale. This estate bridge which was erected in the 1970’s was suitable for general estate use however lacked capacity for the proposed timber extraction. UPM-Tilhill were engaged to carry out the harvesting operation and carried out a feasibility study into replacing the bridge. This study found that the most cost effective and quickest solution was to replace the existing 33 metre span Acrow 300 panel bridge with a Mabey 200 reinforced panel bridge. Access by foot to the estate was required throughout the project.

The bridge crosses the River Helmsdale which is an important salmon fishing river and environmentally sensitive. An overhead power line is situated downstream of the bridge and a BT cable supplying services to the estate and a Network Rail Level crossing is connected to the bridge.

UPM –Tilhill appointed GMR Henderson ltd as the sub-contractor to deliver this project.

Project:

The project consisted of the following elements:

  • Providing environmental protection to safeguard the River Helmsdale.
  • Repairing and improving the concrete abutments.
  • Taking delivery of the Mabey 200 Bridge and transporting in sections to storage across the bridge.
  • Preparing the bridge approaches and work areas.
  • Connecting the existing bridge to the new Mabey 200 Bridge and pushing the structure across the river removing sections of the existing bridge and adding sections of the new bridge until the new structure fully across the River Helmsdale.
  • Making good the bridge approaches and construct new concrete curtain walls.

The operation:

Prior to the work commencing all the involved staff received a tool box talk to ensure that all understood the scope of the works, agreed the risk assessments and the emergency procedures should an incident occur. Protection measures were then erected to protect the river and surrounding area.

The existing abutments were found to have areas of poor quality concrete which required maintenance and extra width and mass added to suit this new structure.   The unsuitable concrete was removed from the abutments with dowel bars and steel mesh fixed to the structure to enable additional concrete to be added. This stage of the work was completed safely, to time and budget with no environmental incidents.

The working and storage areas were prepared to allow stage 3 to proceed. During stage 3 the bridge was raised using jacks, propped and rollers placed to allow 2 sections of the new bridge to be attached utilising proprietary fixings. The structure was then launched in a sequence that allowed 2 new panels to be added and 2 old sections removed. When the new bridge was fully across the bridge was slowly lowered into place and the final deck sections added allowing the curtain walls to be constructed.

Results:

The launch of the new bridge was critical and 5 days was allowed in the programme to complete this stage of the project. The bridge started on the Monday morning and open to light traffic on Thursday morning with heavy traffic crossing soon after.

The estate owner, Sir Michael Wiggin was involved throughout the operation and is delighted with the manner in which the works were completed and has a bridge which improves access to the estate and will do so for many years to come.

UPM-Tilhill are very pleased with the outcome in that they are now able to extract the 20,000 tonnes of timber knowing that the bridge is fit for purpose and the works were completed safely, with no environmental incidents, to time and budget.

Photographs:

Stage 1: Repairing the Abutments

The unsuitable concrete was removed and dowels inserted to support steel mesh prior to shuttering and providing additional width to the abutments.

Borrobol Stage 1 (4)

Stage 2: Prepare Storage and Working areas

Areas prepared for storage of working around the structure.

Stage 3: Jack up Existing Bridge and connect new structure