- 14th December 2018
- Posted by: Sophie Bunker
- Category: Projects
We were appointed by Calderdale Metropolitan Borough Council (CMBC) to undertake geotechnical and structural design for a major road widening scheme at Salterhebble Hill, Halifax. The works form part of the A629 improvement program, funded by the West Yorkshire-plus Transport Fund.
Proposed works included excavation of a new road cutting, 160m long and up to 6m high and construction of numerous retaining walls. The site is in a residential area and on a major transport route, therefore access to the site was extremely restricted throughout the project.
The new cutting was to be formed by removing an existing masonry retaining wall which was in poor condition and excavating into a hillside comprising of soil, rock and numerous historic structures. There was a significant risk of slope instability during the excavation of the cutting which had to be managed in design.
We designed and managed delivery of a targeted ground investigation, ecological and preliminary structural surveys. Due to access constraints, significant uncertainty remained regarding ground conditions prior to construction. This risk was managed in design using the observational method outlined in Eurocode 7.
An innovative engineering solution for the new road cutting was developed using soil nails to stabilise the excavated slope and installing a greenwall facing tied to the nails using geogrids. This solution improved construction efficiency and safety by integrating temporary and permanent works.
The greenwall option provided the client with a more sustainable structure than the concrete retaining wall originally proposed. We worked closely with the client and the greenwall supplier to enable the successful installation of the first large-scale greenwall of this type in the UK.
Working closely with the principal contractor, we provided support during construction supervising the testing of soil nails and monitoring works to ensure compliance with the design. Numerous changes to the design resulting from unforeseen ground conditions were managed including the discovery of three uncharted stone culverts which required the installation of additional drainage.
The greenwall is the first significant structure of its type in the UK. CMBC has received a very positive response to the structure from both residents and the media and has provided positive feedback regarding the innovative solution designed by us. We:
- Maximised data collection from the site through designed and managed delivery of three phases of targeted ground investigation
- Completed ecological surveys and advised on tree felling operations
- Delivered pre-construction structural inspections of adjacent properties
- Developed an innovative sustainable engineering solution for a challenging site with complex ground conditions and challenging access
- Overcame numerous challenges during construction by working closely with the client, Principal Contractor and other consultants
- Delivered best value for the client