Complex Reconstruction of a Retaining Wall with a Hybrid Soil Nail Geogrid System

DYWIDAG supplied the materials and new development to enable our geotechnical partners to complete complex reconstruction of a collapsed rural stone retaining wall and road adjacent to a stone cottage. It required innovation and new products, collaboration between suppliers and consultants, and a multidisciplinary set geotechnical engineering and construction skills.

Context

A storm in February 2020 significantly damaged the busy B4224 road between Fownhope and Hereford. Investigation confirmed a new wall would need to be constructed while supporting the existing highway and upper slope. Site-specific conditions challenged the team to devise new product solutions, including the development and testing of new connection idea. The safety of those working near the failed slope and the public was critical.

Solution

DYWIDAG worked with Huesker - a global manufacturer of geosynthetics, agricultural, and industrial textiles - to develop a part to connect the soil nail and geogrid system, considering ease of construction, design life, and settlement issues of the reinforced soil over time. DYWIDAG carried out in-house testing on the connection piece.

The hybrid soil nail geogrid system method for constructing retaining structures in sites with limited access is a long-term, reliable solution that:

  • Minimized excavation and soil removal.

  • Enabled construction of reinforced earth walls in a restricted site.

  • Reduced lorry traffic (due to less excavation), lowering impact on local community and minimizing CO2 emissions.

  • Provided a safe working area while keeping the foot path open and gas main in place.

  • Reduced overalls costings due to less excavation and time on site

The Stone Cottage was successfully completed with a reopening of the road in March 2021.

Going Further

In addition of the conception of the hybrid soil nail geogrid system method, WSP were instrumental in design and implementation of the project. Alun Griffiths, a construction contractor with geotechnical capabilities including a specialized knowledge of soil nailing, the right equipment, and civil engineering expertise, completed the construction.

This multidisciplinary team installed the custom hybrid soil nail and high tensile mesh geogrid system to stabilize the slope.

This acted as a temporary support while difficult excavations were completed.

This project has been nominated for the Ground Engineering Awards 2022.

DevelopmentSupplyTechnical Assistance

Herefordshire County Council

Balfour Beatty Roads (framework)

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