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BAM Ritchies

Case Study: Flax Bourton Cutting Stabilisation – Phases 3 & 4

Location: Near Bristol

Client: Network Rail

Main Contractor: Alfred McAlpine Capital Projects (GWESPA)

Designer: Donaldson Associates

Date: 2004 - 2005

Flax Bourton railway cutting has a history of shallow slope failures, the larger of which disrupted railway operations. The cutting is slightly under 3km in length, up to 16m deep and was excavated through mudstone and limestone strata of the Mercia Mudstone group, with the slopes being 30° to 50°.

Network Rail undertook a risk assessment to identify areas at risk so as to target and design a deep drains stabilisation works. However, there were some concerns over the logistics of implementation. Ritchies offered an alternative solution, on a design and construct basis, using ground nails and TECCO® high tensile steel wire mesh to stabilise the cutting, together with some drains.

Working in partnership with Alfred McAlpine Capital Projects, Ritchies used their in-house designed and built, rope supported Terrapin rigs as well as specially selected soft formation DTH drilling bits to cope with the weathered mudstone and limestone bands. The principal quantities were:

Area of mesh: 22,555 square metres

Number of anchors: 332

Number of soil nails: 1411

Number of dowels: 349

Number of drains: 280

There was no disruption to railway operations and only a few possessions were required.