BAM Ritchies

Case Study: Flax Bourton Cutting Stabilisation – Phase 6

Location: Near Bristol

Client: Network Rail

Engineer: Donaldson Associates

Main Contractor: Carillion

Date: 2007

Phase six followed on from the successfully completed phases 3,4 and 5.

Works comprised the stabilisation of a further 490m of the railway cutting with a slope length of 18m to 20m at an angle of 45-50° to the horizontal. The works where spread over 530m of the cutting dissected by a 40m section that Ritchies had previously treated as 'emergency works' with Nuttall as the main contractor in 2006.

Once again the 'Renewal' design developed by Ritchies and Donaldson Associates was utilised exclusively and involved the drilling of 1,850 holes in lengths varying from four to eight metres, comprising four to six metres long 50mm Gewi temporary dowels; four, seven and eight metre long 25mm and 28mm Gewi bar nails and dowels and six metres drain holes.

Access to the crest of the works was very good, with the site compound adjacent and a much higher density of nails meant shorter and quicker moves resulting in increased daily drilling output.

The drilling was undertaken using a tracked ECM rig along the crest, three Terrapin drill rigs transversing along the face by means of hydraulically powered Tirfors, and two road/rail mounted masts along the toe.

Following anchor/nail installation, 9,550m2 of Geobrugg TECCO® mesh was placed over the slope and pinned down using diamond spike plates and a variety of cabling systems specially designed for the job.

400mm diameter clay pipe drainage channels (four 20 metres long) were also constructed by roped access operatives.