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BAM Ritchies

Case Study: Sebastopol Slope Stabilisation

Client: Network Rail

Main Contractor: Carillion

Designer: Tony Gee & Partners

Location: South Wales

Date: 2008

A landslide on the railway line at Sebastopol in the Rhymney Valley in South Wales has been causing problems for a number of years. Despite previous attempts to arrest the movement of the hillside – one by using Grundomat piles, the movement resulted in a long term Temporary Speed Restriction (TSR).

The main element of the solution was deep piles and ground anchors and a significant amount of the work was carried out during a critical six week blockade.

Trials

Owing to the difficult nature of piling through an active landslide in the Welsh valleys, extensive piling and anchoring trials were undertaken initially to prove and hone the piling methodology, in advance of the critical blockade dates. These trials comprised nine piles up to 19m deep at 450-600mm diameter and two anchors 27m and 37m deep with a SWL of 200kN.

Trial pile drilling was undertaken using Soilmec and Casagrande piling rigs with continuous flight augers. Ground anchors installed were 35mm diameter GEWI bar anchors.

Main Works

With the trials successfully completed the main work proceeded and comprised 436 piles 12m-23m deep at 600mm diameter and 149 anchors 27m-37m deep with a SWL of 187-225kN.

Pile drilling was carried out using Soilmec piling rigs with continuous flight augers at 600mm diameter. The piles were reinforced with 406mm x 16mm wall thickness steel tubes inserted by casing vibrators to full depth.

Ground anchors installed were 28mm diameter GEWI Plus bar anchors.