Retaining the Rail Network

A ‘Lego’ style concrete retaining wall block is helping Network rail reduce the disruption to services when trackside landslips endanger the rail network.

The concrete block system was first used by Dean and Dyball Rail on the Blackboy Tunnel/Exmouth Junction where a section in a cutting, approximately 20 meters long, required stabilising. Historically, there had been several small slips which had resulted in a timber post and sleeper retaining wall being constructed and this was in the process of collapsing onto the S&T trough route.

A modular block retaining wall was designed to replace this arrangement, which allowed for short sections (4-6 metres) of the proposed concrete block wall to be constructed at a time, thus eliminating the possibility of damaged to the S&T route.

The installation gang consisted of three men and an excavator (with an operator). The blocks were transferred to the worksite by a Road Railer towing a trailer, under the supervision of a Machine Controller and excavated material was removed from site using the same resource.

One of the three-man gang was tasked to act as a slinger; blocks were removed from the trailer to be placed into the modular block wall by the excavator. In this instance the foundation was constructed using compacted lean-mix concrete.

All works were completed during the night-time possessions, with less than a four-hour working window.

The location for the retaining wall also suffered from ingress of water from natural springs and fissures in the rock. Due to the nature of the mass concrete blocks, temporary control of the water was easily dealt with by forcing the water around the blocks to the existing track drainage by forming small bunds.

The design called for a second wall constructed behind the main wall with a small void between the two walls, which was filled with concrete. This greatly reduced the volume of loose material which would require compacting, thus increasing the works to be completed within the planned possession programme.

Since this first project, the concrete block system has been used for other retaining walls on the rail network as its strength and earth retaining capabilities keeps both the train and track safe whilst offering a pleasant viewing experience.

About the Author: John O'Gara

John is Marshalls CPM's Specifications Sales Manager and specialises in our award winning Redi-Rock modular walling and precast Off-Site Solutions. John is available for lunchtime CPD style presentations.

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