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Case studies

Track Worker Safety Sites – Slope Stability

Geotechnical Design

Project Commenced: December 2020

Project Completed: April 2021

Client: Network Rail

 

About the Project

As part of Network Rails ongoing drive to improve safety for rail workers, the Track Worker Safety Sites project was set up to improve existing access points, and provide additional access points where significant existing risks had been identified. BCM Construction were engaged to assist with this through the CAPEX framework for Network Rail South East, employing Equate Design to undertake the design works. 

As a significant number of the sites were located on embankments, or in cuttings, step access was required and this required careful assessment of the existing slopes to determine the likelihood of existing slope stability issues, or whether the proposals would affect the stability of the existing slopes. 

 

The Challenge 

To accurately determine the Factor of Safety (FOS) for slope stability, a comprehensive slope stability assessment is required, necessitating several deep boreholes to map the underlying strata. Without this, and in particular without knowledge of the dip (inclination) of the strata, any determined theoretical FOS would be almost meaningless, particularly where slopes of relatively low existing FOS are concerned. For this project the time, and cost constraints deemed this approach prohibitive. 

The Solution 

With multiple sites under consideration and insufficient budget to compete them all, it was agreed that the sites would be risk assessed to identify slope stability risks. Due cognisance was paid to available geotechnical information, including the Earthwork Condition Reports, and only sites with the lowest risk were taken forward for design. Several sites were discounted at this stage. 

Simultaneously the access proposals were worked up to determine the vertical alignment. Where practicable the stairs were designed to follow the natural slope, but for long slopes, a compliant stair requires intermediate landings and this frequently requires cut or fill on the slope to facilitate a level area. These locations, and the general cut/fill requirements were again assessed to understand the likely effect on the slopes and determine if this was acceptable. 

 

The Deliverables: 

  • Cost effective solution meeting clients timescales, budget and acceptable risk levels. 
  • The assessment methodology was agreed with the Network Rail DPE (Designated Project Engineer) and Geotechnical RAM (Route Asset Manager). 
  • Earthwork Risk Assessments undertaken considering site topography, geological mapping data, existing known slope stability issues (at and adjacent to the site), and the proposed groundworks for the preferred solution. 
  • Stair configurations determined to best suit existing topography, preferably avoiding cutting in at the toe of slopes, and building up at the top of slopes as these would have the greatest risk of affecting the overall slope stability. 
  • Stair designs were produced compliant with BS5935-1 and Network Rail Standard Details where practicable. 
  • Handrailing provided to provide safe access and interface with trains. 
  • Ensured track clearances were compliant with Network Rail standards. 
  • Upgrading of security fences.  
  • Provision of Access Point signage. 
  • Provision of additional signage including ///what3words and QR codes to aid locating access points. 

 

Outputs and Benefits:

Reduced risk of slope failureBy risk assessing the slopes the sites that could lead to potential slope stability issues were identified, and if the risks could not be mitigated within the project constraints, the sites were removed from scope early on, allowing additional designs to be undertaken and constructed within the available time.