The existing slope drainage system had insufficient capacity to cope with the surface and subsurface flow from the adjacent land. Frequent spring lines were present at various locations along the cutting in the upper and lower slope. Network Rail required an upgrade to the drainage system to reduce the detrimental impact on the stability of the slope, giving control over waterflow and generally making the area safer.
The site is located approximately 200m north of Ashley in Wiltshire on the Great Western Main Line from London Paddington to Plymouth at 101m1710yds to 102m1000yds on the Down Line and comprises a cutting up to 25 m high, with a slope angle up to 35 degrees.
The scope included: –
The existing slope drainage system had insufficient capacity to cope with the surface and subsurface flow from the adjacent land. Frequent spring lines were present at various locations along the cutting in the upper and lower slope. Network Rail required an upgrade to the drainage system to reduce the detrimental impact on the stability of the slope, giving control over waterflow and generally making the area safer.
Failure modes included localised slumping, terracing on the mid slope, washouts and persistent cracking observed throughout the cutting slope. The work was preventative rather than reactive to target improvements in the Earthwork Score and to create more stable and reliable infrastructure.
The site was split into 3 No. zones (A, B & C) during the design phase identifying works required within each zone to compile a tailored project plan to factor in individual health and safety requirements.
| Innovation: The use of bespoke Rendezvous Point (RVP) Boards was developed specifically for the use on this site, due to the sheer size and scale of the worksite. This made it easier for any operative or subcontractor working on the site to know exactly which area they are working in should the emergency services be required and for reporting of any accidents or incidents.
The boards were deployed at planned agreed stopping points, a suitable distance from the worksite, to alert operators of the worksite limits. Specific information was displayed relating to the location of the board to enable emergency services to pinpoint the location of an incident. The boards also contained emergency kits (first aid etc), H&S briefings, and phone numbers for line managers and the Network Rail signal box, for emergency communication purposes. This best practice has now been adopted on all Network Rail Western projects. Contract Management: With circa 40 No. Technical Queries submitted prior to and during the physical works, the CML management team developed a tracking system that could capture technical and commercial elements in real-time. This was shared with the client for clarity periodically to enable both parties to have a common understanding of project progression. |
| Challenge/Risk: On-site driven design changes
The design was at Approved For Construction (AFC) stage during tender award but upon commencement on site, supplied setting out points had multiple anomalies present which meant that the drainage did not work with the natural fall of land. Mitigation: CML worked collaboratively with the Network Rail team, utilising our in-house design and engineering resource to redesign/adjust the setting out positions of start/finish points of drain runs/deep hole drains, and mid-slope bench details, to ensure a fully functioning drainage system could be installed. Our swift recognition and approach to this challenge mitigated delay to the programme and ensured follow on works were constructed safely, and on time. Challenge/Risk: Any Line Open (ALO) Working The line is the primary route for trains between London and Penzance, with a minimum of 4 No. trains per hour (passenger and freight). To ensure disruption to train services was kept to a minimum, Network Rail required the works to be carried out in accordance with the Any Line Open (ALO) Code of Practice. Mitigation: CML scheduled work predominantly for days, rather than relying on night-time possessions, removing the associated risks surrounding night-working, worker fatigue and resident disruption. CML’s proposed method of working involved the use of large items of plant working in an ALO environment, working from the existing mid-slope bench. A robust ALO plan was completed for each of the items of plant, which consisted of a combination of our own in-house sourced machines and supply chain plant, and this was integrated into the master programme. CML selected to use specialist items such as Long Reach Excavators fitted with GKD Series 2 Virtual Wall Slew Limited Devices. The reason for this plant selection was predominately health and safety as the long reach machines allowed for works to take place from a safe position. Due to the volume of traffic still using the lines and the location in which excavators needed to be placed, there was a risk potential of excavator arms swinging into the path of moving trains. The GKD series is more advanced than conventional slew restriction systems and prevented this from happening by detecting where the lines and working parameters were. |
This enabled the majority of works to be completed during non-possession working within normal daytime hours creating an efficiency of £275k. 30 No. possessions were negated and the associated cost of RRV’s and personnel reduced.
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