Re-signalling schemes, large scale, excellent to deliver, challenging build conditions, all the usual phrases you hear when project teams embark on another re-signalling scheme
Usually 12-18 months prior to that team forming in earnest the GI and survey elements are commissioned in order to provide the upfront knowledge required to enable the design of piled foundations for each signal and new structure locations.
Due to the ever increasing number of locations invariably involved in these schemes the investigation alone needs careful planning. In line with the theory of the planning and delivery of safe works (PDSW) principles, this always involves a detailed walkout of each location to ensure all challenges to accessing and executing the task at hand are identified. Post walkover a revised detailed plan is produced, the scope revisited with the client, a new detailed plan drawn up and then access booked. As with any task the task is made simpler by breaking it down into bite sized tasks, this is where the expertise of Bridgeway Consulting (BCL) comes into its own.
BCL has over 20 years of rail planning experience combined with extensive experience of conducting ground investigations within the rail environment. BCL’s staged approached has been refined over 13 re-signalling schemes with ever increasing efficiencies being gained offering the client ever more value for money.
BCL received an instruction following a successful tender undertaken as part of their existing NR4 (MT) intrusive and non-intrusive framework with the integrated design group (IDG) to undertake ground investigation, topographical surveys, and phase one habitat ecological surveys for phase two (package A).
The package consisted of:
- 70 signal locations
- six level crossings (Truro, Long Rock, Western Growers, Gwinear Road, Camborne, Roskear
- one platform extension (Truro station).
The survey had to pick up boundary fencing, drainage, trees, ballast shoulders, edge of cess, top of cutting/embankment, toe of cutting/embankment, the tracks (utilising reflectorless) and all other railway infrastructure and features e.g. signals and cables.
The purpose of the ground investigation works was to:
- classify the near surface geology for the design of level crossings, signal foundations and platform extensions. Shallow foundations are proposed in areas with competent sub-surface materials; piles may be required where ground conditions are poor
- determine the strength profile of the subsurface material at all locations
- obtain samples for laboratory testing (including BRE soil aggressivity to buried concrete, soil classification and soil strength testing)
- where possible, gain an understanding of ground water levels.
The topographical survey element was conducted to provide data to allow for the design of the new signals and signal bases. The survey at each location had to fully cover an area 30 metres in front of and 30 metres to the rear of the proposed signal location from boundary fence to boundary fence.
The scope was then split into two categories, areas with superficial deposits and areas without. Areas of superficial deposits were investigated utilising the dart and competitor window sample (WS) rigs to a target depth of 8 metres with follow on dynamic probing super heavy (DPSH).
Areas without superficial deposits were investigated utilising BCL’s geotool dynamic probe heavy (DPH) to the same target depths as the WS locations.
A detailed walkover was completed by the PM in charge of the task accompanied by one of BCL’s senior SI drillers in a safety critical role. This allows BCL to have all aspects of knowledge required on site at any one time. Each location was assessed against initial assumptions and then the scope refined in collaboration with both the client and the project team to ensure the correct information could be gained to satisfy all parties.
Due to timescales on this project line blockages were utilised to complete the works. BCL has in-depth knowledge of the region due to having delivered the possession management contract in the region for the past 15 years providing PICOPs and PSS to the region. This local knowledge became invaluable in planning the trickier of the locations and again ensured value for money for the client.
Following the successful completion of site works, geotechnical and geo-environmental samples were sent for laboratory testing. SI/GI Information was presented in factual report pulling together site data, logs, drawings and photographs alongside the laboratory testing results. Raw geotechnical and geo-environmental data has also been issued in AGS4.0 format.
Euston Station enabling works
As a precursor to the enabling works Bridgeway Consulting was asked to act as principal contractor for all survey works on the behalf of Network Rail, and also to undertake the majority of the surveys including ground investigation works using its inhouse engineering teams. For such a complex area much thought and consideration in planning and executing survey works while maintaining a fully operational rail infrastructure were required.
To successfully carry out the planned works, Bridgeway appointed a project team to work in conjunction with Network Rail at their Euston site and which included access planning, operational and technical leadership and the utilisation of multiple site teams. Investigations required were:
- cable percussive holes (25-50 metres in depth)
- rotary percussive holes (30-55 metres in depth)
- cone penetration testing (CPT) to 30 metres
- structural coring of the retaining wall (7.5 metres thick)
- window sampling
- trial pitting
- ground penetrating radar (GPR) survey.
Prior to these works BCL had developed its limited access cable percussive (CP) rig the D1500 Cabtrak. This rig was a hybrid of a standard cable percussive rig with the manoeuvrability of a WS rig and is capable of moving under its own power between locations unlike a standard CP rig which needs to be vehicle towed.
Complying with ALO procedures the SI/GI team carried out the required site visits, plans, drawings and roles to successfully work adjacent to open lines. During the project this rig proved to be the mainstay of the project and achieved depths well in excess of expectations with the deepest depth achieved of 43 metres with in-situ testing.
Another area BCL innovated with was the use of a cantilever prefabricated access suppliers and manufacturers association (PASMA) tower. Requiring significant upskilling of current PASMA Operatives BCL employed an external training body to deliver the first prototype course for the erection and use of this type of tower.
The gravity retaining wall at site was some 20 metres high with a batter that meant a conventional tower could only access up to three metres from the ground. By utilising the cantilever tower BCL managed to obtain cores 5.8 metres from ground level.
Initially the wall was thought to be 2.5-3.5 metres thick, this proved to be false and the longest cores measured 7.5 metres at the base of the wall.
Following the successful completion of site works, geotechnical and geoenvironmental samples and core samples where required were sent for laboratory testing. SI/GI information was presented in a factual report summarising all site data captured, logs, photos, drawings and photos. Raw geotechnical and geo-environmental data has also been issued in AGS4.0 format.