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Window sampling made simple

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Network Rail’s target in Control Period 5 (CP5 2014-2019) is to do more for less. To achieve more renewals and replacements for less money, which can only be done by introducing innovation in all areas of its work.

Slope stabilisation is one of the hot topics. Recent landslips such as the one at Harbury have demonstrated the need for new ways both to repair damaged embankments and cuttings and to prevent future failures. This has identified a need in the market for innovative drilling equipment.

Versatile new rig

The Lightweight Limited Access Modular Rig (LLAMR®) is a window sampling rig which overcomes the difficulty of site investigations in locations with limited space, headroom or problematic accesses and egresses, without compromising safety. It has the capability of carrying out site investigation and installations in virtually any environment or location, from housing basements and low-ceiling bridges to failing embankment cesses, toe, crests and mid-slopes. With a much smaller footprint, the LLAMR also minimises the risk of further damage/ destabilisation to the environment.

With most locations of the CP5 Earthworks project on steep and/or unstable rail-side embankments with limited access, most standard window sampling rigs required expensive and problematic weekend possessions.

Topdrill, which was established in 2006 and has since become one of the UK’s leading geotechnical investigation (GI) sub-contractors specialising in the railway industry, introduced the LLAMR in 2014.

It can carry out geotechnical investigations in high-risk areas during midweek day shifts, thereby avoiding costly and time-limiting weekend night possessions.

The rig has consistently sampled to depths of 12 to 15 metres on CP5 earthworks projects. Supplemented by calibrated in-situ testing, including SPT (standard penetration testing), dynamic probing and undisturbed sampling (U70s), as well as the installation of varied monitoring equipment, Topdrill is able to produce high- quality results which greatly reduce the design risk.

These GI results, along with any laboratory testing undertaken, allow engineers to provide a client-specific report which can range from ‘basic factual’ through to fully interpretive.

Investigation and reporting

Factual reporting can simply be the provision of the exploratory borehole records and laboratory test results or a formal presentation with full descriptions of the techniques and methodologies used, in accordance with Eurocode 7 EN 1997-2:2007 Annex E.

Depending on the level of ‘consultancy’ required by the client, interpretive reports can range from a short paragraph added to the factual section where only a single parameter may be required (for example an allowable ground bearing pressure at a particular location), through to a fully interpretive report with desk study, in accordance with Eurocode 7. The latter would provide recommendations and geotechnical parameters in the context of the investigation and/or proposed development, such as retaining wall design parameters, discussion of foundation options, allowable ground bearing pressures and settlement estimates.

For example, interpretive reports for the North Lincolnshire Resignalling and South Kirkby and Wakefield Westgate projects required analysis and correlation of medium-weight dynamic probing (DPM) and borehole SPT to provide allowable bearing pressures for the gantries, signal bases and various other structures at several hundred locations.

Using this and other technologies, Topdrill provides an all-round, bespoke engineering service, including on-site and post-site support and consultation for the client, and can also undertake an extensive range of environmental investigations, risk assessments and remediation audits.

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