Free Hand Diamond Drilling For The Tube




Built in 1863 the London Underground throughout its' lifetime has transported over 1.2 billion passengers and today continues to handles over 4 million passenger journeys per day. The Ruislip depot maintains the rolling stock for the London Underground and is one of the fifteen depots positioned in and around Greater London. The depot is approximately 250 metres in length and has 3 lines into the depot which contains 2 pits enabling work to the underside of the rolling stock.

'We selected Castle and Pryor as they are a highly experienced and well certified diamond drilling company. The work they completed was of the highest standard, their operatives were professional, friendly, organised and well supervised by Allan Fennell, who was a pleasure to liaise with. They were easy to work with and delivered the project on time and I have no hesitation in using Castle and Pryor again and highly recommend them to other construction companies' Richard Taylor, Senior Quantity Surveyor, Clancy Docwra Group Ltd.


The Ruislip train depot required an upgrade to its existing track system and concrete hard standing. The old rail tracks and supporting structure were removed and replaced by civil engineers Clancy Docwra. With the new hard standing surface in place works could commence to prepare for the re-installation of the railway track infrastructure.

Clancy Docwra commissioned Castle and Pryor for our diamond drilling services to drill over 1.500 holes to facilitate the new track installation. The hole size nominated was 30mm diameter with a penetration of 210mm, as this would facilitate the resin anchor fixing which would secure the track to the concrete


A major challenge in this particular project was the presence of the steel alloy rail tracks and rail anchors as they impaired the ergonomics of the drilling machinery. Typically a diamond drilling rig is set up with the drill motor attached to a drill stand which is then bolted down via the drill stand baseplate, however, with the rail track and rail anchors in situ this made this traditional method non workable.

Whilst there are several other methods that can be employed to stabilise the drill stand i.e. suction vacuum, back propping or metal weights the hand held method was adopted as this was deemed the most workable solution to overcome the ergonomics of drilling between the tracks. In fact a free hand drilling method significantly expedited the process, as there is no requirement to move the stand from hole to hole. Ruislip Train Depot

Alongside this challenge is the use of rotary percussive drilling as there is an increased potential for Hand and Arm Vibration Syndrome or H.A.V.S. However to overcome this challenge a mix of diamond drilling and percussive drilling was used. Percussive drilling leaves a rough sided hole which is suitable for resin anchors as it helps the resin to adhere to the sides aiding stability. However percussive drilling will not penetrate steel reinforcement so when steel is in-countered the percussive drill is removed and replaced with a diamond tipped core to complete the steel cutting process. Once complete then the percussive drilling can be reinstated until the depth of hole has been fulfilled.

Using the combination of diamond and percussive drilling significantly lessens the implications of H.A.V.S as the trigger time spent on diamond drilling is very low compared to percussive drilling. Percussive drilling requires the use of H.A.V monitors to be placed on each machine so that the monitor can evaluate the amount of vibration the operator is exposed to as not to not exceed the recommended regulated limits known as the exposure action value EAV and exposure limit value ELV.

In all cases using a free hand drilling method requires significant expertise and experience as the ability to drill with accuracy, precision and exactness is demanded to meet the quality standards assured by a professional and accomplished diamond drilling company that is Castle and Pryor.

Key Benefits

Environmental – Reduced Hand and Arm vibration through the use of combined diamond drilling and percussive drilling, along with reduced noise and waste by lessening silt contaminated water through this methodology.

Financial – Cost considerate as completed on time and by the use of expertise and deconstruction methodology.

Time – 3 Operatives over 3 weeks completed the project on time.

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