Following a series of heavy storms during late 2015 and early 2016 the Settle to Carlisle Railway line had to be closed at Armathwaite due to a landslip. The rain caused severe erosion of the embankment near to the River Eden. A 130m long x 70 m wide section of ground slipped with around 500,000 tonnes of material down the hillside and forcing the closure of the railway line on the 9th February last year.
The closure of the railway line on the route through Cumbria had a significant effect on railway passengers as well as the local economy. Income generated by visitors to this scenic part of the world was reduced and a replacement bus route had to be set up on sections of the route as an alternative means of travel.
It was imperative that a solution to secure the integrity of the railway line was found. Network Rail began to examine solutions and as part of the process Van Elle were invited to tender for the piling works associated with the project.
Van Elle have a long established working relationship with Atlas Copco. Wayne Allen (Senior Operations Manager, Van Elle) contacted Duncan Mackenzie (Sales Manager, Atlas Copco) to discuss the use of Elemex on this difficult site. The discussions centred around the tight production schedule, the selection of the tools to carry out the work and the support from Atlas Copco.
Atlas Copco’s Elemex solution has an extended ring bit which redirects the air flow across the bit face resulting in an efficient flushing without air escaping to the surrounding ground. This significantly reduces the vibration whilst drilling and also helps it to deliver unequalled tolerances. This was of particular importance as the location had the potential to suffer a second failure; something that was closely monitored using inclinometers throughout the project.
Van Elle were subsequently awarded the contract from Story Rail and Elemex was chosen as the best method to drill the rotary percussive piles at the site in the North East of England.
Considering both the geotechnical and design challenges presented to us by the project at Eden Brows, there was only one casing advancement system which would satisfy all the project requirements.
We had utilised the Elemex casing advancement drilling system on a number of projects previously to great success although we had never been faced with such demanding ground conditions or such stringent design criteria in which to deploy the drill system. In addition to this, the design criteria stipulated a 660mm diameter casing to be drilled permanently to a depth of 20m from working platform level with steel reinforcement cages weighing close to 3 tons in a single length of 18m.
Considering the restricted highways and remote villages en-route, we were faced with additional logistical challenges in transporting the aforementioned consumables and our own plant and equipment to the project work site. The design required the 660mm casings to be drilled in 10m sections and therefore significant modifications needed to be made to the 8m mast extension of our Klemm 709 piling rig. We further fabricated two eighteen-meter-long drill strings, shrouded up to 508mm to provide the required-up hole velocity we needed to ensure the maximum penetration rates were achieved.
The drill rods utilised the Atlas Copco 135mm hex joint system, which Van Elle use on most of our drill systems owing to the significant programme benefits to make and break drill rod sections. The entire drilling system was driven by the Atlas Copco Ql200s, of which we have a number within our fleet. These hammers perform without falter on every project and their reliability was essential at Eden Brows with works being carried out on a twenty-four-hour shift pattern to meet the short programme duration.”
The first stage of the project was to clear the slip and install a piling platform. Van Elle were then asked to install three 610mm diameter preliminary test piles to 20m depth to prove the installation method worked and to carry out integrity tests on the piles.
In order to drill the test piles a 30 tonne rig with a 16.5m mast had to be lowered onto the platform so that 28No. 610mmØ ramp piles could be installed. These piles took less than 10 working days to install.
The final pile design consisted of two rows of high-strength piles totalling 198 in number. The front in compression and were installed to 20m depth whilst the rear row were in tension and were installed to 18m depth. In addition the final pile design required a 660Ø steel casing to be installed to achieve the correct pile design characteristics. Van Elle and Atlas Copco discussed the redesign of the P660E system to enable it to install a 660Ø x 16mm wall casing. Further to this, a new face design was introduced to further improve the air flow across the bit face, enhancing flushing and efficiency.
The quality of the construction of the piles was essential due to the nature of the project and the various loadings that were to be applied to the piles. The required tolerance was 1 in 800. This meant that there was only an allowed 25mm vertical tolerance for the 20m piles and 22.5mm vertical tolerance for the 18m piles. Using conventional piling systems was not considered as a viable option as the accuracy of the ICE spec only goes as high as 1 in 200.
Each rig was setup with an Atlas Copco QL200S DTH Hammer, 20” class in-line shock absorber and crossover adapter, encased in a hammer shroud along with 2 x 10m shrouded hex drill pipe. The main advantage of using hex shrouded drill pipe is to finely tune the annulus of the borehole to achieve the optimum up-hole-air velocity, reducing the volume of compressed air required. Secondary the hex drill pipe allows for easy make up and break out of the tool joints with no large oscillating rod holder/breaker jaws required.
Atlas Copco Environmentally Safe Oil was supplied to the hammer using an Atlas Copco LD60C unit. This combined unit allows the multiple compressors to be linked together to an air receiver, whilst simultaneously injecting the required amount of oil directly into the drill string allowing consistent oil feed to the hammer.
Using their Hutte 207MP and bespoke Klemm 709 drilling rigs the main piling works commenced, working day and night in order to achieve the completion date. In total, there were 6 piling teams operating, 4 during the day and 2 at night as well as a team of 8 welders working on the casings.
Van Elle’s piling works were completed by 20th January on time and within budget enabling Story Contracting to complete the project to get the line replaced and were ready for the planned re-opening in March.
The project was completed within programme and on budget!!
Yet another successful project carried out by the Van Elle and Atlas Copco alliance.