Airdrie To Bathgate Railway &
Linked Improvements Scotland

Difficult Drilling Conditions - Coring Strong Dolerite

In March 2007 the Scottish Parliament passed unanimously the Airdrie to Bathgate Railway & Linked Improvements Bill, giving the green light for this £300M project which opens up and reinstates the railway line that had been closed since 1956.

The object of the project, funded by Transport Scotland and delivered by Network Rail, was to improve public transport connections between local communities and businesses in central Scotland with the major centres of Edinburgh and Glasgow. This would in turn reduce traffic congestion and associated pollution on the adjacent M8 motorway.

The work involved the demolition and rebuilding of numerous bridges and retaining walls together with the construction of new stations where none had existed previously. The majority of the structures required piled foundations. In recent times the route had been adopted as National Cycleway No 75. The project also had to provide for the reinstatement of this major cycleway. Several of the structures were designed with adjacent cycleway bridges which were also piled.

The project demanded the full complement of our geotechnical expertise to deal with the difficult geology encountered along the length of the project.

Along the 15 mile route ground conditions varied enormously and led to the following piling techniques being deployed...

1. Rotary Bored and Cased Piling
2. Continuous Flight Auger Piling
3. Rotary Bored using Down The Hole Hammer (DTHH)
4. Driven Steel Piling

Along the eastern sections of the route the strata encountered was primarily Coal Measures geology of the Carboniferous Period. This consisted of sequences of strong sandstones, mudstones, siltstones and coal. They were overlain by superficial deposits of sandy clays, sands and gravels, boulder clays and soft peat which at certain locations required permanent casings to be installed. Boulders of extremely strong igneous rocks were often encountered at depth, requiring the use of core barrels to achieve penetration.

Along the more westerly sections of the route the presence of igneous bedrocks became more pronounced. These were mainly strong intrusive Dolerites and again required coring techniques to be used.

At several locations substantial penetrations into these hard bedrocks were required to satisfy the pile design, which had to take into account the possible risk of earlier mine workings and slope stability issues.

The piles were designed to support vertical loads from new bridge structures and also act as earth retention systems at some locations. Generally, they were specified as contiguous bored pile walls, king post piles or driven steel piles.

Ground conditions at depth usually proved to be water bearing and the piles were concreted by the tremmie technique of upward displacement. At one location the ground water level was actually artesian - resting at a level above the piling platform. Here dewatering techniques were specified to allow the large diameter piles to be concreted in stable water conditions.

Alongside the Hillend Reservoir the Dolerite bedrock outcropped and where piles were required to anchor down retaining walls they had to be installed using Down The Hole Hammer (DTHH) techniques

Maintained load tests on special preliminary trial piles at each structure were carried out to confirm the pile design. These were followed up with similar tests on selected working piles. The test loads were applied by hydraulic ram reacting against a test frame restrained by special anchor piles. The load tests were carried out by an independent specialist. At some locations adjacent working piles had to be used as anchor piles due to the dense pile spacing.

For further photos relating to this contract, download the complete case study PDF.