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Flight crew

Ground investigation work is helping a new rail link take off at Glasgow Airport in Scotland.

Airport operators and road and rail networks face growing pressure to keep transport moving against the background of an increasingly mobile world. One example of this can be seen with Strathclyde Partnership for Transport (SPT) and its new direct rail link between Glasgow Central Station and Glasgow International Airport.

In 2003, 8.2M people used the airport, with 95% travelling to it by road. The airport's operator BAA forecasts that patronage at the airport could grow to 24M by 2030. The M8 motorway is already suffering from congestion and an alternative fast direct route between Glasgow city centre and the airport is needed if the city and wider region is to remain competitive.

The new Glasgow Airport Rail Link (GARL) should provide this link and help reduce congestion on the M8. Ground investigation contractor Soil Mechanics has been working on a £1.3M contract from SPT to carry out detailed investigations along the planned 2km stretch of new track. This will run from near Paisley St James Station to Glasgow Airport and will be called the St James Spur.

Its contract is the latest in a number that Soil Mechanics has worked on to help shape Scotland's transport network.

Soil Mechanics project manager Julian Lovell says: "Geotechnical properties of the sub-grade of existing networks and plans to upgrade operational or abandoned networks, or indeed build new track, exert huge control over the performance of railways. Their efficient running relies heavily on quality geotechnical information.Large-scale, complex geotechnical investigations of this nature have to provide detailed information of the ground conditions for economic planning of design."

At GARL, ground conditions across varied terrain need to be assessed for a wide range of design requirements that include building new rail track, new viaducts, reinforced embankments and bridge crossings for existing highways.

The contract has meant using a range of techniques to evaluate engineering properties for foundation, earthwork and pavement design. As a result, the contractor has been investigating the integrity of the track bed for a 9km upgrade of existing track between Shields Junction (near Kinning Park in Glasgow) and Paisley Gilmour Street Station (currently the nearest station to the airport), and laying 1.9km of new track between Paisley St James Station and the new Glasgow Airport Station.

The new track will cross St James Park via a new viaduct and the M8 motorway. A new platform will also be built at Glasgow Central Station and new track laid at Elderslie sidings.

The varied ground conditions at GARL required a number of exploratory techniques. Site workers primarily used rotary open hole methods to identify strata, succession of layers and any underground voids and deep rotary boreholes to locate unrecorded mine workings.

The project also needed in situ cone penetration tests to measure cone resistance, local friction and porewater pressure of variable materials ranging from soft to stiff clays/silts to loose and dense sands.

The results will eventually include an assessment of undrained shear strength and relative density to identify areas of poor settlement. They will also validate the stress-strain loads with respect to new foundations, track-modelling and the assessment of risk.

These techniques are particularly useful for fast, non-invasive, non-destructive testing of the sub-base and sub-grade of existing railway track and pavement, or to calculate load transfer along the length of, for example, railway embankments.

The crew also used pressuremeters to test shear strengths, contamination and ground water levels, and assess the site's suitability for re-use.

Ground investigation work began last November and was expected to be complete by May.

The new rail link will provide a dedicated train service every 15 minutes between Glasgow Central Station and the new station at Glasgow airport. It will give airport users more travel options and establish a sustainable transport link to the airport. The link will also benefit the tourist industry, helping to bring in an estimated 52,500 additional UK and overseas visitors every year, and an extra £10M to Glasgow, Renfrewshire and Inverclyde.

GARL is funded by Transport Scotland with financial support from SPT, airport operator BAA and the European Union through the Trans-European Transport network budget.

Transport links such as GARL play an important role in providing crucial links between towns, cities, regions and countries. Geotechnical investigations and the data they provide must continue to contribute in the planning of such initiatives.

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