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Logical conclusion


Completion of Scotland's M74 motorway involves a major site investigation along the 7.9km route, much of it through derelict industrial land.

Maps of Scotland show the M74 motorway from the south-east ending abruptly on the outskirts of Glasgow while the M8 from Edinburgh runs into the city and connects with major north-east and south-west routes.

Completion of the M74 will join it to the M8, reducing congestion on that busy motorway and stopping motorists rat-running through Glasgow's suburbs.

The route extends the M74 from Fullarton Road to the M8 at the Kingston Road Bridge. The 7.9km project will incorporate eight road and rail bridges, three viaducts up to 0.8km long and a crossing over the River Clyde.

Costing £250M, the project was given the green light last year by the Scottish Executive. Subject to a possible public inquiry, it is due to open in 2008.

The £3M site investigation contract has been awarded to contractor Norwest Holst Soil Engineering.

Work is being carried out under the direction of Glasgow City Council, which is acting as agent and project manager for the Scottish Executive.

Consultants to the council include Bullen Consultants, the Mason Evans Partnership and Babtie Group.

The proposed route crosses an area with a diverse industrial history. It has a number of highly contaminated sites as well as abandoned mine workings, infilled clay pits and lagoons.

Bullen is supervising the site investigation as part of its responsibilities, which include overall contract management and all geotechnical aspects of the investigation.

Contamination and environmental aspects are Babtie's responsibility, while Mason Evans Partnership is supervising the mining investigation.

The scale of the investigation is indicated by the fact that so far Norwest Holst has used no fewer than 16 drilling rigs, backed up by a 75 strong team, 15 of whom are engineering staff.

Four teams have been formed, each comprising a dedicated unit engineer, four cable percussive rigs, one rotary rig, a two-man labouring crew, jet wash and decontamination unit.

A networked computer system has been installed on site. linking the various consultants and the contracting staff to allow prompt data distribution.

Derelict land is a major element of the contract. These areas are heavily contaminated and have been designated red sites under British Drilling Association guidelines.

Each area is assessed before drilling starts and individual sampling, monitoring and PPE requirements issued.

Asbestos and chromium are known to be in the made ground and the extent of the contamination must be determined at investigation stage. A specialist chemist is on site to advise on this and any precautions required during work.

Desk studies revealed more than 40 different industrial land uses, each type requiring individual and bespoke risk assessment for environmental monitoring and sampling. Detailed method statement procedures have been issued.

Daily monitoring of airborne particulate contamination is carried out by the site chemist.

Random daily monitoring is undertaken with an SKC Sidekick personal air sampling pump unit and boundary monitoring is done with a larger APEC Environmental unit.

The personal monitor is worn during normal drilling work.

Boundary monitoring is undertaken with the sniffer positioned downwind of the borehole or drilling activities, positioned between 20m and 50m away and 1m to 2m above ground level.

Any airborne particulates or contamination are drawn through the equipment and filters, which are removed, sealed and dispatched to APEC Environmental for asbestos analysis or to Norwest Holst's Environmental Analysis laboratory for chromium analysis.

Norwest Holst's unit engineer screens every sample recovered for volatile organic contamination using either a photo ionisation detector (PID) or flame ionisation detector (FID). Samples are screened for a further 3m below the made ground to check for any leaching of the contaminants.

All groundwater samples are monitored on site for pH, temperature, redox potential, dissolved oxygen and conductivity with 2.5 litre samples taken at every water strike, 0.5l of which is immediately fixed with sulphuric acid to enable later testing for chemical oxygen demand, total organic carbon and ammoniacal nitrogen.

Soil contamination testing is undertaken by Norwest Holst's specialist laboratory ECoS Environmental of Bradford, while groundwater contamination testing is performed by Norwest Holst's Environmental Analysis Laboratory.

A total of 360 boreholes will be sunk to a maximum depth of 50m using cable percussive techniques with casing and tool sizes between 300mm and 150mm diameter. Because of the level of contamination, the boundary between made ground and natural deposits must be sealed with a 1m bentonite plug and casing size reduced to avoid downward migration.

The majority of boreholes will be completed by rotary coring techniques using 412 core barrels and semi rigid core liner and producing 76mm diameter cores. The rigs on site comprise tractor mounted and track mounted Dando 250 and Edeco T30 rigs producing an average of 200m of core a week.

Airdrie-based Terra Tek, a subsidiary of Raeburn Drilling and Geotechnical, is undertaking standard geotechnical testing with effective stress, shear box and rock testing being undertaken at Norwest Holst's Leeds Laboratory. Raeburn has also provided engineering staff and drilling capacity on the contract.

About 10t of soil samples are sent to the various laboratories for testing each week and it is estimated that by the end of the contract some 3000m of core will have been drilled, logged, photographed, sub sampled, tested and put into long term storage.

The next phase is a detailed investigation of former mine workings using trial trenching and open hole percussive drilling.

Probing, trial pitting, window sampling, road coring and soil gas surveys also form part of the investigation.

Site investigation contractor Fugro will be joining the site team in the near future to commence geophysical surveying and CPT works.

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