Site investigation for the M74 motorway extension

Challenge

Glasgow is the location of the much publicised construction of a £500 million 8.5km section of motorway linking the existing M74 to the M8. The new route passes through many former industrial areas of contaminated land.

To complete their understanding of potential contamination problems, Interlink M74 JV required a major ground investigation to be undertaken.

ERS was delighted to win the contract to undertake ground investigation work for a 4.5km section of the route.  Working closely with the client and the consulting engineers, ERS agreed a detailed programme and schedule to achieve the demanding timescale for the completion of works.

It was already known that large areas were affected by a variety of contaminants, most notably the toxic and leachable hexavalent chromium (CrVI). It was therefore important that drilling activities did not impact on the environment from the uncontrolled discharge of drilling waste.

It was also vital that high quality samples were recovered to identify accurate strata depths for installations and for additional information on contamination. The precision logging of each borehole and each collected sample was required to satisfy the environmental programme.

Our project team recognised that an alternative approach to gathering information from this site could solve many of the problems associated with traditional techniques.

Solution

ERS proposed the use of a rotary-sonic drilling system to minimise disturbance and improve efficiency.  We mobilised two rigs and equipment for simultaneous programmed operation along the proposed route. ERS established a mobile decontamination unit and welfare facilities on site to meet the stringent health and safety standards required.

The use of rotary-sonic drilling allowed rapid recovery of high quality, continuous samples from the ground surface through rock head to bedrock without the requirement for changes of drilling method.

This approach also ensured minimal contact with any contaminated soil arisings and contaminated flush was controlled and collected in bulk containers using a novel tank and pump containment system feeding to an on-site treatment unit.

In addition to satifying the environmental programme, ERS undertook in situ geotechnical testing over the proposed route, including cone penetration testing (CPT), measurement of porewater pressure and dissipation testing, together with shear vane tests.

Outcomes

• The flexibility of our rotary-sonic drilling system allowed continuous shallow-deep investigation to simultaneously obtain environmental and geotechnical information.
• 100 boreholes were successfully completed with minimum distrurbance to site.
• These were supervised by ERS engineering geologists and results logged in accordance with BS5930 and BS10175.
• Close working between ERS and Interlink M74 JV resulted in an efficient, high quality ground investigation, completed on time and within budget.
• ERS have since been awarded additional site investigation and remediation work with the consortium.