19-Mar-2018

Chess Association - Notes

 

David McCann, Senior project manager, Sector C1

• Project now half way through 16month design phase, leading to a priced design by November
• Expect about 3.5 years Tunnel boring at around 100m/week
• Surveys & more Ground Investigation in progress

Mike Hutchinson - Groundwater manager, Phase 1

• Boreholes in place with monitoring (of G/water levels)
• Limited deviation permitted upwards & side to side
• Choice of TBMs to be made - technology exists
• Affinity water concerned by any turbidity - affects (UV) purification
• Runoff from compounds must be controlled
• Groundwater Flow models being developed

Gareth Jones - Geotechnical Lead, Align JV

• 110 deep and 15 shallow boreholes drilled, 200m ctrs
• LIDAR survey to detect Sinkholes
• Borehole map reveals interesting geology (data is public )
• Faulting is present (in chalk), as expected
  
• Water flows mainly through upper & middle chalk
  
• (Question) Artesian wells are found in the area. Any evidence of water under pressure ? No.
  
• TBM records geology as it progresses
  
• 43 more GI locations to be investigated over next 12months
  
• Pumping tests to be undertaken (pump water out - see what happens)
• Historic data consulted
• (Q) Any chance of benefit to Misbourne (eg finding additional water sources) ?

Didier Jaques - Tunnelling Lead, Align JV

• Plan to use Variable Density TBM- can switch between Mix Shield (Slurry) & Earth Pressure Balance operation
• Cutting fluid - Water only with chalk finings, to vary mud texture
  
• Expect to encounter Voids (full of clay ?) Automatic shut off if pressure (at cutting face) changes
• Closed water loop within TBM recirculates water for cutting
• Spoil will create Chalk grassland around S. Portal - an improvement ? Topsoil reused. This will keep spoil off the roads
• Initial lining with quick setting cement (5 sec ?) to limit penetration into rock

Mathew Wales - Permitting & Phase 1 Lead
Environment Agency controls

• Environment Agency Consent is required for final scheme
• (Qs) What is an acceptable level of risk ?
• Why no Indemnity for other stakeholders ?
  
• Affinity indemnity to provide alternative sources, in worst case
• When will design be approved ? 1 year lead in. Need more time to establish conditions, monitoring ...
• Local compliance officers will be in place & could stop the work (in theory)
• What EA expertise is available? Hydrogeologists, Engineers ...
• What monitoring of TBM Ops ? Ea would see data.
• H&S are also involved in monitoring
• Daily monitoring schedule to involve EA; Online data with continuous analysis is required for safety reasons
• Approval process - iterative approach; conditionscan be imposed. Refusal possible but unlikely
• Company can appeal -Inst of arbitration would appoint arbitrater.
• Treatment of water discharges also requires approval
• Post construction monitoring now open ended, maybe 10 years ?