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Tunnelling the Chilterns
April 14 @ 7:30 pm - 9:30 pmFree
Progress so far; understanding the risks; and how technology, planning and logistics help address the challenges of tunnelling through a highly fractured chalk aquifer.
given by David Eve, Align (Head of Engagement & Compliance for HS2)
Who are Align and how does the company fit within the HS2 structure? This leads on to an overview of HS2. The HS2 route is split into various sectors, so I need to give an overview of Sector C1. What progress have we made to date and what were the results of the Ground Investigation?
What are the risks?
Volume loss; frac in and out;
Loss of slurry to surface;
Loss of ground stability within excavation chamber;
Loss of air to surface (if intervention conducted under hyperbaric conditions);
Loss of grout to surface; and over-excavation within excavation chamber.
Leading to: Ground deformation; and excessive movement of structures.
How do we mitigate for these risks?
Overview of the ‘system’ – TBM to Slurry Treatment Plant;
Pre-treatment where required (shafts);
Technology of the TBM (selection) – speed, variable slurry density control, anulus Grouting to maintain <1% volume loss, continuous monitoring (MobyDic, borehole data, ground instrumentation) and adaption;
Logistics and processing of slurry;
Exclusion zones and planning of appropriate maintenance stops;
Securing of land in higher risk areas.