CVEN9522 Describe the expected geology and geotechnical conditions along the tunnel route? This should include cross-sections and long-sections drawn to scale.

Overview

The tunnels need to be big enough to accommodate the kinematic traffic envelope which comprises a 1.5 m breakdown lane, two 3.5 m wide traffic lanes and a 1.5 m walkway. Barriers separating traffic from the walkway are included in these dimensions. The height of the kinematic traffic envelope is a minimum of 5.3 m. An additional 2 m height above the kinematic traffic envelope is required for fans, lights, signs etc. The tunnel is to be driven from the south towards the north

You will need to work through the following steps to offer a robust tunnel support scheme. 

  1. Draw a stereonet of the expected geological structures and discuss implications for design. [Remember variability in orientation is natural and should be considered]
  2. Describe the expected geology and geotechnical conditions along the tunnel route? This should include cross-sections and long-sections drawn to scale.
  3. What are the stresses around the tunnel? What cross sectional shape would best suit this environment? Give your reasons.
  4. What is your tunnelling method of choice? TBM or roadheader excavation? Give reasons.
  5. What ground behaviour types do you expect? What is the controlling mechanism for tunnel stability in this environment? Your answer should include your reasoning [Bullet form is acceptable].
  6. Calculate the ground reaction curve for the tunnel.
  7. What rock block sizes / shapes do you expect can be formed during tunnelling? What are the typical size and the maximum size?
  8. Classify the rock mass according to the RMR and Q systems. Show each of the parameters that combine to give the RMR and Q values giving reasons for your selections.
  9. Using your typical and maximum block sizes, what is your rock bolt design? Length, spacing, capacity, type? Give reasons with calculations showing the bolts have enough capacity. How does this compare to bolt design from Q? What bolt design will you adopt?)
  10. Using Barrett and McCreath, how thick does the shotcrete need to be? How does this compare to shotcrete thickness suggested by Q? What design thickness will you adopt? [For your answer you can use either steel reinforced or mesh reinforced shotcrete, but you must show workings.]
  11. In about half a page sketch and/or discuss the excavation sequence you would recommend. How does your sequence mitigate the possibility of poorer than expected ground conditions?