Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
12 Cards in this Set
- Front
- Back
|
Learning Goals |
1) List and describe the 5 key factors that control the ground conditions encountered in underground engineering 2) Compare rock mass deformation and strength characteristics under different stress regimes 3) Determine ground support measures based on rock quality 4) Compare failures and hazards associated with different ground conditions in tunnel construction |
|
|
Tunnels |
Underground structures recognized as a means of attaining convenient transportation through conditions posing natural difficulty or special hazards
Traffic, conveyance, mining tunnels |
|
|
Significant tunneling projects |
"The Big Dig" (Boston)
Canada Line
St Gotthard rail tunnel (Switzerland): cut travel times from Milan to Zurich from 27 hrs to 5.5 hrs! |
|
|
Geological factors |
Intact rock divided by discontinuities to form the rock mass structure. Rock is subject to in situ stress. Superimposed on this are influence of pore fluid/water flow and time. |
|
|
Discontinuities |
Discontinuities such as faults & joints may lead to instabilities whereby blocks form through the intersections of several discontinuities, which are free to fall or slide when excavation takes place |
|
|
Rock Quality Designation (RQD) |
Overall quality of the rock mass cut by the different fracture systems |
|
|
In Situ Stress |
Pre-exiting state of stress exists in the rock mass. With excavation, these pre-existing loads are redistributed.
Total stress = in situ stress + excavation-induced stress |
|
|
Pore pressures |
Water under pressure acts to reduce effective stress and induces instabilities |
|
|
Tunnel Excavation Methods |
Drill & blast, tunnel boring machine |
|
|
Rockbursts |
Involve sudden releases of stored strain energy through the brittle failure of strong rock. Manifested by sudden ejection of rock into the excavation. |
|
|
Squeezing |
Weak, plastic rock material displaces into the tunnel excavation because of gravity and induced stresses. May result in damage/failure to ground support system & may require re-excavation of affected section |
|
|
Running ground |
Ground flows freely; can occur with loose sand or other cohesionless materials. Affect not only tunnel works but also develop into chimney collapse feature which may propagate to the surface |
