Term
| What is a tunnel and what kind is there? |
|
Definition
Tunnels are underground structures which are recognised as a means of attaining convenient transportation through conditions posing natural difficulty or special hazards.
-traffic
-conveyance
-mining |
|
|
Term
| 5 factors for Tunnel Design and Underground Engineering |
|
Definition
-intact rock
-divided by discontinuities
-in situ stress
-pore fluid/water flow
-time |
|
|
Term
|
Definition
The most useful description of the mechanical behavior of intact rock is the complete stress-strain curve in compression. From this curve, several features of interest are derived:
-deformation moduli
-peak strength criteria
-the post peak behavior |
|
|
Term
|
Definition
| Discontinuities such as faults and joints may lead to structurally-controlled instabilities whereby blocks form through the intersection of several discontinuities, which are kinematically free to fall or slide from the excavation periphery as a result of gravity. |
|
|
Term
|
Definition
| When considering the loading conditions imposed on the rock mass, it must be recognized that an in situ pre-existing state of stress already exists in the rock |
|
|
Term
|
Definition
| A primary concern is water is under pressure, which in turn acts to reduce the effective stress and/or induce instabilities. Other aspects, such as groundwater chemistry and the alteration of rock and fracture surfaces by fluid movement may also be of concern. |
|
|
Term
| Tunnel excavation methods |
|
Definition
-drill and blast
-tunnel boring machine |
|
|
Term
| Tunnel/GeoEng Hazards - Squeezing ground |
|
Definition
| refers to weak, plastic rock material which displaces into the tunnel excavation under the action of gravity and induced stresses. This squeezing action may result in damage/failure to the ground support system, or require the costly re-excavation of the tunnel section. |
|
|
Term
| Tunnel/GeoEng Hazards – Bursting |
|
Definition
Rockbursts involve sudden releases of stored strain energy through the brittle failure of strong rock. They manifest themselves through the sudden ejection of rock into the excavation. Rockbursting
otential is of special concern in cases of deep tunnelling where high stress concentrations form due to overburden loads or tectonic activity. |
|
|
Term
| Tunnel/GeoEng Hazards – Running Ground |
|
Definition
| Where ground possesses the ability to flow freely (i.e. “running ground”), as for example with loose sand or other cohesionless materials, then special support and control difficulties can arise. Major inflows may not only flood tunnel works, but may also develop into a chimney collapse feature which may propagate to the surface. |
|
|
Term
| Tunnel/GeoEng Hazards – Fault Zones |
|
Definition
-rock may fall
-form highly permeable conduits for groundwater
-weakened zones -> failure and collapse |
|
|
