Rock Reinforcement Design Flashcards
What are the different sources of instability in excavations
structurally controlled (from geological structures)
stress controlled (from differences in instability)
where is stress concentrated in a circle profile excavation
on the side walls there is 3x the stress while the floor has -1 and is in tensile stress
How is the failure in massive rock
generally doesnt fail a lot
what is the support for swelling and squeezing
it is hard to provide support but if not supported can lead to a squeezing failure
What are the techniques for control of the rock behaviour to create stability
*rock reinforcement used to provide stability to the overall rock mass
*rock support used to provide support to the excavation surfaces
What are rock bolts
generally plain steel rods with mechanical anchor at one end and a face plate and nut at the other, always tensioned after installation
What are dowels
dowels differ to rock bolts as they are not tensioned and rely on the movement of the rock to generate the reinforcement action
when are dowels preferred to rockbolts
when blasting close to the face is heavy dowels are the support system that is preferred
What are limitation to mechanical anchored bolts
*capacity of strength can be limited
*mechanical anchors tend to slip progressively due to blast vibrations
*expansion shells are ineffective in soft rock
What do friction anchors rely on
it is a hollow tube that relies on the friction between the tube and the rock and is useful in fissure, buckling or sheared ground that it is sometimes difficult to drill a hole.
What are limitations to friction anchors
tolerance to hole size is small, they have a very low bond strength per meter, and they are unable to reinforce blocky ground
What are features of swellex bolts
they are a circular tube that is folded and then water is injected into the bolt at high pressures where it adapts to the shape of the hole.
they rely on mechanical and frictional interlocking
What are the features of swellex bolts
immediate reinforcement
relatively expensive
but are susceptible to corrosion
it also takes more install time than resin
What are features of grouted rebar
they rely on grouted material between the bolt and wall
they have high transfer loads and have some degree of corrosion protection
what are features of cable bolting
provide effective reinforcement for very large spans and have a very high bearing capacity (25t/strand)
