If your talking about the North Vancouver tunnels where the work has been stopped. I noted a suggestion of rock anchors being proposed to stop spalling. Rock anchoring into what, how do you know where your fractures end.. You need to use a high adhesive grout to permeate and hold all the cracked areas together.
Actually the question was more general in terms of measurement of the intensity of spalling and depth of spalling. Are you involved in design issues or construction. How do you suggest grouting to prevent spalling or improve ground spalled. Please could you elaborate.
Depends entirely on what you are attempting to do. I am sure there are a few tunneling engineers who have come accross this problem and have appropriate solutions.
If you have extensive fractured rock one possible solution is to drill ahead of excavation 10 , 20 or 30 meters in a cone shape. Inject the proper grout and turn your fractured rock in Prepakt concrete . This would provide you with an area to cut through that would be stable as the surrounding rock/concrete would form an arch.
This technique injecting grout into stone from sized from 1" to mansize is used in Mining,To construct reactor cradels and to make radiation shielding.It provides similar strenghts to normal concrete mixes.
Grouts are available with very high adhesive qualities.
Prepakt suppied the grouts for the repairs and resurfacing of the spillways on the Hoover Dam and to anchor the mast on the CN tower,
What you would need is a grout with both good permeation qualities and high adhesion. It may be available off the shelf or may need to be designed.
As for what Intrusion prepakt actually does we do both construction and supply engineering specs mostly of a very specialist nature. ( reactor and marine constuction)
Prepakt's observations are certainly correct under specific geological conditions but I suspect the way the term spalling is being used here might lead to ambiguity and confusion. To me, spalling implies rock "flaking" off of previously excavated areas, usually due to high stresses, almost always associated with depths greater than 1000 metres deep.
Reports from the Vancouver tunnel referred to, do not meet this definition. There it would appear large volumes of rock fell into the the excavation before ground support could be installed and depth is almost certainly only a few hundered metres maximum. stress levels were almost certainly low, it would have been geological weaknesses that probably initiated this.
please let us know what type of rock you are talking about; for example, some shales and mudstones in tunnels i worked on beneath lake ontario were spalling. this was due to the rock drying out and shattering then falling. entirely different would be miningman's definition for hard rock stress related spalling.
