Sjotroll
Geotechnical
- Jan 2, 2018
- 30
Hello everybody,
I have an interesting problem so I'm interested in your takes. It regards constructing a tunnel in rock at shallow depths. As we know, very often the stress ratio, K, in rock is >>1 at shallow depths (in my case 3.6, but same behaviour as described is observed even for K<2). When constructing a shallow tunnel, we are interested in surface settlements if they occur under sensitive areas. When we try to make a numerical model of this problem, we get surface swelling just above the tunnel excavation, and small settlements as we move farther away from the excavation. It looks like an inverse settlement diagram that we would expect. This is not a numerical issue because looking at the stressess generated for high K values, the high lateral pressures will cause upwards movements of the rock mass above the tunnel. However, this is a very real situation. So what would be a solution to this problem? How would you determine the surface settlements when constructing a tunnel in such a rock and at shallow depths? All examples found on the internet that show numerical modeling of shallow tunnels are made with K<1, and all examples that use K>1 are made for deep tunnels where the top boundary is also fixed. I have tried many "workarounds", but none are satisfactory.
I have an interesting problem so I'm interested in your takes. It regards constructing a tunnel in rock at shallow depths. As we know, very often the stress ratio, K, in rock is >>1 at shallow depths (in my case 3.6, but same behaviour as described is observed even for K<2). When constructing a shallow tunnel, we are interested in surface settlements if they occur under sensitive areas. When we try to make a numerical model of this problem, we get surface swelling just above the tunnel excavation, and small settlements as we move farther away from the excavation. It looks like an inverse settlement diagram that we would expect. This is not a numerical issue because looking at the stressess generated for high K values, the high lateral pressures will cause upwards movements of the rock mass above the tunnel. However, this is a very real situation. So what would be a solution to this problem? How would you determine the surface settlements when constructing a tunnel in such a rock and at shallow depths? All examples found on the internet that show numerical modeling of shallow tunnels are made with K<1, and all examples that use K>1 are made for deep tunnels where the top boundary is also fixed. I have tried many "workarounds", but none are satisfactory.