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Back-Analysis of Initial Stress at Shallow Depth – A Case Study
BeFo (Swedish Rock Engineering Research Foundation)
At shallow depth, the initial stress state can significantly affect the behavior of the rock mass around excavations, but stress measurements are usually subjected to high levels of uncertainty. This was the case at the Odenplan railway station in Stockholm where unexpectedly large deformations were measured during the excavation.
Itasca conducted a sensitivity analysis of the initial stress state in this area. As the rock mass is highly discontinuous, discrete modeling using 3DEC was performed with three different initial stress cases, estimated from measurements.
The results showed that joint slip and rock mass dilatancy explain the large displacements and heaving of the ground and that a continuum approach is not reliable for these conditions. A comparison between the displacements from numerical modeling and those measured in situ provided indication on the range of initial stress to be used in the future for this area.