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The deformation induced by excavation of tunnels is usually many times or even tens of times larger than that of hard rock. The low strength and rigidity are mechanical reasons. In addition, it must be emphasized that such rocks are often rich in clay minerals or rich in clay minerals. Mezzanine. Some clay minerals such as montmorillonite and illite are very unstable. When they lose water and then re-receive water, the volume expands, creating additional expansion pressure on the surrounding rock, and at the same time, it disintegrates rapidly. Support may encounter great difficulties and deserve special attention.
If the roadway is surrounded by soft rock, its deformation and failure usually show full-section convergence and collapse. When the bottom plate is composed of soft rock, the foot may occur. If the soft rock is exposed in the two gangs, it is common for the two gangs to be squeezed. When the two hills are steeply poured, they can also produce severe wall deformation.
Most of the deformations in soft rock are irreversible, so they need to be simulated with inelastic models. A lot of research has been done on the most typical problems shown.
Most of the weak rock masses are composed of low-strength argillaceous rocks. It is also possible that the rock mass composed of hard rock with deep weathering, broken structure but still maintaining integrity and low overall strength and rigidity is included in such rock mass.