The effect of weak interlayer on the failure pattern of rock mass around tunnel – Scaled model tests and numerical analysis

Weak interlayer is one of unfavorable geological discontinuities often encountered in underground engineering. Many failures of underground openings were reported to be closely related to the existence of weak interlayer nearby. For the purpose of exploring the effect of weak interlayer on failure pattern of rock mass around tunnel, both physical model tests and numerical analysis were carried out to simulate tunnel excavation near an interlayer. In the model tests, by comparison of the failure patterns between homogenous ground and ground with a weak interlayer, it was found that the weak interlayer affected the stability of tunnel by increasing the failure zones and causing asymmetrical stress distribution. The results of model tests were then verified by numerical analysis. Furthermore, based on the numerical analysis results, the location, dip and thickness of the interlayer as well as the distance from the interlayer to the tunnel were proved to be important factors influencing tunnel stability, and the relationships of the induced damage zones with these parameters of the weak interlayer were established. These results can provide a useful guidance for support design and safe excavation of tunnel near or crossing through a weak interlayer.

► The coalescence of model test and numerical simulation is useful and valid.
► Numerical damage zone can represent the rock failure area in model test.
► Interlayer affects failure pattern by inducing asymmetrical stress distribution.
► The parameters of interlayer are important factors influencing the failure pattern.