Analysis of TBM tunnelling in swelling soils

Abstract

The soil containing swelling clay minerals in TBM tunneling is studied and presented using the numerical investigations. Most swelling is due to the simultaneous presence of unhydrated swelling clay minerals and free water. The water that may be taken up in the crystal lattice will increase the volume of the unhydrated crystal up to 10 times the volume. The displacements resulting from this increase in volume give rise to the observed swelling pressures. Hence, the tunnel support must be designed to resist the swelling pressure, even if it proves possible to let some swelling take plaace without creating problems. Two dimensional (2D) finite element analysis of TBM tunnelling in swelling argillaceous soil is carried out. The model describes the development of time-dependent strains and stresses due to swelling considering elastic and viscoplastic behavior. Furthermore, the anisotropic swelling behavior is considered. The analysis is applied to the TBM tunnel that was driven for line 2 of Cairo metro and El-Azhar road tunnels. The analysis results successfully interpret the behavior observed on site. The relationship between the ground swelling pressure and the rigidity of liner support is studied. The conclusions from the experimental study work are useful for the design and the construction of tunnel in swelling soils. (A) This paper was presented at Safety in the underground sppace - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. “Reprinted with permission from Elsevier”.