Chapter 8: Discontinuities

EFFECT OF EXCAVATION SEQUENCE AND FAULT ORIENTATION ON STRESSES AND DEFORMATION AROUND A CAVERN

H.C.CHUA and E.C.LEONG

Nanyang Technological University, Singapore

(e-mail of corresponding author: cecleong@ntu.edu.sg )

The presence of discontinuity in the form of joints and faults may have a significant influence on the deformation and stability of an underground opening, In addition, the stability of an underground opening may also be governed by the excavation sequence adopted for the construction. An investigation into these factors is therefore crucial to ensure that excessive stresses and deformation do not develop around the cavern, both during and after cavern construction.

A series of numerical parametric studies has been performed to investigate the effect of excavation sequence and fault orientation on the stresses and deformation induced around an underground cavern. The two-dimensional Universal Distinct Element Code (UDEC) was adopted in the investigation. The jointed rock mass was modelled as an equivalent rock material and the fault was modelled as a joint. The joint normal stiffness and shear stiffness in the numerical model was calibrated using data from published literature, and the general validity of the proposed numerical model has been affirmed.

The numerical results for various excavation sequences demonstrate that excavation sequence S3 is most favourable considering cavern roof and wall displacements only, whereas excavation sequence S6 produced the least number of plastic points around the cavern. A shear zone was formed near the right cavern wall at an angle of 43 to the horizontal, equal to the friction angle...