The Spalling Failure Around Deep Excavations in Rock Masses

The process of spalling failure around a deep excavation in a rock mass is one of the main problems in tunnel construction. It consists in a brittle failure, produced by the crushing of compressed rock, during which strain localization appears as a shear crack. Both the tensile damage and the confinement reduction, produced by the excavation of the tunnel, play a fundamental role in the production of the spalling failure [

1

]. To better understand and to prevent this failure, a plane strain model able to evaluate the structural response of the rock around the excavation is here proposed. In particular, under the hypothesis of circular tunnel (of radius

R

0

), within an undefined rock mass having an initial hydrostatic pressure σ

0

, the stress σ

θ

in the tangential direction is evaluated during the progressive reduction of the radial stress σ

r

(Fig. 1a). This reduction represents the loss of confinement produced by the excavation.