Experimental study of failure behavior of disturbed zone around an opening in non-persistent jointed rock masses

A small excavating system was used to experimentally investigate crack initiation, propagation and coalescence mechanisms and failure behavior around an opening in nonpersistent jointed rock masses with biaxial loading. The specimens were made of modelling material with holes drilled to various stress levels to simulate underground excavation. The opening process was then monitored by a digital video camera. When the applied axial loading reached about 75% of the peak axial loading, the ratio, λ, of the lateral loading to the axial loading remained constant. The experimental results showed that the final failure behavior and modes around the opening were dominated by sliding along the joints, by coalescence between the joints and the opening, and by the strain in the disturbed zone around the opening. The deformation of the inner disturbed zone was greater than that of the outer compressed zone during the postexcavation process. Release of the stresses during postexcavation increases the interaction between microfractures and causes preexisting joints to slip when λ is constant. The specimen failure stress decreased with increasing values of λ.