Abstract
The dynamic shear failure of rocks with confinements is important in rock engineering and it is thus desirable to quantify the dynamic Mode II fracture toughness of rocks under confining conditions. This paper presents a punch-through shear (PTS) method to measure such material parameter of rocks under different confining pressures. A split Hopkinson pressure bar system with a Hoek cell is used to exert the dynamic PTS tests. The dynamic PTS specimen is a 50 mm diameter and 30 mm long cylinder with two 10 mm-deep circular notches at both ends. The finite element method is used to obtain equations calculating Mode II fracture toughness. The validity and applicability of the proposed method are demonstrated via the dynamic PTS tests of an isotropic and fine-grained Fangshan marble (FM) under five confining pressures. The PTS specimens are punched into a short rod and a hollow cylinder. The dynamic Mode II fracture pattern of the recovered FM are analyzed using the X-ray micro-CT technique. The results show that the rock specimen failure is shear dominant and the Mode II fracture toughness of FM increases with the loading rate under a certain confining pressure and increases with the lateral confinement at a given loading rate.
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