A Study on Isotropic Rock Breaking with TBM Cutters Under Different Confining Stresses

Theoretical investigation on the rock breaking and chipping characteristics subjected to TBM cutters under varying confining stresses is conducted. Theoretical study presents that the deflection angle of the lateral crack will increase as the increase of confining stress. Combining previous conclusions on initiation angle with above conclusion on deflection angle, theoretical study shows that in the low confining stress conditions, the chip composed of a triangle shaped part in deep part and a rectangle shaped part in shallow part will be formed; secondly, the triangle shaped part tends to diminish as the confining stress increases. Thirdly, as the confining stress increases in further, the chips are nearly rectangle shaped, and the height of chips will be decreased. Laboratory and numerical studies are also conducted for verification. In both laboratory and numerical tests, the shape evolution mentioned above is verified. And then, due to the varying shapes of chips under different confining stresses, when the spacing is fixed, experimental and numerical tests show that cutting efficiency will be increased as the confining stress increases in a certain degree, while the efficiency will be restrained by the increasing confining stress as the confining stress exceeds a critical value.