A Viscous Elasto-plastic Analysis on Rheological Effects of Fault Weakness on Underground Openings

This paper presents a viscous elasto-plastic numerical analysis on stability of rock mass surrounding an under-ground opening which is specially cut by two sets of adjacent faults. To simulate the rheological behaviour of the faults, the shear creep characteristics of soft clay fillings inside the fault is analyzed, and, then, an innovative rheological model is proposed to reflect the influence of thickness of the fault. The relevant coefficients involved in the mechanical model can be measured by a special designed apparatus which is discribed in the paper.The results show that by considering the rheological behaviour of faults neighbouring an opening, the loading state of surrounding rock mass is deteriorated considerably. The creep effects of faults on an oponing are dependent mainly on the ratio of fault distance (D) away from the opening and the geometry scales (d) of the opening, i.e. the yalue of D/d. Usually, e. g., when D/d≤1 , the situation has to be considered seriously. Besides, the influence is also related to the physical properties of rock mass as well as the fillings of faults, and the relative position and direction between faults and opening. Local implemental reinforcements by adopting bolts and shotcrete lining support are suggested in region of surrounding rock mass where tensile stresses appeared.