The deterioration of shear mechanical properties of surrounding rock caused by dynamic cyclic load introduced by traffic load and earthquake has an important influence on the long-term safe operation of tunnel engineering.The mechanical characteristics of tunnel surrounding rock under the influence of complex disturbance load were scientifically condensed,and the direct shear test of sandstone under dynamic cyclic shear load was carried out to explore the strength degradation characteristics of sandstone with different shear static prestress levels.The results show that:(1)In the process of dynamic cyclic shear load with amplitude of 20%τj,the sand-stone with low shear static prestress level will not be destroyed.(2)The damage caused by dynamic cyclic shear load is proportional to the static prestress level.After dynamic cyclic shear load,the strength of sandstone with shear static prestress levels of 60%τj and 70%τj is reduced by 1.68%and 6.91%respectively compared with the static shear control group.In tunnel design and long-term stable operation monitoring,the deterioration of surrounding rock shear strength caused by disturbance stress wave introduced by traffic load and earthquake should be fully considered.(3)The dilatancy effect of unstable sandstone is significant in the process of dynamic cyclic shear.In tunnel and other rock engineering,special attention should be paid to the influence of surrounding rock dilatancy caused by dynamic shear stress on tunnel lining.
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