GEOLOGICAL CONDITIONS OF DUCTILE SHEAR ZONE EXPOSED BY MOUNTAIN TUNNEL

The paper solves rock mass classification problem for design and construction of a railroad tunnel through the brittle ductile shear zone(faults) and its secondary ductile shear belt in mountainous area. It discusses the characteristics of ductile shear zones including the aspects of geometry, structure, movement track, tectonic, deformation and metamorphic mylonite, and mechanical action. It summarizes the construction surrounding rock classification from the aspects of macroscopical, microcosmic, field research and testing, analog, and compares engineering properties of rock mass and engineering design of the classification of surrounding rock between ductile shear zone(brittle ductile and brittle) and joint concentrated zone. Based on these results, the paper concludes that the mountain tunnel by ductile shear zone should be studied separately, especially on rock mass classification indexes and surrounding rock classification principle. Special attention should be paid on its design and construction.