| With the rapid development of transportation construction in China, opportunities and challenges of tunnel and underground engineering has been brought about. But only a few researches have been done with the thin-layered fracture hard rock which mainly exists in the sedimentary rocks and karst area in Yunnan, Guizhou and Sichuan province. This thesis compared the field measurement data with the results of DEM numerical simulation, and drew conclusions as follows:(1) The engineering characteristics of the thin-layered fracture hard rocks are determined by the weak structural plane sets which including one coherent stratification set and two intercross joint sets. The thin-layered fracture rock tends to slip through the smooth stratifications. A higher flexural strength than other rock and soil was made in the thin-layered hard rock conditions. The layered rock will be peeled from inside to outside when the tunnel is being excavated, the convergence displacement caused by the tension joints is larger than that caused by shear joints, while the displacement region caused by shear joints is wider. The joints tension displacement and the joints shear displacement is perpendicular to each other in the shape of a cross, which slopes coincidentally with the stratification apparent dip.(2) The pressure arch effect in the thin-layered fracture hard rock will emerge when the tunnel deeper than the critical depth being excavated. The boundary of the pressure arch can be determined through the pressure arch contribution coefficient, which is calculated by the ratio of the circumferential stress increments in one section and the summation of the stress increment in this path, be put forward. The cohesion and friction of the joints seems to have no influence on the range of the pressure arch when the mechanical property of weak structural plane is much worse than the rock blocks. The stratification dip angle has little influence on the pressure arch when it was shallow than 40°, but when the stratification dip angle is steep, the range of pressure arch will expand drastically. The depth of tunnel had little influence on the range of the pressure arch. The range of the pressure arch linearly increases with the span of the tunnel. Formula of the range of the pressure arch is fitted through the conclusion above.(3) Modified Protodyakonov’s mountain rock pressure theory was presented, which is more adaptable to the thin-layered hard rock condition. The conditions of the rock pillar theory applied were specified. The pressure arch structure theory used to calculate the surrounding rock pressure was proposed. The suitable scope of the surrounding rock pressure method in the current code for railway tunnel design, the modified Protodyakonov’s mountain rock pressure theory and the pressure arch structure theory are limited by the comparison of the computing results.(4) The surrounding rock stress state in Guiyang Longdongbao Airport, which adjacent parallel tunnels was excavated, was analyzed through the comparison between the field measurement data and the results of DEM numerical simulation. The tunnel to be excavated later will destroy the pressure arch effect of the existing tunnel, and a combine arch will be formed in the surrounding rock. So the tunnel being excavated later had a decisive influence upon the ground surface settlement. Measures should be taken in case of sliding failure when the width of middle rock pillar was less than 8.5 meters.(5) The DEM numerical software can well simulate tunnel excavation, which can be confirmed by comparing the field data with the results calculated by DEM numerical software. |
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