Disturbance of Shield Tunnel Construction to Sandy Stratum and Load Bearing Characteristics of Segment Lining

On the background of earth pressure balanced shield tunneling passing through sandy stratum for Xi'an Metro,the particle flow code( PFC) method was used to study the disturbance of shield tunnel construction on sandy stratum. A field test was also carried out to obtain the load distribution and internal force characteristics of shield tunnel segment lining. The results show that compared with loess stratum,the sandy stratum has more prominent features of particle. Ground displacement caused by tunnel excavation had poor continuity in spatial distribution,and partial looseness or uncompleted compacted zone occurred. There is a good permeability of sandy stratum,and pore water pressure tested in sandy stratum had good correlation with height of water head. Earth pressure tested was lower than its actual value. Influenced by shield construction loads,bending moment and axial force of segment ring had great fluctuation during the process of decyclization in the tail. With the driving of shield machine,construction loads had more slight influence on tunnel structure. When there were 10 ~ 15 rings out of shield tail,the internal force of segment ring was becoming stable. The results can offer references for the design and construction of EPB shield tunnel in sandy stratum.