Study on the sources of passing through error in subway and distribution of its limits in different phases

Based on a lof of survery practice and the demand of tunneling technology with shield driving method at TA7 Mark in Nanjing subway engineering,five error sourses to influence on the tunnel passing throngh survey auuracy are analysed,including the horizontal error caused by ground control survey,the survey error at the shaft connected with sheild exit,the central coordinate errors of sheild entrance and exit,the error of the underground traversing,and the sheild fixed position error.Acoording to the error distribution principle in construction survey,distribution of tunel passing through survey error limits and the precision rate of tunnel passing through survey in different phases are discussed and its reasonableness is approved by practice.