Factor Analysis Of The Uneven Transverse Surface Settlement Caused By EPB Shield Construction

In the urban subway construction, the settlement of ground surface, especially the uneven settlement flowed from stratum movement and ground deformation due to shield tunneling is one of the causes of instability and failure of superstructure. Taking the EPBS(Earth Pressure Balance Shield) for example, this dissertation analyses the influencing factors of differential settlement during shield construction process combining with the correlation theory and monitoring data in practical engineering, and then makes corresponding numerical simulation. The main research contents and results are as follows:(1)Trough analyzing the stress state variation of surrounding soils during shield construction process, summarizes the main factors affecting of ground surface settlement in construction from both stratum condition and shield excavation parameters. According to shield posture when eccentric over-dredging occurs, amends the theoretical expression of correlative gap parameter. Combined with the actual grouting result in engineering practice, establishes the plane equivalent plane model reflecting the filling and infiltration of grouting.(2)In the influencing factors of soil condition analysis, the result shows soil gravity has the greatest influence over the ground surface settlement, and the Poisson’s ratio of soil has the greatest influence over the differential settlement. When soil gravity increases from 16 k N/m3 to 26 k N/m3,the surface settlement reduce by 1.638mm(y=0m) and 3.375mm(y=-11.5m); When the Poisson’s ratio of soil gravity increases from 0.3 to 0.1, s+-s- reduce by 0.213mm(y=±14.5m), |(s+-s-) /s0| reduce by 2.11%(y=±13m).(3)In the influencing factors of construction technology, the result shows the rate of synchronous grouting has the greatest influence over the ground surface settlement and the differential settlement When the rate of synchronous grouting increases from 1 to 2.65, the surface settlement reduce by 12.171mm(y=0m) and 1.373mm(y=-11.5m); When the rate of synchronous grouting increases from 1 to 2.9, s+-s- reduce by 0.451mm(y=±14.5m), |(s+-s-) /s0| reduce by 0.73%(y=±14.5m).(4)In several worst operating conditions, concentrated distribution of grouting liquid in the lower parts of tunnel would induce the larger ground displacement, which is 27.35mm; Concentrated distribution of grouting liquid in the upper parts of tunnel would induce the less ground settlement, which is-7.551mm; Concentrated distribution of grouting liquid in one side of tunnel would induce the larger differential settlement, which is 4.524mm(y=±14.7m); When the continuous grouting pressure mainly distribute in the one side of the upper parts of tunnel(p=500k Pa), |(s+-s-) /s0| reaches 121%(y=±10m).(5)Based on a shield tunnel construction in Xi’an, establishes a three dimensional numerical model. By adjusting the value and distribution of the gap connected with the practical situation could get the result agreeing well with measured value.