重叠隧道盾构施工对先建隧道影响模型试验研究

针对软土地区重叠盾构隧道施工中，由于不同开挖顺序及不同推进速度下既有隧道位移和内力变化规律，设计了4组模型试验，试验结果表明，先上后下施工时，下线隧道的施工引起上线隧道纵向的沉降，且上线隧道管片环向内力发生偏转，拱底两侧内力变化最大；先下后上施工时，上线隧道的施工引起下线隧道纵向隆起，且下线隧道管片环向内力发生偏转，拱顶两侧内力变化最大；不管何种施工顺序，都会引起隧道纵向附加内力，但纵向内力表现为波动性和临时性。从纵向位移及既有隧道的内力改变来看，先下后上施工顺序的安全性优于先上后下的施工顺序。在重叠盾构隧道施工过程中，既有隧道的附加变位和内力值均随着推进速度的增大而增大，并且推进速度的影响范围也相应增大，所以在施工期间，应合理控制盾构机的推进速度，以免对近接既有隧道的结构安全造成较大的影响。

MODEL TEST FOR EFFECTS OF CONSTRUCTION OF SHIELD TUNNELLING IN OVERLAPPING TUNNELS ON EXISTING TUNNEL

According to the construction of overlapping shield tunnel in soft soil area，four model tests have been carried out to simulate displacement and force variation rules of the existing tunnel due to the different construction orders and the different tunneling speeds. Experimental results indicate that：(1) In case of the upper tunnel first and the lower tunnel last，the lower tunnel construction leads to the longitudinal settlement of the upper tunnel. The circumferential internal force of tunnel segment of the upper tunnel generates deflection. The internal force in the arch bottom changes the most. (2) In case of the lower tunnel first and the upper tunnel last，the upper tunnel construction leads to the longitudinal uplift of the lower tunnel. The circumferential internal force of tunnel segment of the lower tunnel generates deflection. The internal force in the arch vault changes the most. (3) Regardless of the kind of construction orders，additional internal force along the longitudinal dimension will always be observed，with features of fluctuation and temporality. Comparing the influence of displacement and internal force on the existing tunnel induced by constructing overlapping tunnels，the lower tunnel first is better for the construction safety than the upper tunnel first. In the process of construction of overlapping shield tunnel，the additional deformation and force of the existing tunnel increase with the increase of tunnelling speed；and the impact range of tunnelling speed also increases. In this case，the tunnelling speed of the shield machine should be controlled in a proper range to avoid significant influence on the safety of adjacent existing tunnel structure.