为探明对接距离对海底大直径盾构开挖面失稳机制及规律的影响，依托甬舟铁路金塘海底盾构隧道工程，建立考虑渗流的盾构隧道对接有限元模型，研究对接距离L对开挖面失稳机制以及极限支护压力的影响，并基于极限平衡法建立考虑渗流的盾构近距离对接开挖面极限支护压力理论模型。随着对接距离的增大，开挖面失稳形状和极限支护压力的变化可分为3个阶段。1)快速增长阶段(0<L/D≤0.4) (D为隧道直径)： 该阶段与单个隧道工况区别最明显，失稳区域由楔形体与仓筒组成； 此时受对接隧道的阻碍作用最大，且开挖面附近水头场变化剧烈，渗流力占据主要部分。2)缓慢增长阶段(0.4<L/D≤0.7)： 失稳区域由对数螺旋体与仓筒组成，此时对接隧道的阻碍作用减小，因此极限支护压力在该阶段受对接距离的影响减小，增长缓慢。3)趋于平缓阶段(0.7<L/D≤1.5)： 失稳区域由对数螺旋体与倒棱台组成，此阶段对接隧道的阻碍作用可忽略不计，极限支护压力、失稳区域形状与非对接情况相近，可视为单个隧道工况。建立的理论模型得出的结果与数值模拟的结果接近，两者误差在10%以内，验证了该模型的可行性。
Herein, a case study is conducted on the Jintang
subsea shield tunnel project of the NingboZhoushan railway to
investigate the effect of docking distance on the instability mechanism and
pattern of the excavation face for a largediameter
subsea shield. A finite element model of shield tunnel docking considering
seepage is developed. Then, the effect of the docking distance (〖WT5BX〗L〖WT〗〖WT5《TNR》〗) on the
instability mechanism of the excavation face and ultimate support pressure is
examined. A theoretical model for determining the ultimate support pressure for
shield closedistance docking is established using the
limit equilibrium method and considering seepage. As the docking distance
increases, the shape variation of the excavation face and variation of the
ultimate support pressure can be divided into three stages. (1) The rapid
growth stage (0<〖WT5BX〗L/D≤0.4)(D〖WT〗〖WT5《TNR》〗 represents the tunnel diameter) : the
difference between the condition of this stage and a single tunnel working
condition is the most obvious, and the instability zone comprises wedge bodies
and silos. At this stage, the docking tunnel causes maximum inhibition,
resulting in significant changes in the waterhead field near the excavation
face, with the seepage force playing a dominant role. (2) The slow growth stage
(0.4<〖WT5BX〗L/D〖WT〗〖WT5《TNR》〗≤0.7): the instability zone comprises logarithmic spirochetes and
silos. At this stage, the reduction in the inhibition caused by the docking
tunnel leads to a decrease in the influence of the ultimate support pressure on
the docking distance and the growth of the ultimate support pressure occurs at
a low rate. (3) The gentle growth stage (0.7<〖WT5BX〗L/D〖WT〗〖WT5《TNR》〗≤1.5): the instability zone comprises
logarithmic spirochetes and chamfers. At this stage, the inhibition caused by
the docking tunnel can be ignored and the ultimate support pressure and
instabilityzone shape are comparable to those without
docking conditions, which can be considered as a single tunnel working
condition. The results obtained from the established theoretical model are
close to those obtained by numerical simulations, with an error within 10%,
thereby confirming model feasibility.
