复合式连拱隧道曲中墙施工力学行为时空演化规律

为解决连拱隧道开挖过程中曲中墙安全承载问题，依托浙江省某在建复合式曲中墙连拱隧道，采用数值计算及现场监测手段对施工阶段曲中墙力学演化规律及偏压机制进行分析，并从设计、施工层面分别就曲中墙厚度及主洞施工步距对曲中墙应力及偏压影响规律进行研究。研究结果表明： 1）连拱隧道主洞上台阶开挖对曲中墙应力分布影响显著，此阶段应力增量约占应力终值的50%，曲中墙以承受竖向应力为主，横断面最小截面为受力最不利位置。2）连拱隧道非对称开挖造成曲中墙承受偏压荷载，导致曲中墙发生向先行洞一侧偏转，偏转现象在先行洞开挖过渡至后行洞开挖阶段尤为显著。3）曲中墙厚度对其应力分布、偏转效应影响显著，曲中墙厚度的减小降低了结构承载能力； 当曲中墙厚度为1.3 m时，曲中墙墙身应力急剧增大，曲中墙可能发生压溃失稳。4）主洞施工步距对曲中墙应力分布影响较大，但不改变曲中墙应力终值； 随着主洞施工步距增大，曲中墙偏压弯矩越大，偏转效应持续时间越长。

Spatial and Temporal Evolution Characteristics of Mechanical Behavior ofCurved Middle Wall of Composite Double Arch Tunnel

To solve the problem of safety bearing load for the curved middle wall during construction of the double arch tunnel, the mechanical evolution law and bias mechanism of the curved middle wall during the construction of a composite double arch tunnel in Zhejiang province, China, are analyzed using numerical calculation and field monitoring methods. Furthermore, the influence laws of the curved middle wall thickness and the main tunnel excavation distance on the stress and bias effect of the curved middle wall are investigated from the design and construction perspectives. The results reveal the following: (1) Excavation of the top heading of the main tunnel has a significant influence on the stress distribution of the curved middle wall. The stress increase accounts for roughly half of the total stress value. The curved middle wall bears the majority of the vertical stress, and the smallest cross section is the least favorable position. (2) Unsymmetrical excavation of the multi arch tunnel causes the bias load on the curved middle wall, leading to deflection to the side of the first tunnel. The transition from the first tunnel excavation to the later tunnel excavation has a significant deflection effect. (3) Thickness of the curved middle wall has a significant influence on its stress distribution and deflection effect. The reduction in thickness of the middle wall reduces the structure′s bearing capacity. When the thickness is 1.3 m, the stress in the curved middle wall increases dramatically, potentially resulting in collapse instability. (4) The main tunnel excavation distance has a greater influence on the stress distribution of the curved middle wall, but has no effect on the final stress of the curved middle wall. The deflection moment of the curved middle wall increases as the excavation distance of the main tunnel increases, and the deflection effect lasts longer.