中墙顶部回填混凝土弹性模量对连拱隧道稳定性的影响

根据某高速公路连拱隧道衬砌结构形式,建立有限元计算模型,通过改变回填混凝土单元的弹性模量模拟回填混凝土的不同密实程度,采用数值模拟方法研究回填混凝土弹性模量变化对连拱隧道稳定性的影响.研究结果表明:围岩的变形和应力以及衬砌内力均随着中墙顶部回填混凝土弹性模量的增大而大幅度降低；当回填混凝土弹性模量比由0(完全脱离)增加到100％(完全密实)时,拱顶沉降和围岩拉应力分别降至75％和20％左右,内衬弯矩可降至17％左右；当弹性模量比达到60％以上时,内衬弯矩基本保持不变；中墙应力随着回填混凝土弹性模量的增大而增大,且弹性模量比越低,中墙应力变化幅度越显著,回填混凝土完全脱离时中墙两侧最大压应力仅为完全密实时的33％左右,中墙承受的荷载主要来自上方围岩通过回填混凝土传递到中墙的压力.在实际施工中,应使中墙回填混凝土的弹性模量比至少达到设计标号混凝土标准值的60％以上方可进行隧道正洞开挖.

Influence of elastic modulus of back-fill concrete above mid-wall on stability of multi-arch tunnel

A FEM analysis based on a model of an expressway multi-arch tunnel was carried out to study the influence of different elastic modulus of back- fill concrete. The results show that the deformation and tension stress of surrounding rock decrease greatly with the increase of elastic modulus. When the elastic modulus ratio of the back-fill concrete increases from 0 (completely separated) to 100% (completely dense), the settlement and the tensile stress of the surrounding rock at the arch crown decrease to about 75% and 20% respectively, and the bending moment of the inner lining decreases to about 17%. However, the values do not change much after the elastic modulus ratio is larger than about 60%. On the other hand, the compression stress of the mid-wall increases with the increase of elastic modulus. The compression stress of the mid-wall in the case that the back-fill concrete is completely separated from the surrounding rock is only 33% of the case that the back-fill concrete is completely dense, which means that the compression load of mid-wall is mainly from the surrounding rock. During the construction, the excavation of the main hole should start after the elastic modulus of the backfill-concrete reaches 60% of the characteristic value of the concrete.