特大跨度隧道双侧壁导坑法施工步距优化分析

Optimization Analysis of Construction Step Length of Double Wall Heading Method for Large Span Section

大型机械在特大跨度隧道施工中易产生导坑施工步距加大等问题。以厦门机场高速公路巷东隧道工程为例,采用数值分析结合现场实测的方法,针对双侧壁导坑法施工中存在的导坑尺寸偏小、无法满足机械化施工操作空间、工效低等问题,通过扩大各导坑上下台阶的步距,增加掌子面与二衬的间距,提高了洞内机械化作业水平。数值分析表明,优化方案中初支轴力只有个别点的压应力增加较多,大部分的轴力及剪力变化幅度在4%以内,初支弯矩极值降低6%;围岩位移及初支结构内力极值变化都不大,处于合理范围内。地表沉降监测表明,最大沉降值为9.1 mm,最大变化速率为0.5 mm/d,均未超过允许范围,且沉降总体上趋于稳定。

Large mechanical equipment used in the construction of large span tunnel has a problem of increasing construction step.Taking the Xiangdong tunnel project of Xiamen airport expressway as an example,the method of numerical analysis combined with field measurement was adopted,aiming at problems including small heading size,limited mechanized construction operation space and low work efficiency.By expanding the step length of each heading pits and increasing the distance between support surface and second lining,the level of mechanism inside hole was enhanced.The results show that,the initial supported axial force of the optimization scheme only increases at a few points,most of the axial force and shear force change within 4%,and the extreme value of the initial supported bending moment decreases by 6%.The displacement of the surrounding rock and the extreme value of the internal force of the primary supporting structure have little change and are in a reasonable range;Surface settlement monitoring shows that the maximum settlement is about 9.1 mm and the maximum change rate is 0.5 mm/d,which does not exceed the allowable range and tends to be stable.