新建大头岘黄土隧道出口浅埋段地表为耕地，间歇性浇水和地表降水导致围岩土体抗剪强度降低，加之施工工序的不紧凑等原因引起初期支护下沉变形并侵入二次衬砌。本文应用有限元软件MIDAS/GTS对初期支护侵限段结构安全性进行了分析。依据分析结果，建议根据初期支护下沉侵限程度分别采取措施：对初期支护侵限≤5 cm且变形基本稳定段不做处理；对初期支护侵限≤10 cm且变形基本稳定段通过增强配筋进行处理；对初期支护侵限＞10 cm 的段落宜进行换拱处理。这样可减小大面积换拱带来的安全风险，并节约投资。%T he shallow buried section at the exit of the newly-built Datouxian loess tunnel is covered by cultivated land,therefore rainfall and interim irrigation weaken the shear strength of the soil mass. At the same time,the inconsistent construction procedure and other factors at play contribute to the settlement and deformation of the primary support,which further invades into the secondary lining. In this light,the paper introduces the finite-element software M IDAS/GT S in the reliability analysis of the infringed section. T he results point out that differentiated measures need to be applied in accordance with the settlement and clearance invasion occurred. For 5 cm or less clearance invasion,whose deformation has reached a stable stage,no treatment measure is needed;for 10 cm or less clearance invasion,whose deformation has too reached a stable stage,better reinforcement is suggested;and for more than 10 cm clearance invasion,arch replacement shall be performed. T he differentiated approach reduces the risks in large-scale arch replacement and helps cut investment.
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