Due to the uncertainty and complexity of geological conditions,the stress state of supporting struc-ture has changed when the tunnel was excavated.Therefore,it is of great significance to understand the stress distribution of the supporting structure for the safety construction of the tunnel proj ect.Tunnel underneath the Yu-Xiang highway,numerical simulation and practical monitoring have been applied to study the stress distri-bution law of the steel arch of initial tunnel support in different rock and different arch spacing.Researches have shown that:(1)The maximum arch spacing in poor Class V rock was advised to take 0.8 m while the value can rise to 1.0 m in good Class V rock.(2)In terms of the stress distribution,tensile stress mostly appeared in the lateral and medial sides of the steel arch and the maximum tension stress of the steel arch appears on the foot of the arch while the maximum compressive stress on the crown.(3)The worse quality of the surrounding rock will cause rapid increase in stress and stress gradient of the steel arch and significant increase in force inhomo-geneity of the arch steel.(4)The stress of the steel arch increased rapidly with the increase of arch spacing in poor Class V rock.Strict control of the arch spacing is very important.%隧道开挖时,由于地质条件的不确定性和复杂性,导致支护结构受力状态发生变化,因此掌握支护结构应力分布规律对于隧道工程安全施工具有十分重大的意义.以下穿渝湘高速公路的凤咀江铁路隧道为背景,利用数值模拟和实际监测研究不同围岩和不同拱架间距下隧道初期支护钢拱架的应力分布规律,研究表明:(1)Ⅴ级偏差围岩最大拱架间距取0.8 m,Ⅴ级偏好围岩最大拱架间距可增大至1.0 m;(2)从应力分布角度看,钢拱架内外侧应力大部分为拉应力,且钢拱架最大拉应力出现在拱脚处,最大压应力在拱顶处;(3)当围岩质量状况变差时,钢拱架应力和应力梯度会迅速增大,钢拱架受力不均匀性也会显著增加;(4)在Ⅴ级偏差围岩条件下,当增大拱架间距时,钢拱架应力会迅速增加,因此要严格控制好拱架间距.
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