超大断面隧道在双层初期支护下的拆撑安全性研究

On Safety in Dismantling Temporary Strut of Super-large Tunnels with Double-layer Primary Support

目前多线隧道及超大断面隧道的修建呈发展趋势。但在施作二次衬砌时,临时支撑的拆除将是整个结构受力转换的薄弱点,故保证拆撑过程中的结构安全具有重要意义。鉴于目前国内外关于超大断面隧道双层初期支护下的拆撑安全性分析仍缺乏系统的研究,文章结合实际工程,采用以数值分析为主,现场实测印证为辅的方式,对新考塘隧道拆撑时两层初期支护的内力演变以及各自的安全性进行了分析,初步证明了双层初期支护对于拆撑过程安全性的控制效果。研究结果表明:(1)在支护厚度和纵向一次性拆撑长度保持不变时,拆撑前后的安全系数表现为:双层初期支护下的二次初期支护>双层初期支护下的一次初期支护>单层初期支护。安全系数的变化幅度表现为:双层初期支护下的一次初期支护<单层初期支护<双层初期支护下的二次初期支护;(2)在支护形式相同时,随着一次性拆撑长度的增加,其安全系数呈现先增大后减小的趋势。根据各工况计算结果,该工程合理的一次性拆撑长度为9 m左右。

More and more multiple-track tunnels and super-large section tunnels have been built,and dismantling of temporary strut is a weak point of the whole structure during force transfer when the secondary lining is constructed.It is significant to guarantee structure safety during dismantling of temporary strut.Little systematic research on safety in dismantling of temporary strut of the super-large section tunnel with double-layer primary support has been conducted,so the internal force and security of the two-layer primary support of the Xinkaotang tunnel were analyzed by a numerical analysis and site measurement,and it proves the effect of two-layer primary support on the safety during strut dismantling.The research results indicate that:(1)with constant support thickness and one-time longitudinal dismantling length,the safety factor of secondary primary support is larger than that of the first primary support,and the safety factor of the first primary support is larger than that of the single-layer primary support.Change range of safety factor for the first primary support is smaller than that of the single-layer primary support,and the safe factor for the single-layer primary support is smaller than that of the secondary primary support; (2)with the same support pattern,the safety factors increase firstly and then decrease with an increase of the one- time dismantling length.The calculated results of various cases show that the reasonable one-time dismantling length for this project is about 9 m.