石膏质岩隧道新置换衬砌结构受力特征研究

为分析石膏质岩隧道衬砌结构置换施工后的受力特征,依托杜公岭隧道病害处治工程实例,在隧道病害处治施工阶段和运营阶段对6个不同病害现象的典型断面新置换衬砌结构的初期支护变形、初期支护钢架应力、初期支护-围岩接触压力、初期支护-二次衬砌接触压力等进行为期2.5年的现场测试。测试结果表明:在新置换初期支护单独承载的3~5个月时间内,初期支护的变形速率和变形量均较小,其中5个测试断面的拱顶沉降和周边收敛量最大,其分别为6.8,6.4mm;新置换初期支护钢架应力较小并且在二衬浇筑后较短时间就达到稳定状态,其中64处测点(总计72处)应力小于100 MPa;边墙芯样发现石膏、硬石膏成分的断面在二次衬砌浇筑后的26个月内,其边墙或拱顶测点的初期支护-围岩接触压力和初期支护-二次衬砌接触压力仍有明显变化,其中个别测点经过10~20个月才能达到峰值,另有个别测点在3~8个月到达峰值后受干湿交替环境影响会出现变化;综合分析认为,杜公岭隧道衬砌结构主要受到围岩中硬石膏的膨胀作用,石膏的吸水软化作用不明显,其围岩压力具有缓慢发展的特点,新置换二次衬砌承担了主要的围岩压力,新置换初期支护安全性较高;建议石膏质岩地层隧道二次衬砌不宜过早施作或者初期支护与二次衬砌间设置缓冲变形层,以充分发挥初期支护的承载力、减小二次衬砌承担的围岩压力。

Mechanical Characteristics of New Replacing Tunnel Lining Structure in Gypsum Rock

This study aimed to analyze the mechanical characteristics of new replacing tunnel lining structures in gypsum rock. During the defects treatment construction and tunnel operation of the Dugongling tunnel, field tests were performed for 2.5 years in six typical sections with different defects, analyzing initial support deformation, steel frame stress, contact pressure between initial support and surrounding rock, and contact pressure between initial support and secondary lining of new replacing tunnel linings. The test results show that the deformation rate and amount of new replacing initial support are small within 3-5 months, when the new replacing initial support independently bear the pressure of the surrounding rock, and the maximum vault settlement and convergence of five test sections are 6.8 mm and 6.4 mm, respectively. The steel frame stress of the new replacing initial support is small, and it tends to be stable for a short time after the secondary lining pouring. The steel frame stress of 64 out of 72 monitoring points is lower than 100 MPa. In the section where gypsum and anhydrite were found in core samples of the side wall, after 26 months of the secondary lining pouring, the contact pressure between initial support and surrounding rock and contact pressure between initial support and secondary lining of the side wall or vault monitoring points have changed. Among them, some reached the peak in 10-20 months after the secondary lining pouring and others in 3-8 months, which varies under the influence of alternate wet and dry environments. Through comprehensive analysis, it is considered that the lining structure of the Dugongling tunnel is mainly affected by the expansion of anhydrite in the surrounding rock, and the softening effect of gypsum is not evident. The surrounding rock pressure of the Dugongling tunnel is characterized by slow development. The new replacing secondary lining in the gypsum rock tunnel bears most of the surrounding rock pressure, and the new replacing initial support provides high safety. To make full use of the bearing capacity of the initial support and reduce the surrounding rock pressure bore by the secondary lining, either the secondary lining should not be constructed at early stages or a deformation layer between the initial support and secondary lining should be used.