秦岭终南山特长公路隧道大埋深段施工监测及分析

Construction Monitoring and Measuring in Segments of Large Embedded Depth in Qinling Zhongnanshan Super-Long Highway Tunnel

为了探讨在大埋深、软弱围岩条件下,隧道围岩变形、围岩压应力和支护结构的力学特征,采用SWJ-Ⅳ型收敛计、振弦式土压力盒等测试元件,对秦岭终南山特长公路隧道埋深大于1 200 m的Ⅲ类围岩地段,进行了净空收敛变形、围岩压应力、喷射混凝土应力、钢架应变、锚杆轴力等监控量测。结果表明,即使是在初期支护作用下,净空收敛的量值和速率在测试初期也是很大的;初期支护受力很大,特别是钢架内、外缘均处于受压状态,而且钢架大部分均超过钢材的屈服极限,钢架处于失稳状态;采用Ⅰ16型钢钢架(间距1榀.m-1)、3.5 m锚杆和20 cm喷射混凝土支护,其支护强度是不够的,应采取减小型钢钢架间距[改为3榀.(2 m)-1]等措施予以加强;施工中喷射混凝土必须及时、饱满,才能保证锚喷网钢架共同作用,否则会引起钢架变形很大,甚至导致塌方事故的发生。

To discuss the mechanical characteristics of tunnel surrounding rock distortion, surrounding rock pressure stress and supporting structure when tunnel was under the conditions of large embedded depth and weak surrounding rock, authors took some testing organs, such as SWJ-IV type convergence indicator, vibrational chord type soil pressure cell, etc. In Ⅲ class surrounding rock segments with embedded depth more than 1 200 m in Qinling Zhongnanshan super-long highway tunnel, those monitoring and measuring as net convergence distortion, surrounding rock pressure stress, sprayed concrete stress, steel frame strain and axial force of anchor bar were made. The results show that tunnel in conditions of large embedded depth and weak surrounding rock can produce large distortion, even if on the effect of primary support, the measured value and speed of convergence are still large;the stress in primary support is very large especially in profiled bar steel frame, the inner and outside edge of steel frame are in stress condition and most steel frame stresses exceed steel yield limit, the steel stress in unstable condition; the support like I16 profiled bar steel frame（space belween 1 set . m ^-1）, 3.5 m length rock bolts and 20 cm depth sprayed concrete are not enough in that segments; lhe supporting strength should be consolidated through some measures, such as reducing the space between steel frameEreduceto3 set .（2 m） ^-1] and so on; sprayed concrete should be made in time and full in construction, then it can ensure rock bolts, sprayed concrete, bar mat reinforcement and steel frame in chorus, if not, the distortion of steel frame would be large and collapse accidents may happen indeed.