深埋中风化泥岩大跨公路隧道系统锚杆支护效果试验研究

Experimental Study of Support Effect of System Bolts of a Deeply-Buried Large-Span Tunnel in Moderately-Weathered Mudstone

为探明中风化泥岩隧道中系统锚杆的支护效用及其适用性,依托深埋大跨公路隧道建设项目,进行有、无系统锚杆的现场对比试验,分析不同工况下围岩变形、围岩压力、喷射混凝土应力、锚杆轴力以及初期支护-二次衬砌间接触压力的变化规律,并进一步从隧道施工安全性和经济性等方面对此类地层中系统锚杆的支护效果进行分析。研究结果表明:1)在中风化泥岩地层中,是否施作系统锚杆对围岩变形和衬砌结构受力特性影响不大,系统锚杆未能显著改善隧道衬砌结构的受力性能;2)由于施作系统锚杆后,延长了围岩的封闭时间,使得有系统锚杆的监测断面围岩变形反而大于无系统锚杆的监测断面;3)现场监测的锚杆最大轴力仅为3.40 kN,在该地层条件下未能发挥其承载优势;4)各类指标的监测结果表明此类地层中系统锚杆的支护效用十分有限,取消系统锚杆可降低对围岩的二次扰动,有利于缩短围岩封闭时间,从而有效控制围岩变形;5)在保证隧道安全的情况下,取消系统锚杆的经济效益同样十分显著。

To explore the support effect and applicability of system bolt in moderately-weathered mudstone tunnel,field comparative tests with and without system anchor are conducted by taking a deep-buried large-span tunnel project as an example.The variation patterns of surrounding rock deformation,surrounding rock pressure,shotcrete stress,axial force of anchor bolt,and contact pressure between primary support and secondary lining are analyzed under different working conditions.Further,the support effect of the system bolt is examined from the aspects of construction safety and economy.The results show the following:(1)The system bolt slightly affects the deformation of surrounding rock and the mechanical properties of lining structure in moderately-weathered mudstone formation.(2)The application of the system bolt prolongs the closing time of the surrounding rock,thus the deformation of the monitoring section of the surrounding rock with system bolt is greater than that without system bolt.(3)The maximum axial force of the bolt monitored on site is only 3.40 kN,which fails to give full play to its bearing capacity under such formation.(4)The monitoring results of various indexes show that the support effect of system bolt is limited,and the removal of system bolt can reduce the secondary disturbance to surrounding rock,shorten the closing time of surrounding rock,and effectively control the deformation of surrounding rock.(5)In the case of ensuring the safety of the tunnel,the economic benefits of removing the system anchor are also significant.