高地应力千枚岩隧道二次衬砌施作时机研究

二次衬砌施作时机一直是高地应力软岩隧道工程设计与施工过程中面临的关键技术难题之一。为此,依托在建成都-兰州铁路典型千枚岩隧道工程,基于隧道变形长期监测结果,分析高地应力软岩隧道变形时程特点,考虑软岩隧道荷载特点,确定了二次衬砌施作时机原则;考虑隧道测量丢失变形,提出软岩隧道第1稳定阶段变形量确定方法;通过现场实测变形数据统计回归,基于一定保证率确定不同大变形等级和不同断面下的软岩隧道二次衬砌施作时机,并进行现场试验验证。研究结果表明:适当刚度的初期支护可以实现高地应力软岩隧道前期变形稳定,但无法保持围岩长期稳定,二次衬砌应该在初期支护变形达到第1稳定阶段后施作,既可以减少二次衬砌荷载,又可以控制围岩变形;采用指数函数拟合软岩隧道变形具有较好的相关性,但参数差异性较大,同时在确定隧道第1稳定阶段变形量时应考虑测量丢失变形;轻微、中等大变形段拱顶下沉变形速率小于0.1~0.2mm·d^-1,边墙收敛速率小于0.5mm·d^-1,严重、极严重大变形段拱顶下沉变形速率小于0.4mm·d^-1,边墙收敛小于0.6mm·d^-1,即可进行二次衬砌施作;轻微大变形段、中等大变形段和严重大变形段分别在隧道开挖45~55 d,55~60 d和80~90 d后达到二次衬砌施作标准。

Study on the Construction Time of Secondary Lining in Phyllite Tunnel Under High Geo-stress

The construction time of secondary lining is one of the key technical problems in the design and construction of soft rock tunnels under high geo-stress. Therefore, based on the typical phyllite tunnels of Chengdu Lanzhou Railway under construction, this study analyzed the deformation time history characteristics of soft rock tunnels under high geo-stress with long-term monitoring results of tunnel deformation. Furthermore, the construction timing principle of the secondary lining considering the load characteristics of the soft rock tunnel was determined. Considering the loss of deformation in the tunnel measurement, a method to determine the deformation in the first stable stage of a soft rock tunnel was proposed. The construction time of the secondary lining in the soft rock tunnel with different large deformation grades and different sections was determined based on the statistical regression of the measured deformation data and on a certain assurance rate, and a field test was performed to verify the results. The main conclusions are as follows:the initial support with proper rigidity can achieve the early deformation stability of soft rock tunnels under high geo-stress, but it cannot maintain the long-term stability of the surrounding rock. The secondary lining should be constructed after the initial support deformation reaches the first stable stage, which can reduce the secondary lining load and also control the deformation of the surrounding rock; an exponential function to adjust the deformation of a soft rock tunnel provides a good correlation, but the parameters are considerably different. In addition, the loss of deformation should be considered when determining the deformation of the first stable stage of the tunnel; the settlement deformation rate of the arch crown in the slight and medium-large deformation sections is lower than 0.1-0.2 mm·d^-1, the convergence rate of the side wall is lower than 0.5 mm·d^-1, the settlement deformation rate of the arch crown in the severe and extremely severe deformation sections is lower than 0.4 mm·d^-1, and the convergence rate of the side wall is lower than 0.6 mm·d^-1. Thus, the secondary lining construction can be performed; according to the statistics of the field measurement data, after 45-55, 55-60, and 80-90 days of tunnel excavation, the standards of secondary lining construction can be achieved for the slight, medium, and severe large deformation sections, respectively.