砂砾地层盾构隧道受力光弹试验

为满足城市地下管廊、城际快速地下交通网的建设需求,中国隧道工程的应用率与日俱增。砂砾地层因黏聚力较低,与其他地质条件地层相比工程特性明显。在分析类似地质情况下的盾构隧道受力时,连续性介质假设已不能满足实际需求,应从非连续介质角度分析隧道及其周围岩石介质的受力分布。通过光弹试验观测砂砾地层中隧道-围岩系统内的力链强弱及其分布形式,并应用数字图像处理方法提取力链信息。在光弹颗粒中设置圆形管道以模拟盾构隧道,并通过改变内置管道的直径大小,改变上部及侧部载荷大小,以及在管道底部进行光弹颗粒释放,来分析砂砾地层中隧道直径、埋深变化及隧道底部的地层破坏、流动对隧道-围岩系统中力链分布的影响。利用颗粒元软件PFC对试验过程进行数值模拟,对比分析模拟结果与试验结果以验证试验的可靠性。结果表明:力链是砂砾地层与隧道之间载荷传递的主要方式,围岩与隧道间的接触力分布具有非对称性;隧道的椭圆化程度及其周围砂砾岩层中的力链密度,均随着隧道直径和埋深的增加而增大;当砂砾地层破坏、流动时,隧道-围岩系统内的力链也被破坏并重新分布,地层内维持系统稳定的"环状"强力链退化成为"拱形"强力链,系统自稳性产生破坏,此时应采取措施强化系统的稳定性。

Photoelastic Experiment on Stress of Shield Tunnels in Gravel Strata

To satisfy the construction demand for urban underground tube corridor and intercity rapid underground transportation network, the application rate of tunnel engineering in China has been increasing daily. Because of low cohesiveness, the engineering characteristics of gravel strata compared with the rock stratum are obvious. In the analysis of tunnels under similar geological conditions, the assumption of a continuous medium cannot satisfy the actual demand. Thus, the stress distribution in the tunnel and its surrounding rock should be analyzed from the perspective of a discontinuous medium. In this paper, a photoelastic experiment was employed to study the strength and distribution of the force chain in a tunnel-surrounding rock system in the gravel strata and extract the chain information using digital image processing. A round-tunnel simulation shield was set up in the photoelastic particles. By changing the diameter of the built-in pipeline and the size of the upper and side loads, the photoelastic particles at the bottom of the pipeline were released. The tunnel diameter of the gravel layer was analyzed. The influence of the changes in the burial depth and damage flow of the surrounding rock at the bottom of the tunnel on the distribution of the force chain in the tunnel-surrounding rock system was investigated. Particle element software PFC was used to simulate the experimental process. The simulation and experimental results were analyzed and compared to verify the reliability of the methods. The results show that force chain is the main method of load transfer between the gravel strata and tunnel. The contact-force distribution between the surrounding rock and tunnel is asymmetrical. The elliptical degree of the tunnel and the force-chain density in the surrounding sand and gravel strata are enhanced with the increase in the tunnel diameter and burial depth. The gravel strata are damaged and flow. The force chain in the tunnel-surrounding rock system is destroyed and redistributed. The “ring” strong force chain that maintains the system stability in the rock strata is reduced to an “arch” strong force chain. The stability of the system is damaged.