隧道复合式衬砌结构破坏的模型试验与分形特征研究

Model Test and Research of Fractal Characteristics on Structure Damage of Composite Lining of Tunnel

采用C20混凝土制作两端固支的双层复合混凝土板作为隧道复合衬砌结构模型,通过模型试验模拟高围岩应力地区铁路隧道复合衬砌结构在外力作用下的破坏过程,分析应变和位移随时间变化的规律。由于测量数据在时间上的分布具有分形特征,所以采用分形几何方法,分析应变和位移的分形维数及其与应力水平的关系。结果表明:应变和位移随着加载时间的增加而增大,自加载开始至加载全程时间的约50%时,应变和位移较小且基本呈线性增加;当加载超过全程时间的约80%时,各测点的应变和位移快速增大;应变和位移的分形维数随着应力水平的增加呈现降维—升维特征,当应力水平达到极限应力的约80%时,出现分形维数由降维向升维转变的临界点,因此,在隧道施工安全监测过程中,可以将该点作为隧道复合衬砌结构破坏的临界点进行安全预报。

Using C20 concrete,the double-layer composite concrete slab with fixed ends was made as the structure model of tunnel composite lining.Based on model test,the failure process of railway high stress tunnel lining structure under external force was simulated,and the variation laws of the strain and displacement with time were obtained.Because the distribution of measured data had fractal characteristics in time domain,the fractal dimensions of strain and displacement as well as their relationships with stress levels of tunnel lining were analyzed by fractal geometry method.The results show that the strain and displacement increases with the increase of loading time,from the start to about 50％ of the whole loading time,the strain and displacement is smaller and increases linearly.When the loading time is more than about 80％ of the whole time,the strain and displacement of each measuring point increases quickly.With the increase of stress level,the fractal dimensions of the strain and displacement appear from falling to rising characteristics.When the stress level is about 80％ of the ultimate stress,the critical point of fractal dimension change is appeared.So,as the critical point of structure failure,the critical point of fractal dimension change can be used for safety forecast during tunnel construction.