为研究椭圆形隧洞破坏过程及演化预警问题，开展真实砂岩横置椭圆形隧洞双轴压缩试验，结合声发射、DIC实时采集系统分析横置椭圆形隧洞裂纹渐进扩展过程特征。结果表明： 1）隧洞首先在拱顶和拱底出现张拉裂纹，随后在洞口两侧出现剪切裂纹和远场裂纹，在洞口右侧壁形成V形槽，最终远场裂纹与V形槽连通导致隧洞发生脆性破坏； 2）隧洞表面应变集中区先于裂纹出现，能够预判裂纹出现的位置； 3）裂纹稳定扩展阶段，分形维数逐渐增大，剪切裂纹起裂时分形维数增速率加快，峰值荷载前分形维数出现突增； 4）隧洞破坏前会出现声发射平静期、b值突降、熵值突增、应变场方差突增、裂纹分形维数突增等预警信息，不同物理场监测数据的预警时间不同步，预警荷载为峰值荷载的87%~97%，b值突降出现最早，应变场方差突增出现最晚。
A biaxial compression test is conducted on a real
sandstone transverse elliptical tunnel; moreover, the characteristics of the
progressive crack propagation process of the transverse elliptical tunnel are
analyzed with acoustic emission and a digital image correlation realtime
acquisition system to investigate the failure process and evolution warning of
the elliptical tunnel. The results show the following: (1) Tensile cracks first
appear in the tunnel′s crown and bottom; subsequently,
shear and farfield cracks appear on both sides of the
tunnel. Furthermore, a Vshaped groove is formed on the
right sidewall of the tunnel, and the farfield cracks
extend to the Vshaped groove, leading to the brittle
failure of the tunnel. (2) The strain concentration area on the tunnel surface
appears before the crack, and the crack′s location can
be predicted. (3) The fractal dimension gradually increases from zero in the
stable crack propagation stage. When the tunnel shear crack starts, the growth
rate of the fractal dimension accelerates. The fractal dimension shows a sudden
increase before reaching the peak tunnel load. (4) At a quiet period, the
sudden drop of the 〖WTBX〗b〖WT５《TNR》〗 value, a
sudden increase in the entropy value, a sudden increase in strain field
variance, and a sudden increase in the crack fractal dimension can be used as
early warning information before tunnel failure. The early warning time of
different physical fields′ monitoring data is not
synchronized, and the early warning load is 87% to 97% of the peak load. The
sudden drop of the 〖WTBX〗b〖WT５《TNR》〗 value is
the earliest and the sudden strain field variance increase is the latest.
