深部直墙拱形隧洞围岩板裂破坏的模拟试验研究

Simulation tests on spalling failure in deep straight-wall-top-arch tunnels

为了解深部直墙拱形隧洞板裂破坏的发生过程和机制,采用TRW-3000真三轴试验系统对含直墙拱形孔洞的红砂岩立方体试样(100 mm×100 mm×100 mm)进行了真三轴试验,模拟了深度500 m初始地应力环境下直墙拱形隧洞板裂破坏过程,并利用岩样内部破坏视频监控系统对试验过程进行实时记录和监测。试验完成后,对试验过程中孔洞侧壁破坏过程、破坏特征进行了分析,并与同等深度的圆形孔洞洞壁破坏进行了对比。结果表明:在竖直应力为最大主应力和水平径向应力为最小主应力的条件下,直墙拱形孔洞破坏主要发生在两侧拱脚和拱腰之间,靠近自由面的围岩破裂为近似平行于最大主应力的板状薄岩片,呈典型的张拉板裂破裂特征;随最大主应力的增加,板裂破坏逐渐向孔洞水平径向发展,板裂岩片呈现中间厚、两翼薄的弧形特征,最终形成对称的V型槽破坏区,并具有明显的时间效应。与圆形孔洞的动力破坏特征相比,直墙拱形孔洞主要偏于静力破坏,且初始破坏所需应力水平高,孔洞侧壁在高应力环境中破坏更严重。

To deeply understand the failure process and mechanism of spalling in deep straight-wall-top-arch tunnels, a true triaxial test is performed on the red sandstone cube sample(100 mm×100 mm×100 mm) with a straight-wall-top-arch hole using the TRW-3000 true triaxial test system to simulate the spalling process of the straight-wall-top-arch tunnel under the initial in-situ stress environment at depth of 500 m. The test process is monitored and recorded by using a video surveillance system. The failure process and failure characteristics of the sidewalls during the tests are analyzed, and compared with the failure of the circular hole sidewall at the same depth. The results show that under the condition that the vertical stress is the maximum principal stress and the horizontal radial stress is the minimum principal stress, the failure of straight-wall-top-arch tunnel mainly occurs in the area between the hance and the spandrel. The rock near the free surface is fractured into plate-like thin rock slabs that are approximately parallel to the maximum principal stress, which is characterized by typical tensile spalling fracture. With the increase of the maximum principal stress, spalling gradually develops toward the horizontal radial direction of the hole, and eventually forms a symmetrical V-shaped damage zone. The spalling slabs exhibit the arc-shaped feature with thick middle and thin wings, and spalling has obvious time effect. Compared with those of the circular hole sidewall, the dynamic failure characteristics of the straight-wall-top-arch hole sidewall are more prone to static failure, and the initial failure requires higher stress, but the sidewalls are more severely damaged under a high stress environment.