Abstract: Underground excavation adjacent to existing tunnels/stations may induce unloading of stress and/or shear diastrophism in the excavation-disturbed zone. However, the impact of such hybrid stress state on the shear failure and deformation characteristic of tunnel concrete is not clear. The direct shear test on tunnel concrete specimens under hybrid stress state was designed to investigate the impact of this kind of hybrid stress state on the shear behaviors. The implement of this kind of hybrid stress state consisted of three main steps: ① loading the normal stress to the initial normal stress (INS); ② loading the shear stress to the initial shear stress (ISS); ③ unloading the normal stress and simultaneously re-loading the shear stress until the failure occurred. Different combinations of INS and ISS were considered during the test. The results show that this hybrid stress state significantly affects the shear failure and deformation characteristic of tunnel concrete specimens. For example, with the increase of INS, the shear displacement in step-③ (Vu) decreases and the normal displacement in step-③ (Uu) increases. As ISS increases, however, Vu decreases and Uu just has a little undulation. A larger unload amount (mu) doesnt always give rise to a larger displacement in step-③. In addition, the hybrid stress state results in an elevation of failure shear stress (τf) and a reduction of unload amount (mu) under current test conditions.

Key words: tunnel engineering, tunnel concrete, shear behaviour, load path, hybrid stress state

摘要： 邻近现有隧道或车站的地下工程开挖可能会引起挖掘扰动区域的应力卸载和剪切变形。然而，此类混合应力状态对隧道混凝土剪切破坏和变形特征的影响尚不明确。为了研究此类混合应力状态对剪切性能的影响，设计了隧道混凝土试件在混合应力状态下的直剪试验。此类混合应力状态的实现包括3个主要步骤：①加载法向应力到初始法向应力(INS)；②加载剪向应力到初始剪向应力(ISS)；③卸载法向应力并同时再次加载剪向应力直至发生破坏。试验中考虑了INS和ISS的不同组合。结果表明:该混合应力状态对隧道混凝土试件的剪切破坏和变形特征具有显著影响;随着INS的升高，步骤③中的剪向位移(Vu)减小，法向位移(Uu)增大，而随着ISS的升高，Vu下降，Uu仅略微波动；在步骤③中，较大的卸载量(mu)并不总会产生较大的位移；在当前测试条件下，混合应力状态导致破坏剪向应力的增大和卸载量(mu)的减少。

关键词: 隧道工程, 隧道混凝土, 剪切性能, 加载路径, 混合应力状态