Abstract En-echelon joints widely exist in rock slopes and underground rock masses, which seriously threaten the stability of rock engineerings. Majority of earlier studies have focused on conventional continuous joint, while the shear behavior of en-echelon joints has rarely been studied, especially under constant normal stiffness conditions. Therefore, in this study, the direct shear tests of en-echelon joints were conducted under constant normal stiffness conditions. The effect of joint angle and normal stiffness on shear strength characteristics and acoustic emission behavior was analysed. The test results showed that the shearing process of en-echelon joints includes two stages, i.e., Stage I and Stage II. Three different shearing mechanisms can be observed. Stage I involves the generation of wing cracks and Brazilian-like splitting of blocks, while Stage II is dominated by slipping and dilation of through-going shear zones. Accordingly, three shear strength indexes were distinguished, i.e., SR1a, SR1b and SR2. These three strength indexes vary greatly with the joint angle and normal stiffness, and can be predicted using numerical or theoretical method. In addition, the acoustic emission response of en-echelon joints during the shear can be divided into three stages according to the evolution of cumulative hit, i.e., initial growth phase, accelerated growth phase and decelerated growth phase. The increasing normal stiffness tends to cause a more intense energy release in Stage I and a larger number of cumulative hit in Stage II. Furthermore, an analysis of b-value showed that the shear failure intensity of en-echelon joints is greater when the joint angle is positive, especially close to 60°.

中文翻译：

---

常法向刚度条件下梯队节点的剪切行为和声发射特性

摘要 岩体边坡和地下岩体中广泛存在梯级节理，严重威胁岩石工程的稳定性。大多数早期研究都集中在传统的连续接头上，而很少研究梯形接头的剪切行为，特别是在恒定的法向刚度条件下。因此，在本研究中，在恒定的法向刚度条件下进行了梯级接头的直接剪切试验。分析了接头角度和法向刚度对剪切强度特性和声发射行为的影响。试验结果表明，梯级接头的剪切过程包括两个阶段，即阶段I和阶段II。可以观察到三种不同的剪切机制。第一阶段涉及翼裂缝的产生和巴西式的块体分裂，而第二阶段则以贯穿剪切带的滑动和扩张为主。因此，区分了三个剪切强度指标，即SR1a、SR1b和SR2。这三个强度指标随关节角度和法向刚度变化很大，可以用数值或理论方法预测。此外，根据累积冲击的演变，梯级接头在剪切过程中的声发射响应可分为三个阶段，即初始生长期、加速生长期和减速生长期。增加的法向刚度往往会导致阶段 I 中更强烈的能量释放和阶段 II 中更多的累积命中。此外，对b值的分析表明，当接头角度为正时，梯形接头的剪切破坏强度更大，