Cumulative damage effect and stability analysis of the rock slope with a locked segment under cyclic blasting
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摘要: 岩石中存在许多微裂纹和微孔洞，这些微裂纹和微孔洞在动荷载作用下会萌生、扩展和聚并，导致岩石失稳和破坏。在进行爆破开挖时，预留岩体会受到循环爆破产生的动载荷影响，产生累积损伤，从而导致岩体强度降低，甚至破坏。为了模拟这一物理过程，将现有的能够较好地描述岩石动力损伤的岩石动力损伤本构模型通过二次开发嵌入到FLAC中，用于分析锁固型岩质边坡在循环爆破作用下的损伤效应及稳定性。结果表明：考虑岩质边坡累积损伤效应后，随着循环爆破次数的增加，边坡稳定性逐渐降低。对于锁固型岩质边坡，锁固段的破坏首先发生在两端，然后向中间扩散，岩体在其中呈现递进破坏模式。由于考虑了岩质边坡的累积损伤，每次爆破后边坡的安全系数都会减小。当不考虑累积损伤时，边坡的安全系数基本不变。另外，锁固段在软弱夹层中的位置影响边坡的破坏模式和稳定性。因此，在进行类似工程活动时，应考虑岩体的累积损伤效应，避免工程事故的发生。Abstract: There are many microcracks and micropores in the rock, which will initiate, propagate, and coalescence under dynamic loading, leading to rock instability and failure. When blasting excavation is carried out, the retained rock mass will be subjected to the dynamic loading generated by cyclic blasting, resulting in cumulative damage, which will lead to the reduction of the rock mass strength, and even failure. In order to simulate this physical process, the existing rock dynamic damage constitutive model, which could perfectly describe the rock dynamic damage induced by blasting, was embedded into FLAC through secondary development to analyze the cumulative damage of rock mass under cyclic blasting. And then it was adopted to simulate the damage effect and stability of the rock slope with the locked segment under cyclic blasting. The stability of the slope under cyclic blasting was determined by the displacement criterion method, and the safety factor of the slope after each blasting was obtained by the strength reduction method. Finally, the relationship between the failure mode and stability of the slope and the location of the locked segment was discussed by analyzing the damage, displacement field, and safety factor of the numerical models for different locations of the locked segment in the soft interlayer. The results show that the slope stability gradually decreases with increasing the number of cyclic blasting after considering the cumulative damage effect of the rock slope. For the rock slope with the locked segment, the damage of the locked segment firstly occurs at both ends, and then propagates to the middle, in which the rock mass shows a progressive failure mode. Because the cumulative damage of the rock slope is considered, the stability factor of the slope will decrease after each blasting. When the cumulative damage is not considered, the stability factor of the slope is basically unchanged. The failure mode of the rock slope with a locked segment under cyclic blasting is the combination of dynamic tensile failure and shear failure caused by rock mass slip. The location of the locked segment in the weak interlayer affects the failure mode and stability of the slope. Therefore, when carrying out similar engineering activities, the cumulative damage effect of rock mass should be considered to avoid engineering accidents.
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图 5 每次爆破结束后锁固型边坡位移场及位移矢量图
Figure 5. Displacement field and displacement vector field of the slope after each blasting cycle
图 6 每次爆破结束后锁固型边坡的损伤分布
Figure 6. Damage distribution of the slope after each blasting cycle
图 8 边坡在一次爆破作用下不同折减系数的位移
Figure 8. Displacements of monitor points with different strength-reduction ratios under the action of once blasting cycle
图 9 不同爆破次数下锁固型边坡的安全系数
Figure 9. Safety factor of the slope with the locked segment after each blasting
图 11 Model Ⅰ和Model Ⅲ边坡的累积损伤和位移云图
Figure 11. Cumulative damage and displacement distributions of Model Ⅰ and Model Ⅲ
表 1 动力损伤本构模型的计算参数[40]
Table 1. The calculation parameters for the dynamic damage constitutive model[40]
密度/(kg·m−3) 弹性模量/GPa 泊松比 黏聚力/MPa 内摩擦角/(°) 抗拉强度/MPa 剪胀角/(°) α β 2700 68.69 0.228 27.7 55 5.6 12 3.15×106 2 
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表 2 模型物理力学参数
Table 2. The physical parameters for the models
岩体类型 密度/(kg·m−3) 弹性模量/GPa 泊松比 粘聚力/MPa 内摩擦角/(°) 抗拉强度/MPa 基岩 2700 20 0.24 5 42 3 风化岩体及锁固段 2500 0.8 0.25 0.2 34 0.2 软弱夹层 2200 0.6 0.25 0.04 18 0.02
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