Displacement mutation characteristics and energy mechanisms of anchored jointed rock slopes under blasting excavation disturbance
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摘要: 针对白鹤滩水电站左岸坝基河谷底部边坡岩体爆破开挖，采用现场岩体位移监测、锚索轴力监测及数值模拟的手段，研究了爆破开挖扰动下锚固节理岩质边坡的位移突变特征及其能量机理。研究结果表明：对于深切河谷底部高地应力边坡岩体爆破开挖，爆炸荷载挤压及地应力作用下，岩体所积聚的应变能快速释放，导致了节理岩质边坡的位移突变，突变位移包括节理张开位移和岩体回弹位移两部分；地应力水平越高、岩体弹性模量越低，总的突变位移量越大；预应力锚索主要通过抑制节理张开位移来控制边坡岩体的位移突变，锚索预应力等级越高，其吸能和释能速率越高，对节理岩体位移突变的控制效果越好，当锚索的预应力等级高到一定程度后，节理岩体的突变位移不再随锚索预应力等级的升高而显著减小。Abstract: The stability of anchored jointed rock slopes under dynamic disturbance of blasting excavation is a major concern for designers and constructors. For the left-bank slope at the valley bottom of the Baihetan hydropower station, the displacement characteristics and related energy mechanism of the anchored jointed rock slope under blasting excavation disturbance were investigated. The field monitoring data of the rock mass displacement and the anchor cable axial force were first presented to show their synchronous mutation characteristics under blasting excavation disturbance. A three-dimensional numerical simulation was then conducted by using FLAC3D to reveal the energy mechanism of the rock mass displacement mutation. The controlling effect of prestressed anchor cables on the rock mass displacement mutation was finally analyzed from the perspective of energy absorption and release. The results show that for the blasting excavation of the rock mass subjected to high in-situ stress at the valley bottom, the displacement mutation of the jointed rock slope is attributed to the rapid release of accumulated strain energy. The accumulated strain energy originates two actions, one is the blasting pressure, and the other one is the in-situ stress. The abrupt displacement of the jointed rock slope includes joint opening displacement and rock springback displacement. The total abrupt displacement will increase as the result of the in-situ stress level increases and the elastic modulus of the rock mass decreases. The prestressed anchor cable has a restraining effect on the displacement mutation of the jointed rock slope, and it mainly controls the joint opening displacement. The anchor cable with a higher prestress level corresponds to higher energy absorption and release rates, and thus has a stronger restraint on the displacement mutation of the jointed rock slope. However, when the prestress of the anchor cable is increased to a higher level, the displacement mutation of the jointed rock slope no longer decreases significantly with an increase in the prestress level.
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Key words:
- slope /
- jointed rock mass /
- prestressed anchor cable /
- blasting excavation /
- displacement mutation
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图 1 白鹤滩水电站左岸坝基边坡地质剖面图
Figure 1. Geological section of the left-bank dam foundation slope at the Baihetan hydropower station
图 2 边坡位移与预应力锚索轴力监测点布置
Figure 2. Arrangement of the observation points for monitoringthe slope displacement and anchor cable axial force
图 3 各监测点位移随时间变化曲线
Figure 3. Slope displacement histories at the different observation points
图 4 各监测点预应力锚索轴力随时间变化曲线
Figure 4. Axial force histories of the prestressed anchor cables at the different observation points
图 6 爆破开挖面上等效爆炸荷载与地应力瞬态卸荷历程曲线
Figure 6. Time-histories of the equivalent blasting pressure and the transient unloading of in-situ stress on the blasting excavation boundary
图 7 无预应力锚索时各监测点的岩体位移和应变能密度时程曲线
Figure 7. Rock mass displacement and strain energy density histories at the observation points without prestressed anchor cables
图 8 不同等级预应力锚索作用下监测点A的位移和应变能密度的时程曲线
Figure 8. Rock mass displacement and strain energy density histories at the monitoring point A under different levels of the prestressed anchor cables
图 9 不同预应力等级下的节理最终张开位移与岩体最终回弹位移
Figure 9. Joint opening displacement and rebound displacement under different levels of the prestressed anchor cables
图 10 不同等级预应力锚索的总应变能时程变化曲线
Figure 10. Time-histories of the total strain energy of the anchor cables under different prestress levels
图 11 岩体地应力和弹性模量对不同等级预应力锚索作用下监测点A的最终突变位移的影响
Figure 11. Effects of in-situ stress level and elastic modulus of the rock mass on final mutation displacement of the monitoring point A under different levels of the prestressed anchor cables
表 1 岩石与节理的物理力学参数
Table 1. Physical and mechanical parameters of the rock and joints
岩石 节理 弹性模量/GPa 泊松比 密度/(kg·m−3) 内摩擦角/(°) 法向刚度/GPa 剪切刚度/GPa 40 0.25 2700 25 20 10 
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表 2 锚索的物理力学参数
Table 2. Physical and mechanical parameters of the anchor cable
锚索索体 锚固剂 弹性模量/GPa 密度/(kg·m−3) 横截面积/mm2 黏聚力/(N·m−1) 内摩擦角/(°) 剪切刚度/GPa 锚固外圈周长/mm 锚固剂厚度/mm 200 7 890 3 465.8 2×107 38 10 518.1 49.2
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