Analysis of three-dimensional movement characteristics of rockfall: A case study at a railway tunnel entrance in the southwestern mountainous area, China
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摘要: 西南山区某铁路隧道口上部广泛分布着高位危岩体,对下部隧道建(构)造物具有严重的威胁。采用Rockfall Analyst软件对该隧道上部五类不同尺寸的高位危岩体进行三维运动轨迹数值模拟,研究表明:研究区的高位危岩落石具有弹跳高度大、速度快、冲击能量高的特点;弹跳高度、运动速度与危岩落石的质量无关,冲击能量大小与落石质量成正比。分析表明:该地区高位危岩体的防护应避免单一防护措施,建议综合使用多种防护措施。Abstract: High unstable rock masses are widely distributed in the upper part of a railway tunnel entrance in the southwestern mountainous area, which causes serious hazards to the construction of the lower tunnel. The Rockfall Analyst software was used to simulate the three-dimensional movement track of five kinds of high unstable rock masses in the upper part of the tunnel, and it shows that the rockfalls in the study area have the characteristics of high bounce height, fast speed and high impact energy. There is no relation between the bounce height, the movement speed and the mass of rockfall, while the impact energy is proportional to the mass of rockfall. The analysis shows that multiple and comprehensive protective measures should be recommended for the protection of unstable rock masses in this area instead of single protective measure.
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Key words:
- unstable rock mass /
- rockfall /
- movement characteristics /
- tunnel entrance /
- protection
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表 1 落石碰撞恢复系数及滚动摩擦系数(吕庆等,2003)
Table 1. Restitution coefficients and rolling friction coefficient of the rockfall collision(Lv et al., 2003)
坡面特征 法向恢复系数eN 坡面特征 切向恢复系数eT 坡面特征 滚动摩擦系数tanβγ 光滑而坚硬的表面和铺砌面,如人行道或光滑的基岩面 0.37~0.42 光滑而坚硬的表面和铺砌面,如人行道或光滑的基岩面 0.87~0.92 光滑岩面、混凝土表面 0.40~0.60 多数为基岩或砾岩区的斜面 0.33~0.37 多数为基岩和无植被覆盖的斜坡 0.83~0.87 块石堆积坡面 0.55~0.70 多数为有少量植被的斜坡 0.82~0.85 硬土边坡 0.30~0.33 植被覆盖的斜坡或有稀少植被覆盖的土质边坡 0.80~0.83 密实碎石堆积坡面、硬土坡面 0.55~0.85 软土边坡 0.28~0.3 灌木林覆盖的土质边坡 0.78~0.82 松散碎石坡面、软土坡面 0.50~0.85 表 2 危岩落石尺寸
Table 2. Sizes of the rockfalls
危岩编号 长L/m 宽B/m 厚H/m 不规则系数k 岩性 体积V/m3 密度ρ/(kg/m3) 质量m/kg W1 0.18 0.19 0.10 0.90 花岗岩 0.0031 2850 约10 W2 0.46 0.23 0.22 0.75 花岗岩 0.0175 2850 约50 W3 1.30 1.00 0.37 0.65 花岗岩 0.3127 2850 约1000 W4 2.47 1.63 0.89 0.60 花岗岩 2.1499 2850 约6200 W5 3.82 3.89 3.10 0.70 花岗岩 32.2458 2850 约92000 注:①不规则系数k根据现场不规则程度决定;②V=L×B×H×k; ③m=ρ×V 表 3 坡面特征计算参数表
Table 3. Table of calculation parameters for the slope features
坡面特征 法向恢复系数eN 切向恢复系数eT 动摩擦角/(°) 硬岩+大量植被 0.37 0.85 13 风化岩石坡面 0.35 0.85 15 风化岩石坡面+少量植被覆盖 0.33 0.75 18 岩堆 0.30 0.82 20 岩土坡面 0.28 0.82 23 岩土坡面+少量植被 0.25 0.78 25 岩土坡面+大量植被 0.20 0.60 30 房屋 0.40 0.85 10 泥坡+植被 0.30 0.75 21 路基路面 0.40 0.90 10 水(遇水停止) 0.00 0.00 89 大棚 0.10 0.30 50 表 4 落石初始运动参数
Table 4. Initial motion parameters for the rockfalls
危岩编号 质量m/kg 初始水平速度Vp/(m/s) 初始竖向速度V0z/(m/s) 初始弹跳高度h/m W1 约10 0.30 0.30 0.05 W2 约50 0.30 0.30 0.05 W3 约1000 0.30 0.30 0.05 W4 约6 200 0.30 0.30 0.05 W5 约92 000 0.30 0.30 0.05 注:${V_{\rm{P}}} = \sqrt {V_{0x}^2 + V_{0y}^2} $(V0x和V0y为沿x和沿y向的初始水平速度) 表 5 不同落石尺寸的最大运动特征值
Table 5. Maximum motion eigenvalues of different sized rockfalls
危岩编号 质量m/kg 弹跳高度/m 速度/(m/s) 冲击能量/kJ W1 约10 77.07 71.16 22.21 W2 约50 57.77 68.31 116.10 W3 约1000 45.90 61.33 2864.00 W4 约6200 45.92 61.06 11423.00 W5 约92000 43.00 61.00 170974.00 表 6 常见滚石防护结构选择的依据(何思明等,2015)
Table 6. Basis for choosing protective structures for common rockfalls(He et al., 2015)
主动防治 被动防治 清除危岩/m3 混凝土喷锚/m2 主动柔性防护/m2 被动柔性防护/m3 棚洞/kJ 落石槽/kJ 柔性挡石墙/kJ 0~500 300~1500 100~1000 200~1000 1000~3000 100~500 1000~5000 -
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