Feature acquisition and stability evaluation of high dangerous rock mass based on oblique photography: A case study at Guanyinshan in Wanzhou , Chongqing Province
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摘要:
观音山危岩带对拟建恩广高速万开段庙垭隧道、苎溪河特大桥和临近居民构成安全威胁，急需调查治理，但因危岩地处高位，传统调查、评价手段难以实施。通过地质调查、钻孔取样和室内试验获取基础地质信息；利用倾斜摄影对危岩进行识别、几何特征获取和边界条件分析；以赤平投影法和刚体极限平衡法分别进行危岩带、危岩体的稳定性分析；对不稳定危岩单体利用Rocfall软件进行运动学模拟。结果表明：陡崖发育6处主要危岩单体，体积400～5000 m3不等；岩体受2组节理面切割和结构面组合控制，整体稳定性较差，易发生坠落式和倾倒式破坏；其中W3、W6危岩体在暴雨工况下处于不稳定状态，对拟建工程形成滚动冲击，动能为5～12 kJ不等。研究结果可以为观音山危岩治理措施的选型、规模提供设计参数，为高位危岩的调查防治提供参考，对利用航测手段提高传统地质调查效率和精度做出了新思考。
Abstract:The Guanyin mountain dangerous rock belt poses a security threat to the Miaoya tunnel of the proposed Wankai section of the Enguang Expressway, as well as Zhuxihe Bridge and the neighboring residents. It is urgent to be investigated and controled. Traditional investigation and evaluation methods are difficult to implement on the high dabgerous rock mass. Basic geological information is obtained through geological survey, drilling sampling and experiments, identification, geometric feature acquisition and boundary condition analysis of the dangerous rock mass are carried out by oblique photography, stability analysis of the dangerous rock belts and the dangerous rock masses are carried out by stereographic projection method and rigid body limit balance method, respectively. Simulation is carried out by Rocfall software for unstable dangerous rock. The results show that the cliffs develop six main dangerous rock zones with a volume of 400−5000 m3, and the rock mass is controlled by two groups of joint surfaces and structural surfaces combination, the overall stability is poor, prone to fall and tipping; among them, the W3 and W6 dangerous rock masses are in an unstable state under heavy rain conditions, forming a rolling impact on the proposed project, and the kinetic energy is 5−12 kJ. The research results can provide design parameters for the selection of the control measures of the dangerous rocks in Guanyin Mountain, and provide reference for the investigation and prevention of high dangerous rock mass, it puts forward new idea on the use of aerial survey methods to improve the efficiency and accuracy of traditional geological surveys.
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Key words:
- perilous rock /
- oblique photography /
- stability /
- rockfall simulation /
- disaster prevention measures
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表 1 危岩体发育特征
Table 1. Development characteristics of dangerous rocks
编号 分布高程/m 形态 危岩体尺寸（长×厚×高）/m 体积/m3 凹腔尺寸（高×深）/m 失稳
模式类别 W1 340~386 不规则 46.0×9.7×12.4 5532.88 14.0×4.7 坠落式 高位/特大型 W2 345~381 长方形 24.3×6.2×7.0 1054.62 8.5×3.8 坠落式 高位/特大型 W3 350~380 长方形 19.4×8.5×9.8 1616.02 11.0×4.0 坠落式 高位/特大型 W4 280~300 不规则 13.4×7.2×5.0 482.40 2.0×1.5 倾倒式 低位/特大型 W5 270~280 长方形 25.0×6.8×4.5 765.00 1.5×1.2 倾倒式 低位/大型 W6 280~285 长方形 22.0×7.0×3.7 569.80 1.0×0.8 倾倒式 低位/大型 注：类别划分依据《重庆地质灾害防治工程勘查规范》（DB 50/ T 143—2018）。 
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表 2 岩体物理力学参数
Table 2. Physical and mechanical parameters of rock mass
岩性 工况 γ
/（kN·m−3）c/kPa φ/（°） flk/kPa J2s
砂岩天然 24.6～25.2 737～1034 32.9～35.1 280～580 暴雨 24.9～25.8 643～976 31.6～34.8 220～495
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表 3 岩体稳定性计算结果
Table 3. Rock mass stability calculation results
编号 工况 断面面积/m2 危岩高度/m Fs 评价 W1 天然 120.3 12.40 1.385 基本稳定 暴雨 1.162 欠稳定 W2 天然 43.40 7.00 1.741 稳定 暴雨 1.368 基本稳定 W3 天然 83.30 9.80 1.169 欠稳定 暴雨 0.895 不稳定 W4 天然 36.00 5.00 1.389 基本稳定 暴雨 1.102 欠稳定 W5 天然 30.60 4.50 1.483 稳定 暴雨 1.169 欠稳定 W6 天然 25.90 3.70 1.083 欠稳定 暴雨 0.925 不稳定
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表 4 恢复系数
Table 4. Coefficient of restitution
碰撞系数 地面岩性 坚硬岩、较硬岩 较软岩、软岩、极软岩 硬土 普通土 松土 法向回弹系数Rn 0.4 0.35 0.3 0.26 0.22 切向回弹系数Rt 0.86 0.84 0.8 0.75 0.65
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表 5 滚动摩擦系数
Table 5. Coefficient of rolling friction
坡面特征 滚动摩擦系数 摩擦角/（°） 光滑岩面、混凝土表面 0.30～0.60 21.8～31.0 块石堆积坡面 0.55～0.70 28.8～35.0 密实碎石堆积坡面、硬土坡面、
植被（灌木丛为主）发育0.55～0.85 28.8～40.4 软土坡面、植被不发育或少量杂草 0.50～0.85 26.6～40.4
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表 6 模拟参数选取
Table 6. Selection of simulation parameters
边坡部位 Rn/St Rt/St φ/St 粗糙度 上部基岩裸露区 0.4/0.03 0.86/0.04 25.1/0.03 2.42 下部堆积区 0.3/0.03 0.84/0.02 31/0.02 3.00
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