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摘要:
岩崩坡面撞击破碎是运动轨迹难以预测的重要原因, 其中坡体几何特征是影响破碎块体运动变化特征的关键因素。为了研究岩崩撞击破碎过程及坡体几何特征对岩崩块体运动特征的影响, 利用离散单元法(PFC2D)模拟技术, 通过统计典型岩崩灾害点岩体结构与坡体几何特征, 建立了岩崩自由落体-撞击破碎-运动堆积模型, 剖析了在不同坠落高度、撞击角度条件下岩崩坡面撞击碎裂过程, 获得了块体运动速度、裂纹数量和冲击力变化曲线, 同时采用双参数Weibull分布对碎裂块体破碎程度进行了描述。实验结果表明: 破裂过程分为接触-解体、挤压-碎裂及独立运动3个阶段; 岩体碎裂由撞击点开始, 沿结构面先出现解体, 再产生新断裂面的岩石破碎; 块体速度、裂纹数量和冲击力的骤变均发生在接触-解体与挤压-碎裂阶段, 块体速度骤降, 呈现出"阶梯效应", 冲击力骤升, 表现为"双峰现象", 同时随着坠落高度增加或撞击角度减小, "阶梯效应"与"双峰现象"更为明显; 同一撞击角度条件下, 坠落高度的增加使得撞击动能增加, 进而增大了破碎程度, 导致粒径分布范围与特征粒径尺寸的减小; 同一坠落高度下, 撞击角度的增加, 意味着接触面积的减小, 进而降低了破碎程度, 导致粒径分布范围与特征粒径尺寸的增大。研究成果对揭示岩崩坡面撞击碎裂机理及预测块体运动轨迹提供了技术支撑。
Abstract:Objective The impact and fracture of rockfall are important reasons for the difficulty in predicting movement trajectories, and the geometric characteristics of slope bodies are key factors affecting the movement.
Methods To study the crushing process of rockfalls and the influence of slope geometry characteristics on the movement of rockfall blocks, discrete element method (PFC2D) simulation technology was used to establish a rockfall free-fall-impact model to analysethe rock mass structure and slope geometry characteristics of typical rockfall disaster points. The fragmentation process of rockfall under different fall heights and impact angles is analysed, and the block motion velocity, crack number and impact force are obtained. Moreover, the two-parameter Weibull distribution is used to describe the fragmentation degree of blocks.
Results The experimental results reveal that the fracture process can be divided into three stages: Contact-disintegration, extrusion-fragmentation and independent movement. Rock mass fragmentation starts at the impact point, disintegration occurs along the structural plane first, and fragmentation occurs on the new fracture plane. Sudden changes of the block velocity, crack quantity and impact force occur in the contact-disintegration and compression-fragmentation stages. The block velocity plummets, exhibiting a "step effect", and the impact force rises sharply, revealing a "double peak phenomenon". Moreover, when the fall height increases or the impact angle decreases, the "step effect" and "double peak phenomenon" become more obvious. Under the same impact angle, an increase of the fall height results in the increase of impact kinetic energy, thus increasing the degree of fragmentation and decreasing the particle size distribution range and characteristic particle size. At the same fall height, an increase in the impact angle causes that the contact area is reduced, and the degree of breakage is reduced, increasing the particle size distribution range and characteristic particle size.
Conclusion The present results provide technical support for revealing the impact fragmentation mechanism of rockfall slopes and predicting the trajectory of block motion.
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Key words:
- rockfall /
- dynamic fragmentation /
- discrete element method(DEM) /
- Weibull distribution /
- slope impact
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图 1 岩崩坡面撞击碎裂过程示意图
Figure 1. Diagram of the rockfall fragmentation process upon slope impact
图 4 岩体坡面撞击碎裂过程数值模型
a.坡中坡度30°；b.坡中坡度45°；c.坡中坡度60°
Figure 4. Numerical model of rockfall fragmentation process upon slope impact
图 5 灰岩静态单轴压缩应力-应变曲线
Figure 5. Stress-strain curves for limestone under static uniaxial compression
图 6 岩崩坡面撞击碎裂过程
a.岩体撞击前; b.岩体沿着层面破碎; c.岩体沿节理破碎; d.碎裂块体相互挤压
Figure 6. Rockfall fragmentation process upon slope impact
图 7 岩体速度、裂纹数量、冲击力随时间变化曲线
Figure 7. Curves of rock mass velocity, number of cracks, and ground impact force over time
图 8 不同坠落高度下岩体速度、裂纹数量、地面冲击力随时间变化曲线
Figure 8. Curves of the rock mass velocity, crack number and impact force under the different heights
图 9 不同撞击面坡度下岩体速度、裂纹数量、地面冲击力随时间变化曲线
Figure 9. Curves of the rock mass velocity, crack number and impact force under different impact angles
图 11 不同条件下Weibull分布函数拟合直线
Figure 11. Fitting resluts through Weibull distribution function under different conditions
图 12 不同撞击面坡度下参数m, η随坠落高度变化曲线
Figure 12. Parameter m, η under different impact angles of slopes
表 1 贵州省典型岩崩灾害统计
Table 1. Statistical table of typical rockfalls in Guizhou Province
灾害点名称 岩性 坡高/m 崩源坡度/(°) 坡中坡度/(°) 坡脚坡度/(°) 坠落高度/m 层面 优势节理J1 优势节理J2 节理贯通度 产状/(°) 黔南瓮安县白岩崩塌 灰岩 90 82 58 15 5 295∠11 192∠82 115∠72 0.3~0.6 思南县徐家大塝崩塌 灰岩 240 89 54 9 18 310∠15 150∠70 0.4~0.5 思南县椒子坪崩塌 灰岩 140 86 65 16 24 175∠12 215∠81 0.5~0.8 思南县新华村崩塌 灰岩 50 79 68 21 10 270∠41 80∠61 0.4~0.7 开阳县寨子组崩塌 白云岩 130 75 46 14 20 110∠40 285∠80 300∠65 0.7 三都县羊福民校崩塌 板岩 50 70 10 0 10 230∠84 250∠83 155∠85 0.4 三渡镇杨莫洞崩塌 灰岩 200 79 55 5 20 320∠22 275∠79 0.4~0.8 凤岗县新民街上崩塌 灰岩 80 71 28 12 15 300∠13 190∠70 0.4~0.7 赤水县集镇后山崩塌 砂岩 170 75 45 12 13 315∠3 65∠70 0.2~0.4 赤水市实验学校崩塌 泥岩 120 83 55 11 12 140∠10 230∠90 0.6 赤水市石鹅嘴崩塌 砂岩 130 71 51 13 11 170∠8 15∠85 0.3 学孔镇田坝崩塌 灰岩 130 73 35 14 9 300∠75 345∠70 0.2~0.5 安顺市小寨组崩塌 白云岩 80 87 45 9 15 135∠7 250∠86 0.3~0.4 安顺市元江煤矿崩塌 白云岩 140 76 60 10 24 220∠17 215∠75 已治理 盘州市白岩村崩塌 灰岩 40 82 35 5 9 225∠16 25∠75 0.3~0.5 兴义市村木扎崩塌 砂岩 350 88 31 9 50 151∠4 310∠87 0.4~0.6 水城县丫口组崩塌 灰岩 240 87 28 8 29 162∠18 247∠82 333∠89 0.5~0.8 六枝特区青龙山崩塌 灰岩 130 73 26 17 10 180∠17 47∠66 304∠60 0.4~0.7 大方县岩脚组崩塌 灰岩 180 85 55 23 23 296∠18 225∠78 0.5~0.8 大方县勤勇组崩塌 灰岩 360 75 65 13 35 343∠21 160∠70 0.4~0.6 大方县杓柏组崩塌 灰岩 380 85 62 12 20 63∠25 154∠72 0.5~0.6 纳雍县谢家岩崩塌 灰岩 210 83 53 17 15 20∠19 320∠79 216∠62 0.3~0.6 纳雍县营上组崩塌 灰岩 190 87 57 15 16 51∠18 216∠65 288∠50 0.5~0.6 纳雍县殷家岩崩塌 灰岩 260 72 55 11 28 51∠18 215∠76 115∠72 0.5~0.7 纳雍县拉落寨崩塌 灰岩 150 87 55 23 16 47∠17 175∠78 0.4~0.5 九仓镇大岭山崩塌 砂岩 350 70 45 19 20 284∠20 210∠78 0.3~0.6 纳雍县大偏坡崩塌 灰岩 280 71 42 16 23 112∠16 290∠80 0.3~0.5 
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表 2 岩体动力破碎实验参数
Table 2. Parameters of dynamic fragmentation
实验编号 坡中撞击面坡度/(°) 岩性 坠落高度/m 坡脚撞击面坡度/(°) 节理倾角/(°) 节理连通率 1 30 灰岩 10 10 70 0.5 2 30 灰岩 20 10 70 0.5 3 30 灰岩 30 10 70 0.5 4 45 灰岩 10 10 70 0.5 5 45 灰岩 20 10 70 0.5 6 45 灰岩 30 10 70 0.5 7 60 灰岩 10 10 70 0.5 8 60 灰岩 20 10 70 0.5 9 60 灰岩 30 10 70 0.5
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表 3 灰岩细观参数
Table 3. Microproperties of limestone
离散元参数 数值 离散元参数 数值 颗粒密度/(kg·m-3) 2 600 孔隙率/% 10 最小粒径/mm 0.5 平行黏结模量/GPa 25 粒径比(Rmax/Rmin) 1.66 平行黏结刚度比 2.5 颗粒接触模量/GPa 25 平行黏结法向刚度/MPa 20 颗粒刚度比 2.5 平行黏结切向刚度/MPa 15
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表 4 光滑节理模型细观参数
Table 4. Microproperties of the smooth joint model
离散元参数 数值 离散元参数 数值 接触径向单元数 1 接触间距/mm 0.1 接触弹性模量/GPa 44 平行黏结模量/GPa 25 刚度比 1.1 摩擦系数 0.5 接触抗拉强度/MPa 15 接触黏结强度/MPa 12 内摩擦角/(°) 5
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表 5 拟合参数值
Table 5. Fitting parameters
实验组 拟合结果 可决系数 m值 η值 1 Y=3.543 9X-22.981 1 0.973 2 3.543 9 655.04 2 Y=3.502 9X-22.561 1 0.978 7 3.502 9 626.84 3 Y=3.444 9X-22.084 2 0.984 5 3.444 9 608.31 4 Y=3.623 3X-23.547 5 0.965 4 3.623 3 664.42 5 Y=3.573 1X-23.054 6 0.987 7 3.573 1 634.25 6 Y=3.483 2X-22.394 2 0.981 4 3.483 2 619.68 7 Y=3.640 1X-23.699 9 0.980 8 3.640 1 672.36 8 Y=3.633 1X-23.517 8 0.983 8 3.633 1 647.55 9 Y=3.547 5X-22.856 7 0.982 3 3.547 5 628.31 式中: Pn为在第n点的累积质量概率；$ \sum\limits_{i = 1}^n {{V_i}} $为在第n点的累计体积；$ \sum\limits_{i = 1}^n {{V_i}} $为碎片总体积。
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