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RAINFALL INDUCED INSTABILITY MECHANISM OF HIGH EMBANK-MENT RETAINING LOESS SLOPE
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摘要: 近些年，由于机场建设、公路铁路等地面交通网以及城镇化的建设在黄土丘陵地区开展越来越频繁，形成大量的黄土填方高陡边坡，虽然这些地区的年降雨量较小，但是降雨已经是诱发黄土滑坡的主要因素，通过对研究区黄土高填方边坡进行原位渗流实验和裂缝存在条件下暂态非饱和渗流以及饱和黄土力学特性进行分析的基础上，对降雨诱发黄土高填方支挡边坡失稳机理研究，研究表明：（1）3d后的原位渗流中实验试坑中心的最大入渗深度为1.30m，湿润锋最大深度位于入渗最大深度以下0.20m，但降雨条件下，裂缝的存在是黄土边坡发生浅层滑动的重要因素；（2）当围压小于300kPa时，饱和土体的轴向应变增长到20%左右时，达到稳定状态，在静力驱动剪应力大于稳态抗剪强度的条件下则会使高填方坡体的局部发生流滑破坏；（3）总体来说黄土高填方支挡边坡变形破坏的形成机制为：推移式蠕滑-支挡结构失效-累进性滑移剪断-牵引式溃滑。Abstract: In recent years, the constructions of airport, highway and railway transportation network and urbanization in the loess hilly areas have been carried out more and more frequent. They have formed a large quantities of high loess embankment slope. Although the annual rainfall of these areas is semiarid, rainfall is the main factor for the failure of loess slopes. This paper analyses the in-situ seepage experiment and the transient unsaturated seepage under the conditions considering the fractures and the mechanical properties of saturated loess. It examines the failure mechanism of high fill retaining loess slope. The results show the following. (1) The maximum infiltration depth of the test pit center is 1.30m after 3 days in the in situ seepage experiment. The maximum depth of the wetting front is 0.20m below the maximum infiltration depth. (2) When the confining pressure is less than 300kPa, the axial strain of the saturated soil increases to about 20%, and reaches the steady state. Under the condition that static driving shearing stress is larger than the steady shear strength, the local flowslide failure of the high fill slope can occur. (3) In general, the formation mechanism of deformation and failure of the retaining high embankment slopes is as follows:push creeping-retaining structural failure-progressive slip shear-traction collapse.
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图 1 黄土高填方边坡全景图和滑塌后点云图
a.填土边坡全景图；b.滑塌后三维激光扫描点云图
Figure 1. The loess high embankment slope of the panorama and slide after the point cloud
图 3 A1区进山公路发育的裂缝
a.进山公路裂缝贯穿位置及长度；b.进山公路裂缝最宽处距离桩板墙位置；c.进山公路裂缝宽度及可见深度
Figure 3. Development of the cracks in the mountain road at A1 region
图 6 不同钻孔不同深度的体积含水率变化分布图
Figure 6. Change chart different drilling water volume in different depth rate
图 9 无裂缝存在时边坡体积含水率等值线图
Figure 9. Volumetric water content contour map withnot cracks in the slope
图 10 无裂缝存在时边坡孔隙水压力等值线图
Figure 10. Pore water pressure contour map withnot cracks in the slope
图 11 有裂缝存在时边坡体积含水率等值线图
Figure 11. Volumetric water content contour map with cracks in the slope
图 12 有裂缝存在时高填方边坡孔隙水压力等值线图
Figure 12. Pore water pressure contour map with cracks in the slope
图 13 不同围压梯度下的偏应力和轴向应变关系曲线
Figure 13. The relation curves of partial stress and axial strain under different radial pressures
图 17 饱和黄土的稳态线图
a.稳态孔隙比与最小有效主应力曲线图；b.稳态时偏应力和平均有效应力关系图
Figure 17. Steady state line of saturated loess
图 18 饱和黄土围压与稳态抗剪强度的关系曲线
Figure 18. Relationship between radial pressure and steady shear strength of saturated loess
图 19 高填方坡体滑塌后揭露的某一层黄土流痕迹图
Figure 19. A layer of loess flow diagram of high fill slope after slumping
表 1 填方边坡填土物理力学指标
Table 1. Physical and mechanical indexes of soil embankment slope
地层
时代土体
名称取样深度
/m含水量ω
/%土粒比重
GS重度γ
/kN·m-3干重度γd
/kN·m-3孔隙比e 饱和度Sr
/%液限ωL
/%塑限ωP
/%塑性指数
Ip液性指数
ILQ4pl+al 粉土 1 13.6 2.69 15.0 13.2 1.000 35.8 23.8 16.9 6.88 0.1 10 15.4 2.69 17.2 14.9 0.771 53.8 24.4 17.1 7.24 0.1 20 8.9 2.69 17.7 14.9 0.782 66.5 24.3 17.1 7.21 0.3 30 9.8 2.70 19.2 16.0 0.654 82.3 25.6 17.6 8.04 0.3 粉质
黏土35 20.9 2.71 1.8 15.6 0.105 80.8 29.4 19.0 10.0 0.2 40 21.5 2.71 19.3 15.9 0.672 87.0 29.9 19.2 10.70 0.2 
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表 2 渗透参数计算取值
Table 2. Seepage parameters for calculation
类别 饱和渗透系数
/m·s-1体积含水率/% VG模型参数 θr θs a n 填方黄土 1.26×10-6 47.1 8.64 0.0610 1.7371 原状黄土 6.78×10-7 45.7 9.6 0.0315 1.472 软弱夹层 7.26×10-5 47.1 8.64 0.0610 1.7371
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