降雨入渗下裂土边坡水分运移时空特征与失稳机理

周峙; 张家铭; 宁伏龙; 罗易; 王建立

doi:10.19818/j.cnki.1671-1637.2020.04.008

降雨入渗下裂土边坡水分运移时空特征与失稳机理

doi: 10.19818/j.cnki.1671-1637.2020.04.008

周峙^1,,
张家铭^1, ,,
宁伏龙¹,
罗易¹,
王建立²

1.
中国地质大学(武汉) 工程学院，湖北武汉 430074
2.
安徽交通控股集团有限公司，安徽合肥 230088

基金项目:

国家自然科学基金项目 41372311

安徽省交通运输科技进步计划项目 2018030

中央高校基本科研业务费专项资金项目 1810491A24

详细信息

作者简介:
周峙(1987-), 男, 湖北仙桃人, 中国地质大学工学博士研究生, 从事路基特殊性岩土边坡防治研究

通讯作者:
张家铭(1976-), 男, 内蒙古呼和浩特人, 中国地质大学副教授, 工学博士

中图分类号: U416.13
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出版历程
- 收稿日期: 2020-03-01
- 刊出日期: 2020-04-25

Temporal and spatial characteristics of moisture migration and instability mechanism of cracked soil slope under rainfall infiltration

1.
School of Engineering, China University of Geosciences, Wuhan 430074, Hubei, China
2.
Anhui Transportation Holding Group Co., Ltd., Hefei 230088, Anhui, China

Funds:

National Natural Science Foundation of China 41372311

Science and Technology Progress Plan of Anhui Province Transport 2018030

Fundamental Research Funds for the Central Universities 1810491A24

More Information

Author Bio:
ZHOU Zhi(1987-), male, doctoral student, 332440995@qq.com

Corresponding author: ZHANG Jia-ming(1976-), male, associate professor, PhD, zjmnm@163.com

摘要

摘要: 为探究降雨入渗下裂土边坡水分运移时空特征与失稳机理, 自主研制了足尺模型试验系统和光纤布拉格光栅(FBG)深部柔性位移系统, 对边坡渐进破坏进行了全过程、多物理量联合监测, 揭示了降雨入渗作用下裂土边坡的渐进变形和破坏演化模式; 基于裂土边坡的渐进破坏模式, 提出了土体饱和比概念, 将裂隙深度范围滑体分为饱和层和非饱和层; 以土体饱和度变化描述了含随机分布裂隙的边坡水分运移规律, 并结合刚体极限平衡法探讨了由裂隙控制的边坡失稳机制。研究结果表明: 对于未形成裂隙的边坡, 连续降小雨时浅层变形受表层基质吸力控制; 裂隙形成后, 雨水沿裂隙快速入渗形成暂态饱和区, 导致基质吸力降幅达82.50%~87.14%, 而由其贡献的抗剪强度迅速损失, 从而形成初期溜滑、片蚀等浅层变形, 降雨停止后坡体仍处于蠕变过程, 坡脚与坡顶位移增幅分别为23.40%和19.39%;蒸发后裂隙规模发展增大了雨水对渗流场的影响范围和边坡破坏规模; 土体经历胀缩、蠕变而变得松散, 裂缝区深部土体体积含水率较初始状态的增幅为205.7%;同一降雨条件下, 初始裂隙深度愈深, 稳定系数愈低, 破坏愈快; 对具有同一裂隙深度的边坡, 其稳定系数随土体饱和比的增加逐渐降低, 土体饱和比增长愈快, 表征边坡内部出现大面积连通型饱和区, 这是裂土边坡出现整体失稳的主要原因。
- 路基工程 /
- 裂土边坡 /
- 足尺模型 /
- 变形机理 /
- 土体饱和比 /
- 光纤布拉格光栅
Abstract: To reveal the temporal and spatial characteristics of moisture migration and instability mechanism of cracked soil slope under the rainfall infiltration. The full-scale model test and fiber Bragg grating(FBG) displacement systems were developed independently to conduct the whole-process and multi-physical monitoring of slope progressive failure. The progressive deformation and failure evolution mode of cracked soil slope under the rainfall infiltration were revealed. Based on the progressive failure mode of cracked soil slope, the concept of soil saturation ratio was proposed. The sliding body within the crack depth range was divided into the saturated layer and unsaturated layer. The change of soil saturation degree was used to describe the water transport law of slope with randomly distributed cracks, and the slope instability mechanism controlled by cracks was discussed by combining with the rigid body limit equilibrium method. Research result indicates that the shallow deformation is controlled by the surface matrix suction in the case of continuous light rain for the slope without cracks. After the formation of cracks, the rainwater infiltrates rapidly along the cracks to form a transient saturated zone. It causes a rapid loss of shear strength contributed by the matrix suction with a drop of 82.50%-87.14%, and produces the initial slip flow, sheet erosion and other shallow deformations. After the rainfall stops, the slope is still in the creep process, and the displacements of slope foot and roof increase by 23.40% and 19.39%, respectively. After the evaporation, the development of crack increases the influence range of rainwater on the seepage field and slope failure scale. The soil becomes loose after experienced swelling, shrinking and creep process. The volumetric moisture content of soil at the deep layer of crack zone increases by 205.7% compared with the initial state. Under the same rainfall condition, the deeper the initial crack depth is, the lower the stability coefficient is, and the faster the failure occurs. For a slope with the same crack depth, its stability coefficient decreases with the increase of soil saturation ratio. The faster the soil saturation ratio increases, the wider the connected saturated zone inside the slope is. It is the main reason for the overall instability of cracked soil slope.
- subgrade engineering /
- cracked soil slope /
- full-scale model /
- deformation mechanism /
- soil saturation ratio /
- fiber Bragg grating

HTML全文

图 1 模型试验系统与模型边坡

Figure 1. Model test system and model slope

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图 2 监测元件布设示意(单位: cm)

Figure 2. Schematic of monitoring instruments layout (unit: cm)

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图 3 光纤光栅位移计标定结果

Figure 3. Calibration results of fiber grating displacement meter

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图 4 裂隙发展与边坡破坏形态

Figure 4. Cracking development and slope failure patterns

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图 5 边坡表层体积含水率时程曲线

Figure 5. Time-history curves of volumetric moisture content in shallow layers of slope

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图 6 开挖初期边坡中部溜滑典型破坏现象

Figure 6. Typical failure phenomenon of slip flow in middle of slope at initial excavation

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图 7 边坡深层体积含水率时程曲线

Figure 7. Time-history curves of volumetric moisture content in deep layers of slope

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图 8 边坡干湿循环后坡面出现的网状裂隙

Figure 8. Network-pattern cracks in slope surface after wetting-drying cycles

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图 9 坡体不同深度土体孔隙水压力时程曲线

Figure 9. Time-history curves of pore water pressure of soil in different depths of slope

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图 10 边坡表层不同位置饱和度与基质吸力变化曲线

Figure 10. Change curves of saturation and matrix suction of slope surface at different positions

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图 11 降雨-蒸发期间基质吸力与坡体水平位移变化

Figure 11. Variations of matrix suction and horizontal displacement of slope during rainfall and evaporation

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图 12 裂土边坡破坏概念模式

Figure 12. Conceptual failure modes of cracked soil slope

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图 13 裂隙优势流作用下裂土边坡稳定性简化计算模型

Figure 13. Simplified calculation model for stability of cracked soil slope under action of fissure preferred flow

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图 14 裂土边坡单元体受力模型

Figure 14. Cracked soil slope mechanical model of element body

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图 15 不同裂隙深度边坡的破坏时间与稳定性系数曲线

Figure 15. Failure time and stability coefficient curves of slope with different crack depths

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图 16 降雨强度对裂土边坡破坏的影响

Figure 16. Influence of rainfall intensity on failure of cracked soil slope

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图 17 边坡理论破坏时间与模型试验结果对比

Figure 17. Comparison between theoretical failure time and model test result of slope

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表 1 土体物理力学参数

Table 1. Physical and mechanical parameters of soil

土体基本物理性质指标	天然干密度/(g·cm^-3)	天然质量含水率/%	最大干密度/(g·cm^-3)	最优质量含水率/%	饱和体积含水率/%	液限/%	塑限/%
实测值	1.59	13.8	1.71	16.5	48.2	35.7	18.4
土体基本力学性质指标	缩限/%	峰值黏聚力/kPa	内摩擦角/(°)	残余黏聚力/kPa	残余内摩擦角/(°)	自由膨胀率/%	土体相对密度
实测值	8.2	34.86	16.97	8.2	5.1	42.5	2.71

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表 2 模型边坡变形全过程特征

Table 2. Characteristics of whole deformation process of slope model

典型变形时间结束节点/h	降雨阶段	破坏阶段	变形现象描述
26.45	连续小雨	片蚀	静置期出现的胀缩裂隙较浅, 雨水快速进入裂隙后, 导致裂隙周围土体很快形成暂态饱和, 坡面出现片蚀破坏
95.20		溜滑	随着裂隙底部土体逐渐饱和, 边坡中部、坡脚表层土体因重度增大发生溜滑
100.13		蠕滑	坡中部表层以下30 cm处逐渐饱和, 并牵引坡肩顶部沿冲沟出现蠕滑下错, 坡顶下错位移为2.5 cm
120.00		表层牵引式剧烈滑移	边坡出现深约45 cm的剧烈滑移, 坡中、坡脚为滑流形式, 牵引坡顶坍塌
126.00	蒸发阶段	坡体蠕变	干燥期间湿润锋逐渐下移, 深部土体逐渐饱和并出现蠕动变形, 并牵引坡顶土体形成张拉裂隙
196.00	蒸发阶段	裂隙加深	在胀缩裂隙与张拉裂隙共同作用下, 裂隙宽度和深度增加, 坡脚形成羽毛状次生裂隙, 形成更多渗流通道
208.53	短时强降雨	后缘张拉裂隙贯通, 坡体整体垮塌	后缘裂隙贯通, 坡顶径流直接进入贯通裂隙, 边坡中上部土体由于饱和重度增加, 随即边坡后缘出现推移式滑移破坏, 形成了整体式坍塌
240.00	短时强降雨	后壁形成陡坡, 在重力作用下继续坍塌	地表径流主要沿冲沟流出坡面, 变形趋于平缓, 滑坡后壁较陡, 坡脚趋于饱和

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表 3 滑移主断面各高程处累计水平位移

Table 3. Accumulated horizontal displacements at all elevations of sliding main section

自上而下测绳位置/cm	不同时间(h)的累计水平位移/cm
自上而下测绳位置/cm	208	240
40	53.2	147.7
80	60.7	143.2
120	37.3	141.3
160	64.8	133.3
200	48.6	111.6
240	20.8	28.0

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表 4 不同土体的拟合参数

Table 4. Fitting parameters for different types of soils

土体分类	λ	A
软土	0.4	100
硬黏土	0.4	100
中砂	0.4	40
粗砂	0.4	40

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表 5 模型计算参数

Table 5. Calculation parameters of model

参数	参数值	数据来源
K/h^-1	6.9×10^-7	双环渗透试验
A	100	硬黏土^[18]
λ	0.4
β	3.1
c′/kPa	8.2	室内环剪试验
φ/(°)	5.1	室内环剪试验
α/(°)	45	几何模型参数
n	0.5	室内试验
H/m	1.0、1.4、1.8	模型试验
g	2.71	室内试验
θ_s/%	48.2	室内试验
θ_r/%	6.0	V-G模型非线性拟合
h′/(mm·h^-1)	45.2、100.6	模型试验

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