Regional Hillslope Stability Analysis under Rainfall Based on Characterization of Overburden Soil Layer Thickness
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摘要: 区域内覆盖土层孕育着斜坡浅表层破坏，是区域斜坡破坏的最主要来源，但由于覆盖土层厚度的空间变化，导致堆积层滑坡灾害发育的底界难以合理确定，进而使稳定性评价结果未能指示实际滑坡状况.以黄冈市九资河镇为例，对该区域的覆盖层厚度进行详细调查，并通过基于地貌过程的估计方法确定了研究区覆盖层厚度的空间分布；在此基础上，运用斜坡稳定性定量模型，分析了研究区斜坡在降雨条件下的稳定性，并据此估计了区域堆积层滑坡的分布情况和可能性.结果显示：所提出的方法有效且具有很强的实用性，基于GIST模型估计的区域覆盖层厚度与实际情况较为接近（集中在0.5~3.0 m）.覆盖层厚度的合理确定使得区域斜坡降雨入渗稳定性评价结果更加精细且具有实际滑坡指示意义；该区基本稳定和稳定斜坡主要分布于阶地平台或河漫滩等覆盖层厚度大但坡度较小区域，欠稳定及不稳定斜坡主要分布在水库及各支流靠岸位置，这些部位覆盖层厚度虽小但坡度较大、地形外凸且受地下水影响明显；短时间的强降雨对斜坡稳定性影响巨大.该研究有助于推动区域斜坡灾害评价向精细化方向发展.Abstract: The overburden layer in the region conceives the shallow surface damage of slopes and is the main source for the regional slope damage. But, the spatial variation in the thickness of the overburden layer makes it difficult to reasonably determine the bottom of hazard development, which in turn makes it difficult for the stability assessment results to indicate actual landslide conditions. Taking Jiuzihe Town of Huanggang City as an example, the overburden thickness in this area was investigated in detail, and the spatial distribution of overburden thickness was determined by a geomorphic process-based method. On this basis, the stability of slopes in the study area under rainfall conditions was analyzed using a quantitative model of slope stability, and the distribution and likelihood of regional accumulated layer landslide were estimated accordingly. The results show that the proposed method is effective and highly practical, and that the estimated regional overburden thickness based on GIST model is close to the actual situation, mainly concentrated in 0.5-3.0 m. The reasonable determination of overburden thickness makes the evaluation results of regional slope rainfall infiltration stability more precise and has practical landslide indication significance. The basically stable and stable slopes are mainly distributed in the areas with large overburden thickness but small slope, such as terrace platform or floodplain. While the less stable and unstable slopes are mainly distributed in the reservoir and the bank of various tributaries. Short period of heavy rainfall has great influence on slope stability. This study is helpful to the development of regional slope disaster assessment towards the fine direction.
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图 1 罗田县域及研究区地质概况
Fig. 1. General geological situation of Luotian County and the study area
图 2 研究区覆盖层厚度现场测量及分类
Fig. 2. Field measurement and classification of overburden thickness in the study area
图 3 研究区曲率、坡度和相对位置贡献指数分布
Fig. 3. Maps of curvature, slope and relative location contribution index in the study area
图 4 不同坡形拟合图、示意图和现场图
Fig. 4. Fitting diagram, schematic diagram and site diagram of different slope shapes
图 5 研究区覆盖层厚度分布估计结果
Fig. 5. Estimation results of overburden thickness distribution in the study area
图 7 两种模型厚度的估计值与实测值散点图
Fig. 7. Scatter plot of estimated and measured thickness of two models
图 9 基于覆盖层厚度识别的区域斜坡降雨入渗稳定性定量评价方法流程
Fig. 9. Flow chart of quantitative evaluation method for regional slope rainfall infiltration stability based on overlay thickness identification
图 10 研究区水流流向、初始地下水位分布
Fig. 10. Distribution diagrams of flow direction and initial groundwater level
图 13 工况二不同阶段的斜坡稳定情况面积占比
Fig. 13. Area proportion of slope stability at different stages of working condition 2
图 14 两种工况的不同稳定性分区面积占比
Fig. 14. Area ratio of slope stability under two working conditions
图 15 历史滑坡与工况2-2稳定性结果对比
Fig. 15. Comparison of historical landslide and stability results under working condition 2-2
图 16 研究区斜坡稳定性评价结果的现场验证
Fig. 16. Field verification of slope stability evaluation results in the study area
表 1 研究区岩性强度参数及坡度临界值
Table 1. Lithological strength parameters and slope critical value in the study area
岩性分区 平均内摩擦角$ \varphi $（°） 平均粘聚力$ C $（kPa） 坡度临界值$ {\theta }_{\mathrm{t}\mathrm{h}} $（°） 第四系堆积物 15.3 25.3 22 残坡积物 22.6 27.1 28 花岗岩风化残积物 37.8 35.6 32 
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表 2 不同斜坡坡形P与η关系式及拟合度R2
Table 2. The P and η relation and fit R2 of different slope shape
斜坡坡形 P与$ \eta $拟合公式 R2 凹凸形 $ \eta =1.9-21.3p+78.6{p}^{2}-103.1{p}^{3}+44.4{p}^{4} $ 0.967 凸凹凸形 $ \eta =1.9-15.1p+41.3{p}^{2}-38.1{p}^{3}+10.13{p}^{4} $ 0.935 凸形 $ \eta =1.21-1.7p+0.53{p}^{2} $ 0.961
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表 3 不同斜坡坡形校准参数$ {{K}}_{{c}} $取值
Table 3. Calibration parameter $ {{K}}_{{c}} $ value of different slope shape
斜坡坡形 覆盖层厚度调查值的最大值 $ \mathrm{M}\mathrm{a}\mathrm{x}\left[\right(1-C)\cdot \eta \cdot \psi ] $平均值 $ {K}_{c} $取值 凹凸形 5.0 m 0.782 6.4 凸凹凸形 5.5 m 0.822 6.7 凸形 6.0 m 0.902 6.6
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表 4 覆盖层厚度区间分布占比
Table 4. Proportion of overburden thickness interval distribution
覆盖层厚度区间（m） 栅格总数（个） 栅格比重（%） 0~0.5 134 463 12.23 0.5~1.5 408 305 37.15 1.5~2.0 314 150 28.58 2.0~3.0 240 282 21.85 3.0~6.0 2 158 0.19 合计 1 099 358 100
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表 5 研究区物理力学参数
Table 5. Physio-mechanical parameters of the study area
岩性 土体容重（kN/m3） 有效粘聚力（kPa） 有效内摩擦角（°） max min 均值 max min 均值 第四系堆积物 19.6 30.6 20.5 25.3 18.5 12.6 15.3 残坡积物 22.6 33.5 22.0 27.1 28.1 17.6 22.6 花岗岩风化残积物 27.8 46.9 25.6 35.6 45.3 32.6 37.8
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表 6 研究区水文参数
Table 6. Hydrological parameters of the study area
岩性 水力扩散系数（m2/s） 饱和土体竖直渗透系数（m/s） 初始地表入渗系数（m/s） 体积含水率（%） 饱和 残余 第四系堆积物 2.5×10‒5 3×10‒7 3×10‒7 33 9 残坡积物 7.8×10‒4 9×10‒6 5×10‒6 48 7 花岗岩风化残积物 4.6×10‒4 8.5×10‒6 5.6×10‒8 27 6
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表 7 降雨工况
Table 7. Working condition of rainfall
工况 阶段 降雨强度（mm/h） 降雨历时（h） 一 1-1 18 12 二 2-1 10 4 2-2 25 4 2-3 50 1 2-4 13 2
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表 8 斜坡稳定性等级划分
Table 8. Classification of slope stability
稳定性系数(Fs) 稳定性等级 Fs < 1.0 不稳定 1.0≤Fs < 1.05 欠稳定 1.05≤Fs < 1.25 基本稳定 Fs≥1.25 稳定
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