Influence mechanism of vegetation infiltration effect on shallow landslides of granite residual soil
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摘要:
华南地区台风暴雨诱发的滑坡往往呈浅层、流态化、群发性等特征，大量调查发现植被增渗效应对花岗岩残积土滑坡的形成具有显著影响，但目前研究大多探讨植被根系对土体渗透性的影响，未能揭示植被增渗效应对浅层滑坡的影响机理。基于此，以“2019.6.9”广东省龙川县群发性滑坡灾害为例，通过大量现场勘查，查明滑坡区域地质环境条件与植被发育情况，分析植被对浅层滑坡的增渗效应；采用“双环入渗法”测得不同植被样地的入渗速率，分析其下渗过程和渗透规律；选取典型滑坡剖面，建立地质模型，运用Geo-Studio软件对强降雨条件下浅层滑坡渗流规律和土体应力-应变特征进行模拟；最后结合模拟结果和现场调查情况，分析强降雨条件下植被增渗效应对浅层滑坡的影响机理。结果表明：植被能够有效地增强土壤渗透能力，渗透能力大小依次为针叶林地、灌木林地、裸土地；在植被增渗效应影响下，雨水入渗到根土复合层底部会发生滞水现象，浅层土体迅速趋于饱和，土体中孔隙水压力及渗流力瞬时剧增，土体饱水使得残积土发生软化，同时边坡自重增加，最终导致斜坡失稳。研究结果可为华南地区暴雨群发性滑坡的形成机理、预警预报等提供科学依据，具有重要的意义。
Abstract:The landslides induced by typhoons and rainstorms in Southern China are often shallow, fluidized and clustered. A large number of investigations have shown that vegetation infiltration has a significant impact on the formation of granite residual soil landslides. However, most of the current studies have focused on the effect of vegetation roots on soil infiltration. The influence mechanism of vegetation infiltration enhancement effect on shallow landslides has not been revealed. Therefore, the mass landslide disaster on September 9, 2019 in Longchuan County in Guangdong is taken as an example, and a large number of landslide site investigations are made to identify the geological environment conditions and vegetation development in the landslide area and analyze the infiltration effect of vegetation on shallow landslides. The “double-ring method” is used to measure infiltration rate of different vegetation types, and to analyze the infiltration process and infiltration law of different vegetation types. A typical landslide profile is selected to establish a geological model, and the Geo-Studio software is used to simulate the seepage law of shallow landslide and the stress-strain characteristics of the soil under heavy rainfall conditions (250 mm/d). Finally, combined with the simulation results and field investigations, the infiltration effects of vegetation and their response mechanisms to shallow landslides under heavy rainfall are analyzed. The results show that vegetation can effectively enhance the permeability of soil, and the order of permeability is coniferous forest land, shrub forest land and bare land. Under the influence of vegetation infiltration effect, rainwater infiltration to the bottom of the root-soil composite layer will cause water stagnation, the shallow soil tends to be saturated rapidly, the pore water pressure and seepage force in the soil increase instantaneously, the soil is saturated with water, the residual soil softens, and the weight of the slope increases, which eventually leads to the overall instability of the slope. The research results explain the formation mechanism of granite residual soil landslide in high vegetation covered area under heavy rainfall in Southern China, and provide scientific basis for early warning and prediction of such disasters, which are of great significance.
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表 1 岩土体相关物理力学参数
Table 1. Physical and mechanical parameters of soil and rockmass
层序号 岩土体名称 重度/（kN·m−3） 黏聚力/kPa 内摩擦角/（°） 渗透系数/（m·s−1） 饱和含水率/% 弹性模量/MPa 泊松比 1 根土复合层 19.1/19.6 45.8/25.7 22.3/19.5 3.78×10−4 27.7 22.6 0.31 2 砂质黏土 19.1/19.6 36.4/16.3 22.3/19.5 2.34×10−5 27.7 22.6 0.31 3 全风化花岗岩 19.1/19.6 34.2/18.8 21.8/17.6 6.59×10−6 26.8 26.1 0.29 4 强风化花岗岩 19.8/20.6 43.4/25.6 27.4/21.9 5.50×10−6 25.3 39.4 0.27 5 中风化花岗岩 22.0/22.2 200.0/140.0 35.0/30.0 1.23×10−7 5.0 1 000.0 0.31 注：19.1/19.6，斜线左为天然条件下的参数，斜线右为饱和条件下的参数。 
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表 2 3种不同植被样地入渗性能比较
Table 2. Comparison of infiltration performance of three different vegetation plots
样地类型 初渗速率/（mm·min−1） 稳渗速率/（mm·min−1） 样地1 样地2 样地3 样地1 样地2 样地3 针叶林地 36.24 35.05 34.87 6.38 5.70 5.62 灌木林地 22.82 22.75 25.02 2.91 3.08 3.05 裸土地 15.49 16.13 14.77 1.67 1.81 1.81
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