草本植物根系对喀斯特边坡浅层稳定性的影响

Effects of herbaceous plant roots on the stability of shallow layer on karst slopes

为明确草本植物根系对喀斯特边坡浅层稳定性的影响规律,在重庆酉阳选取典型喀斯特坡地分上、中、下坡位种植沿阶草(Ophiopogon bodinieri H.)和拉巴豆(Dolichos lablab L.),并以裸地为对照,取样测定土壤性质和根系性状,利用无限边坡稳定分析模型计算边坡安全系数,通过建立结构方程模型确定影响边坡稳定的关键根系性状。结果表明:(1)沿阶草和拉巴豆处理的边坡安全系数较对照分别提高了149.97%—179.96%和52.27%—75.53%,二者提高效果最优的坡位分别是下坡和上坡;(2)两种草处理的土壤粘聚力是对照的1.97—5.11倍,沿阶草的根质量密度显著大于拉巴豆,是拉巴豆的2.78—5.99倍;(3)土壤粘聚力与边坡安全系数相关性最强,二者呈对数函数关系,结构方程模型表明根质量密度是影响边坡稳定的关键根系性状。研究认为喀斯特坡地上坡宜选择直根系草本植物,而下坡宜选择须根系草本植物,且根系质量密度大的植物有利于边坡稳定。本研究可为科学应用草本植物解决喀斯特坡地边坡失稳提供理论依据。

Plant roots play an important role in preventing and controlling slope instability.This study was conducted on a typical karst slope in Youyang Tujia and Miao Autonomous County,Chongqing to determine the effects of herbaceous roots on the stability of shallow layer on slopes.Ophiopogon bodinieri H.and Dolichos lablab L.were planted on the up-,mid-,and down-slopes,and bare soils corresponding to these slope positions were selected as the control(CK).Composite soil samples were collected and tested for soil properties.Root-soil composites were sampled and subjected to the direct shear tests,and then roots in these composites were picked and measured for root mass,root length,root surface area,and root volume.Slope stability factors of safety were calculated using the infinite slope stability analysis model.The key root traits affecting slope stability were determined by the structural equation model.The results showed that:(1)Ophiopogon bodinieri H.and Dolichos lablab L.improved the stability of shallow layer on slopes and the former with a fibrous root system performed better than the latter with a tap root system.Compared with CK,the slope safety factors of Ophiopogon bodinieri H.and Dolichos lablab L.increased by 149.97% to 179.96% and 52.27% to 75.53%,respectively.The maximum increment of the slope safety factors occurred at the downslope for Ophiopogon bodinieri H.and the upslope for Dolichos lablab L.(2)The roots of Ophiopogon bodinieri H.and Dolichos lablab L.increased the soil cohesion but did not significantly affect the soil internal friction angle(P>0.05).The soil cohesion of Ophiopogon bodinieri H.and Dolichos lablab L.was 1.97 to 5.11 times higher than that of CK.The root mass density of Ophiopogon bodinieri H.was 2.78 to 5.99 times higher than that of Dolichos lablab L.(3)The correlation between soil cohesion and slope safety factor was the strongest(r=0.95,P<0.01),and their relationship could be described by the positive logarithmic function(R2=0.91,P<0.01).The structural equation model showed that root mass density was the key root trait affecting the stability of shallow layer on karst slopes,with a standardized path coefficient of 0.85(P<0.01).The optimal slope stabilization effect of herbaceous plants with a tap root system occurs on the upslope and that of herbaceous plants with a fibrous root system occurs on the downslope.Additionally,herbaceous plants with high root mass density are beneficial for slope stability.Our study can provide a theoretical basis for the scientific application of herbaceous plants on controlling karst slope instability.