| The shear strength of soil is an important index to characterize the stability of slope soil.It is of great significance to study the shear strength of slope soil for soil and water conservation and slope stability protection.The differences in forest vegetation types lead to differences in forest vegetation root characteristics and soil physical and chemical properties,and become important factors affecting soil shear strength parameters.This study takes the evergreen broad-leaved forest,coniferous and broad-leaved mixed forest and shrub-grass forest in the Fengyangshan National Nature Reserve of Zhejiang Province as the research object,through field investigation,fixed-point observation,indoor experiment and other means,the effects of plant root characteristics and basic physical and chemical properties of soil on soil shear strength parameters were studied.The research results are as follows:(1)There was a significant negative correlation between soil capillary porosity(CAP)and soil cohesive force(P<0.05).Soil non-capillary porosity(NCAP)and total porosity(SAT)were significantly negatively correlated with soil internal friction angle(P<0.05).There was a positive correlation between soil pH and shear strength parameters.There was a significant positive correlation between soil clay and soil cohesive force(c)(P<0.05).Soil silt,clay and sand were negatively correlated with soil friction angle(P<0.05).(2)Slope soil shear strength parameters(Internal friction angle ? and cohesion force c)are closely related to vegetation types.The degree of influence of the root characteristics of each vegetation type on the internal friction angle is Root length density(RLD)>Roots surface area density(RSAD)>Roots volume density(RVD)>Roots weight density(RWD).RSAD,RVD and RWD show a positive correlation with the internal friction angle within a certain range.The degree of influence of root characteristics of each vegetation type on the cohesive force is RWD>RLD>RVD>RSAD.RLD and RWD are positively correlated with soil cohesive force within a certain range.(3)There was a significant positive correlation between soil cohesive force(c)and dry bulk density(P<0.05),and a significant negative correlation with water content(P<0.05).There was a significant positive correlation between internal friction angle(?)and dry bulk density(P<0.05).The slope stability coefficient Fs is affected by the soil water content,and decrease with the increase of soil water content.In the evergreen broad-leaved forest,the soil water content reached more than 45%in May,June,and November of 2018,and the slope was in an unstable state;When the soil water content exceeds 39%,the slope soil of the coniferous and broad-leaved mixed forest is unstable.The slop soil is basically stable in the whole year;when the soil water content exceeds 48%,the slope is unstable,and in 2018,there is a dangerous period of possible landslides throughout the year.(4)Under the same water content,the dry bulk density has an enhanced effect on the cohesive force of the three types of soil,and pd-lnc is linearly positively correlated.Considering the combined effect of dry bulk density and water content on soil shear strength,an empirical formula for soil cohesive force is established.Multiple regression analysis was carried out on the influence factors of three vegetation types and the internal friction angle of the soil.It was found that silt,capillary porosity(CAP),root volume density(RVD)and soil water content became predictors of soil internal friction angle.The prediction equation of shear strength variation is established to provide a reliability reference for slope stability prediction and slope remediation.The prediction equations for shear strength of different vegetation types are:Prediction equation of shear strength of shrub-grass forest:(?)Prediction equation of shear strength of coniferous and broad-leaved mixed forest:(?)Prediction formula for shear strength of evergreen broad-leaved forest:(?)... |
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