| Plant slope protection,as an engineering technology that combines slope reinforcement and environmental protection,is widely used in slope management.However,the current research mainly focuses on the influence characteristics of the root system on the root-soil composite,while the influence of the root system in the soil-rock mixture is less studied.In order to explore the strength characteristics of the root-soil-rock composite,digital image processing technology was used in this study to simplify the calculation of soil and rock content on the shear surface,and obtain the distribution pattern of the root system along with the soil layer according to the field profile.Combined with the root area ratio and rock content,the influence of root content on the shear strength of root-soil-rock composite was explored by using the improved direct shear test instrument.the variation characteristics of the shear strength of root-soil-rock composite under different rock content were explored.The variation of cohesion and internal friction angle of root-soil-rock composite was summarized..Based on the existing mechanical model,the maximum static friction at the root-soil interface and the unit frictional resistance at the root-soil interface was used to calculate the improvement range of the root system on the shear strength of the root-soil composite.Finally,the influence of the root system on the displacement and safety coefficient of the slope of the root-soil-rock composite was analyzed based on the strength discount method using FLAC 3D software,and the main research results and conclusions obtained are as follows:1)The shear strength of the root-soil composite,soil-stone mixture,and root-soil-stone composite increased linearly with the increase of positive stress when the root content and rock content were certain,and all of them were following the Coulomb strength criterion.Malus halliana Koehne roots can increase the shear strength of the root-soil-rock composite.2)The roots mainly improve the shear strength of the root-soil-rock composite in two ways.One is to use the flexible performance of the roots to resist shear deformation.The other is that the existence of the roots makes the rap rock slip in the shear,thereby increasing the displacement of the shear failure.However,with the increase of root area ratio,the number of roots increases,which accelerates the expansion of through cracks.When the root area ratio is greater than 0.2 %,the shear strength of root-soil-rock composite decreases.3)The internal friction angle of the root-soil-rock composite increased with the increase of rock content,and the change in root area ratio was not obvious.The cohesive force increased and then decreased with the increase of root area ratio,and the change in rock content was not obvious.Indicating that the internal friction angle of the root-soil-rock composite was mainly influenced by the rock content,and the cohesive force was mainly influenced by the root content,and the increase of root system on the shear strength of the root-soil-rock composite was mainly manifested by the increase of cohesive force.That is,the root system mainly improves the shear strength of the root-soil-rock composite by reinforcement effect.4)Under different rock content,the maximum static friction of a single root all showed a trend of increasing with the increase of root diameter.The frictional resistance at the root-soil-rock interface was all greater than that at the root-soil composite.It means that the root system had a better effect on enhancing the shear strength of the root-soil-rock composite than that of the root-soil composite.5)The measured shear strength of the root-soil-rock composite is within the range of the theoretical calculated values of the root-soil-rock interaction mechanical model,and the obtained results correspond to the shear test.And the theoretical calculated values do not differ much under different RAR,which also show the rule that the maximum value is reached at RAR=0.2%,and the growth rate of the theoretical calculated values is higher at30% of rock content than at 50% of rock content.This mechanical interaction model also indicates that the mechanical model can be combined with frictional resistance to calculate the range of increase in shear strength of root-soil(rock)composite by the root system without fracture,which provides theoretical support for assessing the stability of vegetated slopes.6)The root system can reduce the horizontal displacement and vertical displacement of the slope,in which the reduction of horizontal displacement is 16.2%～51.5% and the reduction of vertical displacement is 14.8%～49.5%.The influence of the root system on the safety coefficient of the slope is small,and the improvement of the safety coefficient of the slope under different rock content is only 0.9%～1.1%.According to the change of plastic zone,it is known that the shear damage of the slope occurs in the deep weak part of the slope.The root system only has a traction effect on the surface soil and cannot radiate to the deeply damaged surface,so the root system mainly plays a limiting role in the displacement of the surface soil,and should be considered in the actual slope management in combination with engineering measures. |
