Dynamic Effect Of Plant Roots On Soil Reinforcement And Slope Protection Under Earthquake

As an environment-friendly ecological slope protection technology,vegetation slope protection has been widely used in the wound repair of many natural slopes and engineering slopes in southwest mountainous areas.It has been widely agreed that the shallow root reinforcement,deep root anchorage and lateral root traction of plants can improve the stability of slope under static conditions.However,few studies have been carried out on whether vegetation slope protection can effectively improve the stability of slope under earthquake.There are fewer studies on the seismic stability of slope protection by collaborated vegetation and engineering.However,with the deepening of the western development strategy and the construction of the Sichuan-Tibet Railway,it has been exposed that the shallow protection of engineering wounds in high intensity earthquake areas and the corresponding seismic design methods are the blind spots of previous research,so it is necessary to study them.On spatial and temporal scales,dynamic effect of shrub plant roots on soil reinforcement and slope protection under earthquake were studied through indoor geotechnical test,largescale shaking table test,numerical simulation and theoretical analysis.Aiming at the tension failure form found in the seismic failure of shallow overburden slope,the traction mechanism of lateral roots of shrubs was studied based on the self-developed uniaxial tensile test device.On the basis of revealing the deep root anchorage mechanism of shrub plants under earthquake,the large-scale shaking table test and theoretical analysis of the slope protection by collaborated vegetation and bamboo frame beam were carried out.The working mechanism of the collaborative slope protection and the seismic performance of the ecological frame structure integrating plant roots were discussed.The research results of this paper can provide a reference for revealing the dynamic interaction between root and soil and fully considering the contribution of plant root in the seismic design of ecological protection structures in highintensity earthquake areas.The main research results and conclusions of this paper are as follows:(1)A new uniaxial geotechnical tensile test device with programmable control was developedA self-developed uniaxial tensile test device was used to carry out the direct tensile tests of sandy cohesive soil and root-soil complex of shrub plant Lespedeza.The test device can accurately obtain the entire process displacement-tensile stress relationship curve and the tensile strength of test material.For the sandy cohesive soils,a nonlinear failure criterion was proposed that can account for soil tensile and shear strength at low normal stress levels.For the root-soil composite,the tensile failure mechanism of the root-soil composite was analyzed,and the enhancement effect of the root system on the tensile strength of the soil was quantitatively studied.(2)The seismic response characteristics of shallow overburden slope protected by shrub vegetation were revealedThrough the shaking table test of the shallow overburden slope protected by shrub vegetation,taking the unprotected shallow overburden slope as the control group,the acceleration response and slope crest deformation of the vegetated slope under earthquake were analyzed in time domain.The transmission characteristics of seismic wave energy in vegetated slope were discussed from the perspective of time-frequency domain.The oblique incidence of seismic waves in a homogeneous two-dimensional half-space field was realized in ABAQUS finite element software based on wave field separation theory.The most unfavorable incident angle of the shallow overburden slope protected by vegetation under the actions of SV wave and P waves was obtained.(3)The calculation method of energy consumption for the stability of shallow overburden slope protected by shrub vegetation were proposedBased on the shallow translational failure model considering boundary effect,the calculation formulas of dimensionless stability coefficient and yield acceleration of shallow overburden slope were derived by using the upper bound method of limit analysis.The validity of the proposed calculation method was verified by comparison with the calculation results of infinite slope model and the finite element.Considering the anchoring effect of plant roots,the calculation formulas of dimensionless stability coefficient and yield acceleration of the shallow overburden slope protected by shrub vegetation were deduced.The variation law of vegetated slope stability factor and root contribution rate with horizontal seismic force coefficient was obtained.(4)The seismic response characteristics of the shallow overburden slope reinforced by bamboo frame structure integrating plant roots were revealedTwo groups of large shaking table model tests of the shallow overburden slope reinforced by bamboo frame structure integrating plant roots and the shallow overburden slope reinforced by single bamboo frame structure were carried out.The characteristics and differences of acceleration,displacement and spectrum responses of underlying stable slope,overlying shallow sliding body and frame structure were studied.The seismic failure mode of the shallow overburden slope protected by collaborated vegetation and bamboo frame beam and its relationship with slope dynamic characteristic parameters were revealed.The characterization and evaluation ability of different ground motion intensity indexes on the dynamic response of the shallow overburden slope protected by collaborated vegetation and bamboo frame beam were explored.(5)The calculation method of time-varying stability of shallow overburden slope reinforced by bamboo frame structure incorporating plant roots were proposedBased on the translational instability model of the infinitely long slope,the time-dependent growth models of plant roots and the time-dependent calculation model of anchoring force were introduced.Taking the bamboo frame reinforcement unit as the research object,the interaction analysis between the cooperative slope protection measures and the shallow sliding body were carried out.The calculation formulas for the static and dynamic time-varying stability of shallow overburden slopes reinforced by different protective measures were established.The stability variation law of the shallow overburden slope reinforced by the bamboo frame structure incorporating plant roots under the influence of time factor was explored.