Analysis Of Soil Reinforcement By Plant Roots Based On Asymptotic Homogenization Theory

Tight combinations between the roots of vegetation and soil particles form a natural composite material with a certain degree of spatial heterogeneity,which can not only effectively reduce the erosion of runoff on slopes,enhance the stability of slope deposit,but also improve the local ecosystem.Research has been done to analyze the root system holding soil and improving the safety factor of accumulation,but the coupling mechanism of root system and soil needs to be further explored.Most of the existing theories are based on the model of single root or root bundle,so it is difficult to estimate the reinforcement effect of a large number of roots on the soil,and most of them belong to the weak coupling mechanism,lacking of high-precision and practical simulation modeling methods.Based on the current situation of this study,several drought resistant dominant shrubs,grasses and trees in Jixian District of Shanxi Province were investigated.It was found that the root system not only has the characteristics of vertical and deep growth,but also some vertical roots of plants present a uniform arrangement state in the slope profile,forming a long fiber composite material with periodic distribution.According to the simulation technology of reinforced concrete,this paper constructs the strong coupling mechanism between roots and soil,and explores the mechanical mechanism of plant root slope stabilization by using plane "single cell" model,numerical simulation model and composite triaxial compression test.Based on the theory of periodic structure and homogenization,the composite crosssection is selected as the "unit cell" to construct the generalized plane strain element,and the gain effect of the root system on the soil is obtained through the plane unit cell numerical calculation.In order to verify the accuracy of the "cell" in practical application,the triaxial compression test of root soil complex was designed with Robinia pseudoacacia root,Platycladus orientalis root and Pinus tabulaeformis root collected from Shanxi experimental site as test materials.Because the experiment aims to verify the results of numerical calculation,the remolded soil method,which is more suitable to the theory of this paper,is chosen to make the test pieces,including the plain soil and the composite.Through the test of shear resistance of soil samples,the failure mode and stress change rule of specimens under different root adding modes are analyzed.The parameters obtained from the experiment are brought into the root soil complex "single cell" for comparison,as prepare for the numerical calculation of facade slope.In order to develop the multi-scale coupling mechanical model of the slope with roots,this paper attempts to reveal the soil consolidation mechanism of the slope with forests from the perspective of periodic composite materials.The influence of tree root system on the mechanical properties of shallow slope was analyzed by solid element and homogenization.Finally,the slope stability with a large number of roots is estimated by numerical simulation,which provides theoretical basis for slope protection and afforestation.The results are as follows:(1)Based on the constitutive equation of root-soil complex,this thesis successfully established a planar “composite unit cell” simulation model using finite element method.The influence of elastic modulus,cell size and other factors on the ultimate load is compared,and the accuracy of this method is further confirmed by triaxial test.(2)Through the establishment of a slope model without the roots of vegetation and a slope model with the roots of vegetation,it was proved that Elymus and arbor root systems can improve the stress field of the shallow soil of the slope and make the shear stress in the root distribution area more evenly and the shallow layer of the slope tends to be more stable.(3)Compared with the slope model with solid root system,the homogenized slope simulation model proposed in this thesis has similar accuracy,but greatly reduces the model calculation workload(saving about 95.58% of the number of units).(4)When the slope of the slope is small(the slope angle is 30 °),the safety factor of the grassless slope is large(F = 4.28),and the stability of the root system on the slope is small(only an average increase of 2.92%);When the slope angle was increased to 45°,the safety factor of grassless slopes decreased to 2.90,while the average safety factor of grassy slopes increased by 13.45%,and the root soil fixing effect was more significant.(5)Three-axial compression test was conducted on the root systems of Chinese pine,prorobinetinidin and Chinese arbor-vitae,and the error between the theoretical model and the test results was only 4.9 ? 13.3%.The error may be due to the existence of a few curved edges in the test piece,which also shows that the square plane "unit cell" model in this paper is a good applicability and high accuracy.