The Simulation Study On The Mechanics Of Soil Reinforcement And Erosion Resistance From Robinia Pseudoacacia In Debris Flow Valley In Bailong River Basin

Bailong River Basin is famous of its widely distributed and frequently happened geohazards and is listed as one of the four major areas that is attacked by geohazards in China.Vegetation can reinforce soil strength and increase erosion resistance,and play an important role in controlling mountainous geohazards such as landslide and debris flow.Quantitative study the ability of vegetation root in reinforcing soil is the key in applying vegetation to disaster prevention.However,current researches are still not abundant in this field.At present,the disaster prevention and control methods in the study region is civil engineering,while main purpose of greening is still to improve the vegetation coverage.The use the vegetation in controlling soil erosion and geohazards have not been taken into consideration.Thus,the selection species is blind and the ability of vegetation in different location of the valley are not clearly studied.In deal with above problems,based on the existing research results,this paper is under the guidance of the theories of ecology,material mechanics,soil mechanics,hydraulics and soil and water conservation.In situ experiments,indoor tests and simulation analysis were accomplished by using Large-scale direct shear machine,universal testing machine and other equipment.As a result,the shear strength and the particle size distribution of the loose deposits in the channel and the slope were measured.Based on this,the mechanics of soil reinforcement and erosion resistance from vegetation was studied systematically.The main results are as follows:(1)The distribution characteristics and mechanical strength of the root of three greening species of Robinia pseudoacacia,Populus euphratica and Amorpha fruticosa in Bailong River Basin were investigated.Based on this,the pioneer species of ecological restoration were selected.Compared with other two species,Robinia pseudoacacia adapts to local environmental well,has high growth rate and has high tensile strength and extended range roots.Therefore,it is appropriate to use Robinia pseudoacacia as a pioneer species for disaster control in the region;(2)The effects of Robinia pseudoacacia on the stability of shallow landslide under different conditions were studied.The results showed that the stability of the slope was enhanced to the maximum extent,and the trees planted in the middle of the slope had little effect on the slope stability because of its root maybe above on the potential sliding surface.In general,although the root of Robinia pseudoacacia can increase the cohesion of the surface soil(the average increase of 15 kPa),and some of the roots can penetrate into the soil to produce some anchorage,the contribution of Robinia pseudounda to the overall stability of the slope is limited(contribution to factor of safty between 4 and 11%);(3)The effects of different age Robinia pseudoacacia forest on the low riverbank under debris flow in different intensities were studied.Based on the analysis of the distribution and intensity of Robinia pseudoacacia roots at different age(1 year,2 year and 4 years)on the low river bank,the BSTEM(Bank Stability and Toe Erosion Model)model was used to evaluate the stability effects under different vegetation protection.The results showed that the protective effect of the plant was gradually increased with the increase of the age and the bank protected by 4-year-old Robinia pseudoacacia forest could be stable in the debris flow with the peak flow rate of 73.06 m3 / s;(4)The effects of vegetation coverage on the runoff in the valley bed were studied.Based on the measurement of the valley bed,the virtual runoff field was constructed based on the cellular braided model of runoff and channel development.The effects of vegetation on the runoff were calculated.The results showed that with the increase of vegetation planting density,the runoff shape in the ditch bed will change from the current braiding flow to the meandering flow,and the width occupied by the water flow in the valley bed will be reduced by 18-24% on average;In conclusion,slope,river bank and valley bed are the main components of debris flow valley.The results of this paper show that the plants represented by Robinia pseudoacacia can play the role in soil reinforcement and erosion resistance in all three positions.With the growth of vegetation,such effects will increase.Therefore,it is suggested that Robinia pseudoacacia should be selected as the pioneer species of ecological restoration in this area.It is recommended that the trees are planted in slope,river bank and valley bed at in the density of 1.0 m × 1.0 m to make the best use of their ability in controlling geohazards such as soil erosion and debris flow.