Research On Failure Mechanism Of Rainfall Root-soil Slope Based On Centrifugal Model Test

In the process of rainfall-induced landslide destabilization of soil slopes,the change of moisture conditions is an important triggering factor.Among the landslide prevention and control measures,vegetation slope protection is widely used because of the advantages of low cost,environment friendly and landscape enhancement.However,there is no systematic research on the role of vegetation root system in reinforcing and consolidating soil and regulating moisture on slopes.In this paper,in the stability analysis of vegetation covered soil slope under rainfall conditions,we consider the influence of root system and rainfall on the physical and mechanical properties of soil moisture content and matrix suction on the shear strength of soil.The main methods are centrifugal tests and numerical simulations to study the process of rainfall runoff,scouring and infiltration during the rainfall of root-soil slopes,to study the mode of water transport inside the slope and the influence of the root system on the moisture field of the shallow soil of the slope,and to discuss the influence of the root system on the stability of the slope,and the main conclusions and understandings have been achieved.(1)Triaxial shear test was conducted on the sandy soil used in the centrifugal test to obtain the stress-strain relationship and shear strength index of the soil under different water content states.The experimental results show that the effective internal friction angle of this sandy soil varies between 28° and 31° with the change of water content,and does not vary much with the water content.The minimum and maximum values of effective cohesion are 1.81 k Pa and6.84 k Pa respectively,and the variation law is not obvious.(2)The damage patterns of sandy soil slopes with different root reinforcement under rainfall conditions were collected and analyzed by centrifugal model tests.Delineate the deformation and damage stages of root-soil slopes under rainfall conditions.It is found that the deformation of the root-soil slope under rainfall is significantly reduced,and the slope gully depth and slope damage are also lower.The root reinforcement plays a better role in limiting the horizontal displacement of the slope,and the depth of root reinforcement has more influence on the overall deformation of the slope than the size of the reinforced area.It has more influence on the overall deformation of the slope.(3)Comparing the difference of substrate suction and pore water pressure response rate at different depths,the effect of different root systems on water infiltration of slopes was investigated in terms of blocking and retaining effects.Among them,the retention effect of tap roots,plate roots and heart roots on slope reinforcement is higher than that of no root system.The retention effect of reinforced slope is increased by 9.7%,37.7% and 54.2%.(4)The water content of slope soil showed obvious response changes with following different rainfall stages.The transpiration effect of plate roots was shallow in depth,and the transpiration effect of tap root and heart roots was deeper and the depth of drying area was deeper because of deeper depth.The water regulation effect of the slope reinforced by tap root,plate root and heart root increased by 106%,76% and 134% compared with that of the slope reinforced by no root system.(5)In this paper,based on FLAC3 D platform,the unsaturated seepage field of rainfall and stress field of root-soil slopes written by the program to calculate the numerical simulation of rainfall root-soil slopes,and analyze the change law of water content in the calculation results.The mean values of water content at different depths at the end moment were used to evaluate the influence of different forms of reinforcement of root system on the slope moisture field.The moisture reduction of tap rooted slopes,plate rooted slopes,heart rooted slopes,double density of tap root and double density of tap-plate mixed reinforced slope compared with slopes without root reinforcement,and the resulting influence factors of roots on the slope moisture field were 1,1.85,1.63,2.53 and 2.61,which were consistent with the ratios of root surface area are basically the same,but differently affected by the depth of the root system,and the shallower plate roots bring more influence on the slope rainfall moisture content.(6)Summarizing the change law of horizontal displacement of slope during rainfall in the simulation calculation results,it is found that the horizontal displacement of slope follows the rainfall stage;and it shows stage change.The displacement rate is fast during the rainfall and slow after the rain stops.The displacement rate is slow when the rain stops.The displacement rate increases gradually with the number of rainfall days.The horizontal displacement of tap root,plate root,heart root system,double density of tap root and double density of tap-plate mixed reinforced slope decreased by 12.0%,6.0%,5.9%,17.6% and 11.8%compared with the slope without root reinforcement,and the greater root depth and density played a better role in limiting the slope displacement.