Experimental Investigation On The Stability Of Colluvium Slope Reinforced By Umbrella-shaped Anchor Under Rainfall Condition

Colluvium layer is common in most large-scale hydropower engineering construction.Under the influence of rainfall,earthquake,human activity and other factors,it is very easy to occur instability phenomenon and produce colluvium layer landslide.As one of the most dangerous types of landslides in China,the colluvium landslides not only have a large number,but also have a relatively large scale,which often cause huge economic and property losses.Therefore,it is very necessary to control and prevent colluvium landslides,where the bolt reinforcement technology is widely used in various projects.In the anchoring technology,due to the end expanding bolt can increase the uplift bearing capacity,many scholars have developed their design concept in a new direction.As a result,new umbrella-shaped anchors have been proposed.Based on the project background of the Cangjiangqiao-Yingpan Colluvium slope,this thesis analyzed the climate and engineering geological conditions of the research area.Relying on the national key research and development plan "the mechanism of collaborative evolution of major landslide and anchorage system"(Project No.: 2017YFC1501300),scale model test as well as modern analysis and monitoring methods are adopted upon the colluvium slope reinforced by umbrella-shaped anchors under the condition of rainfall to monitor and study the slope change,temperature change,soil pressure and pore water pressure change.The main work and conclusions are as follows:(1)In the Cangjiangqiao-Yingpan landslide project area,rainstorm occurs all year round,gullies are obvious in some areas,and secondary landslides occurred.Therefore,reinforcement treatment should be carried out in the study area to control the stability of the slope in the colluvium layer.According to this engineering case,a scale model test equipment was developed,and the model tests for different anchorage conditions of shallow landslide and bedding landslide were designed and completed.(2)The results of rainfall scale model test showed that the rainfall infiltration accelerated the deterioration of the soil and promotes the occurrence of slope instability.The test results of rock anchoring showed that the study area selected in the test was not easy to occur bedding landslide along the soil rock contact surface,and the results was not obvious.The test results of soil anchoring showed that shallow landslide occurred in the area without umbrella-shaped anchors.With the disturbance and erosion of rainfall,the lateral and liner erosion of rainwater would form gullies on the slope surface,which was consistent with the gullies found in the field research,then slope instability mode was developed from shallow landslide turned into debris flow.(3)The results of monitoring and excavation showed that the grouting slurry can combine anchors and soil particles to form an anchorage system.In the process of rainfall,the self-weight and pore water pressure of soil mass increase due to rainwater infiltration.In the process of downward movement of water,the anchorage system moved simultaneously.Meanwhile,the umbrella-shaped end at the front of the anchor system reacted with the soil mass,exerting active soil pressure on the soil mass to control the pore water pressure of the soil by changing the porosity of the soil,and maintain the overall stability of the slope.During the continuous rainfall,the anchorage system of umbrella-shaped anchor and colluvium slope could continuously and dynamically act on the soil behind,resist the deterioration effect of rainfall on the soil,and dynamically control the continuous stability of the slope.(4)Through the stability calculation of the scale model slope and sensitivity analysis of each factor against the safety factor of the slope stability,the influence of different factors on the slope stability was determined,the changes of different factors on the slope was discussed,and the calculation method of the safety factor of the stability of the anchorage system was put forward after the reinforcement by umbrella-shaped anchors.The paper includes 72 figures,15 tables,and 133 references.