Research On Mechanism And Effect Of Natural Soil Arching On Spoon-shape Landslides

All kinds of geological disasters,especially slope failure take place frequently in Sichuan Province,located in the southwest of China,due to the geomorphic features of the mountainous and hilly landform as well as the effects of rainfall,earthquake and human activities.Stable piles have the advantages on convenient construction and valid resistance,thus have been widely used in practical engineering.When stable piles are applied to support slopes,the soil arching occurring between piles has an important influence on the stability of the slope.When treating the landslides with spoon-shape topography,the nature soil arching produced by the special topography should be taken account for it can act as part of resistance force and has great effect on the overall stability of the landslide.In order to study the mechanism and effect of natural soil arching on spoon-shape landslides,first,the generalized mechanical model was established based on elastic theory to prove the existence of natural soil arching in such landslides;then,Lizixiang spoon-shape landslide was taken as an example to conduct numerical simulation by FLAC3D.The main research contents and results are as follows:(1)The existence of natural soil arching in spoon-shape landslides was proved by the stress analytical expressions,derived from the mechanical analysis model,of arbitrary point located behind the narrow part of the landslide.The variation of soil arching effect shows that the phenomenon of soil arching only appears under the condition of a certain open degree of the topography.There is significant stress concentration phenomenon when the necking angle is between 20 to 40degrees,otherwise,the soil arching will quickly weaken even disappeared.(2)The increase of pushing pressure and frictional resistance would have a great effect on the soil arching occurring at the narrow part of the special topography,and the stability of the landslide would be improved significantly when the pushing pressure is between 200kPa?400kPa and the frictional resistance is less than 300kPa.(3)Compared with the circular and parabolic shape of soil arching between piles,the shape of the nature soil arching in spoon-shape landslide has different features,With the gradual change of the depth of the slope and the boundary of the narrow part,it is adjusted to fit the changing stress.The shape of the nature soil arching is an irregular horseshoe shape,which is one of the most remarkable characteristics of the natural arch in the landslide.(4)The effective depth of soil arching effect in the landslide is between z=69m and z=61m,where the soil arching is stable.The effect of soil arching on the stability of landslide will decrease gradually when the range of effective depth is exceeded.The effective area of soil arching in Lizixiang landslide is 80m to 140m in x-direction and 20m to 80m in y-direction,respectively,which is critical to the stability of the landslide.The natural soil arching can be fully utilized in later Landslide prevention.Based on the above conclusions,the research has important theoretical value and engineering application prospect.