Study On Mechanism Of Loess Landslides Caused By Erosion In Yan’an District

The erosion-induced loess landslide is a typical landslide in the loess plateau. It hasimportant practical significance to do some research on its mechanism.The field investigation in north of Shannxi shows that most shear export of largelandslide are on the terraces of rivers, the small loess landside happens at two sides ofV-shaped valley. This is showed with8typical landslides in this paper.The relationshipbetween the landslide development cycle and the river terraces is analyzed combining theformation of river terraces in north of Shannxi. The result shows that when the tectonicmovement is stable,the two sides of river is eroded, the terraces is formed and large-scalelandslides happened;through the uplifted terrain, rivers cut vertically, the next level terracebegin to form and small loess landside happens. If the tectonic movement is alternately stableand uplift, levels of terraces formed, large-scale landslide and small loess landside happenintermittently.Taking Anli landslide, Yintaishan landslide, Luochuan landslide as examples, this paperdiscusses the initiation mechanism, establishes finite element models at different stage causedby headward erosion before sliding through finite element method, and calculates the stressand strain fields in each stage. On this basis, the shear stress, normal stress and shear strengthon the final sliding surface in every model are obtained. The stability factors are also acquiredby limit equilibrium method. The result shows that, with the deepening headword erosion, theshear stress on sliding surface increases constantly; but the shear strength decreasesconversely. The stability of the whole landslide never reduced until failure. The experimentalresult shows that, the low-strain can produce a significant excess pore water pressure insaturated loess. Therefore, the excess pore water pressure in saturated sliding zone fosters thefailure of this landslide. Comparing the shear stress and the shear strength, the erosion-induced landslide has a failure from the foot to the back part gradually. Therefore, this kind oflandslides has characteristics of traction damage.The apparent friction strenth by K.Sassa is successfully used to analyse the mechanicscharacter of undisturbed specimen in traxial test and explan the performance of strenth’spelter of soil during the prosess of insect before destory, which provides a applicable theoreticalmethod for the mechanism of such loess landslides.