Study On The Formation Mechanism Of Loess Landslide Triggered By Excavated Slope

Plateau is the natural testing ground to carry out the research of hazard effects ofhuman activities on the environment. In recent years, With the implement of WesternDevelopment Strategy, social economy in the Loess Plateau develops rapidly, humanactivities increasing frequently, thus, engineering loess landslide hazards growing seriously,which becomes an important factor blocking economic development of the Loess Plateau.By aiming at excavation-induced mechanism of loess landslide, setting Yan’an Liuwanjiagou landslide as research subject, and field investigations, landslide deformation aswell as failure characteristics are analyzed in this paper. Combing indoor stress path tests,the deformation characteristics and mechanical behavior of landslide soil under unloadingstress path are also studied. Based on these, genetic mechanism of excavation-inducedlandslide is discussed in depth. Conclusions are as follow:(1) Undisturbed loess triaxial shear tests show: The shear strength of Q2loess in studyarea increases with depth, and the initial deformation modulus also presents anincreasing trend; Q2loess in study area shows a strong strain softening characteristics; InCTC stress paths, samples’ volumetric strains show a significant volume contraction, andthe initial consolidation pressure has little effect on the volumetric strain, when samplesdestroyed, their volumetric strains become almost equal.(2) Under the conditions of isobaric and K0consolidation, RTC tests of saturated andundisturbed loess show that different consolidation conditions have different impacts onloess nature, which mainly reflect in the differences of strengths and volumetricstrains.The same points of the two kinds consolidation tests are: stress-strain relationshipsof both are showing weak strain softening characteristics; when the axial strain is less than1%, sample has slight volume contraction, as axial strain increases, volumetric strain showsan obvious dilatancy feature; but under low confining pressure(100kpa), volumetric strainonly exhibit dilatancy. The different points are: peak strength in K0consolidation state issignificantly higher than isobaric consolidation, while dilatancy trend showed in volumetricstrain curve is less obvious than that, what’s more, its overall volumetric strain would belower.(3) The study of landslide mechanism shows that excavation and rainfall are the mainexternal factors caused landslide, and the inherent nature of loess as well as the existence of relatively impermeable layer are internal factors. Genesis process of that can be expressedas follow: Toe excavation, local damage of soilâ†'Trailing edge slope cutting, increment ofstabilityâ†'Continuous excavation, steepening of toeâ†'toe damage and upwardextensionâ†'emerge of crest fissuresâ†'â†'Anti-sliding segment damage, slope becomesinstabilityâ†'fissures appear after slidingâ†'Fissures extension under rainfall, sustaineddeformation of landslide.