Study On Pile-soil Contact Effect Of Anti-sliding Piles In Swelling Soft Rock Landslide Of Wangqing-yanji Highway

The swelling soft rock landslide in Xinyan section of the Wangqing-Yanjihighway is called Xinyan landslide. For many years, the landslide always slides afterits prevention, which blocked the normal operation of the highway. The fieldinvestigations show that the geological characteristics of the Xinyan landslide withthe layer of Tertiary hunchun formation sedimentary rock and quaternary looseaccumulation. The slip mass of Xinyan landslide possess low shear strength andexpansive characteristic.The deformation of Xinyan landslide is a very complicated process and aintegrated response to various factors. The deformation and damage mechanism canbe interpreted by the following contents: the embankment of Xinyan landslide iscomposed of swelling soil with low consolidation/cementation degree and largenumbers of cracks. The main clay mineral is montmorillonite, which will expandwhen absorbing water and contract when losing water. Drying and wetting cycle willproduce a large number of cracks leading，this will decrease shear strength of soils. Asa result of roadbed filling, the terrain will become steeper, which provides favourableconditions for landslide occurrences. The fill located in the rear of the landslide, thiswill change the original stress balance condition. Because of these factors, stressconcentration phenomenon will easily occurred in slope foot of the fill subgrade andgradually extend inward, forming a stepwise landslide. The failure is degressive fromthe roadbed slope foot to the pavement.The mechanism of the anti-slide piles reinforcing landslide is transferring theresidual downslide thrust to the stabilized soil layers mainly through the interactionbetween the pile and soil surrounding the piles. Under the action of bond force andfrictional resistance between particles, the soils between anti-slide piles can form the soil arching similar to the top of tunnel and bridge arching, called the "soil archingeffects”. At present, there are two kinds of methods used for explaining thetransferring mechanism of downslide thrust from the soil arching between adjacentanti-slide piles.In Xinyan landslide, the main factors influencing the forming of the soil archingis the shear strength parameter of slip mass, expansive force and roughness of thesoils between anti-slide piles. Based on the fully knowledge of the geologicalconditions, the genetic mechanism of Xinyan landslide, and the site topography, a3Dgeological model with width of40m is established and simulated the anti-slidereinforcing process to study both the mechanism of pile-soil mass interaction and theinfluence factors. The soil arching under the influencing of different factors issimulated. The research results shown that the bigger the cohesiveness and the angleof internal friction, the stronger the soil arching effects. However, the sensitivity washigher when they were small. Therefore, we should pay attention to the weakeningeffect of the soil arching effects in soil masses with low shear strength.The more rough the pile soil contact surface, the more obvious the soil archingeffects. However, the impact is very small. The arching effects can be used as asecondary factor when the impact is small. The larger the pile space, the smaller thesoil arching effects. The expansive force has a heavy influence on soil arching effects.The soil arching effects is weakened and disappeared completely with the increase ofexpansive force. Thus, in expansive rock soil areas, the adverse impact of expansiveforce should be considered when designing the anti-slide piles.