Stability Analysis Of Pile-Slope System Using Shear Strength Reduction Finite Element Method

The stability evaluation of the slope and the engineering problems of landslide treatment have been studied for a long history, but they are still hot topics in academic and engineering world because of their complexities and difficulties. The anti-slide pile is one of the most common measures for the slope reinforcement, but the theory and calculation method of anti-slide pile are not mature enough, so that there are still some problems which are not unified and clearly understanding. To explore the effect of anti-slide piles on slope stability and the failure modes, the displacement and internal force response of the anti-slide pile itself, and to provide reliable references for theoretical research and engineering practice, some classical numerical examples and actual project cases are adopted for further revealing the interaction relationships among the slope, anti-slide piles and soil, by means of shear strength reduction finite element method. The research works are carried out as follows:The relationships among the dimensionless parameter λ=c/(γHtanφ), the safety factor and the critical slip surface of simple homogeneous slope are gained by calculating and analyzing a couple of examples.Taking advantage of this important law, the author proposes one method to back calculate the shear strength parameters of simple homogeneous slope based on strength reduction finite element method. The pseudo-static stability analysis of a high fill slope is carried out to explore the influence on slope stability and failure modes in different ways of ground treatment (gravel piles and dynamic compaction replacement).With a single row of anti-slide piles to reinforce the slope, the reinforcement effect and the failure modes, the displacement and internal force response of the pile body and the earth pressure distribution along the pile shaft are deeply analyzed; Considering the four different pile head conditions (free, irrotional, hinged and fixed), the safety factor and critical slip surface of the slope are analyzed, as well the deformation and stress pattern of the pile are also discussed, at last the earth pressure distribution along the pile shaft is showed to analyze their causes; Models with different pile spacings are calculated and analyzed to obtain the upper and lower bound of the slope safety factor, and the effect of pile spacing on the soil arching effect between adjacent piles; The best reinforcement location of a single row of piles is obtained, by changing and analyzing the location of the pile reinforcement.With double rows of anti-slide piles to reinforce the slope, three types of arrangements of double rows of piles (conventional double rows of piles, staggered double rows of piles and equivalent staggered double rows of piles) are proposed based on the concept of equivalent pile frame.The best arrangement of piles is determined from three aspects:the slope safety factor, the response of the pile, and the soil arching effect, under conditions with two different groups of soil parameters. As same as the condition with a single row of piles, the pile head conditions are considered to study its effect on the pile-slope system with double rows of piles and the different responses of the pile between the front row and the rear row of piles are compared to verify the shadow effect. The row spacing (distance between the front row of piles and the rear row of piles) is changed in different models to explore its effect on shadow effect by analyzing the slope safety factor and the internal force response of the pile. With the change of row spacing, the position effect of double row of piles on the safety factor, and subsequently pile-response is analyzed and the effect of pile position on the failure mode of slope is analyzed under one special condition (S/D=1). Finally the optimum location of double-row-pile mode of piles is obtained.Taking Cha’an landslide in Dalian, China as an engineering example, the effect of excavation on the stability and collapse mode of the slope is investigated. Groundwater may reduce the strength parameters of slip-zone clay, thus, the author discusses the effect of changing the groundwater level on the overall slope stability, the local embankment stability and the failure mode. With a single row of piles embedded in the lower part of the slope,the reinforcement effect, the critical slip surface and the internal force response of the pile are discussed under free or hinged pile head restrained condition.