Numerical Analysis Of A Slope Reinforced With Anti-slide Piles Considering Soil Arching Effect

Slope stability analysis and stabilization countermeasures against sliding have been a hot topic in engineering and academics for a long time. Piles have been widely used at home and abroad in recent years to prevent landslides and improve slope stability in practice, and various numerical and analytical methods have been successfully developed to analyze the slopes with reinforcing piles. To achieve an optimum design solution which provides a desirable factor of safety for the slope/pile system, a serial of study on slope reinforced with anti-slide piles have been done in this paper. Three-dimensional elasto-plastic finite element method (EP-FEM) using shear strength reduction technique (SRT) are employed to discuss the problems combined with typical slope cases. The detailed researches can be generalized as below:(1) Infinitely long slope in homogeneous soil as the object of study, five scale of computational models such as single half pile, single pile, double half piles, a single pile and double half piles, and double piles, are employed to study the model size’s influence on slope stability. Some factors, such as the ratio of pile spacing to pile diameter, pile diameter, pile length, material property of soil and pile, and stabilizing location of piles, influencing the factor of safety (FOS) and the critical sliding surface (CSS) for a reinforce slope, have been discussed in detail. In addition, to achieve the distribution of internal force, displacement and earth pressure along pile depth, the following four possible boundary conditions (BCs) at the pile top such as free head, unrotated head, hinged head and fixed head are considered. Meanwhile, two computational models with non-socketed and rock socketed pile modes are both discussed.(2) Anti-slide piles are mainly designed in the form of circular and rectangular at home and abroad. Different forms of cross section are certainly determined by construction method, which directly affects the project cost. In order to investigate the reinforcing effect of different cross-sections of pile, the following six forms of pile-shaped cross-section such as T-shaped, triangular, square, pentagon, hexagon, and circular are utilized to analyze the slope stability and the pile internal forces when the strength reduction factor is equal to1.35and1.50, respectively. A pile lying directly behind another pile will not contribute as substantially to the increase of the total reaction force. This is defined as shadow effect, which is created from the front pile to the rear pile, causing the action of soil against the rear pile to be more minimal than that against the front pile. To investigate the shadow effect and exploit the performance of pile absolutely, the four cases (a single row of piles, double row of piles, staggered arrangement of the equivalent spacing, and staggered arrangement) under free and fixed head of piles respectively are considered to calculate pile internal forces and safety factor.(3) In practical projects, road (river) embankment and foundation pit excavation that reinforced with anti-slide piles, are usually affected by the role of load factors on the slope top, such as traffic, the crowd and temporary buildings, surcharge, etc. The uniformly distributed load is assumed as bar foundation placed on the ground surface. To investigate the effect of load impacting on slope stability and failure mechanism, according to the standard code, taking uniformly distributed load q in order as0,20,40,60, and80kPa, and combined with the bearing capacity of foundation, the slope safety factors and the internal forces along anti-slide piles are illustrated in this paper. Meanwhile, the different Lq (outside edge line of the uniformly distributed load to top level distance) as0,3.0,6.0, and12.0m are utilized to discuss this problem in detail.(4) Whether natural or artificial slope, it cannot be always assumed as an infinite homogeneous long slope. Changeful geometry shape and the complex geological condition are the important factors resulting in the complex slope problems. When the anti-slide piles are reinforced in the corner of railway, highway or the foundation pit, the corner effect sometimes should be taken into account. Therefore, this paper takes four cases (the concave-and convex-shaped slopes with corner angle90°and135°respectively) to discuss the influence of special geometries on the internal forces of stabilizing piles and the CSS of slopes.(5) When stabilizing piles are inserted in a potential sliding slope, soil arching phenomina will be generated in certain pile spacing. The soil arching adjacent to the two piles can reflect the work performance of anti-slide piles in a certain extent. Therefore, the factors such as the ratio of pile spacing to pile diameter, pile cross-section, pile arrangement, the intensity of uniformly distributed loads and the position of surcharge on the slope top, slope geometries etc, are considered to investigate the soil arching effect among piles.(6) A practical project as Cha’an landslide located at Dalian is examined in the present study to illustrate the application of stabilizing piles, by combining with3-D elasto-plastic FEM using strength reduction technique.