| Retaining structure is an indispensable mechanical control measure on steep embankment slope. With intensive studies on the failure mechanism of retaining structures, researches about disasters prevention are unprecedented active at home and abroad. Based on existing structure styles, a develop tendency of integral, combinational, economical and environmental has occurred. Among all the new retaining structures that have come into the sight of researchers, the Chair-Shaped Pile-Sheet Retaining Wall is the most representative one. The application of similar structures on railway industry began in early1970s. However, theoretical study of these structures has always been far behind engineering application, with no mature design codes available, which is seriously restricting the development and promotion of this type of retaining structure.Relying on following projects, such as "Research on the Chair-Shaped Pile-Board Structure of the steep embankment on the unballasted track railway" of the research and development of science and technology plan project of China Railway Group Limited,"Research on the Application of the Chair-Shaped Pile-Sheet Retaining Wall on the Long Mountain Station of the Xuyong-Dacun Railway " of China Railway Eryuan Engineering Group CO.LTD, and "The Analysis and Design of the Chair-Shaped Pile-Board Structure on the Theory" supported by the open research fund of Key Laboratory of Highway Engineering of Sichuan Province, Southwest Jiaotong University, the paper conducted the research, introduced the definition, classification and research status and the working mechanism on rock and soil slopes of the Chair-Shaped Pile-Sheet Retaining Wall. We carried on the studies of the large scale model test of the Chair-Shaped Pile-Sheet Retaining Wall on both rock slope and soil slope respectively, analyzed the mechanism of deformation and stress and failure characteristics on rock slope and soil slopes under different technical conditions, developed the micro strain type hydraulic pressure gauge suitable for indoor model test. In structure design and calculation, the loading plate and soil retaining plate are simplified to simply supported beam, the chair-shaped pile is simplified to flat structure, the displacement of elastic foundation beam method and the structural mechanics method are adopted to calculate the structure internal force and deformation. Finally, the design cycle of Chair-Shaped Pile-Sheet Retaining Wall is put forward by using theoretical calculation method to analyze and discuss the key parameters. Some conclusions are drawn below.1. The paper defines the new type of the Chair-Shaped Pile-Sheet Retaining Wall as a composite anti-sliding retaining structure, consisted of chair-shaped pile, the bearing plate and soil retaining plate, which combines the technical characteristics of the Embedded Continuous Pile-Board Structure, Cantilever Sheet Pile Wall and Double-Row Anti-Slide Pile. It has the triple functions of retaining, anti-sliding and bearing, and could be classified according to the layout position, combination form and load types.2. When the bearing plate and beam support vertical load, the gravity center of Chair-Shaped Pile-Sheet Retaining Wall would move behind, which enhances its ability to resist deformation and overall stability and has a unloading effect to the main pile. Chair-Shaped Pile-Sheet Retaining Wall has following advantages, such as good anti deformation ability, good durability, fast slope withdrawing and covering small area etc. It is applied to following complex conditions of subgrade slope retaining engineering, such as high fill embankment, deep cutting, deep slope of soft soil, large landslide, and steep slope and city road in mountain area.3. When the Chair-Shaped Pile-Sheet Retaining Wall is located on rock slopes, the vertical loads pass through the bearing plate and distribute on the chair-shaped piles. Since the deputy piles are connected through a beam to resist lateral loads, the structure performs both bearing and retaining functions. When joint plane or weakness appears in the rock, the chair-shaped pile reflects the merits of slide resistance. When the Chair-Shaped Pile-Sheet Retaining Wall is located on soil slopes, partial loads and landslide thrust are transmitted to the chair-shaped pile due to the soil arch effect in the slope. Under this condition, the structure shows both resistance and retaining effects.4. When the rock integrity is better, rock pressure acting on the pile is calculated according to the theoretical calculation method, experience or elastic resistance method. When the rock structural plane is extraverted, the most unfavorable conditions of rock pressure needs to be determined. Soil similar slope can be considered as soil slopes. Active earth pressure on soil slopes is determined by maximum value of the classical earth pressure theory, the soil arch theory or the landslide thrust. Passive earth pressure is determined by minimum value of the classical earth pressure theory and elastic foundation beam method or residual sliding resistance. Because the calculation of the landslide thrust and residual sliding resistance is relatively cumbersome, rock pressure acting on the pile can be determined by the revised earth pressure.5. Internal coordination mechanism induces multiple inflection points on the chair-shaped pile, which greatly reduces the structure internal force. Chair-shaped pile failure mode is generally that one of the components generating plastic hinges which results in losing of structure’s normal function. But chair-shaped pile-sheet retaining wall won’t occur capsizing failure under excessively large loads.6. When deputy pile is arranged on the main pile side, it can effectively reduce the internal force of chair-shaped pile, and converse compressive and tensile property of pile. It can be effectively guaranteed that the self-regulatory role of chair-shaped pile’s load by controlling stiffness ratio of pile and beam among1to3. The chair-shaped pile’s vertical pile spacing is general3to5times of the pile diameter or width, or5m to8m, the lateral pile spacing is general2.5to4times of the pile diameter or width, and the value of optimal cantilever coefficient of main pile is0.4to0.6.7. The chair-shaped pile is simplified as a vertical and lateral jointly stressed planar-structure without considering the structure deformation in the process of structural design calculation. According to the constraint conditions between pile top and pile bottom as well as the internal force and continuous deformation conditions among each members and the typical internal segments, the mechanics and deformation of the structure are calculated by using elastic foundation beam method or displacement method in structural mechanics, and the applicability of different calculation methods is put forward. |
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