| Summary: | 碩士 === 國立高雄第一科技大學 === 營建工程所 === 92 === ABSTRACT
Current failure models and analysis methods of retaining reinforcement structure (wall or slope) are influenced by plane strain situations. The security design of the structure merely includes the standard tensile strength or the embedment length of the design section. It does not enclose the distribution of tensile stress of different depth, which is vertical to the cross section of the structure. However, based on numerous failure cases of the retaining reinforcement structure located in several valleys, we can discover that the behavior of the tensile stress vertical to the cross section is an important factor to the stability of the retaining reinforcement structure. They are not in considerations in conventional analysis methods and the failure mechanisms of general retaining reinforcement structure (wall or slope).
The purpose of this thesis is to exploit the 3D finite element program, “Plaxis 3DT”, which analyzes “three-dimensional effects” on the retaining reinforcement structure in valleys. This study considers the retaining reinforcement structures which are located in valleys of different topographic features, such as different two wing slopes, longitudinal slopes, and slope width, and of various situations, including the backfill of the wall in the completion stage and simulated rainstorm. By analyzing the behavior of the stresses and comparing 2D plane strain to 3D’s, we anticipate improving our understanding on the three-dimensional effect of the retaining reinforcement structure.
The results of this thesis indicate that： (1) the behavior of the axial force on longitudinal reinforcements：with different topographical situations of the valleys, the behavior of the axial force on longitudinal reinforcements, which would be generated when the reinforcement structures are constructed step by step. According to recent studies, when the backfill of the wall is in the stage of completion or in the simulated storms, the increase of the layer affects the axial force slightly. However, in the V valley terrain the distribution behavior of the axial force N1 of longitudinal reinforcement could be divided into three stages from top of wall to the bottom of wall. a) In the upper part of wall formation, the peak value of reinforcement structure of N1 for each level occurs to the position of half-slope high of two sides of valley. Furthermore it is influenced by the valley longitudinal slope slightly. Only the peak value of the axial force(N1) in upper wall-formation slow down along with the valley side slopes but goes gradually to the valley central centralism. b)In intermediate-high part of wall formation, the peak value of the structure N1 for each level occurs to the valley central position. c)In lower part of wall formation, the peak value of the structure N1 for each level gathered gradually in front of the wall as well as behind the wall. When the valley cross profile is "(U)" shape, in the upper part of wall formation the peak value of the structure N1 for each level occurs to the position of half-slope high valley of two wings. The position of peak value does not change along with the valley width. The distribution behavior of peak value in intermediate-high part and lower part of wall formation in different valley width is similar to the common valley terrain. (2) The distribution of the axial force
with transverse reinforcement of the reinforcement structure：This is attributed to “Long-Beam Effect”, which is weak to the structures of different mid-high valleys. Below the middle layers, the influence of “Long-Beam Effect” becomes stronger. As a result, the axial force on the fringe of the reinforcement structure becomes stronger. Moreover, the peak value of the axial force decreases with the increase of the bottom width and the gentle slope of both wings of the valleys. When we perform the simulation of the axial force on each layer of the reinforcement structure along the vertical section in the simulated storm, the influence of “Long-Beam Effect” on the fringe of each layer of the structure is stronger. Thus, the increase of the axial force along the vertical section on the fringe of each layer of the retaining reinforcement structure is more intensive than the backfill in the completion stage in the different valleys. Above the middle layer, it demonstrates that the axial force on the middle fringe of each layer enhances. The peak deformation value of reinforced retaining structure is decreased by decreasing side slope of valley or increasing the valley width above 0.25~0.3H of the structure on v-shape valley terrain in the backfill finished situation, and the peak deformation value of reinforced retaining structure is increased by decreasing side slope of valley or increasing the valley width above 0.25~0.3H of the structure. The peak deformation of reinforced retaining structure is decreased by decreasing longitudinal slope of valley above 0.4H of the structure on differential longitudinal slope, and increased by increasing longitudinal slope of valley under 0.4H of the structure. The peak deformation of front valley terrain with central section occurs to the 0.5H of the structure, and it occurs to the 0.6~0.8H with back side of the structure. The deformation is obviously on the top of the structure in the simulation rainstorm stage.
Therefore, the results of analyzing plane-strain (2D) and three-dimension (3D) of the retaining reinforcement structure shows that the axial force or deformation value on longitudinal reinforcement by using plane-strain (2D) is much stronger than by adopting three-dimension (3D). Even so, the analysis of the 2D uses a single design sectional view so it will lead the users to misjudge the peak value of the axial force on this section. The conclusions of this study by using 3D method indicate that the peak value of the axial force on each layer is not on the same sectional view. The peak value of each layer of the reinforcement structure is different with different topographical situations of valleys. This type of failure mechanism in the retaining reinforcement structure is completely different from the current considerations in designing failure models of the retaining reinforcement structure.
|
|---|
