Print Email Facebook Twitter Reinforced grass on inner dike slopes Title Reinforced grass on inner dike slopes Author Hinostroza Garcia, S. Contributor Stive, M.J.F. (mentor) Fraaij, A. (mentor) Verhagen, H.J. (mentor) Faculty Civil Engineering and Geosciences Department Hydraulic Engineering Date 2007-12-01 Abstract This thesis shows a set of equations that define the micro-stability and macro-stability of reinforced grass revetments with geosynthetics on inner dike slope during an overtopping event. At micro-stability level, it has been analyzed that the equilibrium in a soil particle using the criterion of incipient motion of soil particle. The forces in normal direction to water flow are considered the most important to keep in equilibrium the soil particles of the reinforced grass revetment. As unstable forces are considered: Lift force, this force can be defined in function of depth-averaged relative turbulence intensity and averaged-velocity (Hoffmans’ Model, 2006). Likewise, the averaged-velocity can be defined in function of concentration factor of stems, bent vegetation height and vegetation height (Carollo’s Model, 2005). As stable forces are taken account: Friction force due to cohesion stress, the cohesion forces produced by root and geosynthetic in the soil are assumed in the same direction of the water flow and they cause a frictional forces in the normal direction of water flow when the particle tend to detach. Also, gravity force, as it is referred to submerged weight of soil particle. The stability equation of a soil particle of reinforced grass revetment is deduced from the application of the equilibrium between these forces; it means unstable forces must be equal or less than stable forces. At macro-stability level, it has been analyzed the acting forces on reinforced grass revetment during an overtopping event has been applied to the equilibrium in the system. The diagram of free body of reinforced grass revetment is divided in two wedges and identified like active and passive wedges (Koerner’s model 1991). The wedge located at top of the slope exerts an active function in the system that means it tends to push away the soil of the revetment so that is in the toe of the slope. The other wedge located at toe exerts a passive function that consist to hold the active wedge giving equilibrium to the system. The forces taken account in the diagram of free body of both wedges are: the weight of the soil, the shear force of the water, the cohesion forces produced by cohesive soil, roots and geosynthetics, reactive forces located in the failure plane and pressure forces between the passive and active wedges. To define the stability of the system, the safety factor is introduced in the friction angles of different soils and soil-geosyntethic besides in the cohesion produced by root and geosynthetics. The polygon method is applied in the forces acting on each wedge and it is deduced in a quadratic equation in function of safety factor. A safety factor higher than one defines a stable system. The geosynthetic analyzed are the geogrid and geocell. Unlike geogrid for the geocell an additional force is considered and this is the shear force which is generated in the contact between geocell wall and soil and it is in normal direction of the surface. This additional force is independent of the geocell tension; it means the geocell does not need to be in tension to help the stability of the system. In the case of geogrid could not be affirm the same. With much analysis of micro-stability as macro-stability of the system, the cohesive forces produced by roots and geosynthetics are important. In this thesis is described in brief mathematical models, based on equation’s coulomb, which defined these cohesions. The cohesion produced by root in the soil is calculated using the simple root perpendicular model (Model of Wu et al, 1979). The additional cohesion produced by the geosynthetic uses the model of Jewell, 1980, to be calculated. Both cohesion models are based on the tension stress of the root or geosynthetic located inside of the soil layer produce shear stress in this layer. The shear stress could be in any plane but it is used the failure plane. This shear stress in the failure plane is composed of two components, one of the component is the projection of tension stress in the failure plane and the other is the friction stress produced by the normal component to the failure plane of tension. The tension of roots and geosynthetics are important in both cohesion models. The tension of root is easily to obtain from laboratory. Subject grassovertoppingdikes To reference this document use: http://resolver.tudelft.nl/uuid:33a91948-efbf-40d1-a5c6-7404c8cf36c1 Part of collection Student theses Document type master thesis Rights (c) 2007 Hinostroza Garcia, S. Files PDF THESIS_REINFORCED-GRASS-R ... ETMENT.pdf 2.2 MB Close viewer /islandora/object/uuid:33a91948-efbf-40d1-a5c6-7404c8cf36c1/datastream/OBJ/view