River Bank Stability Analysis

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Chapter-IV MATHEMATICAL FORMULATION 4.1 Introduction: In the analysis of river bank stability and the analysis of protection work a number of parameters affecting have to be taken into consideration. The most important of them are seasonal fluctuation of water level of the stream which results in pore pressure variation and seepage action one of the most important factor of Bank instability. 4.2 Study Area: A 250m range of the Ganga river at Raninagar block-II, Murshidabad district. 4.3 Mathematical Formulation: 4.3.1 Governing Equations for analysis The stability analysis of river bank is a complex and multidirectional problem as the actual interaction of all internal and external forces cannot be analyze simultaneously for a particular…show more content…
where, u= pore pressure at the time of failure. ϕ’ can be determined if c’ is assumed to be reduced to zero. Then (4.2) Effect of Degree of Saturation on Shear Strength of Soil: For Transient unsaturated seepage in soil slope have subjected to a modified strength form based on Mohr-Coulomb failure criteria for unsaturated soil proposed Fredlund et al. which can be described by (4.3) Where, τf is the shear stress at failure for unsaturated soil. c/ and ϕ/ are effective cohesion and friction angle respectively. ua , uw are pore air and pore water pressure respectively. ϕb is the friction angle varying with matric suction. The angle ϕb is a material property. For practical purposes ϕb can be taken to be about 1/2 ϕ/. In the capillary zone where the soil is saturated but the pore water pressure is under tension ϕb is equal to the friction angle ϕ/. As the soil desaturates, ϕb decreases. As a better alternative to the use of ϕb to model the increase of shear strength due to the soil suction the following estimation equation proposed by Vanapalli et.al. (1996) is implemented in the…show more content…
When Pore pressure is an independent variable and does not depend on the magnitude of the total stresses acting in the soil, in this case pore pressure at a point in the slope is controlled by the water level or flow pattern of underground water or seepage. Engineering problems which come under this class include the long-term stability of slopes and earth fills and the stability of slopes especially river bank slope subject to a rapid drawdown of the water level adjacent to those slopes. 2. When Pore pressure is a dependent variable and is a function of stress change. Some engineering problems in this category include the initial, or short-term, stability of a saturated clay foundation subjected to the rapid loading of an embankment or structure construction, the initial stability of an open cut or sheet-piled excavation in clay, and the stability of clay slope subjected to rapid drawdown. Formulation of Pore Pressure and Seepage

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