Analysis of Dam Foundation in Alluvial Deposits, Method and Material Modelling

Abstract

This thesis presents a study made to analyse a gravity dam foundation on alluvial deposits. Alluvial deposits consist of fine fraction and coarse fraction which can be characterised as boulder mixed soil. The percentage fines fraction of alluvial deposits has direct impact on the engineering characteristics of soil including density compactness and consequently affect the stability of Gravity dam in alluvial deposits. In this thesis, a method is presented to analyse the performance of gravity dam in alluvial deposits at natural and improved soil conditions. For this a relation is established between the percentage of fines fraction with the bulk modulus of elasticity, shear modulus of elasticity and density. This relation is used to predict the mechanical parameters after the improvement of soil with consolidation and compaction grouting which will transform the fine fraction into a cemented material. The value of void ratio, volumetric water content, permeability of improved soil is found out as a function of decrease in percentage fine fraction. As on dam foundation the soil material is modelled as homogeneous and heterogenous material consisting different fraction of boulders and fines. FDM and FEM software are used to model the alluvial deposits at natural and improved soil conditions. Loading of dam is considered for full reservoir condition. The dam and foundation are assumed to be in plane strain condition. The results from FDM and FEM analysis demonstrated the decrease deformation, porewater pressure and seepage in dam foundation with the decrease in percentage fine fraction in alluvial soil. The numerical analysis results showed that heterogenous material distribution better represent the ground condition. Seepage analysis results with and without cutoff wall shows the decrease in seepage with decrease in percentage fine fraction. The dam foundation is analysed for vertical stress, vertical deformation, porewater pressure, and seepage.