BEHAVIOUR OF GRAVITY DAMS USING FINITE ELEMENT TECHNIQUES

Abstract

Foundations play on important part in predicting the behaviour and the stability of the darns. Conventionally, gravity dams are analysed and designed by'the Gravity Method of Stress Analysis', which is based on may simplifying assumptions.. In particular, the method assumes a linear variation of the vertical normal stresses and is not capable of taking into account the variation in material properties and the effect of the foundation which are usually heterogeneous and complex... The finite element techniques, allied to digital computers are now widely used for the stress analysis of the dams as these are capable of handling the above deficiencies in the Gravity Analysis.. Two dimensional stress analysis is carried out here for four gravity dams for obtaining a realistic variation of the normal stresses and the effect of the foundation ranging from very soft to rigid type.. The distribution of normal stresses is found nonlinear in the bottom portion of the dam.. Definite tension of the order of 41 to 64% of tensile strength of material for rigid foundation is noticed, at the heel of the dam. Effect of the foundation is to reduce this range of tension, with increase in flexibility of the foundation rock- from 27% to 19% for hard to soft foundation., The deficiencies of Gravity analysis are further evident in dealing with the foundations containing horizontal, seams with poor shearing properties, endang-ering the sliding stability.. Dams on such weak founda-tionsare, therefore, reviewed to study the deficiences in the foundation system and methods adopted to improve the sliding stability.. The finite element technique is used . as a case study, to evaluate the stresses in the Dudhganga dam and foundations in which a shear key is provided to resist the sliding of dam on a weak shale layer of high deformable nature. The stresses in the dari, in the shear key are found to be within safe limits... Shear friction factor at the shale band level is adequate.. Alternative location and size of shear key are examined. The size of the key, suggested, will save 20% of cost in constructing the shear key... The Finite Element Method is a versatile tool for Engineering problems.. But, for safe and economic design of dams there seems a necessity for analysis of more number of existing dem,,to fix the criteria for allowable tension.