Highway Research Record

III. GEOTECHNICAL ENGINEERING
NEW PROJECTS
Seepage Analysis for Slope Stability using Finite Element Analysis

Date of Start:September 2004
Central Road Research Institute, New Delhi (R, I)

Scope and Objectives
Rainfall induced landslides are common Geotechnical engineering problems. As a measure for preventing the occurrence of landslides, trench drains are provided on the slope. It is required to develop the design of trench drainage system for incompressible, homogeneous and anisotropic soil media using finite element analysis. The objective of the study is to determine maximum quantity of discharge of water flowing in to the trench for the geometrical features such as width, depth and spacing of a trench drainage system for steady and transient cases. The study would consider the width of the trench for various values and compare the results with the results of Hutchinson for isotropic soil media. Based on the numerical results an attempt shall be made to develop mathematical models for the maximum quantity of discharge of water flowing into the trench drains and various other factors.

Methodology
Finite element analysis shall be used to solve the governing differential equation of two dimensional ground water seepage through homogeneous anisotropic and incompressible soil medium for steady and unsteady flow condition. Applying the finite element method Flow Chart and Computer Programme will be developed, from which the values for total head at all the element nodes are to be determined. Based on extensive FEM analysis, it is required to determine (i) the equipotent lines, (ii) the variation of piezometric head between the drains along the drain invert level and (iii) the quantity of discharge of water draining in to the drains for various combinations of depth, width and spacing of trench drains. In addition to the effect of geometry of flow domain, it will examine in detail the influence of soil anisotropy with respect to its permeability. To develop the design guidelines for trench drainage system a number of geometrical configurations such as width, depth and spacing for different soil media will be examined. From the finite element solution the discharge of water flowing into the trench has to be calculated.

Conclusions
(i) For various values of width, spacing depth and permeability of the soil, different diagrams have to be developed from which     comprehensive diagram has to be developed to analyse the results and to develop the guidelines for trench drainage     system.
(ii) Mathematical models are to be developed using regression analysis for maximum quantity of discharge of water.

Significance/ Utilization Potential
The contribution rendered in the present expected output bear a high practical utility towards geotechnical engineers in the field for construction of trench drains to prevent the landslides in hill slopes. From the rich experience in developing diagrams from the Finite Element Method (FEM) solution and Mathematical Models are useful for understanding the relationship between the maximum quantity of discharge of water and various other factors. The maximum quantity of discharge of water corresponding to maximum effective spacing can easily and quickly determined from the proposed comprehensive diagram and the mathematical models there by constructing trench drains from preventing landslides. With the experience of the field visits one can suggest for the installation of the trench drains for the fully saturated slopes.

Reports/Publications
P.Pramada Valli & Sudhir Mathur (2004), ‘Suggested approach for designing trench drains using finite element method’, Proceeding of Indian Geotechnical Conference, Warangal, Dec 2004