SEISMIC STABILITY OF CANAL EMBANKMENT SLOPES

Abstract

Canal embankments,in almost every region of northern India, have inner and outer slopes of 1.5:1. It is well known that the shear strength of the soil available at different sites may be different and hence factors of safety of-these embankments will be different at different sites. Also since the whole of northern India lies in seismic zones of intensites of VII, VIII, and IX, the factor of safety should be evaluated for these embankments considering the seismic effects as applicable, Attempts has been made in this study to provide a solution for evaluating the safety factors of the existing embankments and also for design of new embankments. For this purpose, the ranges of soil parameters, namely, cohesion and the frictional angle are considered as 1 /m2 to 10 t/m2 and 10° to 350 respectively. Embankments of 3 m, 5 m, 9 m and 13 m heights having the various combinations of soil parameters within this range and subjected to horizontal seismic coefficients of 0.02, 0.05 and 0.10 have been analysed. The three conditions of stability analysis considered are (i) Dry for outer slope, (ii) Sudden draw down for inner slope and (iii) Steady seepage for outer slope.. The analysis has been carried out with the help of high speed digital computer to cope with the number of trials needed for arriving at minimum factor of safety. The results of the analysis have brought out that the factor of safety of embankment slope decreases with increase of height of emabankment and increase in numerical value of horizontal seismic coefficient. The factor of safety increases linearly with increase of cohesion iii parameter or frictional angle or both. For the chosen inner and outer slopes of the embankment, the steady seepage condition for the outer slope, with seismic force acting, gives the minimum factor of safety. Charts have been brought out from the study to assess the safe shear parameters of embankment'of soil needed for the safety of the slopes for a given seismic coefficient.