EVALUATION OF SEEPAGE, SLOPE STABILITY AND DEFORMATION IN EMBANKMENT DAM UNDER STATIC CONDITION BY USING GEOSTUDIO AND PLAXIS MODEL (CASE STUDY: DIRE ROCKFILL DAM, OROMIA, ETHIOPIA

Abstract

ABSTRACT Nowadays, monitoring seepage, slope stability, and deformation are the primary and most important activities to establish the overall safety of embankment dams. This study was conducted to evaluate seepage, slope stability, and stress deformation performances of Dire rock fill dam under static condition. In this study, Geostudio and PLAXIS software’s were employed to analysis seepage, slope stability and stress deformation of the dam under different cases of reservoir operation conditions. Seepage analysis such as leakage flow rate, pore water distribution and location of the phreatic line were determined using the finite element (FE) software’s, SEEP/W and PLAXIS. The slope stability evaluation utilizes limit equilibrium (LE) based software (SLOPE/W) and FE based software PLAXIS. The slope stability results determined by SLOPE/W based on Morgenstern-Price method (M PM) was compared with results of the PLAXIS software employing the Mohr Coulomb elasto plastic constitutive model. The stress-deformation was analysed using the FE models, SIGMA/W and PLAXIS software’s. During end of construction and full reservoir conditions the maximum horizontal and vertical settlement were calculated. The seepage simulated results of SEEP/W and PLAXIS software’s show that the average flow rate of leakage for the entire length of the dam at current reservoir condition was equal to 0.000946 m3/s and 0.0012643 m3/s respectively; whereas the actually measured seepage accumulated at the downstream toe of the dam was 0.0054987 m3/s. The slope stability of Dire dam obtained results show that the SLOPE/W software estimates 0.35% higher FoS than PLAXIS for rapid drawdown from current reservoir level, while it estimates 10.28% higher FoS than PLAXIS for a fully saturated slope with hydrostatic pore pressure distributions. The stability analysis results indicated that the critical upstream and downstream slope of the dam is safe within the prescribed USACE range of factors of safety for the possible loading and operation cases. The stress deformation of Dire dam results of vertical settlements obtained from SIGMA/W software for the full reservoir condition were 0.175% and 0.981% of the dam height whereas they were 0.17% and 0.978% of the dam height for PLAXIS software respectively. The vertical settlement measured by a total station at the dam crest was 0.473% of the dam height at the river center. All results of the settlement indicates that the impervious core material is safe against the inside cracking due to the horizontal displacement and the dam could not be affected by overtopping problem through the impact of current vertical settlements