This paper employs a probabilistic analysis method to demonstrate the durability of earth-fill Dam slopes under stress. The Nai Gaj Dam is located around 65 kilometers in the northwestern part of the Dadu district of Sindh, Pakistan. This study calculates and simulates the seepage and rainwater infiltration through the main Dam's embankment for various scenarios, including a full and approximately halfway between the maximum and minimum reservoir levels.

Using Rocscience's Slide 2D slop 6.0 software, deterministic and probabilistic analysis was carried out. Input data utilized to calculate the Dam slope stability unknown seepage included Dam design parameters and geometry information. Nai Gaj Dam seepage behavior is demonstrated by equipotential lines, streamlines, and velocity vectors in net flow. The outcomes display the exit gradient, maximum seepage, and seepage flux. The findings indicate that the flow rate at the highest reservoir level is 60.47 cubic meters per day. Probabilistic analysis is also used to examine the Dam's overall stability side slope at maximum and mid-reservoir levels. It shows that while the reliability index is 3.66 at mid-level and the likelihood of failure is 0%, it is -4.26 at the whole reservoir level and has a 97% probability of failure.

Keywords: Stability of Dam, Bishop Method, Janbu Method, Fellenius Method, Spencer Method, Seepage Analysis.