Evaluation of slope stability at Samarinda tunnel inlet portal using Limit Equilibrium Method

Abstract The stability of tunnel portal slopes is crucial to ensure the safety and continuity of tunnel construction projects. This study evaluates the slope stability at the tunnel inlet portal on Jl. Sultan Alimuddin - Jl. Kakap in Samarinda, East Kalimantan, using the Limit Equilibrium Method (LEM). The geotechnical investigation included interpreting borehole data, sampling soil and rock, and conducting laboratory tests to determine parameters such as cohesion, internal friction angle, and unconfined compressive strength. Slope stability analysis was performed using the Bishop Simplified and Morgenstern-Price methods under static and dynamic conditions with Slide 6 software. The results show that the slopes at this location are generally safe, with safety factors of 1.278 and 1.166 for the Bishop method, and 1.336 and 1.225 for the Morgenstern-Price method under static and dynamic conditions, respectively. Although the obtained safety factors indicate stable slopes, additional reinforcement such as soil nailing, rock bolts, or shotcrete is recommended to meet the higher safety standards suggested by SNI 8460:2017. This study demonstrates that the tunnel portal slopes have a good safety factor but require regular monitoring and maintenance to ensure long-term stability, especially considering the complex geological conditions and climate variability in the area.