Analisis Stabilitas dan Alternatif Perkuatan Lereng Menggunakan Metode Fellenius dan Plaxis 2D pada Kawasan Perumahan Semarang Sky City, Kota Semarang 6 12

Abstrak

Slope instability in hillside residential areas threatens buildings, infrastructure, and residents, particularly where steep cuts are made in fine-grained soils. This study evaluates the stability of an existing cut slope, approximately 10 m high and inclined at about 60°, in the Semarang Sky City residential area, Semarang City, Indonesia, and assesses two remedial alternatives. Soil parameters were obtained from hand-auger sampling at three points and laboratory tests of physical properties, Atterberg limits, grain size, and direct shear strength. The safety factor was calculated manually with the Fellenius limit equilibrium method and numerically with the strength reduction technique in Plaxis 2D using the Mohr–Coulomb model. The soils are fine-grained with low plasticity, a cohesion of 0.75–7.07 kPa, and a friction angle of 13.4°–32.4°. Without traffic load, the Fellenius method gave a safety factor of 1.547, marginally above the minimum of 1.5 for permanent slopes, whereas Plaxis 2D, which included a groundwater table at 3 m depth, gave 1.414. Under a 10 kN/m² traffic surcharge on the crest, the numerical model collapsed. Strengthening with 20 cm shotcrete raised the safety factor to 1.679, and a combination of D60 secant piles and D60 bored piles raised it to 1.652; both satisfy the 1.5 criterion, and the shotcrete alternative produced the smaller vertical displacement. The results indicate that the existing slope is not safe for the planned road and requires strengthening before the road is built.