ANALISIS STABILITAS LERENG DENGAN PEMASANGAN BRONJONG (STUDI KASUS DI SUNGAI GAJAH PUTIH, SURAKARTA)

Abstract

The presence of water on a slope with a high plasticity clays soils condition and accompanied by the magnitude of the life load (vehicles) whose workcould result in instability or failure, so gabion is required for stability at the toe of the slopes. Gabion is often used because it can withstand themovement of both vertical and horizontal. The nature of gabion can filter the water so that the water can continue passing while the movement ofland can be held by gabion. In addition, gabion can withstand failure, prevent soil erosion. When gabion collapsed, it can be reused and canimprove the stability of slopes in an effective manner. This research aims to determine slope stability before and after the gabion installation, as wellas to find out the change influence in fluctuations of groundwater, the configuration gabion installation and the presence a combination of load (deadload + life load) towards safety factor (SF). Four types of gabion configuration were considered in calculation. Installation of gabion like terrace,that is step by step. Variation I condition was two parallel gabion arranged in upper and one gabion on it holding the slopes. Variation II wasthree parallel gabion arranged in upper. Variation III was two parallel gabion arranged in side and one gabion on it holding the slopes. VariationIV condition was one gabion arranged in under and two parallel gabion on it holding the slopes. The analysis was performed with the manualcalculation method using Bishop formula to determine the stability of the slopes. Based on the research results obtained that any fluctuation in theface of the ground water, the magnitude of life load on slopes and presence a gabion installation at the toe of slopes contributed slopes stability. Thehigher of groundwater on slope, the smaller the value of SF (safety factor). The greater of life load work on the slopes then the smaller value ofsafety factor. Slope with gabion have values safety factor larger than slope without gabion. Safety factor before landslide conditions was lower thanthe safety factor after gabion installation by Departemen Pekerjaan Umum (DPU) conditions was lower than the safety factor variation IIIconditions. Comparison of the SF variation III condition with the after gabion installation by the DPU due to dead load produces different SF of± 20%, while due to dead load + life load produce different SF of ± 11%. So, variation III condition relatively most safety and able to improvethe stability of slopes so that installation is apt to overcome the instability or failure that occurs.