Evaluation of the Groundsill's stability at downstream of "Citorek" Bridge in Cimadur River, Banten Province

Scouring problems faced in the Cimadur River especially near to the Citorek bridge abutments have become the major discussion by the local researchers and the local water resources manager in Banten Province. As an effort in reducing the scouring problem around the abutment of the Citorek bridge, a groundsill structure with specific design is going to be installed in Cimadur River at downstream of Citorek bridge. To make sure the optimal function of the structure, the stability of the groundsill structure in Cimadur River need to be evaluated. This study attempt to evaluate the stability of a groundsill structure from the occurrences of rolling and sliding at both normal and flood conditions. The eccentricity of the groundsill structure is also checked during normal and flood conditions to make sure the stability of the structure. The required data (which are consisting of detail description of the groundsill structure, cross section of the river, rainfall data, topography data and sediment/soil data) are observed in the field and obtained from P.T. Saeba Konsulindo. The data are further analysed to determine: 1) design water discharges for several return period, 2) forces acting to the groundsill structure and 3) stability of the groundsill structure in the river. The results showed that the groundsill structure are stable and safety again rolling and sliding occurrences where the safety factor (SF) for rolling and sliding are higher than critical coefficients of rolling and sliding (1.5). At normal water level, safety factors (SF) for rolling and sliding are 8.07>1.5 and 2.7>1.5, respectively, while at flood water level, SF for rolling and sliding are 5.61>1.5 and 1.88>1.5, respectively. Besides, the results also found that the groundsill is safety from eccentricity at both normal and flood conditions where the calculated coefficients of eccentricities are lower than critical coefficient of eccentricity which could cause rolling and sliding.