Geotechnics Analysis: Soil Hardness on Stability of Davit Kecil’s Weir in Ulu Maras, Kepulauan Anambas, Kepulauan Riau

: Davit Kecil’s weir is an irrigation area that located in Ulu Maras Village, East Jemaja District, Kepulauan Anambas Regency, Kepulauan Riau Province. The needs of a geotechnical study are important to determine the soil properties and soil stability of the study area, those parameters will be used to identify the stability of the weir structure. Methods used are field study by taking soil samples and conduct laboratory analysis such as sieve analysis, hydrometer analysis, atterberg limits and direct shear stress that useful for soil resistance identification. Based on the laboratory test result, Hb.2 and Hb.3 are non- plastic soils with uniformity coefficient are 20.92 – 45.38 and coefficient of gradation is 6 – 15.68. So, the soils as categorized as very good on uniformity and good on gradation. The value of direct shear stress with cohesion (c) is 0.06 and φ obtained were in the range of 33.78 – 34.33. Soil grain size identified from sieve analysis is gravel-clay. Based on the analysis result, the stability of Davit Kecil’s weir that was observed from normal water condition and flood water condition is categorized into strong-safe weir characterized by sufficient eccentricity and bearing capacity control. In addition, the weir is withstand rolling and sliding failures.