Potential deformation assessment of Semantok Main Dam in North Nganjuk Region at East Java Indonesia

Semantok Dam was constructed using a zone l embankment type and required safety measures for deformation control. This study aims to understand material specifications, geological conditions, and deformation behavior. The results of the material specifications indicate that the core material and fine filter material meet the design criteria. The geological conditions comprise sand, sandstone, and claystone. The rock’s bearing capacity and settlement in the core zone are considered safe. The elastic vertical deformation of the foundation, analyzed using a flexible foundation approach by Lord, is estimated to be between 4.36 and 6.10 cm. Dynamic analysis is also performed using the Plaxis 8.6 version software to estimate deformation. The software input includes soil properties from the borrow and quarry areas surrounding the dam site. Earthquake design criteria are based on the Operating Basis Earthquake (OBE) with a 100-year return period and the Maximum Design Earthquake (MDE) with a 10,000-year return period. The dynamic analysis results indicate that the maximum deformation during a 100-year return period earthquake is 7.37 cm (horizontal deformation) and 12.68 cm (vertical deformation). In the case of a 10,000-year return period earthquake, the maximum deformation is 83.41 cm (horizontal deformation) and 175 cm (vertical deformation) during rapid drawdown.