Prediksi deformasi tanah akibat likuefaksi berbasis N-SPT serta rekomendasi pondasi untuk rumah tinggal di Kawasan Pesisir Desa Glagah, Kulonprogo

Abstract

Liquefaction has become a major concern in geotechnical engineering, particularly after several large earthquakes caused severe damage to structures in coastal areas of Indonesia dominated by saturated sand layers. In addition to the loss of soil bearing capacity, liquefaction also triggers vertical deformation (ground surface subsidence), which significantly affects simple structures such as low-rise residential houses. This study aims to estimate ground deformation due to liquefaction using Standard Penetration Test (N-SPT) data and to formulate preliminary foundation recommendations based on estimated vertical deformation zones in the coastal area of Glagah Village, Kulonprogo. The analysis uses the Seed & Idriss (1982) method to evaluate liquefaction potential through the factor of safety (FS), and the Zhang et al. (2002) approach to estimate volumetric strain and vertical settlement. Liquefaction was assessed at 2-meter depth intervals, with results indicating potential liquefaction at all boreholes. Under a magnitude 7.5 scenario, it is predicted at depths of 2–12 meters, extending to 16 meters at DB-81. For Mw 6.5, it occurs at 2–10 meters, reaching 12 meters at DB-81. Estimated settlements range from 0.29 to 0.59 meters (Mw 7.5) and 0.17 to 0.42 meters (Mw 6.5), classifying the area as high risk. As a technical response, deep foundation systems (mini piles) combined with structural tie beams are recommended to ensure load transfer and stability. It should be noted that deformation estimates are limited to subsurface soil response and do not incorporate building-specific loads or structural dimensions. Nonetheless, this simple yet field-based approach provides a practical reference for the development of liquefaction-resistant and inclusive residential areas as part of the strategic vision for Indonesia Emas 2045.