Liquefaction Potential Analysis and Soil Improvement Method for Yogyakarta-Bawen Toll Road in Sleman, Yogyakarta

Based on soil investigation using SPT in the planned Yogyakarta-Bawen Toll Road in Sayengan District, Sleman Regency, the soil layers consist of sandy silt, fine-coarse sand, and gravel. Several studies that used the Idriss & Boulanger method showed the liquefaction potential in all observed locations is between high and very high. Therefore, the proposed soil improvement methods are stone columns and jet grouting. Further analysis is conducted to define the effective diameter of the column based on the excess pore pressure ratio (R u ) in both alternatives using the finite difference method (FDM). The result of R u and CSR analysis in BH 78 showed that by using a 1.2 m diameter stone column in the triangular grid with 2.2 m spacing, R u max is reduced by 54.75%, and SF liquefaction is improved to 1.202. Alternatively, soil improvement by using a 1.0 m diameter jet grouting in the rectangular grid with 3.0 m spacing showed R u max is reduced by 11.41% and SF liquefaction is improved to 2.373. Therefore, improvement with the stone column simultaneously reduces R u max and cyclic stress ratio (CSR), on the other hand, the jet grouting only reduces the cyclic stress ratio.