Improvement of Coastal Sandy Soil Using Calcite Precipitation Method for Liquefaction Mitigation

Abstract

Liquefaction is a significant geotechnical hazard in earthquake-prone coastal areas, occurring when saturated sandy soils lose their strength due to seismic shaking. This study investigates the liquefaction potential at Pelabuhan Ratu Beach and evaluates a soil improvement technique using the Soybean Crude Urease Calcite Precipitation (SCU-CP) method, modified with powdered skim milk to enhance treatment effectiveness. Field investigations included the cone penetration test (CPT). In contrast, laboratory tests comprised soil property analysis, precipitation ratio measurement, hydrolysis rate evaluation to determine the optimum soybean extract concentration, and direct shear tests on untreated and treated soil specimens. Liquefaction analysis was based on CPT-derived cyclic stress ratio (CSR) and cyclic resistance ratio (CRR) values. Results showed that at location S-1, shallow layers had a very high liquefaction potential, while at S-2, the 0–6.8 m depth also exhibited a very high potential. Soybean extract concentrations ranging from 20 to 100 g/L were tested, and 80 g/L was identified as the optimum value based on precipitation performance. This optimum concentration was then applied to coastal sandy soils, followed by the addition of powdered skim milk at 4–6 g/L. Calcite precipitation treatment at the optimum soybean concentration increased cohesion to 21.41 kPa, while adding powdered skim milk further enhanced cohesion by 27%, reaching 27.2 kPa. Internal friction angles exceeded 15°, and estimated UCS values reached 54.4 kPa. The combination of SCU-CP and powdered skim milk effectively improved the stability of coastal sandy soils, offering a promising soil improvement alternative for liquefaction mitigation.