Preliminary study of liquefaction potential on the NYIA-Kulon Progo Toll Road Construction Project (Klaten Interchange STA 21+800 - 22+300)

The Solo-Jogja NYIA Kulon Progo toll road construction project section 1 package 1.1, which connects Kartasura to Klaten Regency. Based on the regional geological conditions, the Klaten interchange at STA 21+800-22+300 is situated in the Opak Merapi-Merbabu fault area predominantly composed of sandy lithology. Consequently, there is a potential for liquefaction when an earthquake occurs. This research analysis of liquefaction potential using a field test data approach, namely the SPT (Standard Penetration Test) was conducted to assess the seismic and subsurface conditions at Klaten Interchange STA 21+800 - 22+300. The seismic conditions at the Klaten interchange, located 6-7 km from the Opak fault, result in a Peak Ground Acceleration (PGA) value of 0.78 g, corresponding to class 5 on the BMKG MMI scale, potentially causing serious damage to buildings. The VS30 value in the research area ranges from 278.9 - 654.3 m/s, indicating a medium soil type. Subsurface conditions at STA 21+800-21+300 are divided into three zones based on the distance of each borehole. The SPT result shows that zone 1 is dominated by Silty Sand with Loose to Medium Dense consistency, zone 2 is dominated by Silty Sand to Sand with Medium Dense to Very Dense consistency, zone 3 is dominated by Silty Sand with a Medium Dense to Very Dense consistency. The results of the liquefaction potential calculation study indicate that several borehole points have the potential for liquefaction because the safety factor (FS) value is less than 1. Zone 1 has three points that have the potential for liquefaction: DBs-01, DBs-05, and DBs-07. Zone 2 includes two points with potential liquefaction: DBs-08 and DBs-09. Zone 3 has one point with potential for liquefaction: DBs-10.