Prediction of Liquefaction Potential Study at Bantul Regency the Province of Special Region of Yogyakarta Indonesia

The research was conducted to predict the potential liquefaction that may happen on some areas in Bantul regency the province of Special Region of Yogyakarta. To verify soil profile and N-SPT values, soil exploration was done on 4(four) selected locations in Bantul regency. The field exploration was then followed by some laboratory experiments in regard to physical and mechanical properties of soil. The results of soil exploration indicates that soil deposit is sand from the ground surface up to the depth of 30,00 meter, low to medium N-SPT values (15 < N <30), and high elevation of ground water level (-5.00 to -9.00). Laboratory tests show that the soil is uniform poorly graded sand with Cu < 3, and Cc < 2, and relatively low internal friction angle in between 24° and 31°. The soil data, then analysed by means of the method developed by National Centre of Earthquake Engineering Research (NCEER). Analysis of potential liquefaction for 4 selected locations, during low accelerated earthquake (amax/g = 0.05) there were no liquefaction zone. However, during Yogya earthquake 2006 (amax/g = 0.09) there were liquefaction zone in between 17.00 to 19.00 that was very short and in the depth far below ground level. And at amax/g = 0.15 there were long liquefaction zone from 4.00 to 30.00 meter below ground surface.