MODIFICATION OF ROCK MASS CLASSIFICATION IN THE ROCK SLOPE PLATY JOINTED ANDESITE AT SELOHARJO AREA

Abstract

The research area is located in the Seloharjo Area, the southern hills of Opak River, Bantul
Regency, Yogyakarta Special Region, Indonesia. This study explores the application of rock mass
classification assessment by modifying the Q system (SQR) for rock slope stability (SMR) where the
constituent lithology is platy jointed andesite. Andesite in the research area is lava haze, where currently the
rock slopes are prone to rockfall since the earthquake in 2006. Correction of Q system parameters in the
research area is controlled by oriented slopes and joints that were weathered into clay minerals filling the
joints. Slope between 74° and 78° with strikes of the slope face between N 110° E and N 228° E. Strike
direction of the planar joint plane is between N 136° E and N 238° E with an angle of dip is 20° and 26°. The
presence of secondary minerals dominated by smectite and illite clay minerals. Based on the value of the
RMR between 43 and 72 with the SMR value between 59.99 and 87.03, the Q value between 7.47 and 299.35,
the SQR value between 84.58 and 2,564.10, the equation in the form of SMR = 7LnSQR + 30 is obtained.