SOFT ROCK CHARACTERIZATION AND ITS IMPACT TO SLOPE STABILITY AT SESAYAP FIELD COAL MINING, TANA TIDUNG, NORTH KALIMANTAN, INDONESIA

Abstract

Coal mining operation at Sesayap field, Tana Tidung Regency, North Kalimantan Province, Indonesia lies on material soil, sandy clay, claystone and claystone intercalated sandstone and siltstone. The sliding was occurred on soil and loose sandy clay in October 2022, which caused mining infrastructure and financial losses. The objective of this research is to characterize soft rock lithology and its implication to slope stability. The analysis for soft rock material use RQD, SPT, UCS, water content, mineralogy and cohesion. Material characteristic result: RQD average for sandy clay 1.41%, claystone 56.14%, claystone intercalated sandstone 70.80%; water content average for sandy clay 46%, claystone 9%; mineralogy composition for sandy clay quartz 65%, kaolinite 6%, ilit 28%; UCS average data: sandy clay 0.005 Mpa, claystone 0.47 MPa, claystone intercalated sandstone and carbonaceous 1.32 MPa; refer to ISRM 1981 all lithology classified to soft rock. Unit weight for soil 1.53 Kg/m3, sandy clay 1.47 Kg/m3, claystone intercalated sandstone-siltstone 1.94 Kg/m3; cohesion average for soil 6.30 kPa, sandy clay 12.32 kPa, claystone intercalated sandstone 77.14 kPa. Single slope geometry for soil: bench height 5m, slope 200; sandy clay bench height 7m, slope 200; claystone intercalated sandstone-siltstone bench height 10 m, slope 550. Over all slope stability analysis: slope model 1, total height 58m, over all slope 250, berm between sandy clay and claystone is 10m, FS static 1.019; slope model 2, total height 58m, over all slope 240, berm between sandy clay and claystone is 20m, FS static 1.102; slope model 3, total height 58m, over all slope 220, berm between sandy clay and claystone is 30m, FS static 1.194; slope model 4, total height 58m, overall slope 210, berm between sandy clay and claystone is 40m, FS static 1.314.

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