Spatio-temporal dynamics of surface subsidence over a longwall coal mine in East Kalimantan, Indonesia

Longwall coal mining in East Kalimantan, Indonesia, causes significant surface subsidence, yet specific, data-driven characterisations of this process remain limited. This study offers a detailed spatial and temporal analysis of surface subsidence above a single longwall panel using total station monitoring data collected from February 2021 to December 2022. The analysis identified a maximum final subsidence of 1.336 m. The development of subsidence over time followed four distinct phases: initial, acceleration, deceleration, and stabilisation, with time delays of up to 16 months observed between the passage of the panel and the end of settlement. This behaviour is attributed to subcritical extraction conditions. The subsidence trough was asymmetrical, with its shape strongly influenced by the 12° dip of the coal seam. A comparison with the empirical UK National Coal Board (NCB) method revealed that the observed maximum subsidence was more than twice the predicted value of 0.6 m. These findings highlight the limitations of applying generic empirical models to Indonesia’s unique geological conditions and emphasise the need to develop locally calibrated predictive tools for effective and safe subsidence management.