Fault-controlling safe slope design procedure in an open-pit mine case study: Tunçbilek-Kütahya (Turkey) coal field

Abstract

Miocene age coaly Tuncbilek basin (Kutahya/Turkey), which is named as “Tuncbilek Series”, is located at nearly the top level of the continental sequence. Lignite coal vein is bedded nearly at the base of the M2 unit consisting of claystone-marl interlayers. In the basin, the lignite coal vein with low dip angle (10‑30°) has been operated through open-pit and underground mining operations since the 1920s. At Y2-panel where the coal will be operated with the open-pit mining technique, firstly overburden material is removed by establishing benches, the coal bed is opened up, and then the coal is taken from the panel. Different panel geometries in the field are prepared for coal production. This research aims to predict further possible debris slides which may develop due to existing faults with high dip before excavation works in open-pit mine sites and to prevent land instabilities by changing the preplanned positions of the slope portions with the help of kinematic analyses. In order to safely design the overall slopes of the Y2 panel of Tuncbilek coal field, the relationships between the slopes and existing faults which may cause debris slides and those between the slopes and bedding planes and joints were kinematically investigated using the stereographic projection techniques before the excavations. Debris slides were determined in the slopes of A, C, H and L, wedge-type failures were determined in the slopes of B and C, and toppling failure was determined in the combined slope of E and F. The results obtained from these analyses suggest that the preplanned slope positions against probable slope instabilities should be changed to N5E/45NW for slope B, N36W/40SW for slope C, N80E/45SE for slope D, N20E/45SE for slopes E and F, N40W/45NE for slope G, N50W/45NE for slope H and N40W/45NE for slope L during the excavation phase.