Stability assessment of long gateroad pillar in ultra-thick coal seam: an extensive field and numerical study

Abstract

Abstract Sustainability of an underground longwall operation is highly dependent on stability of the pillars during the panels extractions to ensure the continuous serviceability of gateroads. In Chinese underground longwall mining, the gateroads are typically driven as a single roadway with a “long gateroad pillar” which is different to a common practice where a gateroad consists of a number of pillars known as chain pillars. Such a unique practice has been proven to be more economical with maximum recovery while the safety remains at its highest level. In this study, based on the data obtained from Tongxin coal mine in China, the mechanical stability of the driven long gateroad pillar was investigated. The focus was on two nearby longwall top coal caving panels and their impacts on the mechanical behaviour of long gateroad pillar during the longwall retreat. To do so, initially an area of the gateroad was selected for the field instrumentation and data collection. These included vertical stress measurement and depth of damage assessment within the gateroad pillar and the longwall panel. Hence, the convergence level of gateroad was quantified to be used for the numerical modelling and assessing the performance of the designed long gateroad pillar based on the finite difference modelling technique using FLAC3D. Double-yield and strain-softening ubiquitous-joint constitutive models were used to simulate goaf material and strata, respectively. Finally, an extensive sensitivity analysis was conducted to compare the mechanical behaviour of a range of wide and narrow long gateroad pillars. It was concluded that the 50 m wide pillar is an ideal dimension for the future panels of Tongxin coal mine to achieve the maximum productivity and safety. Article highlights The validated numerical model was used to study on stability of “long gateroad pillar”. Premature yielding of the 38 m pillar would lead to severe geotechnical issues. Deep roof blasting of goaf edge or 50 m pillar can improve pillar conditions