Document Type

Conference Paper

Publication Date


Publication Details

This conference paper was originally published as Colwell, M, Frith, R and Reed, G, Tailgate 802 - Grasstree Mine: A Case Study in Pragmatic Roof Support Design in Aziz, N (ed), Coal 2008: Coal Operators' Conference, University of Wollongong & the Australasian Institute of Mining and Metallurgy, 2008, 75-91.


In February 2007 Colwell Geotechnical Services was commissioned by Anglo Coal’s Grasstree Mine (Grasstree) in the Bowen Basin of Central Queensland to assess the future roadway serviceability and secondary roof support requirements associated with the tailgate of LW 802 (i.e. TG 802). In most instances the ALTS (Analysis of Longwall Tailgate Serviceability) Design Methodology can be directly applied to undertake such an assessment. Whilst ALTS formed the basis for the secondary roof support strategy for the vast bulk of the tailgate, there were two particular aspects associated with TG 802 that required the use other design techniques both in combination with and in addition to ALTS. Firstly, the gateroad development associated with Grasstree is based on a 3-heading rather than the typical 2- heading configuration employed by Australian Collieries (upon which the ALTS database was formulated). To cater for this in assessing tailgate serviceability, ALTS was combined with its US counterpart ALPS (Analysis of Pillar Stability). Secondly, the installation face of LW 802 was located approximately 260 m inbye of the start of LW 801 and due to the tailgate’s orientation and direction of longwall retreat in relation to the major horizontal stress direction, a significant stress concentration acting across the tailgate roof was predicted as the face of LW 802 approached and passed the installation face of LW 801. This situation is sometimes referred to as a “Super Stress Notch”. An analytical approach was adopted when assessing the secondary roof support requirements associated with this section of TG 802. While this paper summarises the process by which the secondary roof support strategy was developed and subsequently implemented for TG 802, the paper primarily focuses on three issues 1) characterisation of the roof, 2) the analytical design procedure associated with the “Super Stress Notch” zone and 3) what roadway performance outcome constitutes a successful design.