Uplift And Closure Of Brennans Creek Dam Due To Underground Coal Mining At West Cliff Colliery, NSW

This paper applies the new ACARP graphical method for predicting valley closure, upsidence and regional horizontal displacements to data measured at Brennans Creek Dam in order to review the effectiveness of the current dam monitoring programme. Analysis of the data shows that the embankment has been compressed by about 60mm and uplifted 50 mm. Regional horizontal movements of up to 7 mm have also occurred. We show that for a valley containing a dam embankment, a closer fit to the ACARP estimates of upsidence movement is obtained if valley depth is measured from crest level rather than from creek or floor of valley level. Dam closure movements are seen to be less predictable in terms of depth of valley, maximum incremental subsidence and in-situ horizontal stress regime. We conclude that the most recent mining by West Cliff Colliery of longwalls LW5A1 to LW5W3 does not appear to have damaged either the dam foundations or the embankment up to the present, and we have provided details of a better focussed monitoring progamme for analysing underground mining induced displacements in and around Brennans Creek Dam.