Bob has over 40 years geotechnical consultancy experience in a wide range of projects conducted both within Australia and overseas. In particular, Bob has led the GHD
Geotechnical input for a range of mine tailings dams and water storages including also the design and project management of many process water dams, lined and unlined, and major port dredging/ reclamation silt storage facilities. Bob has led numerous energy and infrastructure geotechnical/geo- environmental projects, which have included the management of multi-disciplinary design teams across different operating centres.
Presentation Title: Subaerial Coal Tailings Deposition and Change Management Under a Tailings Management Deposition Plan – Design and Implementation
Initially a review of operations was conducted for this site, in order to enable a whole site management and mine planning for life of mine operations in the design approach. The review identified the need to expand the currently proposed TSF area, in order to utilise the maximum available site storage area and to maximise the tailings dry density through the use of a Tailings Deposition Management Plan (TDMP) designed to suit the available area and the proposed tailings throughput under the site climatic conditions.
Geotechnical investigations were undertaken, including evaluation of disused underground bord and pillar workings, some 20m below the TSF floor and to locate a buried highwall along the northern boundary of the proposed TSF development area. Investigations were conducted to ensure that for the design stages up to Stage 3 (final stage) for the TSF design, the subsurface conditions were established into a geotechnical model with adverse conditions either avoided (if possible) or catered for within the design.
The design was based on the geotechnical investigation data; the results of in-house tailings deposition and drying behaviour simulation testing within the GHD laboratory; and was conducted in accordance with the (then) NSW DSC compliance and Mine Safety requirements.
The TSF incorporates placement of washery production Coarse Coal Reject (CCR) under method statement in the downstream zone and a roller compacted CCR upstream zone, thus providing for co-disposal.
The potential for managing seepage into underground workings beneath the TSF embankment, should pillar failure/potholing occur (considered unlikely), was addressed in the inclusion of a vertical sand filter in the affected areas, which were defined by examining the mining records and by down borehole video inspection of the workings.
Clean and dirty water management streams, operational water balance and flood routing requirements (with contingencies) were incorporated into the design. In particular, the previous open pit subaqueous deposition storage was re-used as the water management storage for the TSF to receive gravity decant supernatant and flood routing flows. This pit was then later also incorporated into the Tailings Deposition Management Plan (TDMP) as a Change Management action, in order to extend the cycle time when high ash content coal was encountered.
The system has operated successfully to date, as designed, and as per the TDMP – with operational staff having been trained in Tailings Management operations and significantly dry density achieved some 45 – 65% higher than for the ‘in pit, subaqueous deposition.