12 February 2020
20137096-009 Rev A
embankment does not need to be constructed any higher than needed to store the volume of tailings retreated.
The zoning of the embankment would be:
Upstream seal – either a compacted clay on the upstream side as Option 1 , or with soil covered in a geomembrane (HDPE or equivalent) as Option 2, both will be evaluated at this stage of design
Downstream shell – waste rock from the waste rock dumps left by the Mt Morgan mining operations. The use of PAF mine waste and zoning within the embankment will be considered in the detailed design
Seepage drain – a seepage interception drain between the upstream liner and the rock shell connected to the blanket drain, consisting of gravel wrapped in geotextile
Base drainage – a seepage interception drain wrapped in geotextile to convey the seepage from the upstream of the TSF and flow from the foundation, consisting of gravel finger drains wrapped in geotextile.
6.0 BORROW MATERIAL
It should be noted that no sourcing or testing of the potential embankment materials has been carried out as yet. However, it is expected that:
The rock would come from one or more of the waste rock dumps on site
The soil or clay would be source on site
Gravel would be imported from a local quarry.
An estimate of the material quantities is shown in Table 4.
Table 4 : Cumulative material quantities.
ELEVATION (RL m)
ROCK (m³)
SOIL (m³)
GRAVEL (m³)
GEOTEXTILE (m³)
STAGES
0
29,620
94,281
1
290
670,152
36,012
49,919
80,319
2
300
1,312,398
42,655
69,661
69,480
3
310
2,197,411
48,299
90,077
68,718
4
320
3,277,362
52,242
111,312
69,570
5
330
4,523,217
40,057
122,248
43,362
6
335
5,219,779
7.0 FOUNDATION INVESTIGATION
A detailed site investigation campaign needs to be undertaken to assess the geotechnical characteristics of the TSF. Zones of interest will be:
The residual tailings (left behind from the tailings dredging operation)
The thickness of any soils left in the valley
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