S2_11_10_Franz_Gerressen_rev.pdf

8/9/2019 S2_11_10_Franz_Gerressen_rev.pdf

1/37

Construction of a Cut-off Wall

through Warm Permafrost,

Red Dog Mine, Alaska


2/37

Construction of a Cut-off Wall through Warm Permafrost,



3/37

Project Location




4/37

Project Location

Mine Camp

Main Dam

Runway

Tailings

ImpoundmentOverburden

Stockpile

Waste Dump

Ore Pit




5/37

Design Criteria

Reduce or prevent seepage from tailings impoundment into

downstream watershed (Bons Creek)

Crest elevation of 292.6 m (revised to 295.6 m) and final crest

elevation of 300.5 m

Key into low permeability bedrock Average annual temperature of

- 4ºC with an AFI = 2,628 ºC-days

Design for perpetuity

(consider total thawed condition)




6/37

Site Characteristics

Overburden Stockpile constructed over permafrost that averages about - 1° C Overburden Stockpile composed of mainly Kivalina Shale, having high ice content, low strength

Cofferdams constructed of end dumped waste rock.

Tailings placed over geotextile to reduce seepage.

Additional tailings placed on upstream face of north cofferdams to further reduce seepage.

Overburden Stockpile

Cofferdams with Tailings Between

Tailings

ImpoundmentDD2




7/37


8/37

Embankment SectionTailings

Impoundment

Tailings

Impoundment

Select fill composed of well-graded -2.5 cm crushed rock with less than10% fines

Rockfill composed of waste rock from mine operations (60 cm max with less than

10% fines)

Width of embankment must allow for cut-off wall equipment




9/37

Alignment and Excavation LimitsTailings

Impoundment

Tailings

Impoundment

Dewater about 151,000 m³

Excavate about 91,746 m³ of organics and ice-rich materials




10/37


11/37

Plastic Concrete Mix Design

Performance criteria:

Max permeability of 10-8 m/sec

Min 28-day unconfined compressive strength

of 0.7 MPa at 5% strain

Final mix design: 22.8% water, 6.8% cement,

1.8% bentonite, 68.5% aggregate

Same water/bentonite ratio as slurry during

excavation

Average permeability achieved 5x10-9 m/sec

Average 28-day strength of 0.83 MPa




12/37

Cut-Off Wall Panel Construction

Construction began in 2007 and was completed in 2010 (instrumentation in 2011)

Golder Associates Innovative Applications (GAIA) main contractor for cut-off wall

construction (assisted by AIC)

Excavation and earthworks by

TAK and Paw River

Construction season – May 15 to

October 5

Deep excavation using BAUERTrench Cutter




13/37


Guide Wall Installation

The Guide Wall provides:

Guidance to ensure alignment of excavation

Stability to the upper portion of the trench

Reservoir to maintain slurry level




14/37

Cut-Off Wall Panel ConstructionTailings

Impoundment

Tailings

ImpoundmentPre-Excavate Trench about 3 m




15/37

Cut-Off Wall Panel ConstructionTailings

Impoundment

Tailings

ImpoundmentAdd Slurry to Trench and Excavate Panel




16/37





17/37


Cutting of the first “bite”

2.8 m, 1st bite

Guide Wall




18/37


Cutting of the second “bite”

2.8 m 1st bite 2.8 m 2nd bite

Guide Wall




19/37

Cut-Off Wall Panel ConstructionCutting of the third “bite”

1.5 m 3rd bite

Guide Wall




20/37


7.9 m Triple Primary Panel

Excavated primary panel

Guide Wall




21/37


„Working

Slurry“

1st Primary Panel

Guide Wall

Fresh Slurry

To Desanding Plant

2nd Primary Panel Secondary

Replacing of Working Slurry by Fresh Slurry




22/37

Slurry Recycled Through Desander





23/37

Tailings

Impoundment

Tailings

ImpoundmentBackfill Panel with Tremied Plastic Concrete





24/37

Concreting





25/37

A p p r o x .

4 0

’

BC 40

Distinguishing features of BAUER-Cutter (BC)

robust cutter frame (number indicates cutterweight)

steering flaps to control verticality

pressure balance for major components

(2 x gearbox, 1 x mud pump) 6" mud pump (up to 450 m³/h mud flow) max.

diameter of cobbles 80 mm

powerful cutter gear boxes with shock absorbers(BC 32 with 81 kNm; BC 40 with 100 kNm)

appropriate cutter wheel sets for different soilconditions; free cut of the gear box shield due topatented flipper tooth




26/37

B-Tronic Cutter Control System



Distinguishing features of BAUER-Cutter (BC)


27/37

Construction Issues – Resolved!

Rock cutter replaced clay cutter toimprove trenching productivity

7H:1V slopes used to mobilize

carrier with cutter along alignment

Embankment widened for safety

berms required by MSHA

Sodium bicarbonate used todecrease viscosity of working slurry

when cutting secondary panels

Secondary pumps used to transport

slurry farther away from mixing

tanks (didn’t have to relocate mixing

tanks)

Realigned (offset) cut-off wall to

avoid geologic obstruction

Developed termination criteria (at

abutments) based on cutting rates




28/37

Tailings

Impoundment

Tailings

ImpoundmentEmbankment Construction



Construction Photos


29/37

Tailings

Impoundment

Tailings

ImpoundmentEmbankment Construction



Construction Photos


30/37

Construction Photos

Ice-rich Materials During Excavation




31/37

Mixing Tanks and Desander



Construction Photos


32/37

Tailings

Impoundment

Tailings

ImpoundmentClay Cutter Wheels



Construction Photos


33/37


34/37

Maintenance



Construction Photos

C i f C ff W ll h h W P f


35/37

Tailings

Impoundment

Tailings

ImpoundmentSlurry Loss Through Fractured Rock



Construction Photos

C t ti f C t ff W ll th h W P f t


36/37

Good Job, Good Team, Good People



Construction Photos


37/37

Thank You for Your Attention

Questions?

Documents

S2_11_10_Franz_Gerressen_rev.pdf