The Balangero asbestos open pit mine, located 35km NW of Torino (Italy), was the largest operation of this kind in Western Europe. The dry tailings were lifted by a conveyor belt from the mill and dumped over a natural slope with an approximate angle of 25 degrees, progressively reaching a maximum thickness estimated at 80 m. By the '80s the dump was deeply scarred by various local and large scale instabilities, to the point that houses located at the toe, on the opposite side of the valley, were evacuated. The award winning restoration project used a multidisciplinary approach including hydraulics, geotechnical, pedological and risk engineering to yield a well balanced and sustainable solution. This paper illustrates the Risk Based Decision Making (RBDM) process used through the feasibility, design and construction follow-up of the environmental restoration of the 60 Mm3 dry Balangero asbestos tailings dump. The slopes were hit by storm Quinn and Medicane Rolf and came out unscathed. That was after surviving heavy summer storms in 2010 and 2011.

1. Integrated hydrogeological and
environmental restoration of landslides
affecting a large asbestos mine dry tailings
dump
Franco Oboni, Riskope International, Vancouver, Canada
Cesar Oboni, Riskope International, Vancouver, Canada
Claudio Angelino, Polithema srl, Turin, Italy
Bartolomeo Visconti, Polithema srl, Turin, Italy

2. Width 800 m
Height 200 – 250 m
Estimated Volume 50-60 Mm3
Slope 35 – 45 degrees

3. The site was recognized as one of the most serious environmental
issues of Italy.
-deep seated
instabilities
-erosion gullies
-mud slides
etc...
Leading to the
evacuation of
houses located
at the toe, on
the opposite
side of the
valley.

4. Two communities with about 10,000 inhabitants were
under the influence of the dust plumes.
An international contest was organized by the “owner”
of the project, i.e. an agency named RSA.
Our team recognized two main objectives had to be
met:
a) limiting the volume of earth movements and
b) reducing the overall costs of the restoration to
match stringent financial limitations imposed
by RSA’s budget.

5. The restoration project had to consider numerous other global and sometimes
competing objectives:
- Minimize dusting.
- Limit air pollution.
- Control the geotechnical stability of a large area.
- Control the area water runoff guiding collected water across steep cross slopes.
- Give strong and immediate support to new vegetation on sterile soils.
- Limit the use of concrete/steel or any other artificial material given the sensitive
location of the site at the footsteps of the Alps, in a visible, densely inhabited area.

6. The Team recognized that:
Designs based on codes or recommendations may
differ quite significantly from designs based on Risk
Based Decision Making (RBDM).
Differences may go as deep as choosing a different
material hauling system, a different drainage pattern
etc.
Alternatives which are perfectly code-compliant and
require the same investments and maintenance may
expose the owner to totally different levels of risk all
along their expected life.

7. EXAMPLE: using an
aerial tramway to
haul waste material,
rather than trucks.
It is important to
recognize that
alternatives' risks
may have very
different time frames,
which is taken into
account by CDA/ESM

8. The 4.5 km of dirt tracks between the top and the toe of the
slope were a potential source of dusting and large carbon
footprint, given the need for a fleet of small tonnage trucks.
Thus, hauling trucks were
ultimately discarded because
of environmental risks:
-pollution from exhausts,
-fibres dispersion from the
excavated material
-need to upgrade the existing
tracks
-extra costs for ancillary
temporary structures).

9. Slope stability control procedures:
- Unloading of the crest of the dump slope by digging
three, 10 m wide benches and by storing the resulting
material at the valley bottom in an 8 m high fill.
-Cutting a series of eight, 2.5 m wide, “path-ways
berms” across the slope, each about
600 m long.

10. Runoff control procedure:
Deep gullies, had formed in the upper part of the slope.
- Overall runoff control
through a network of small
“horizontal” wooden channels,
50 to 100 cm wide.
- Transfer of the collected
water towards the toe of the
slope using four main “vertical”
channels located along the
slopes

13. Re-vegetation
The reforestation/re-vegetation of the area was a
major challenge within the project due to the
scarcity of nutrient materials in the sterile soil of
the dump.
Good re-vegetation was a significant project
objective and critical to overall dump stability.

14. The reforestation process was intensely monitored and scrutinized. By the end of the
works, the first trees and shrubs, hydroseeding had already undergone 3 or 4
vegetative seasons and allowed a “real time” control of the success of the operation. In
total the re-vegetation effort included: 450,000 m2 of hydro-seeding, 15,000 shrubs,
7,300 trees and 267,000 live cuttings.

15. Risk Based Decision Making (RBDM) procedures at every
step of the design process were used to develop the
best engineering design in terms of technical results and
budget limitations.

16. The integration of geotechnique, hydraulics, pedology and risk management within
the designers’ multidisciplinary group led to a well-balanced and environmentally
sustainable project allowing the gradual recovery through natural processes of an
otherwise highly compromised area.

17. Integrated hydrogeological and
environmental restoration of landslides
affecting a large asbestos mine dry tailings
dump
Franco Oboni, Riskope International, Vancouver, Canada
Cesar Oboni, Riskope International, Vancouver, Canada
Claudio Angelino, Polithema srl, Turin, Italy
Bartolomeo Visconti, Polithema srl, Turin, Italy
10/11/11 1

18. Width 800 m
Height 200 – 250 m
Estimated Volume 50-60 Mm3
Slope 35 – 45 degrees
10/11/11 2

19. The site was recognized as one of the most serious environmental
issues of Italy.
-deep seated
instabilities
-erosion gullies
-mud slides
etc...
Leading to the
evacuation of
houses located
at the toe, on
the opposite
side of the
valley.
10/11/11 3

20. Two communities with about 10,000 inhabitants were
under the influence of the dust plumes.
An international contest was organized by the “owner”
of the project, i.e. an agency named RSA.
Our team recognized two main objectives had to be
met:
a) limiting the volume of earth movements and
b) reducing the overall costs of the restoration to
match stringent financial limitations imposed
by RSA’s budget.
10/11/11 4

21. The restoration project had to consider numerous other global and sometimes
competing objectives:
- Minimize dusting.
- Limit air pollution.
- Control the geotechnical stability of a large area.
- Control the area water runoff guiding collected water across steep cross slopes.
- Give strong and immediate support to new vegetation on sterile soils.
- Limit the use of concrete/steel or any other artificial material given the sensitive
location of the site at the footsteps of the Alps, in a visible, densely inhabited area.
10/11/11 5

22. The Team recognized that:
Designs based on codes or recommendations may
differ quite significantly from designs based on Risk
Based Decision Making (RBDM).
Differences may go as deep as choosing a different
material hauling system, a different drainage pattern
etc.
Alternatives which are perfectly code-compliant and
require the same investments and maintenance may
expose the owner to totally different levels of risk all
along their expected life.
10/11/11 6

23. EXAMPLE: using an
aerial tramway to
haul waste material,
rather than trucks.
It is important to
recognize that
alternatives' risks
may have very
different time frames,
which is taken into
account by CDA/ESM
10/11/11 7

24. The 4.5 km of dirt tracks between the top and the toe of the
slope were a potential source of dusting and large carbon
footprint, given the need for a fleet of small tonnage trucks.
Thus, hauling trucks were
ultimately discarded because
of environmental risks:
-pollution from exhausts,
-fibres dispersion from the
excavated material
-need to upgrade the existing
tracks
-extra costs for ancillary
temporary structures).
10/11/11 8

25. Slope stability control procedures:
- Unloading of the crest of the dump slope by digging
three, 10 m wide benches and by storing the resulting
material at the valley bottom in an 8 m high fill.
-Cutting a series of eight, 2.5 m wide, “path-ways
berms” across the slope, each about
600 m long.
10/11/11 9

26. Runoff control procedure:
Deep gullies, had formed in the upper part of the slope.
- Overall runoff control
through a network of small
“horizontal” wooden channels,
50 to 100 cm wide.
- Transfer of the collected
water towards the toe of the
slope using four main “vertical”
channels located along the
slopes
10/11/11 10

27. 10/11/11 11

28. 10/11/11 12

29. Re-vegetation
The reforestation/re-vegetation of the area was a
major challenge within the project due to the
scarcity of nutrient materials in the sterile soil of
the dump.
Good re-vegetation was a significant project
objective and critical to overall dump stability.
10/11/11 13

30. The reforestation process was intensely monitored and scrutinized. By the end of the
works, the first trees and shrubs, hydroseeding had already undergone 3 or 4
vegetative seasons and allowed a “real time” control of the success of the operation. In
total the re-vegetation effort included: 450,000 m2 of hydro-seeding, 15,000 shrubs,
7,300 trees and 267,000 live cuttings.
10/11/11 14

31. Risk Based Decision Making (RBDM) procedures at every
step of the design process were used to develop the
best engineering design in terms of technical results and
budget limitations.
10/11/11 15

32. The integration of geotechnique, hydraulics, pedology and risk management within
the designers’ multidisciplinary group led to a well-balanced and environmentally
sustainable project allowing the gradual recovery through natural processes of an
otherwise highly compromised area.
10/11/11 16