| Date post: | 05-Jun-2015 |
| Category: |
Education |
| Upload: | oboni-riskope-associates-inc |
| View: | 972 times |
| Download: | 1 times |
Integrated hydrogeological and environmental restoration of landslides affecting a large asbestos mine dry tailings dumpFranco Oboni, Riskope International, Vancouver, Canada
Cesar Oboni, Riskope International, Vancouver, Canada
Claudio Angelino, Polithema srl, Turin, Italy
Bartolomeo Visconti, Polithema srl, Turin, Italy
Width 800 m
Height 200 – 250 m
Estimated Volume 50-60 Mm3
Slope 35 – 45 degrees
-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.
The site was recognized as one of the most serious environmental issues of Italy.
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 andb) reducing the overall costs of the restoration to match stringent financial limitations imposedby RSA’s budget.
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.
The Team recognized that:Designs based on codes or recommendations may differ quite significantly from designs based on RiskBased 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.
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
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 wereultimately 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).
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 about600 m long.
- 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
Runoff control procedure:
Deep gullies, had formed in the upper part of the slope.
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.
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.
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.
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 1
Integrated hydrogeological and environmental restoration of landslides affecting a large asbestos mine dry tailings dumpFranco 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 2
Width 800 m
Height 200 – 250 m
Estimated Volume 50-60 Mm3
Slope 35 – 45 degrees
10/11/11 3
-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.
The site was recognized as one of the most serious environmental issues of Italy.
10/11/11 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 andb) reducing the overall costs of the restoration to match stringent financial limitations imposedby RSA’s budget.
10/11/11 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.
10/11/11 6
The Team recognized that:Designs based on codes or recommendations may differ quite significantly from designs based on RiskBased 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 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
10/11/11 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 wereultimately 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 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 about600 m long.
10/11/11 10
- 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
Runoff control procedure:
Deep gullies, had formed in the upper part of the slope.
10/11/11 11
10/11/11 12
10/11/11 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.
10/11/11 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.
10/11/11 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.
10/11/11 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.
