Transcript Diapositiva 1 - GDP Consultants

DELLE PIANE LUCA, BOERIO VITTORIO, COMPAGNONI ROBERTO, GIORZA ALESSANDRA,
MUSSO ALESSIA, PIANA FABRIZIO, POLATTINI SIMONA, TALLONE SERGIO, TURCI FRANCESCO
ASSOCIAZIONE TEMPORANEA DI SCOPO:
Università degli Studi di Torino, Centro “G. Scansetti“ per lo studio degli
amianti e di altri particolati nocivi (Mandataria)
Mandante
Mandante
 The new highway ring of the city of Genova, the so-called “Gronda di Ponente”, aims
to reduce road traffic along the existing A10 route, now absorbed by the urban
fabric.
ALESSANDRIA
Road layout (preliminary design)
LIGURIAN SEA
 The design includes a double-tube main tunnel, by-pass and access tunnels for more
than 50 km of underground works, to be excavated by means of both TBM and D&B
technique.
 Asbestos-bearing rocks characterize the road layout west of the Polcevera valley.
STUDY
AREA
LIGURIAN SEA
 A study on the quantification of the asbestos risk has been commissioned to the
inter-department center “G. Scansetti” of the University of Turin.
 Centro G. Scansetti (mandate holder): project coordination & supervision;
petrography; mineralogy, laboratory analyses, medical and legal aspects.
 CNR IGG Pavia, Turin Unit (mandant): field surveys, geological and structural
modeling, laboratory analyses.
 GDP consultants (mandant): field surveys, geological and structural modeling,
analysis of borehole logs, geomorphology.
GOALS:
 Validation of the preliminary geological reference model
 Asbestos distribution model
 Asbestos quantification in tunnels and open pit excavations
 Construction, safety & monitoring procedures.
 In the project area three main Europe-vergent juxtaposed domains crop out, with
the association of upper mantle, oceanic crust and continental margin units and
Apenninic flysch units. These units are affected by a metamorphic grade decreasing
from W to E, from eclogite facies to diagenesis.
calcschists with
ophiolites
prev. ophiolites
(basic)
PalmaroCaffarella
Unit
apenninic flysch
cataclastic shear
zones
Voltri Unit
prev. ophiolites
(ultrabasics)
continental
margin units
Figogna
Unit
GazzoIsoverde
Unit
Ligurian Sea
Apenninic
Flysch
 Minerals considered as “asbestos” by the Italian law (D.L. 15 agosto 1991):
serpentine group: chrysotile
amphibole group: riebeckite (crocidolite)
cummingtonite-grunerite (amosite)
antophyllite
actinolite
tremolite
 Only actinolite, tremolite and chrysotile can be found in the Ligurian hinterland.
 Antigorite, another mineral of the serpentine group being the main component of
metamorphic serpentinites, normally having a lamellar shape, was found to grow in
veins with a fibrous habit.
Photo R. Compagnoni
 Dimensional parameters:
length > 5 mm, diameter < 3 mm, length/diameter ratio > 3:1.
 These parameters define both acicular minerals and really fibrous minerals, having a
D/L ratio above 1:20.
 Asbestos can be found in many different settings:
o joints and faults (e.g. chrysotile)
o cataclastic shear zones (e.g. chrysotile)
o reaction zones at the contact between rocks (e.g. tremolite at the contact
between metabasites and calcschists).
Photo R. Compagnoni
 Problems in defining an asbestos distribution model suitable for a large scale
engineering project:
 geometric and structural complexity: multiphase folding, ductile/brittle shear
zones, topographic cover, outcrop percentage
 heterogeneity in asbestos distribution (e.g. in veins, fractures, fault zones)
 sampling criteria
 lack of standardized analytical procedures
QUANTIFY THE
we must ASBESTOS CONTENT
OF THE ROCKS
reduce the nr. of
samples
extensive
sampling?
link analytical data to
the structural setting
COSTS & TIME
CONSTRAINTS
RELIABILITY
WHERE AND HOW DO
WE COLLECT SAMPLES?
FIND THE RULES CONTROLLING THE SPATIAL
DISTRIBUTION OF FIBROUS MINERALS
STUDY CRITERIA
 Approach in terms of “rock mass” instead of “discrete sample”
(→ excavation methods : TBM, D&B; large tunnels size).
 A determination is needed of the mineralogy and concentration of fibrous minerals
for each rock type, vein type and structural context.
DETAILED STRUCTURAL
RECONSTRUCTION
ON-SITE STRUCTURAL
MEASUREMENTS
PETROGRAPHY &
MINERALOGY
field & boreholes
field
field & laboratory
3D geometry of rock bodies
Homogeneous lithostructural domains
Homogeneous
structural
associations
Correlation between
geology and mineralogy
Asbestos distribution
ASBESTOS-RELATED PETRO-STRUCTURAL FACIES
SAMPLING CRITERIA
PHASE 1
petrographic description
of the main rock-types
PHASE 2
sampling of the previously identified
asbestos-bearing facies
 “Normal” or “random” sampling: whenever the lithological heterogeneity depends
on the intensity of fracturing, giving way to a casual distribution of fibrous minerals
 “Reconstructed” sample: in extremely heterogeneous situations (e.g. within a
cataclastic shear zone), in order to represent all petrographic and structural features
of the rock mass.
HOMOGENEOUS
ROCK MASS
1
A
HETEROGENEOUS
CATACLASTIC ZONE
B
2
3
ACCURATE STRUCTURAL
RECONSTRUCTION
C
ON-SITE STRUCTURAL
MEASUREMENTS
4
D
5
6
PETROGRAPHY &
MINERALOGY
ANALYTICAL CRITERIA
OPTICAL MICROSCOPY
(thin sections, powder)
characterization of asbestos-bearing rocks,
metamorphic evolution, genetic
relationships, etc.
MICRORAMAN
SPECTROPHOTOMETRY
specific for the recognition of fibrous
chrysotile, antigorite & lizardite
X-RAY POWDER DIFFRACTION
SCANNING ELECTRON MICROSCOPE
(XRD)
(SEM)
qualitative/quantitative description
suitable for high asbestos contents
(>5-10% in weight)
quantitative determination
suitable for low asbestos contents
(about 1000 mg/kg)
superposition of chrysotyle & antigorite peaks
no distinction between acicular and fibrous habit
results as weight %
results as total nr. of fibers
detection limit: 1 mm
sample fragmentation: some fibers may break
ASBESTOS-RELATED PETRO-STRUCTURAL FACIES




reaction rims developed at contacts between different lithotypes
rock masses with bounded network of asbestos-bearing veins
rock masses with pervasive asbestos growth in veins/joints
asbestos lacking rocks.
The most critical asbestos-bearing rock types are:
 ductile shear zones with braided tremolite veins at the calcschist-serpentinite
contact
 cataclastic serpentinites within brittle deformation zones
Minor asbestos concentrations have been found in:
 chlorite-tremolite schists at the calcschist-metabasite contacts
 brecciated serpentinites with a stockwork of carbonate veins
 massive serpentinites
 blueschist-facies metabasites with acicular amphibole
Unaltered to slightly serpentinized peridotites commonly lack asbestos minerals.
 For the design purposes, asbestos risk classes have been defined on the basis of the
critical 1000 mg/kg threshold as defined by the Italian law in force, concerning
asbestos concentration in soils.
 Some open issues related to the asbestos risk assessment:
SAMPLING REPRESENTATIVENESS
ANALYTICAL STANDARDS
- A close cooperation between the
geologist and the petrographer is
needed to avoid misinterpretation
- Different laboratories usually apply
different methods and may provide
contradictory results
GAPS IN THE LAW
- Analytical thresholds defined for soils, not specifically for
tunneling muck
- Inapplicability of the Release Index
- Lack of suitable and specific analytical standards
 Reliability analysis of the design Geological Reference Model vs. all variables
affecting the geological predictions (e.g.: number of available boreholes, complexity
of the tectonic setting, etc.).
 A geological section including a quantitative description of the asbestos-risk was
finally drawn.
 Quantitative estimation of rock volumes with different asbestos contents.
PROCEDURES CONCERNING:
- WORKERS SAFETY IN UNDERGROUND AND SURFACE WORKS
- ON-SITE STANDARDIZED LABORATORY ANALYSES
- MONITORING
- MUCK MANAGEMENT PROCEDURES
- STANDARDIZATION OF A REAL-TIME RISK ASSESSMENT PROCESS
- MANAGEMENT OF THE ASBESTOS RISK WITHIN THE INDUSTRIAL CYCLE
in association with:
GRAZIE