Environmental Engineering Reference
In-Depth Information
Table 1.
summary of the main petrographical and mineralogical observations.
Fresh
slightly
Moderately
highly
Totally
Plagioclase
-
?
+++
++
+
Potassic feldspar
-
+++
+++
++
+
Pyroxene
-
?
++
+
+
Biotite
+
+
±
-
-
Mineral oxidation
±
+
++
±
-
Matrix oxidation
-
±
+
++
±
Matrix argilization
-
±
++
+++
+++
+++: abundant; ++: few; +: rare; -: absent; ?: difficult or uncertain identification.
observations at the outcrop and sample scale,
through optical microscopy and by X-ray diffrac-
tion analyses.
on this bases we subdivided the samples in
five main grades of alteration increasing with the
ordering number (sl1, 2, 3, 4 and 5).
summarizing the main characteristics the major
constituents (see
Table 1
) are sodic plagioclase and
potassic feldspar with minor amounts of pyroxene
and biotite. The fresh—less weathered material has
a porphyritic to trachytic texture with euhedral
plagioclase phenocrysts and a matrix with pilo-
taxic texture. alteration is present prevalently as:
oxidation along the boundaries of crystals and as
stains, and as argilization both of the matrix and
crystals.
abundant alunite is evidenced by XRD analy-
ses X-ray power diffraction for grade 4 materials
argilization and silicification are also observed.
complete substitution of the matrix by argilization
and presence of small silica-amorphous minerals
is observed for grade 5 materials and the porosity
characteristics can be observed for example on thin
sections (see
Figure 1
and the companion paper for
more detailed description).
have a size much larger than both the larger and
average particles/crystal and pore at their interior.
Uniaxial compression and Brazilian tests were
carried out in a servo-controlled hydraulic testing
frame (GDs). a constant 5 mm/hr displacement
rate was imposed during the test. axial and radial
deformations were measured by means of strain
gauges (asTM D 3148). The splitting tensile
strength of the specimens was calculated according
the correspondent asTM standard.
Two P-waves ultrasonic transducers were
installed in contact with the upper and lower load
bearings so to perform continuous measurements
during the test under loading conditions. These
measurements should be useful to verify the
progressive changes sustained by the samples during
the tests. Furthermore, ultrasonic velocities have
been measured for all the samples under no applied
load both in dry and wet conditions. For the case
of no load conditions both the compression and
shear waves have been measured, whereas only P
waves have been measured during the loading tests.
concerning the porosity, total and intercon-
nected, this has been evaluated for all the samples
by different techniques (saturation-drying, hg-
porosimetry, pycnometer, X-ray Micro and Medi-
cal cT, thin sections). The resulting values and
their trend with the alteration grade are reported in
the companion paper (this conference, Pola et al.).
3
MeThoDs
Three different physical-mechanical parameters
were studied: compression and splitting tensile
strength, ultrasonic wave velocity both before and
during testing. Uniaxial compression strength
(according to asTM D 2938) and splitting tensile
strength (asTM D 3967) were determined.
23 cylindrical samples (18 mm and 54 mm in
diameter) were prepared, from the five differently
altered rock materials, to perform compression
test. small samples have been tested only to com-
pute some of the values of uniaxial compressive
strength.
27 samples, 54 mm in diameter, were prepared
for the brazilian tests. in general all the samples
4
ResUlTs
all test results demonstrate an evident relation-
ship with the alteration grade (sl1 to sl5, see also
Figure 1
) as attributed to each sample on the basis of
the mineralogical and petrographycal description.
Failure mechanism in fresh samples (sl1) fol-
low the sub-parallel arrangement of phenoc-
rysts (prevalently plagioclase). Dominant failure
mechanism for sl2 samples is the reactivation of
micro-fractures where the oxidation process is con-
centrated. on the other hand, failure mechanism
