Environmental Engineering Reference
In-Depth Information
100
90
80
70
60
50
40
30
20
Tu ffs (β2)
Tu ffs (β1)
10
0
0.001
0.01
0.1
1
10
100
Particle size, mm
Fine
Medium
Coarse
Fine
Medium
Coarse
Fine
Medium
Coarse
Fino
Fino
Médio
Médio
Grosso
Grosso
Fina
Fina
Média
Média
rossa
rossa
Fino
Fino
Médio rosso
Médio rosso
Clay
Silt
Sand
Gravel
Silte
Silte
Areia
Areia
Cascalho
Cascalho
Figure 10.
Grading curves of tuffs.
Figure 9.
common values of Gsi of Madeira's volcanic
rocks.
The dilatometer modulus present values between
1.6 and 5.6 GPa in basalts and between 0.7 and
5.2 GPa in breccias. Due to the limited number of
results collected these values cannot be taken as rep-
resentative though they do not contradict the values
presented afterwards in the abacus of Figure 14.
Figure 11.
casagrande's plasticity chart.
90
6
GeoMechanical PRoPeRTies
oF Volcanic soil DePosiTs
oF MaDeiRa
80
70
60
50
6.1 Index properties
For the soil deposits the results from 13 tests for
particle size distribution test results and 12 tests for
determining the atterberg limits are presented in
Figure 10 and in Figure 11.
as shown in Figure 10 the tuffs can present a
coarse or silty matrix and are classified based on
particle size as breccious tuffs, granular tuffs or
silty clayey tuffs. it should also be noted that in
terms of plasticity, the fines are classified as silt,
with medium to high plasticity.
40
30
20
Triaxial tests
Direct shear tests
10
0
25
30
35
40
angle of shearing resistance,ϕ[º]
Figure 12.
shear strength results on β 2 tuffs.
only 2 from β 1 . it can be concluded that the three
categories of tuffs present similar values although
the silty clayey tuffs are slightly more resistant than
the others. analysing the total data of the tuffs it
can be concluded that most of the compression
strength values varies between 0.3 and 6.9 MPa and
the Young modulus between 0.1 and 3.9 GPa.
6.2 Shear strength tests
a set of 9 triaxial compression test results and 2
direct shear test results from β 2 tuffs were selected.
The cohesion values are plotted against angle of
shearing resistance in Figure 12.
6.3 Unconfined compression tests
Figure 7 presents the compression test results in
tuffs: 58 results from samples collected in β 2 and
6.4 Standard penetration tests
The standard penetration test (sPT) is widely used
in geotechnical designs. The main advantage of the
 
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