Environmental Engineering Reference
In-Depth Information
of better geomechanical quality than those of the
sedimentary rocks or metamorphic rocks (shales-
chert and siltstone).
in order to estimate the Gsi from the cores
recovered from the boreholes, the samples have
been divided into homogeneous sections according
to lithological and geochemical criteria.
The range of RQD value assigned to the rep-
resentative samples of the unit ranges from
10%-84%, with an average of 44%. There are
two levels of values (see frequency histogram in
prevails in the sample. in samples with higher per-
centage of shales, the RQD usually varies between
0% and 40%, whilst in samples with higher per-
centage of lava-basalts slightly fractured basalts,
the RQD ranges from 70% to 100%.
The uniaxial compressive strength of intact rock
is generally low, with an average value of 14.97
MPa and a range of 0.10 MPa to 87.36 MPa. only
11% of the tested samples exceeded 30.0 MPa (see
The joints of discontinuity planes are smooth or
slightly rough, and slightly open to open (0.1 mm
to 5.0 mm) with sandy or clayey infilling material.
The Gsi estimated for this formation varies
between 30 and 52, with an average Gsi value of 47.
in boreholes B2o-3, B2o-4 and B2o-5, the
layers of shale, sandstone and chert are more fre-
quent than the volcanic lavas and basaltic. in addi-
tion, the rock is more fractured which leads to an
average value of Gsi 45 in this boreholes, with
values ranging from 30 to 52.
on the other hand, boreholes B2o-6 and B2o-7
were dominated by basaltic volcanic rocks in which
the degree of fracturing is smaller and the condi-
tion of the joints better than those in previous
group. in this case, the average value of Gsi is 50,
with values ranging from 40 to 68.
Finally, in figure 10 it is shown a comparison of
these Gsi values with the ones proposed by hoek
and Marinos (2001).
3.2.3
Sh geotechnical unit
Unit sh consists of sediments and sedimentary
rocks (shales and cherts), associated with over-
thrusts of large scale. This formation is very tec-
tonized and sheared. it is usual to find lenses of
ophiolitic formations, serpentinized or not, due to
their
mélange
character.
This formation is usually arranged in layers
and/or well-defined bedding planes of 1 to 10 cm
thickness, strongly tectonized, folded and sheared,
with smooth to slickensided at places discontinuity
surfaces and slightly to highly weathered. Due to
the intense tectonism, the mechanical properties of
this rockmass are the lowest of all the formations
that will affect the tunnels.
The uniaxial compressive strength of intact rock
ranges between 0.07 MPa and 16.72 MPa, with an
average value 16.72 MPa. it is worth noting than
80% of the results are below 20 MPa, as shown in
the frequency histogram of Figure 11.
Sch-do RQD
25%
20%
15%
10%
5%
0%
RQD (%)
Figure 8. Frequency histogram of the RQD index in
borehole logs corresponding to the sch-do geologic unit.
UACINCÉTOEG DADIN
Sch-do
(alternancia de lutitas,
chert, doleritas, lavas y
basalto)
*
GIS
30 -52 /45
(1)
40 -70 /50
(2)
FERROVIAL -AGROMAN
Sch-do UCT
(1)Sondeos B2O-3, B2O-4yB2O-5.
(2)Sondeos B2O-6yB2O-7.
70%
60%
50%
40%
30%
20%
10%
0%
Figure 10. Ranges of Gsi estimates for the sch-do unit
in the B2o-1 to B2o-8 boreholes superimposed to those
proposed by Marinos and hoek for pillow lavas with
exfoliated and sheared zones (shales-chert) in ophiolitic
complexes.
MPa
Figure 9. Frequency histogram of the Ucs and PlT
compressive strength test results in the sch-do unit.
