Environmental Engineering Reference
In-Depth Information
including ice in particular, it is still possible to
detect the original position of the crater.
The component materials are fragmented layers
and fairly continuous, with uniform thickness. The
pyroclastics that form them, have grain size distri-
bution and welding grade variables. This was con-
firmed by the geotechnical exploration program.
compactness and clays have medium plasticity that
may experience significant volume changes.
intermediate level: composed by compact basaltic
lava M with a maximum thickness of 6 m, 1 m thick-
ness near the contact with the “cono de los Mucha-
chos”, and increasing thickness when approaching
the axis of the valley filled with “lava del Galileo”.
There are some cracks but given the little altera-
tion of the material it is concluded that the cracks
are closed.
lower level: lava M is supported on a field
formed by clay probably very continuous because
it was originally a pyroclastic mantle Q. The quality
of the rock is improving with depth.
2.1.2
“Lavas del Galileo”
This lava partially covers and surrounds the “cono
de los Muchachos”, forming an inclined plane
where site 2 is located.
The wall of the “caldera de Taburiente” is a
natural geological section of the subsoil structure,
providing an overview and showing that the “lavas
del Galileo” are a succession of lave streams origi-
nating at some point in the “caldera de Taburinte”
and descending in northwest direction.
These lave streams have random laterally vari-
ations in thickness, variations in the relative pro-
portions of slag roof and base and the central
lava layer. near the depression center line, a trend
toward thickness increase is observed. They have
suffered different disintegration grades and trans-
formation in clays.
3
GeoTechnical sTUDY (1)
once the results of the all preliminary studies (sci-
entific parameters, geotechnical parameters, etc.)
were compared it was decided to locate the GTc
at site 2.
Then, the geotechnical exploration program was
focused on site 2.
Being determined the probable location of the
pier, the telescope building is located. in the explo-
ration program, 6 boreholes are planned: one in
the center of the pier, four around the pier that
are located under the probable position of the tel-
escope building and one in the center of the prob-
able location of the auxiliary building.
These borehole locations help geophysical
research surveys to determine the dynamic proper-
ties of the subsoil and geological continuity of the
soil layers crossed by the boreholes, using Down
hole and cross hole testing.
The boreholes show that the explored area is
composed of a layer of silty clay soil with a thick-
ness of between 0.0 m and 0.40 m, a lava s layer
with granular texture with a variable grade of
weathering but generally thicker when deeper, with
a thickness of between 6.0 m and 7.0 m, a layer of
a pyroclastic mantle P with a maximum thickness
of 1.0 m, an “unrecognizable” layer formed by lava
highly weathered transformed into soils, that have
fresher lava fragments inside (mostly of weather-
ing grade iii) and a stratum which is not continu-
ous with a thickness of 7.5 m, a continuous and
fresh stratum of vacuolar lava (lava M), with an
average thickness of between 3.0 and 3.5 m and a
layer of pyroclastics (Mantle Q) of sand grain size
in some areas with some grade of cementation .
To determine the geotechnical properties of
the materials found in the field boring dynamic
penetration tests were planned, samples (undis-
turbed when possible and disturbed) were taken to
estimate the soil properties in laboratory and in the
seismic geophysics exploration program.
2.2
Preliminary studies (4)
The preliminary drilling program shows the reali-
zation of six mechanical boreholes with continu-
ous coring sample retrieve. Were made five, two at
site 1 (one being a reserve, used depending on the
results) and three at site 2.
With the information obtained by the geological
natural sections of the subsoil and the mechanical
boreholes done, the following kind of materials are
distinguished in this area:
lava s, Pyroclastic mantle P, Unrecognizable
stratum, lava M, Pyroclastic mantle Q.
some features are: lava s partially weathered,
pyroclastic mantle Q: typical red, Unrecognizable
stratum: material that has suffered a high grade of
transformation in clays so that is not possible to
assign it to a particular lithological type. its name
results from the fact that its characteristics do not
allow recognizing the parent. it is possible to dis-
tinguish that it is lava and not pyroclastic, lava M:
rock with interconnected vacuoles stretched paral-
lel to the direction of flow, does not have visible
crystals with a magnifying glass, Pyroclastic man-
tle Q: yellowish.
Finally, the studies were focused on site 2 and
three levels (7) were defined:
Upper level: it is composed by lava s, mantle P,
Unrecognizable stratum and some of the lava M.
it's an inhomogeneous mass soil, characterized by
disintegration and transformation in clay, complete
or in part, of the original rock. exhibits a medium
