samples because it was very difficult to extract undisturbed samples
(Table 12). The samples were compacted to a density similar
to the samples undisturbed. The dry density of these shales ranged
between 1.8 and 1.9 g/cm3 while the specific density varied
between 2.44 and 2.68 g/cm3.
Direct shear tests were performed with controlled deformation
(3.3 l/min) for normal stress between 0.1 and 0.5 MPa. The consolidated
undrained triaxial tests were performed to obtain shear
strength parameters for verification of slope stability under seismic
actions. Cyclic testing of the remolded weak shales samples
indicates that the material is not susceptible to degradation under
cyclic loading resistance. Creep tests (creep) indicate that these
shales have negligible creep.
Vardé published the only state of the art on the mechanics of
weak rocks in Argentina, approaching the subject from its conceptual
aspects to the presentation of several cases of work in which
the author took part [1]. He discusses the issue of weak rocks analyzing
three cases: (a) poor cementing sedimentary rocks; (b)
slightly lithified tuffaceous volcanic rocks; (c) decomposed igneous
and metamorphic rocks.
The Chocón-Cerros Colorados is an earth dam with clay core
and gravel shoulders, currently in operation built between 1972
and 1977 by Hidronor and located on the Rio Limay (Neuquén-
Rio Negro Province). In the design stage great efforts were made
in the campaign of investigations to characterize the soft sedimentary
rocks of the Upper Cretaceous. These formations belong to the
group called Neuquén and the stratigraphic sequence comprises
Upper Sandstones, El Chocón Sandstone and Lower Sandstone.
The former is formed by alternating layers of sandstones and calcarenites
with siltstone and claystone lenses from 3 to 5 cm thick.
Found Gypsum lenses thin and discontinuous side in both the base
and the roof of formation. El Chocón sandstones, outcrop in the left
margin, they are massive rocks with little jointing and good
foundation conditions. The lower sandstones lying below the
elevation 290 m emerge on the site. All sequence is subhorizontal.
The presence of secondary gypsum in rock discontinuities is common,
in the first 15 m higher, with thickness reaching to 1–2 cm.
The presence of gypsum causes leakage problems and the stability
of the dam [1].
Plate loading tests were performed in situ from exploratory
galleries in 3 levels deep. The plates of small diameter (0.28 m)
and 300 kg/cm2 pressure and plate of high diameter (0.6 1.3 m)
and pressures of 50 kg/cm2 were used (Table 13).