1. Introduction
The soft rocks in Argentina have not received the deserved
attention despite being present in a great part of the territory.
Many hydroelectric dams, roads and railways have been built in
this type of rocks.
In order to encourage the study of the geomechanics of soft
rocks in Argentina for its application in engineering, the petroleum
industry has made a compilation of studies published in
conferences and journals.
This work is a synthesis presented by the commission of soft
rocks as a preliminary report to the ISRM International Symposium
in Poland, in September 2013.
2. What are soft rocks?
From the point of view of the intact rock or rock matrix, there
has been a deep debate as regards soft rocks or weak rocks because
it is not easy to define this concept [1]. They have used different
criteria to define them: criteria for strength deformability, durability,
weathering degradation, strength-stress relationship, etc.
Finally it seems that an ‘‘agreement’’ has been reached between
major International Associations (ISRM, IAEG and ISSMFE) and
researchers to use the simple compressive strength as a criterion
to separate soft rocks from hard soils at the lower limit and from
hard rocks in its upper limit. The simple compressive strength is
a property commonly used by professionals involved in the design
of engineering projects, although it is understood that it is not
possible to use only one of the many geomechanical properties
to classify soft rocks [1]. Broader classification systems should be
developed.
However, not all this systems agree on the limits that should be
adopted to characterize a soft rock as shown in Fig. 1, extracted
from the paper recently presented by Professor M. Kanji in the
2nd South American Symposium on Rock Excavations in Costa Rica
[2].
Fig. 1 shows the upper limits with hard rock to be between 25
and 30 MPa of UCS (strength, resistance). The lower limit with soils
shows a greater divergence between different authors, varying
between 1 to 6 MPa of the UCS. The criteria for establishing these
limits are varied and in all cases related to geological and
geodynamics conditions in the site of projects. The geomechanics