Environmental Engineering Reference
In-Depth Information
Figure 1. Detail of roadbed limits extremely close
to the top of a vertical rock slope, restricting widening
solutions.
The rock mass structure stratification had a dip
angle around 8°. Two additional main joint sets
can be distinguished. Rock blocks are subangular,
of metric and decimetric size with big cavities at
the slope toe. Modes of slope failure are mainly
vertical movements as rock fall and collapse
phenomena, in addition to block slips or rock
wedge and planar slides created by jointing, in
accordance with corominas (2004).
in order to characterize the rock mass,
3 geomechanical stations have been implemented,
in which rock matrix properties and main joint sets
were studied according to the international society
of Rock Mechanics (isRM 1981). These data
were employed to classify the rock masses using
the geomechanical classifications of Bieniawski
(RMR) and Barton (Q index). likewise, the
aforementioned empirical classification criteria and
performed laboratory tests have allowed to esti-
mate some rock mass geotechnical properties for
designing such us uniaxial compressive strength,
cohesion, angle of internal friction, the
m
and
s
hoek & Brown (1980) failure criterion param-
eters and deformation modulus. The most rep-
resentative discontinuities could be grouped into
three prevailing sets using a hierarchical cluster
analysis and were represented on sterographic
projection. The shear strength of rock joints has
been analysed applying the Barton & choubey
(1977) failure criterion with the obtained val-
ues of JRc and Jcs from Tilt test and schmidt
rebound hammer.
The rock mass degree of weathering, according
to isRM (1981), has been assessed as W
2
(slightly
weathered), and was also determined using the
United alteration index classification (Uai)
proposed by kilic (1999) with a similar result.
The Rockslope Deterioration assesment (RDa)
index to evaluate the potential for deterioration of
engineered slopes (nicholson & hencher 1997)
was applied, with a result of class number 4 (high
Figure 2. Gc-503 road on an extremely narrow cross
section between two deep ravines with vertical jointed
rock slopes on phonolitic ignimbrites.
sensitivity). similarly, the Rockfall hazard Rating
system, RhRs (Pierson
et al
. 1990) and the
ontario Rockfall hazard Rating system, RhRon
(Franklin & senior 1997) have been assessed,
revealing a medium rock-fall hazard (RhRs = 464).
Moreover, the rock mass was classified according
to its rippability (hadjigeorgiou & scoble 1990)
yielding ie = 50 (very difficult case of excavation).
