Vol. 9(3) March 2016
Deep Seated Gravitational Slope Deformations in a
Ligurian Apennines catchment (Italy): evidences, characterizations and consequences
Sacchini Alessandro, Faccini Francesco and Luino Fabio
The Upper Scrivia Valley in the Ligurian Apennines is
characterized by a large-scale landslides area wider than regional and national
averages. A number of deep-seated gravitational slope deformations (DSGSDs) were
detected and mapped on the basis of geomorphological constraints such as closed
depressions, trenches, double ridges, counterscarps and para-karst formations. The
DSGSDs make up about 10% of the area studied. The majority of large, paleo-and active
landslides spread out within these DSGSDs and processes due to gravity are the main
geomorphological issue. DSGSDs were distinguished according to geological and geo-mechanical
features of rock masses into six case studies. Each case study represents different
slope dynamic and exhibits its own geomorphological features. These case studies
can be a valuable model for the study of DSGSDs within the Apennines. The authors
hypothesize as a factor of main trigger a phase of gravitational instability related
to the evolution of the Ligurian-Adriatic watershed and a deepening of the erosional
base levels set up at the end of the Pleistocene. The reasons are: i) the distribution
and the geological and tectonic characteristics of the case studies, ii) the geomorphological
conditions of this sector of Apennines, iii) the absence of a glacial withdrawal
phase and iv) the low seismicity. The massive presence of DSGSDs raises important
implications for geological cartography, land planning and monitoring because of
the extent and kinematics of these phenomena.
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Influence of blasting on concrete lining and rock
bolts at adjacent tunnels
Jeon Sang-Soo
In this study, the effects of blast-induced vibration
on the structural stability of adjacent tunnels were estimated with respect to the
allowable peak particle velocity (PPV). The distance from the blast satisfying the
allowable PPV was estimated based on the analytical solutions and suggestions of
the United States Bureau of Mines. The allowable distance from the blast was estimated
by using finite difference analysis. Additionally, the behaviors of the concrete
lining and rock bolts installed in the tunnel were examined with respect to the
loading density of explosive charges and concrete invert installation as the blasting
load was applied to the tunnel. Numerical results show that the assessed resisting
shear forces and bending moment of the tunnel supports at a blasting distance satisfying
the allowable PPV of 10 mm/s are very small relative to the standard criteria and
that the blasting effect on the concrete lining is sufficiently small to be ignored.
In contrast, the effect on rock bolts is relatively large. When a concrete invert
is not installed, the mobilized resisting forces at the concrete lining decrease
owing to structural effects at the intersection. When a concrete invert is installed,
the resisting forces of tunnel supports generated at the crown are much smaller
than those near the concrete invert and the axial force of concrete lining increases;
in contrast, both its shear strength and bending moment decrease and resisting forces
of rock bolts are not subjected to the blast loading and are not affected by concrete
invert installation.
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