Page 3 - Folchi_simonetti_1992

2. INQUADRAMENTO GEOLOGICO 2. GEOLOGY
La morfologia del sito è caratterizzata da versanti aspri che Morphology of the site is characterized by sharp slopes quickly
degradano rapidamente verso il mare. Oltre la quota 60 m dipping downword. Over contour of 60 m (on a.s.1.) at East
(s.l.m.) sul versante Est. ed oltre la quota 100 m sui versanti and over 100 m at Sud and East sides, slopes are sub-veriical
Sud ed Ovest, le pareti dell'ammasso roccioso sono subver- (photo 1).
ticaii. Excavation was carried out in a layered limestone formation
La galleria è stata realizzata in un ammasso calcareo slratiti- with stratas up to 2m thick (photo 2). Geomechanical charac-
calo in banchi ootenli sino a 2 m. Le caratteristiche geomec. teristics may be considered as -average-good* (Q=3+ 9.6
caniche possono essere definite come adiscretebuonen in the Barion classification. RMR=51 i 65 in the Bieniawski
(Q= 3+9,6 nella classifica di Barion, RMR=51 t 65 nella clas- classification). Overconsolidatedmarllevels up to 1.5 m thick
sifica di Bieniawski). Durante lo scavo sono stati intercettati (photo 3) and large volumes of rock with carsic cavities were
intercalari di marna sovraconsolidata con potenza sino ad 1,5 also meet.
m e zone interessate da un'intensa azione carsica. From lield survey il was possible to distinguish 3 main joint
Da rilievi effettuati l'ammasso 6 risultato interessato da tre fa- families: strata and tectonic joints define pseudc-parallelepiped
-
miglie di giunti che isolano porzioni di roccia di forma pseudo
rock blocks (fig. 3).
parallelepipeda (fig. 3). Joints are plane and rough. Outcrapping joints are opened
Le superfici di giunto sono piane e scabre. In aftioramento i (up to 5 mm) and loosed, frequently filled with silt and top soil;
oiunti sono aoerii (da 1 a 5 mm) ed allentati, spesso riempiti inside the rock mass fhey are generally well closedand local-
;a limo e terrikio."ell'ammass~sono ben ser- ly cementaded by calcite.
rati e localmente ricementati da calcile.
Sul versante Est è stata incontrata una caicarenite debolmente In excavating the East adit a ligthly cementated calcarenite
cementata. localmente ben cementata da calcite. Nella cal- formation (locally well cementated by calcite) was meet. In the
carenite sono stati intercettati grossi trovanti di roccia calcarea. calcarenite large erratic limestone boulders were meet.
Sul versante Ovest è stata incontrata una formazione di de- In excavating the West adir a scree formation, composed by
trito di falda costituito da ghiaia e blocchi calcarei immersi in grave1 and carbonafic blocks with sandy-siliy matrix, was meet.
una matrice sabbioso-limosa. Sottostante il detrito di falda una Under the scree a breccia made of irregularly shaped lime-
breccia a clasti calcarei di forma irregolare a locale matrice stone clasts, wilh a local sandy matrix generally cementated
sabbiosa cementata da calcite. with calcite, was meet.

3. ANALYSIS ANO PROJECT
FOR CONTROLLED BLASTING

3.1. Preliminary remarks
The presence of the slope in unstable condition has obliged
to do put pariicular care in defining safety rules in the blast
rounds projects. As a matter of fact il was necessary to keep
stresses induced in the rock mass by the blast, below those
values which would have affected the slopes preexisting con-
dition of static stability.
Field survey, geomechanicalprospeclion and analysis of the
mechanical and structural characteristics of the mass has
showed that the most probable rupture mechanism consist-
ed in the sliding of blocks (about2 m large and 1.5 m thick)
along the strata joint (whose dip is 46O to horimn).
In performing static stability analysis, adopting a conservative
hypotesis, were omitted the forces mobilized along adjoining
planes of the blocks.
The resulting mode1 consists, therefore, in a pseudo parallele-
piped block laying on the strata joint (fig. 4).

3.2. Static stability
Acting forces are the following (fig. 4a):
W (block weight)=ro.gV=ro.g.A.h;
T (component of W parallel to strata joint)= W.sinB;
N (component of W orihogonal to strata joint)= W.cosQ;
TR (resisting force developed because of the friction on the
strata joint) = N. tga.
Fig. 3 Safety factor "FS* can be, therefore, assumed to be equa1 lo:
Curve di isodensità dei giunti rilevali nell'ammasso e meridiani rap-
presentativi delle famiglie principali.
-
=-.
Isodensily curves ol/olnls, ai surveyed in Ihe Ilmestone rock mass, FS = resisting forces - TR - N. tga - W, cose. tga tga
and representallve meridians ot the maln lolnt lamilies. acting forces T W.sinB W.sinB tge