Environmental Engineering Reference
In-Depth Information
those phenocrysts. sometime they appear micro-
crystalline and vacuolar types lava flows. Basaltic
lava flows with enough thickness show disjunc-
tion in bowling, or more frequently, columnar
disjunction.
The tunnel crosses the basaltic lava flows from
the initial portal to chainage 1 + 170 km (approx)
where ground gradually turns into piroclastics all
the way down to the final portal.
• Full-face excavation and 3 cm thick shotcrete
layer (σ c = 25 MPa). The tunnel stretch in
pyroclastics was completed on 01/10/2000
approx. shortly after, cracks appeared in the
shotcrete shell. These were more important in
the deeper zone, in which pieces of about 30 cm
thick detached from the tunnel crown and the
walls (see igure 10 ).
• on 08/11/2000 a 10 cm thick steel ibre reinforced
shotcrete layer was sprayed to the pyroclastics
tunnel stretch. sections measuring convergence
were installed. These comprised 3 bolts of
convergence (tunnel crown and both walls).
The first measurement, or measurement 0, was
made on 09/11/2000. in the following months,
measurements showed a horizontal deformation
rate of 3 mm/month on the deepest sections.
however, by February 2001 values showed a
trend towards steadiness.
• on 13/02/2001 the repié (overwidth of the
shotcrete layer at the base of the sidewalls
formed by the fall of the rebound material) was
removed. The repiés have triangular form with a
base width of 50 cm approx. and a similar height.
its removal caused an abrupt increase of up to
17 mm in convergence values in a few days (sec-
tion 1 + 213). subsequently, a fast stabilization of
the convergences took place, with a lower defor-
mation rate than before the removal of repiés .
• on 23/04/2001, an additional 10 cm thick steel
fibre reinforced shotcrete layer (σ c = 25 MPa) was
sprayed between chainage 1 + 180 and 1 + 220
• on 01/06/2001, two 0.5 × 0.5 m drain ditches
were excavated at each sidewall base. This caused
a clear rise in the convergences, more gradual
than the previous one. Deformation rate peaked
at 9 mm/month on section 1 + 213 (see igure 9 ).
• in the irst two weeks of august of 2001 the
ditches were filled up, subgrade was formed
and pavement laid, which resulted in a new
stabilization of the convergences. convergence
value due to the excavation of the ditches was
22 mm on section 1 + 213. since deformation
had not become totally stable as the ditches were
filled up, the actual total value was probably
somewhat greater.
• after the pavement was laid, convergences got
stable. however, a certain deformation remains,
the rate of which is steady until now. on
section 1 + 213, its value is 0.25 mm /month.
• Figures 8 and 9 show the horizontal convergences
evolution with tabs to each stage for the deep-
est stretch of the tunnel, chainage 1 + 180 and
1 + 213. overall horizontal convergence value is
31.55 mm on section 1 + 180 and 54.9 mm on
section 1 + 213. Figures show how values on
both sections are approximately proportional.
3
consTRUcTion sTaGes
The tunnel was made by full-face mechanical
excavation. Tunnel support has consisted exclu-
sively of shotcrete layers. The different construc-
tion stages were the following (see figure 7 ) :
PHASE 0
Initial stage
PHASE 1
Tunnel excavation
PHASE 2
Plain shotcrete layer (3 cm)
Repiés (0,25 m)
PHASE 3
1st reinforcement shotcrete layer (10 cm)
Repiés (0,50 m)
PHASE 4
Removal of the repiés
PHASE 5
2nd reinforcement shotcrete layer (10 cm)
PHASE 6
Excavation of ditches (0,5 x 0,5 m)
Figure 7.
constructive phases.
 
Search WWH ::




Custom Search