Environmental Engineering Reference
In-Depth Information
35,00
30,00
11 mm
25,00
1+180
20,00
15,00
10,00
8 mm
TRENDLINE
5,00
0,00
01/10/2000
01/02/2001
01/06/2001
01/10/2001
01/02/2002 1/06/2002
01/10/2002
01/02/2003
PHASE
0
1+2
3
4
5
6
Figure 8.
horizontal convergences in section 1 + 180, with constructive phases.
60,00
50,00
28 mm
40,00
1+213
30,00
20,00
17 mm
TRENDLINE
10,00
0,00
01/10/2000
01/02/2001 01/06/2001
01/10/2001
01/02/2002
01/06/2002
01/10/2002
01/02/2003
PHASE
0
1+2
3
4
5
6
Figure 9.
horizontal convergences in section 1 + 213, with constructive phases.
4.2
Section of analysis
The chosen section for analysis belongs to chainage
1 + 213, since it showed the greatest convergences
of all sections. its parameters are:
• Depth: 103.7 m above road level
• Ground: Up to 15 m above road level, soil is
formed by pyroclastics. From that level up to
the surface, it is formed by basalt and slag. The
basalt-pyroclastics interface was modeled as a
straight line from the outcrop at the final portal
and the section where basalts appeared at tunnel
crown.
• section for convergences data reading: one
measurement bolt was placed at the tunnel crown
and one at each sidewall, 5 m below crown level.
horizontal convergences between the two
sidewall bolts are shown in figure 9. Fewer data
are available for convergences between crown and
4
Back analYsis
4.1
Analysis method
a finite differences back-analysis of the tunnel
was made using Flac2D. The model takes into
account the different construction stages such as
excavation, shotcrete shell installation, removal of
repié
and excavation of ditches.
Flac2D, version 4.00 (Fast lagrangian analy-
sis of continua), developed by itasca consulting
Group, is a two-dimensional explicit finite differ-
ence program that simulates the behavior of struc-
tures built of soil, rock or other materials that may
undergo plastic flow when their yield limits are
reached. an isotrop elastic-plastic Mohr-coulomb
model has been used.
The analysis aimed to obtain not only horizon-
tal convergence values but also vertical values and
observed behaviour of the shotcrete shell.
