Environmental Engineering Reference
In-Depth Information
designing drainage solutions for the retaining wall
itself, so as to collect water efficiently, an overall
surface drainage system was designed.
The main function of which is to ensure suitable
drainage of waters that rise up behind the pile wall,
as not only is it important to avoid hydrostatic pres-
sure, to which the drainage ssen that the resistance
characteristics of the terrain are highly dependent
on the existence of water, and thereby avoiding sig-
nificant earth pressure that are hard to determine
and control.
in this way, a wall drainage system was designed
made up of geocomposite strips drains placed
between the piles. The water collected drains to
the outside in culverts that discharge into half-pipe
lined culverts built into the edge of the road at the
same elevation as the base of the excavation and
connected to the general drainage system.
a drainage culvert made up of a collector built
in perforated concrete connected to a geotextile
wrapped gravel drain was built behind the top of
the anchored pile wall over which runs a half-pipe
intercepting culvert. in addition, drainage spurs
were designed, perpendicular to the wall and con-
nected to the drainage ditch located behind the
wall. complementing this surface drainage sys-
tem it was defined a drainage ditch parallel to the
wall and incorporating a collector in porous con-
crete inserted in a geotextile enclosed gravel drain
with a top culvert, at a relatively large depth, that
discharge the water collected at the extremities
The ground in front of the pile wall was defined
taking into account esthetics considerations,
with the option made to include a 4.0 meter wide
sidewalk in front of the wall, with the gap to the
road elevation overcame by a slope with 1V:6h
inclination.
For this slope a surface drainage system was
designed similar to the one used behind the cur-
tain, made up of drainage spurs connected to a
drainage ditch that in turn runs into a porous
concrete collector. a 2.5 meter wide ditch is con-
nected to this drainage ditch. all of the drain-
age elements discharge the water collected into a
Ø1200 Ph.
Regarding the structures to be built along the
right side of the expressway for retaining the road
embankments, two solutions were studied fore-
seeing the site's condition. Thus where the slope
deposits were so deep as to make it impossible to
drive foundations for retaining structures into the
massif, the recommendation was to build reinforced
concrete walls with Ø1000 millimeter diameter jet-
grouting piles normally driven into the bed rock so
Where the slope deposits were not deep, ena-
bling foundations for retaining structures to be
Figure 11. overview of M6 wall in east portal of
Portais Tunnel.
driven into the bedrock, the recommendation was
to build gravity type walls of cyclopean concrete.
Because of the height of the embankments and
the quality of the foundation materials, these walls
provide good guarantees against deformation
and consequently limit any deformations in the
embankments and in the pavement overlying.
4
conclUsions
The design of the retaining and stabilization struc-
tures for the Machico-caniçal expressway was sub-
ject to constraints of diverse nature, primarily due
to the existence of areas with thick slope depos-
its with very poor resistance characteristics and
densely occupied areas all along the expressway.
The combination of these two factors led to the
use of a several solutions. To each case it was given
individual attention in order to adapt the type of
solution designed and the construction methods so
as to obtain economically and technically adequate
solutions.
it should be stressed that it is essential to
fully understand the geological conditions dur-
ing the conception/design phase, thus enabling
an appropriate characterization of the mechani-
cal characteristics of the volcanic formations in
order to allow the optimization of the solutions
designed.
acknoWleDGeMenTs
The authors would like to thank the social equip-
ment Department of the Regional Government of
Madeira (the client), the Zagope/engil consor-
tium (the contractor) and all other stakeholders
involved in the enterprise under analysis, both for
the technical contributions they have made to its
success and for the authorization to disclose the
elements that make up this paper.
