Environmental Engineering Reference
In-Depth Information
Retaining structures in Machico-caniçal expressway
at Madeira island
F.a. sousa, a.R.J. Freitas, M.F.M. conceição & c.J.o. Baião
Cenorgeo, Engenharia Geotécnica, Lda., Lisboa, Portugal
aBsTRacT: Given the conditions found along the entire expressway that connects the city of Machico
and the village of caniçal, on the Madeira island, specifically the topography, the urban occupation and
the highly unfavorable geological-geotechnical conditions, characterized by the existence of slope deposits
of significant depth with very poor resistance characteristics, different solutions had to be used for the
retaining structures, specifically gravity walls, reinforced earth retaining walls with jet-grouting founda-
tion, anchored pile walls and soil nailed walls and slopes.
1
GeneRal DescRiPTion
Rosa
et al.
, 2006). These deposits are the result
from the breakdown of adjacent rocky slopes and
the accumulation of aggregates along the slopes
and their bases, and for this reason they are very
heterogeneous. They are made up of fragments of
various types of rock, predominantly basalts, with
varying size. some are boulders as large as 2 meters
in diameter, more concentrated at greater depths,
and some are cobblestones and angular or semi-
rounded pebbles involved in silt-clay-sand.
The matrix in which these deposits are found is
made up essentially of high plasticity montmorillo-
nite clay with a residual friction angle around 14º.
The geotechnical characteristics of these deposits
are particularly unfavorable, sometimes showing
evidence of recent slides, which required the use of
special retaining solutions creating major problems
for completing the work.
Underlying the slope deposits are very heteroge-
neous post-miocene β
2
and myo-pliocene β
1
com-
plexes. The post-miocene β
2
consists of alternating
deposits of basaltic lava with differing amounts of
brechoid pyroclastic materials and volcanic tuffs,
and the mio-pliocene β
1
is primarily made up of
different levels of tuffs and volcanic bombs.
The expressway is intersected by small water-
ways that favor, not only superficial erosion, but
deep water infiltration, especially where the slope
deposits contact the rock mass.
The geotechnical parameters of the supported
soil and foundation considered in the design projects
are shown in Table 2. These have been selected based
on the results of the tests conducted as part of the
geological and geotechnical study (cenor & Grid
2002b), and considering to the experience acquired
during construction and monitoring of numerous
similar structures under comparable situations.
The Machico-caniçal expressway starts in the Quei-
mada zone at the entrance to Machico, runs around
this city to the West and then continues, for another
7 km, ending at the caniçal roundabout. The main
retaining structures, which are described in this
chapter, are located along a 700 meter stretch known
as the Machico sul interchange, which includes the
initial stretch of the expressway and some access
branches to the city of Machico, and a stretch
known as the caniçal interchange/caniçal Rouond-
about at the exit of the Portais Tunnel.
The Machico sul interchange includes a total of
18 retaining structures and the stabilization for an
important excavated slope; in addition, 3 signifi-
cant retaining walls had to be built to enable a road
bed at the exit to the Portais Tunnel.
The retaining structures required developing an
important set of different solutions, specifically
gravity walls, reinforced earth retaining walls with
jet-grouting foundation, anchored pile walls and
soil nailed walls and nailed slopes, with some situ-
ations requiring a combination of two or more of
these solutions. Table 1 shows the retaining struc-
tures designed, which extend for some 2350 meters.
Figure 1 is a drawing of the expressway along the above
mentioned areas and the location of the structures.
2
GeoloGical anD GeoTechnical
conDiTions
The area along which the expressway runs is char-
acterized by a rather hilly topography with sheer
slopes at the base of which are found slope deposits
reaching a depth of 20 meters (cenor & Grid 2002b,
