Environmental Engineering Reference
In-Depth Information
Table 1b.
Major special engineering structures and support structures characteristics.
Max. height above
found level (m)
Geological
conditions
Wall
Type of structure
length (m)
M01
Tieback wall
120
8
β
2
M02
Tieback wall
33
8
β
2
M03
Gravity wall
48
9
β
2
M04
Tieback wall
166
11
β
2
north abutment
Gravity wall
31
10
β
2
M05
Gravity wall
133
12
β
2
M12
Gravity wall
145
9
β
2
and β
1
M22
Gravity wall
69
9
β
2
Tl2
Tieback covering
760
20
β
2
M1
Gravity wall
83
12
β
1
and β
2
M3
Gravity wall
65
12
β
2
and β
1
M8
semi-gravity wall
165
8
β
1
M5
Gravity wall
84
12
β
1
c - Retaining structures with height equal to or higher than 8 m.
Figure 2.
Geological cross-section of the slope deposits at south Machico interchange.
to a more or less significant degree, in fine pyro-
clastic material. This complex is also occasionally
intercalated with generally highly modified basal-
tic lavas (Rosa
et al.
, 1995, 1997). Throughout the
Machico River valley, both complexes are practi-
cally covered either by alluvial deposits or by slope
deposits.
The alluvial deposits are generally very coarse
and heterogeneous, accumulated along the Machico
River. These are constituted by rounded blocks or
rolled fragments and pebbles of basalt, covered in
a sandy-silt or clay-silt disaggregated matrix. This
formation resulted from the deposit of material
transported under torrential conditions either by
the Machico River itself or its tributaries. These
have been surveyed at depths range from around
6 to 18 m.
The slope deposits result from landslides and
rockfalls from the declivous rocky slopes of the
Machico River valley, and its accumulation along
and at the base of those slopes.
These are very heterogeneous deposits compre-
hending fragments and blocks, predominantly of
basalt, of various sizes, from blocks which range
from 2 m in diameter to small angular or sub-rolled
fragments covered in a clay-silt-sandy matrix of
a brown-red dark colour. They are characterised
by the fact that they show higher concentration
of rocky blocks at the base. The matrix of these
deposits consists essentially of highly plastic clays.
The water table, in most places, is situated
between this formation and the volcanic substrate.
These deposits are generally in limited equilibrium
conditions due to their depth and geotechnical
characteristics, to the substrate inclination on which
they lay on and, above all, to water table variations.
They easily become unstable, provoking landslide
areas of more or less significance. They cover most
of the slopes where the highway was implemented
and gradually increased in depth to the base of
the slope. These deposits have been surveyed and
