Environmental Engineering Reference
In-Depth Information
3
sTRUcTURal sYsTeM FoR oVeRall
sTaBiliZaTion
3.1
General description
The designed structural system is composed of
gravity retaining walls to support the backfill bear-
ing the road cross section widening, and a rock mass
reinforcement of the wall foundation by means of
rock nailing with passive grouted permanent steel
bar anchors. These bars are inserted in predrilled
(in the rock) or precast (in the mass concrete, using
corrugated steel tubular ducts) boreholes to the
design depth and embedded in a cement grout.
Retaining and stabilization structural types had
to be as standardized as possible with the purpose
of achieving the most economical construction,
considering the complicated access to site and
working conditions and the extremely irregular
and erratic rock slope geometry, with the presence
of cavities in the rock mass. hence, the structural
system had to be of uncomplicated insertion on
any irregular rock slope cross section and employ-
ing a systematic building procedure with reliabil-
ity and, simultaneously, without needing highly
skilled labour. For that reason, solutions including
prestressed anchorages had to be discarded.
To facilitate the construction of the retaining
structure, a typology of gravity retaining wall was
selected, built with cast-in-place mass vibrated con-
crete and stair-shaped batter of the wall rear face
(extrados) with steps vertically spaced at distances
of 2.0 m (normally, total lift height should not
exceed this distance according to concrete stand-
ard specifications, as known), which allows simple
placement of concrete in series of horizontal layers
and trouble-free shuttering. stone masonry facing
with local materials is utilized as non-recoverable
formwork system, which provides a high quality
surfacing and environmental integration.
The maximum design wall height at any road
cross section is 10 m. at the foundation base,
below the intersection of the wall rear plane with
the existing rock slope profile, a systematic set of
passive pressure fully-grouted bolts are installed,
joining the mass concrete to the rock with cor-
rugated high strength steel B500s GeWi
®
bars
of diameter 25 mm, to form a strong mechanical
and chemical reinforcement. This solution allows
maximum reduction of wall base width, adapt-
ing its insertion to whichever existing rock profile.
Figure 3 illustrates the main components of the
stabilization system.
additionally, with the intention of stabilizing the
rock mass underneath the bottom of the wall base,
for concentrated loads transferred by the retaining
wall, a rock nailing reinforcement with similar steel
tie rods has been designed and, as Figure 4 shows,
Figure 3. cross section of the stabilization system.
Retaining wall with bar anchors within its foundation
and rock nailing of the rock slope beneath.
similarly even on the adjacent rock slopes where
retaining walls are unnecessary to widen the road
cross section.
The most significant advantages of the selected
stabilization structural system can be summa-
rized in:
- lower volume of excavation for gravity wall
foundations against the bigger base slabs for
reinforced concrete cantilever retaining walls.
in this case, this advantage is essential due to
the confined space to lay the foundation and to
minimize rock excavations. Furthermore, this
base section reduction can be achieved through
anchoring the wall foundation with passive
steel tie bars, allowing an easier adjustment to a
highly irregular rock slope.
- excellent landscape integration as a result of
reclaiming some excavation products (in the
mass concrete and on the stone facing).
- longer long-term integrity of the retaining wall
owing to the non-existence of concrete steel
reinforcing. likewise, some studies have revealed
