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| case history |
| Stabilization of the foundation soil
of the highway embankment in the construction of the third lane of
the Milan-Genoa Highway, Lombardia, Italy |
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| PRODUCT |
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TENAX LBO 301 SAMP bioriented
geogrids
TENAX TNT 500 geocomposites |
| LOCATION |
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Lombardia, Italy |
| OWNER |
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Autostrada Milano-Serravalle
SpA |
| DESIGNER |
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Da Rios Consultants - Milano |
| CONTRACTOR |
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Torno SpA, Itinera SpA, Progetti
Costruzioni SpA,
Rabbiosi SpA, Grassetto SpA |
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problem
In order to improve the quality of its services, Autostrada Milano-Serravalle
SpA decided to enlarge the Milan-Po River section of the highway,
building up a third lane. The geotechnical investigation showed
a number of high plasticity, high compressibility clay layers
at the embankments base elevation. These clays under embankment
consolidation, would have largely settled, badly threatening the
planarity of the new, enlarged highway. A traditional solution
had to face the following problems:
- the presence of thick, compressible, clay layers, interbedded
into sandy deposits;
- the need to avoid differential settlements;
- the budget and time constraints.
solution
To stabilize the base of the embankments and to avoid differential
settlements without cut-and-fill works, the following solution has
been chosen.
A layer of TENAX TNT 500 geocomposite has been placed
at the base of the highway embankment to drain the groundwater.
A layer of 0,30 m of granular mix has been placed and compacted
till 95% of Proctor modified density. A layer of TENAX LBO 301 SAMP
bi-oriented geogrid has been placed to reinforce the soil and then
covered with 0,30 m of compacted granular mix.
TENAX LBO 301 SAMP
geogrid is specifically designed for base reinforcement through
uniform load distribution. The geogrid reinforces the soil through
two main mechanisms: direct resistance to tensile stresses and interlocking,
which prevent any lateral movement of the soil.
The perfect connection between the grid and the soil comes from
both the friction on the solid area of the grid and from the passive
earth pressure generated by the transverse bars of the geogrid under
load.
In order to define the layout of the reinforcement, plate
loading tests on the foundation soil and on the geogrid-reinforced
layer have been carried out. The elastic modulus of the foundation
passed from 3-4 MPa on the foundation soil to 17-18 MPa at the top
of the reinforced layer. Serravalle Highway Specifications were
prescribing a value of the elastic modulus of 15 MPa minimum.
conclusions
TENAX LBO 301 SAMP bi-oriented geogrid and TENAX TNT 500 geocomposite,
which have been widely and successfully used in the past, have once
again confirmed their technical and economical effectiveness. The
use of TENAX geosynthetics allowed for the following advantages:
- Significant reduction of the manpower involved;
- Substantial improvement of the quality of the structure;
- More square metres of base reinforcement and drainage carried
out per unit of time: a team of four workers installed 200 m of
base reinforcement per day (4000 m² per day)
- High and predictable flow rate capacity at a lower price than
a gravel layer;
- Higher elasticity modulus of the base reached with quicker installation;
- Reduction of the thickness of the base: from 1.50 m required
for a traditional road subbase to 0.60 m required for the geosynthetics
stabilized base.
At the same time, the TENAX geosynthetics solution allowed to reduce
the environmental impact that the much greater quantity of gravel
required by a more traditional solution, would have caused. |
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geo@tenax.net