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| case history |
| Waste disposal facility for Urban
Solid Waste for the city of Brescia, Italy |
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| PRODUCT |
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TENAX CE 204 geonets |
| LOCATION |
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Ospitaletto (BS), Italy |
| OWNER |
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Brescia City Council Public Service |
| PROJECT |
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Aprica Studi - Brescia |
| CONTRACTOR |
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Aprica SpA - Brescia |
Problem
The Brescia city council public service had to extend its
own waste disposal system for urban solid waste, situated
in Ospitaletto (BS). The waste disposal covers a surface of
180.000 m2, 90.000 of which are made up of the old disposal
and are already full of waste.
The intention was to carry
out the realization of the 2° block (areas B1 and B2)
over a surface of little more than 40.000 m2
and therefore obtaining an available volume of 1.000.000 m3
for the storage of waste, respecting the Italian law n. 915/82,
which regulates waste disposal system.
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Fig. 1 - Geonets allow to use the maximum
allowable slope
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solution
In order to obtain the required volume, it was decided to build
a 18 m deep tank with sides inclined at 45°, storing the waste
even up to about 7 m. over the ground level. For waterproofing and
drainage of the bottom and of the sides, the solution shown in Fig.
2 has been chosen.
Taking into account the fact that the ground
below consists of very permeable cemented sand and gravel, the safety
waterproofing of the bottom has been obtained by a layer of clay
of a minimum thickness of 1 m. As it is impossible to lay clay on
sides of 45°, a HDPE geomembrane with a minimum thickness of
2 mm has been used, identical to the one used on the bottom and
on the sides for the basic water-proofing.
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| Fig. 2 - Schematic cross-section
of the waste disposal |
The connection between geomembranes and clay has been carried
out as shown in Fig. 2. Since it is impossible to use a layer
of sand as leak detection drainage layer between the two geomembranes
on such a steep slopes, TENAX CE 204 geonets have been chosen
by the design engineer to provide adequate drainage and mechanical
protection.
These geogrids are only 5 mm thick, but are capable
of draining the same quantity of water as 0.50 m of sand. Anchored,
together with the geomembranes in the trenches on top of the slopes,
these geonets allow the side slopes to be built with the maximum
inclination that is compatible with the stability of the soil
below. This method will gain much greater tank volume. A traditional
solution, e.g. with a sand and small gravel layer, joined to the
TENAX CE 204 geonet as shown in Fig. 2, has been chosen for the
drainage on the bottom of the landfill.
No particular problems have arisen in the execution of the project,
which was carried out with machinery normally used at construction
sites. Before placing the geomembranes, the slope has been smoothed
with a thin layer of sand. Extrusion-welding of the two overlapped
edges has been used for geomembranes seaming. Control of the welding
has been carried out by an ultra-sonic method which turned out
to be rather slow and complicated, even though no particular problems
arose.
TENAX CE 204 geonets have been connected together by tying
them with plastic strings. During the testing period, even during
heavy rain, no water reached the control well connected to the
leak detection drainage layers, therefore guaranteeing the perfect
waterproofing of the primary geomembranes.
conclusions
Through the use of TENAX geonets for drainage along the landfill
slopes, the following advantages have been achieved compared to
traditional drainage with sand:
- An increase in the available volume for storage of waste equal
to 0.25 m3 for each m2
of geonet (Fig. 1);
- A great saving in the supply of materials and in the building
costs;
- Protection of the geomembranes during building and during disposal
for waste materials;
- Higher safety factory against slope veneer stability failure
along the smooth HDPE geomembranes.
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geo@tenax.net