PIANC E-Magazine - PIANC AIPCN welcome

7. REDESIGN OF CORE TO
OVERCOME FAILURE MECHANISM 2
The state of the existing core material was unknown
during the design phase (as part of it was
covered under a 500 mm thick deck). In addition,
crawling in under the concrete deck naturally revealed
no fines (as it was all washed out and protected
by a layer of coarser rock that appeared to
be to specification). Therefore, a design change
became vital after construction commenced and
after removal of the dilapidated concrete roadway.
Owing to budgetary constraints the existing fine
core material had to be incorporated into the new
design. The core design between Ch 66 and Ch
96 subsequently changed from the original tender
design, by means of a Variation Order, to the following:
• Reshape existing sand core and cover face with
geotextile.
• Overlay the geotextile with a 450 mm thick layer
of 10-50 kg rock.
• Overlay the 10-50 kg rock layer by a 1,000
mm thick 10-500 kg rock layer. Thus, its profile
would tie into the adjacent core profiles.
• Overlay the 10-500 kg layer with a double layer
1-3 t rock as per the tender design.
• Overlay the 1-3 t rock layer with a single layer
4-6 t rock as per the tender design.
PIANC E-Magazine n° 144, November/novembre 2011
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