14 Revision 33 October 2022
The test foundation should be designed so that the risk of displacement
under impact is avoided when struck at type test angle. (See section 7)
• Establish post centres and excavate foundations to the size established.
When constructing the foundations ensure there is a minimum of 100mm of
concrete
cover to the post socket (70mm on augured foundations). It is
advisable to have some socket length protruding from the finished concrete
level and up to 100mm is acceptable.
• Excess spoil should wherever possible should be spread locally to avoid
unnecessary lorry movement and land fill otherwise it should be disposed of
at a licensed tip. Or at an agreed location on site for disposal by others in a
correct and environmentally responsible manner.
• Where the sides of the excavation cannot be kept vertical then suitable
permanent or temporary casings shall be used.
• Place concrete in the foundation. Concrete should be able to resist the
plastic
moment of the post when loaded at 90 degrees (the posts strongest
axis) RC20/25 is the minimum grade of concrete- ST5 is an accepted
alternative prescribed concrete.
The suitability of any concrete foundation irrelevant of what concrete grade
has
been used can be demonstrated by destructive testing of posts within a
particular foundation. To prove compliance the post must collapse without
causing any cracking or other failing of the concrete. This is not to be
confused with a soil test, when testing to destruction the foundation may
move within the soil before the post collapses unless survivable foundations
have
been installed.
• Put the post and socket (if required) into the concrete, install the reinforcing
ring and set the post to line and level. Make final adjustments to height and
line before the initial set of the concrete. Slope the concrete away from the
post and socket to help avoid corrosion where possible.
• The socket
should be protected from the incursion of detritus by use of a filler
such as expanding foam.(see series 400, 403.10)
• Where
the concrete foundations are in filter drains they may require casings.
The outside
of the casing should be backfilled with uncontaminated filter
media on the line of the filter drain, and backfilled with the excavated spoil
elsewhere. A plastic membrane of at least 125 microns thick should be laid
at the base to prevent contamination of the filter media. In some filter drains
casings may not be required as the filter drain “stands up” and maintains
vertical sides unaided. Consideration should be given by all parties on the
best method of preventing contamination of the filter media, whilst taking into
consideration that in certain circumstances contamination may not be an
issue.
• It is critical when determining the size of all test foundations that the lack of
ground support is considered and the foundation is of sufficient volume to
support the post and allow it to become plastic before the foundation is
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