13 Revision 33 October 2022
Drive the posts to the correct height and line.
When driving the posts some minor damage to the post top is inevitable,
however this is generally superficial and does not affect either performance
of the post or serviceable life. Minor damage could be
Local crushing of galvanizing on post top.
Local micro cracking of posts.
Curling inwards of post top, local to top 10mm.
Driving times of more than 3.5 minutes for each post indicate that the
ground conditions are too hard and excessive damage may occur to the
posts and therefore in these circumstances concrete foundations should be
used as an alternative to driven posts. Examples of excessive damage are
Serious splitting of post top.
Distortion of preformed post holes
Curling inwards of post top, exceeding top 11mm
Unless the driven post has suffered significant deformation, it is unlikely to
lead to any detrimental effect on the VRS performance.
Posts may be up to 5 degrees out of vertical alignment and up to 5 degrees
out of rotational alignment without affecting the performance of the system.
On rotational alignment, the face of post must be in contact with the beam
for more than 75% of designed contact area.
It is also important to be aware that post damage does not only occur above
the ground where it can be seen, hard ground conditions can cause an
unacceptable amount of damage in the ground where it is not readily
detectable.
Regarding damage to the galvanisation, it is useful to note that during
testing of VRS the thickness of galvanizing does not contribute to the
performance level of the system, this is achieved through a combination of
structural shape, steel thickness and grade. It can be reasonably taken that
the system will still perform as tested even without any galvanized coating
thickness. The specified minimum life laid down in the specification for
highways works is generally exceeded in most situations as can be seen by
inspection of galvanized systems that have been installed in excess of 30
years. Saferoad have developed a driven foundation which can be driven as
a post is but is used as a socket. It is soil tested to the same standards as a
driven post.
4.3 Concrete Foundations
Before any excavation is considered the area should be thoroughly checked
for the presence of services. Wherever excavation is with a machine bucket,
it is preferable that the bucket should not be fitted with teeth.
The foundation design and size should be established by the installation of
test foundations before the actual permanent foundations are constructed.
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