In the past a major obstacle
for steel screwpiles has been to successfully found or bear the pile
into any rock stratum with bearing density greater than 750Kpa. In
particular this was the case for soil profiles above the rock
stratum consisting of loose silty sands or clays.
Previous
solutions involved pre-drilling with rock drills. This was time consuming, and expensive and detracted from the
benefits of using screwpiles in the first instance as it slowed the
piling process and made the use of screwpiles uncompetitive.
Through continued research
by Instant Foundations,
we have now developed “RET” technology, (RET abbreviation
for “Rock Engaging Technology”). Special purpose rock drilling
“RET” screwpiles are now available.
RET screwpiles can cut through and into moderate to medium
hard rock stratums. RET
screwpiles have lead hardened steel cutting tips and rock breaking
helix’s enabling the screwpile to be socketed into the rock with
sufficient depth for compression or tension applications.
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Note:
It is always problematic to install screwpiles into hard
ground. For successful installation of RET screwpiles,
Instant Foundations recommends they be limited to sites
where following conditions can be met :
-
The
bearing density of the ground material should be in the
region of 750Kpa
to 2Mpa, (3Mpa maximum.)
-
The founding depth should be established from
a Geotechnical study.
-
For successful installation a
minimum layer
of 1.0 meter of firm clays or
medium dense sand
material should exist directly over the rock stratum.
The remaining overlying layers may be loose or
poorly compacted materials.
-
There should be a combined minimum depth of 4
meters of soil material above the base rock material.
The maximum depth of the soft overlying layers should
be limited to 30 meters.
-
“RET”
piles are suitable for all compression load
applications where the working load does not exceed
1200Kn per pile.
-
Where tension load applications are
required these should not exceed a tensile load value
of 600Kn per pile.
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For sites which do
not comply to the above rock anchors and drilled grout
anchors/piles should be considered.
For estimating
purposes, RET piles add between $100.00 to $150.00 to the
equivalent standard screwpile.
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