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Destruction
Test Results - Resin Bonded ECO Anchors
TEST
DATE: 20.04.93
LOCATION:
Yordas cave, Kingsdale, Yorkshire.
Results
of the Eco/resin anchor test pull in Yordas cave Kingsdale on 20.04.93.
The test pull was carried out by A.Evans Hilti field engineer, I.Moore
Hilti sales and service, L.Sykes CNCC. For the test, the Hilti 10
Tonne test rig was used.
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Test
Anchor No1
The
correct size hole was drilled and then the puffer was used
to expel the dust, this was the only cleaning carried out
on this hole.
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First
movement observed was the anchor bending from its
'P' shape to an oval in the direction of the pull.
This occurred at approx. 130Bars/1950 psi or 1.9 Tons.
The resin bond broke at approx. 200Bars/3000 psi or
3 tons; this was indicated by a distinct crack and
a spalling of the surface rock around the hanger.
At 250Bars/3750 psi or 3.7 tons the anchor was still
in the wall, but Was gradually moving outwards, every
increase in pressure pulled the anchor further out
using a sustained force of 250Bars/3750psi or 3.7Tons.
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Test
Anchor No2
The
correct size hole was drilled, the hole was then cleaned
using a wire brush size 2Omm dia. it was then washed with
water and dried.
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The
anchor changed shape as in No.1 above at about l30Bars/l950psi
or 1.9 Tons. The resin bond-broke at approx. 275Bars/4125psi
or 4.1 Tons again this was indicated as a load crack
and spalling of surface rock, the anchor started to
come out the wall at approx. 400Bars/5000psi or 6Tons.
After about 3cm. of travel the pressure required to
continue outward movement of the anchor fell to approx.
275Bars/4l25psi or 4.1 Tons. There was another crack
sound and the pressure require to pull the remaining
2-3cm was 50Bars/750psi or .75 Tons.
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Test
Anchor No3
This
hole was drilled to the correct size, cleaned and left wet
E.g. water in the hole. To simulate a hang in a wet position.
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The
anchor bent as in tests 1 & 2. At 300Bars/4500psi
or 4.5Tons a cone of rock around the anchor cracked,
this seemed to start from a hair line fracture that
had not been noticed during the installation of the
anchor. It required a force of 275Bars/4125psi or
4.lTons to start the anchor moving out of the wall.
This removal was not completed though due to a hydraulic
failure.
Due
to the hydraulic failure the test had to be abandoned.
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Notes
arising from the tests:
The
results of these bear witness to the superior strength that these
resin-bonded anchors have. I still think that more test beds should
be set up underground, in as many different sites as possible, so
that the readings can be compared and anomalies caused by the lithology
of the limestone taken into account.
It
is also apparent from the results, that no two anchors perform in
the same way during a test, in fact the only consistent part of
the test is the point at which the Eco hanger it's self is mis-shaped
towards the direction of the applied load. In all of the tests that
I have conducted using the Eco anchor/Hilti resin, there has not
been a sudden failure of the anchor or bond, E.g. the hanger has
not come flying out of the hole. The failure has been a gradual
failure every time, thus giving the user ample warning that the
anchor has/or is starting to fail, this gradual failure I feel is
essential in an underground user environment.
The
tests also confirm that whether the hole is dry as in test No.2,
or full of water as in test No.3, the high bond strength is consistent.
With
test results as above I feel that there is no justification for
developing a tool to rifle the holes, to attain greater resin to
rock bond strength. The results of the destruction tests are well
within the minimum standard, set by the B.M.C.
Andy
McCarron...
andy.mccarron@yss.uk.com
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