| |
Additional
Tests Undertaken Using Hilti Hit C50 Resin and the DMM ECO Anchor
Drop
Test Results of ECO/Resin Anchors
Test
Date: 09.07.94
Location:
Dingle quarry, Dalton, Lancashire.
Three
anchors were placed on 05.07.94, they were Installed by L. Sykes
using the correct method of placement. Above two of the anchors
'M8' self-drilling bolts were placed, these were to hold the gauges
in position. The third anchor had a thermometer placed against the
hanger and in the resin to a depth of 45mm.
The readings
for the critical load point, that being the point at which
the rope and anchor arrest the fall of the weight, are approximate,
as we were unable to take this reading accurately.
Critical
Load Point:
The
point at which the rope and anchor arrest the fall of the weight.
At
Rest Under Load:
The
reading that was taken after the F.F. 1 once the weight had stopped
moving.
Off
Load:
The
reading that was taken when the load used for the drop test was
removed, thus, no load on the anchor.
The
following drop tests were done using a 76.5Kg weight, a fall factor
1 was incurred for each drop test.
A 00.01-10mm
gauge was used to record the movement of the anchors in the direction
of the load, these were held in place with pre-installed 'M8'
self-drilling bolts.
During
the next 5 drop tests the gauge was not zeroed after each drop
test.
|
Anchor
number 1
Placed
with the load bearing curvature pointing downwards, as it
would be used in most cases.
| Static
stress test:
For
this test the anchor was loaded with 85Kg. the type
of loading during every day usage.
Under
load a reading of 00.06mm was recorded.
Drop
test 1:
At
the critical load point a reading of 00.20mm was recorded.
Under
load at rest, the reading decreased to 00. 10mm.
Off
load, a reading of 00.025mm was recorded.
Drop
test 2:
At
the critical load point a reading of 00.60mm was recorded.
Under
load at rest, the reading decreased to 00.21mm.
Off'
load, a reading of 00.12mm was recorded.
Drop
test 3:
At
the critical load point a reading of 00.80mm was recorded.
At
rest under load, the reading decreased to 00.26mm.
Off
load, a reading of 00.17mm was recorded.
Drop
test 4:
At
the critical load point a reading of 01.10mm was recorded.
At
rest under load, the reading decreased to 00.29mm.
Off
load, a reading of 00.19mm was recorded.
Drop
test 5:
At
the critical load point a reading of 01.3mm was recorded.
At
rest under load, the reading decreased to 00.34mm.
Off
load, a reading of 00.24mm was recorded.
|
|
The results
of the drop tests confirm the following:
- That
the anchor has considerable strength and, an ability to absorb
the energy created during a fall.
- The
anchor was not deformed, it retained it's integrity and shape,
it would not be possible to ascertain if an anchor had sustained
a fall factor by using eye sight alone.
- Although
the readings at the critical load point are significant, up to
1.3mm on the 5th. drop test, the hanger does not bend considerably,
.24mm unloaded after 5 drop tests.
- The
importance of radiusing the lower edge of the drilled hole to
accept the anchor, ensures that the anchor is snug to the rock,
thus, reducing the stress on the shank of the anchor, during falls
and general usage.
|
Anchor
number 2
Was
placed using the correct method of placement, the load bearing
curvature was parallel to the ground, (e.g. the anchor was
in horizontal position). This was to test for movement of
anchors in traverse lines, where the applied load would not
be in-line with the anchor.
|
Static
stress test:
A
load of 85Kg. was load on the anchor, a reading of 00.
30mm was recorded.
When
off loaded a reading of 00.171mm was recorded.
The
gauge was zeroed, 85Kg. was loaded on the anchor and
the weight was bounced for 30 seconds, this was to simulate
cavers hanging on traverse lines, and, bouncing in their
harnesses, During the bouncing a maximum reading of
00.50mm was observed. When off loaded a reading of 00.059mm
was recorded, (remember the gauge was zeroed after the
previous test).
This
movement 00.50mm is equivalent to a torque of 40psi.
/5.5Kg Metres.
Drop
test 1:
A
76.5 Kg. weight was used and a fall factor 1 was incurred.
Because
of the angle of the anchor to the load the anchor bent
at the head of the shank, thus, the load bearing curvatures
of the anchor were rotated 5.50mm in the direction of
the load. At this point the resin had not cracked or
failed.
When
off loaded the anchor retained it's 5.5mm deflection.
Drop
test 2:
A
76.5Kg weight was used and a fall factor 1 was created.
At
the critical load point, the resin cracked and the anchor
rotated further towards the direction of the load, the
deflection was too great to measure on a 00.01-10mm
gauge. Although the anchor had obviously failed, there
was very little rotational movement.
|
|
Notes
arising from the drop tests:
- There
is normally more than one anchor in a traverse line, therefore
the type of load and the fall factor used would not occur during
normal caving. Any loading of the traverse line would be shared
between anchors, thus reducing the generated forces. This though
is not strictly true, because when rigging traverses the person
rigging should ensure that the traverse line is kept taut. In
the event of a fall on the traverse line, this would produce an
angle of about 170' in the line at the point of loading. This
would result in the 100Kg original loading producing a load of
about 1146 Kg. on each anchor, with a total load of about 2292
Kg. Considered bad practise and bad rigging, a traverse line rigged
with excessive slack rope would offer a lesser loaded angle of
rope, resulting, in a reduced loading of individual anchors.
- The
test was extreme, to test the flexibility of resin bonded anchors.
As the result shows the anchor bent, but, held the load without
failure.
- It
is apparent from the static stress test and the bounce test, that,
the anchor does move when loaded from the side, as in traverse
lines. In fact, as a caving group progress along the traverse
to the head of the pitch, each anchor is being multi-directionally
loaded. If cavers use the rope to pull themselves up/along or
hang in their harnesses in mid-traverse, then, considerable stress
is being placed upon the anchor and resin bond.
- Although
the anchor and resin bond possess strength and flexibility, actions
as mentioned in 2 above, will, ultimately weaken the resin bond
prematurely. This though will not lead to a rapid failure of the
anchor or resin and may only show as a slight rotational movement
in time, I feel that it WOULD NOT compromise the safety of the
user, as anchors that have had slight rotational movement, have
proved, stubborn and hard to remove.
- When
using traverse lines, the body weight should be kept on the feet
and hand holds, the traverse line should be used as a safety line,
not as a means of suspension while traversing.
- The
practise of driving a groove with a chisel in the base of the
hole for about 45mm, will increase the surface area of the resin
and help alleviate slight rotational movement, All installers
who have attended the eco-resin training will be sent an amended
training procedure.
|
Anchor
number 3
Was
installed 3 metres from the ground using the correct method.
A thermometer was inserted with the anchor, the thermometer
was inserted to a depth of 45-mm, half the length of the anchor,
and was in contact with the anchor and resin.
|
This
test was set up to ascertain what amount of heat build
up would be created when a load is lowered on a rope
through the eye of the anchor.
A
51Kg. weight was used for this test.
The
temperature reading before the start of the test was
22'C.
After
10 ascents and 10 descents of the load, a total travel
distance of 60 metres, the anchor was too hot to touch,
the reading on the thermometer remained at 22'C.
A
further to ascents and 10 descents were conducted, the
reading on the thermometer remained at 22'C, the rope
/anchor contact area was extremely hot, after 3 minutes
the anchor could be touched without sustaining a burn.
This
test did glaze the rope and it was obvious that the
rope had been misused.
The
anchor, had a shiny area where the contact had taken
place, there was no obvious grove.
|
|
Notes:
- This
test was conducted mainly for the B.M.C. who 'lower off' after
a climb.
- The
test was conducted using a dry, clean rope. A wet rope would of
reduced friction resulting in a lesser temperature increase on
the exposed anchor, but, a dirty rope would definitely abrade
the anchor's contact curvatures and reduce the diameter of the
contact curvature to 6mm (the minimum) prematurely.
- There
is obviously no appreciable heat build up that is transmitted
to the resin, or down the shank of the anchor. Generated heat
obviously dissipates effectively through the surface medium.
- I
would not recommend that the anchors are used in this way, especially
underground, where the ingress of grit into the rope is inevitable.
Pulleys, crabs or maillons should always be used.
- Where
this practise is the norm, then, a careful, regular check should
be maintained to ensure that anchors stay within the minimum 6mm
in diameter in any plane.
Andy
McCarron...
andy.mccarron@yss.uk.com
|
