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.