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.

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.

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.

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.

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.

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.

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.

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.