HSEHealth & Safety

Executive

Testing and standards for rock reinforcement consumables

Prepared by Rock Mechanics Technology Ltd for the Health and Safety Executive 2006

RESEARCH REPORT 411

HSEHealth & Safety

Executive

Testing and standards for rock reinforcement consumables

Chris Reynolds, BSc (Hons) Rock Mechanics Technology Ltd

Bretby Business Park Ashby Road

Burton-on-Trent Staffordshire DE15 0QD

A research programme has been carried out by RMT in support of the revision of Part 2 of the British Standard for strata reinforcement support system components used in coal mines, specification for birdcaged cablebolting. The present standard is written around one principal long tendon design, and since its publication, a number of resin and cementitious grout bonded systems have been introduced to the mining industry. Additionally, tests to determine bond performance, given in the present standard, are increasingly recognised as unrealistic and new tests more accurately simulating in-situ performance were required.

The laboratory short encapsulation pull test was developed initially for rockbolt evaluation and, through a comprehensive test programme, it has now been refined further for determining axial bond performance of resin and cementitious grout bonded flexible systems. It was found that different procedures and bond lengths were required depending on the grouting medium employed.

Tests on all systems currently used in the UK coal mining industry were carried out with various bond lengths and control products were chosen, the results of which were used to determine benchmark performance data. Test procedures and benchmark recommendations have been supplied to the reviewing committee.

Existing shear test data was used to refine the procedure - for resin bonded flexible reinforcement systems. However, the basic procedure, as outlined in the current Standard, is recommended for retention in the revised Standard.

This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the author alone and do not necessarily reflect HSE policy.

HSE BOOKS

© Crown copyright 2006

First published 2006

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ii

CONTENTS

EXECUTIVE SUMMARY 1

1. INTRODUCTION 2

2. TEST METHODS 42.1 Tensile Tests 4

2.2 Shear Tests 5

3. RESULTS OF AXIAL EMBEDMENT TESTS 73.1 Test Results – Resin Bonded Systems 73.2 Test Results – System Bonded using Cementitious Grout 93.3 Double Embedment Tests with PUR 12

4. RESULTS OF SHEAR EMBEDMENT TESTS 14

5. SHEAR TEST DATA – CEMENTITIOUS GROUT BONDED TENDONS 16

6. DISCUSSION AND CONCLUSIONS 17

7. REFERENCES 19

iii

LIST OF TABLES

Table 1 Laboratory short encapsulation pull test results for Osborn Reflex flexible bolts 7

Table 2 Laboratory short encapsulation pull test results for MMTT flexible bolts, first submission 8

Table 3 Laboratory short encapsulation pull test results for MMTT flexible bolts, second submission 8

Table 4 Table 5 Table 6

Table 7

Table 8

Table 9

Table 10

Laboratory short encapsulation pull test results for Bridon flexible strand Laboratory short encapsulation pull test results for Megabolt Megastrand Laboratory short encapsulation pull test results for Mini-cage cables embedded in CBG grout – 325mm encapsulation Laboratory short encapsulation pull test results for Mini-cage cables embedded in CBG grout – 325mm encapsulation no breather tube Laboratory short encapsulation pull test results for Nut-cage cables embedded in CBG grout – 325mm encapsulation Laboratory short encapsulation pull test results for Nut-cage cables embedded in CBG grout – 325mm encapsulation Double embedment shear test results for Osborn Strata Products Reflex

9 9

11

11

12

12

flexible bolts 14 Table 11 Table 12

Double embedment shear test results for Megastrand flexible bolts Double embedment shear test results for long tendons

15 16

iv

LIST OF FIGURES

Figure 1 Double embedment tensile test for rockbolts, schematic diagram 20 Figure 2 Laboratory short encapsulation pull test, schematic diagram 20 Figure 3 Laboratory pull tests, variation of bond strength with bond length,

flexible bolt seven wire systems in ‘AT’ resin 20 Figure 4 LSEP test on flexible strand 20 Figure 5 Double embedment shear test, schematic diagram 21 Figure 6 Osborn Reflex flexible bolt with end fitting 21 Figure 7 Laboratory pull tests, Osborn Reflex flexible strand, 450mm

encapsulation / ‘AT’ resin 21 Figure 8 Laboratory pull tests, MMTT 19 wire flexible strand – first submission,

450mm encapsulation / ‘AT’ resin 21 Figure 9 Laboratory pull tests, MMTT 19 wire flexible strand – second

Submission, 450mm encapsulation / ‘AT’ resin 22 Figure 10 Laboratory pull tests, Bridon 19 wire flexible strand, 450 mm

encapsulation / ‘AT’ resin 22 Figure 11 Laboratory pull tests, Megastrand cable bolt, 450mm encapsulation /

‘AT’ resin 22 Figure 12 Laboratory short encapsulation pull tests, cable bolts and cementitious

grout, 450mm embedment 22 Figure 13 Laboratory short encapsulation pull tests, cable bolts and cementitious

grout, 325mm embedment 23 Figure 14 Laboratory short encapsulation pull tests, cable bolts and cementitious

grout, 325 and 450mm embedment 23 Figure 15 LSEP test assembly for cementitious grouted cables 23 Figure 16 Laboratory pull tests – gauge results, Mini-cage cablebolts with

breather tube, 325mm encapsulation / CBG grout single embedment tube & end fitting 23

Figure 17 Laboratory pull tests – gauge results, Mini-cage cablebolts - no breather tube, 325mm encapsulation / CBG grout single embedment tube & barrel / wedge 24

Figure 18 Laboratory pull tests – gauge results, Nut-cage cablebolts, 325mm encapsulation / CBG grout single embedment tube & end fitting 24

Figure 19 Laboratory pull tests – gauge results, Megastrand cablebolts, 325mm encapsulation / CBG grout single embedment tube & end fitting / nut 24

Figure 20 Results of shear tests on Osborn Reflex bolt embedded in ‘AT’ resin, 250mm embedment 24

Figure 21 Results of shear tests on Osborn Reflex bolt embedded in ‘AT’ resin, 500mm embedment 25

Figure 22 Results of shear tests on Osborn Reflex bolt embedded in ‘AT’ resin, 900mm embedment 25

Figure 23 Results of shear tests on Megastrand flexible bolts embedded in ‘AT’ resin 25

v

vi

EXECUTIVE SUMMARY

A research programme has been carried out by RMT in support of the revision of Part 2 of the

British Standard for strata reinforcement support system components used in coal mines,

specification for birdcaged cablebolting. The present standard is written around one principal

long tendon design, and since its publication, a number of resin and cementitious grout bonded

systems have been introduced to the mining industry. Additionally, tests to determine bond

performance, given in the present standard, are increasingly recognised as unrealistic and new

tests more accurately simulating in-situ performance were required.

The laboratory short encapsulation pull test was developed initially for rockbolt evaluation and,

through a comprehensive test programme, it has now been refined further for determining axial

bond performance of resin and cementitious grout bonded flexible systems. It was found that

different procedures and bond lengths were required depending on the grouting medium

employed.

Tests on all systems currently used in the UK coal mining industry were carried out with

various bond lengths and control products were chosen, the results of which were used to

determine benchmark performance data. Test procedures and benchmark recommendations have

been supplied to the reviewing committee.

Existing shear test data was used to refine the procedure - for resin bonded flexible

reinforcement systems. However, the basic procedure, as outlined in the current Standard, is

recommended for retention in the revised Standard.

1

1 INTRODUCTION

The British Standard 7861: Strata reinforcement support system components used in coal mines,

Part 2: Specification for birdcaged cable bolting (reference 1), is presently being revised. Since

the publication of this document, the range of long tendons available for reinforcement of coal

mine strata has increased to include additional varieties of cable bolts and also flexible bolts.

Generally the range of tendons now available can be conveniently categorised by grouping

products according to the embedment media used, as follows:

a) Resin bonded tendons – which would normally include all types of flexible bolt so far

available to the industry. Resin is also used to pre-bond tensionable tendons

preparatory to tensioning and post-grouting normally with a cementitious product.

Flexible bolts have been used since the early nineties and are installed by spinning

through long resin capsules with the intention of achieving full column bonding. A new

slower setting resin capsule was developed for the purpose. Installation through

capsules requires mechanical assistance and these bolts are installed using either

portable machines or hydraulic rigs. Installation at the face using hydraulic rigs is the

modern approach. The installation method demands that the tendon, whilst flexible, is

reasonably stiff in order to allow a level of machine thrust to be applied. Strands

commonly used for cable bolting are therefore precluded, and two main types of strand

of nominal diameter 22-23mm were used in development of flexible bolts – a seven

wire group and a nineteen wire group. Both types feature indented wires forming the

peripheral grouping to provide optimum bond stiffness, and consist of winding outer

wires around a central ‘king’ wire’ The nineteen wire strand features three different

wire diameters with the smallest wires about half the diameter of the largest. The seven

wire group is formed from wires about 10% smaller than the central ‘king’. Both types

have a semi-helical winding form which in itself contributes to bond stiffness when the

strand is embedded in resin and subjected to axial loading. Another product which is

included in this group, but which is radically different in construction, is the

Megastrand. This product would normally only be embedded in resin, partially, for pre-

tensioning purposes, and it consists of a group of profiled wires grouped around a steel

tube which is used for injection during post installation grouting.

b) Tendons bonded using cementitious grout – which would include conventional cable

bolts as covered by the existing version of reference 1. Cable bolts of the birdcaged

variety were used throughout the mining industry at the time of writing of the original

Standard and these are made from seven wire compact strand typically 15.2 mm in

diameter and to a British Standard (reference 2). The strand is supplied in wound form

and then, either by hand or by machine, unwound to reveal a bulb type structure

consisting of alternate nodes and anti-nodes. Axial embedment tests showed that such a

structure provides a very high level of bond strength and stiffness. Developments to

cementitious bonded tendons have been orientated toward speeding up installation –

principally through allowing the drilling of smaller diameter holes. The nut-cage and

mini-cage are similar in that they both use a bulb with a fixed pitch spacing. The nut-

cage uses a nut or ferrule on the king wire to provide the bulb geometry whereas the

mini-cage is manufactured by mechanically deforming the strand - compressing it

axially. Both types pair up similarly manufactured strands to form a double capacity

system. All cementitious long tendons used in the UK coal mining industry at present

employ the same specification of compact strand which in paired form has a tensile

strength of 600 kN.

It will be seen therefore, that the revision of the Standard is required to recognise the increased

range and complexity of long tendons in use, and in doing so revision of both specifications and

2

type performance tests is necessary. This document describes the development of test

procedures which are believed to be more appropriate to assessing the performance of long

tendons and presents test results from groups of tests carried out on available long tendons using

these procedures.

Additionally, interest in PUR grouting systems, particularly for embedment of long tendons

arose during the project period and tests were carried out as part of the project remit. Results of

tests – carried out in the main using existing methods, as defined in current standards – are

described briefly.

3

2 TEST METHODS

Tests currently specified in reference 1 to define long tendon performance, comprise double

embedment tensile and shear tests.

2.1 TENSILE TESTS

The Double Embedment Tensile Test (DETT) is the laboratory test specified in the current

versions of the British Standards for mining rock bolts and cable bolts (references 3 and 1) for

measuring system bond strength and stiffness for rock bolts and cable bolts. The test, illustrated

in Figure 1 is essentially an axial tensile test on the bolt or tendon / resin system. The tendon

under test is embedded in hand mixed resin (or in grout as appropriate) in two steel tubes with

an internal thread designed to ensure that, when the assembly is axially loaded, bond failure

occurs between the tendon and the resin. Thus the DETT measures the maximum load transfer

capability of a bolt or tendon / resin system in an ideal host medium.

The Committee reviewing the existing British Standard for rock bolts used in coal mines

considered that the double embedment tensile test was inadequate as a system performance test

for a revised Standard. It was considered to be a very artificial test which did not bear a

significant relationship to the reinforcement mechanisms mobilised in-situ. This was because

the rock, in which the rockbolt system works in-situ, was replaced by a steel tube machined to

ensure that failure was very unlikely to occur at the steel/resin boundary. Previous research

(references 4, 5, and 6) into rockbolt behaviour had shown that, in most cases, where a well

designed rib profile was used, system failure occurred at or associated with the rock / resin

boundary. Also, even when a poor or nearly smooth profile was used in a moderately rifled

hole, failure could still occur at the rock / resin boundary. This was attributed to the failure of a

poor bolt profile to generate significant normal forces against the rock wall. It was therefore

considered that the double embedment tensile test had significant shortcomings as a means of

assessing potential rockbolt system load transfer capabilities.

Experience with developing the Laboratory Short Encapsulation Pull Test (LSEPT) (reference

7) indicated that this test may be a feasible substitute for the double embedment tensile test for

determining a more realistic system bond strength and system stiffness. It was developed to test

the rockbolt / resin / rock system and is designed to simulate the underground installed

condition of the rockbolt. The LSEPT is undertaken in a rock cylinder which is confined to

simulate in-situ conditions and prevent premature failure of the cylinder. The basic arrangement

is shown in Figure 2. A biaxial pressure cell is used to confine a machined rock core sample

both for sample preparation and the test proper. Initially, the cell may be mounted horizontally

on a machine tool bed to allow for drilling of the test hole and, in the case of rockbolts, for

spinning the candidate bolt through grout to complete the installation. Following curing, pull

test equipment can be assembled onto the installed bolt while the cell is still mounted on the

machine tool, or with the cell placed on the floor, or installed into a testing machine. The

purpose of the test is to load incrementally the installed bolt and record the load and resulting

displacement. Plotting a load / displacement characteristic, suitably corrected for extension in

the unbonded section of the bolt, allows the determination of test parameters similar to those

defined for the DETT, as follows:

a) yield bond strength, defined as the load at which the slope of the load / displacement

characteristic falls below 20 kN/mm, and

b) the system stiffness or slope of the load / displacement characteristic over a specified

load range.

4

The LSEPT methodology and benchmark performance parameters have now been incorporated

into the draft revision of the Standard for rockbolts, and a decision was made to apply a similar

methodology for assessment of performance of long tendons, the reasons for replacement of the

double embedment test being equally valid for long tendon evaluation. However, it was

recognised that the methods would need adaptation to suit long tendons – one of the principal

differences being the bond length or lengths necessary for long tendon testing. Choice of bond

length is governed by the need to produce a high bond strength relative to the tensile capacity of

the bolt or tendon, but at the same time avoid reaching levels of bond performance which would

lead to the tendon yielding and hence distort the result into a test of the mechanical performance

of the tendon rather than the inter-related tendon / grout / rock performance. For flexible bolts

bonded with the standard UK polyester resin, research information, which would at least allow a

tentative judgment of required bond length, was already available. This is shown graphically in

Figure 3 – a plot of bond strength from various tests with seven wire strand to a base of the

bond length used. As expected, the characteristic is linear, so a prediction of optimum bond

length is straight-forward. Typical yield strength of currently available flexible bolts is around

400-450 kN. Allowing for variation in system performance, an optimum bond strength of 350

kN is probably correct and this indicates that a bond length of 450mm is appropriate. This bond

length was used for the first tests on all long tendons, and further optimisation is described

below.

2.1.1 Test methods - resin bonded systems For resin bonded systems, where strength development of the bond would be rapid – typically

two hours – it was found convenient to use a tensile testing machine equipped with

computerised data logging of test parameters. A view of the test arrangement is given in Figure

4.

The test procedure and hole diameters used were similar to those included in the draft revision

of Part 1 of the Standard. Initial bond length (450mm) was selected as described above.

The laboratory short encapsulation pull test requires a fitting or termination to be available on

the free end of the bolt or tendon for load to be applied. Most samples were supplied complete

with end fitting; however, one type of strand (Bridon) was supplied without fittings and a barrel

/ wedge assembly was used – with satisfactory results.

2.1.2 Test methods – systems bonded with cementitious grout Evaluation of systems bonded with polyester resin is made easier by the relatively rapid strength

development of resins. Tests can be commenced about an hour after preparation, and

preparation of the sample within a testing machine is practicable. For cementitious grouts, time

scales are quite different, with a curing time of typically 14 days required. Preparation within a

testing machine is not practicable and installation into a machine after preparation can be

difficult – depending on the design of machine available. It was therefore decided to revert to

use of a portable loading ram mounted on to the test-piece – as recommended for rockbolt

testing. However, and again to avoid problems with equipment utilization, it was initially

proposed to dispense with the biaxial cell, and use a method tried previously by RMT where the

rock core would be bonded into a stiff steel shell. In the event, this was the start of an

evolutionary process which is explained, with results, in section 3.2 below.

2.2 SHEAR TESTS

The double embedment shear test (DEST) is a standard type test described in reference 1, for

assessing the shear strength of cable bolt systems. Figure 5 shows a schematic diagram of the

double embedment shear test apparatus, which is basically a shear frame housing a double

embedment tube assembly. The test assembly is similar to that used for the DETT. The test

tendon is bonded using the candidate grout into two steel tubes which have been taped together.

Overall length of the tube assembly is currently specified as 900mm for cable bolts. The tubes

5

have a specified internal diameter with a grooved internal surface to promote a high level of

bond at the tube interface. The tube assembly engages with hardened steel bushes in the shear

frame, which is located in a tensile or stiff testing machine. For the test, load is applied to the

frame at a controlled rate until maximum load has been achieved; load and frame displacement

are recorded. Normally, three tests would be carried out 14 days after preparation of the

samples. A graph is plotted and maximum load noted for comparison with benchmarks given in

the standard. For double birdcaged cable bolts, the system shear strength must exceed 350 kN

(reference 1).

It was judged that the current method provides a ‘worst case’ measurement of shear

performance and that, for reasons outlined in section 6, it should if possible be retained. An

analysis of existing data from the current procedure was carried out, data short falls identified,

and hence additional testing carried out. This is reported below.

6

3 RESULTS OF AXIAL EMBEDMENT TESTS

3.1 TEST RESULTS - RESIN BONDED SYSTEMS

Tests were carried out on all flexible tendons available to the UK mining industry, as follows:

Osborn Reflex flexible bolt

MMTT flexible bolt

Bridon flexible strand (marketed previously by Exchem), and

Megabolt Megastrand reinforcement system.

The first three systems are generally used fully encapsulated with resin grout. The Megastrand

is usually point anchored with resin grout, and post-grouted with a cementitious product. The

tendon in general use in the mining industry – fully resin encapsulated – is the Reflex bolt. A

decision was taken by the Revision Committee that this should therefore be the base tendon, the

test results from which would be used to derive the acceptance criteria to be included in the

revision of the Standard. A photograph of the Reflex Bolt, with typical end termination, is

shown in Figure 6.

The tests on Reflex bolts were carried out at the trial bond length of 450mm. This produced

satisfactory results in terms of the bond strength obtained, and the same bond length was

therefore used for the remaining tests on other products.

Results from the short encapsulation pull test are interpreted to yield the following parameters:

a) bond strength – defined as the load at which the slope of the load / displacement

characteristic falls below 20 kN/mm, and

b) system stiffness – the slope of the load / displacement characteristic between defined

minimum and maximum loads, for example 40 and 80 kN. The maximum and

minimum loads for stiffness calculation are usually chosen to be approximately one

third and two thirds the bond strength acceptance level.

The results given below are as defined above.

3.1.1 Laboratory short encapsulation pull test results – Osborn Reflex bolt The results of the tests on the Reflex bolt are shown graphically in Figure 7 and are summarised

in Table 1 below:

Table 1: Laboratory short encapsulation pull test results for Osborn Reflex flexible bolts

Test reference Bond strength System stiffness (kN/mm)

number (kN) 40-80 kN 50-150 kN 100-200 kN

CR6 310.0 170.43 164.81 152.26

CR7 400.0 296.95 276.43 245.85

CR8 330.0 101.34 125.51 139.52

CR9 300.0 348.73 348.73 261.95

CR10 320.0 170.43 182.90 157.05

CR11 290.0 163.46 167.57 137.60

CR13 290.0 163.46 182.90 145.61

CR14 420.0 242.86 239.95 209.75

CR15 430.0 121.32 142.71 153.68

CR16 430.0 249.55 262.66 226.9

Mean

Best 3

352.0 202.85 209.42 183.02

426.7 298.41 295.94 244.9

7

3.1.2 Laboratory short encapsulation pull test results – MMTT flexible bolt, first submission

MMT supplied samples of 19 wire strand featuring a heavy indent on the outer wires. Further

samples supplied by MMTT exhibited a much lighter indent. The MMTT product was therefore

treated as two submissions. The results of the tests on the first submission (heavy indent)

MMTT bolt are shown graphically in Figure 8 and are summarised in Table 2 below:

Table 2: Laboratory short encapsulation pull test results for MMTT flexible bolts, first submission

Test reference Bond strength System stiffness (kN/mm)

number (kN) 40-80 kN 50-150 kN 100-200 kN

CR2 371.2 125.03 99.76 89.25

CR3 359.33 296.45 183.32 116.63

CR4 N/A 150.38 160.16 101.07

CR5 366.0 256.43 161.42 113.72

CR6 345.0 203.14 182.35 109.84

CR7 352.0 162.61 133.44 97.91

CR8 358.0 256.43 180.36 116.90

Mean

Best 3

358.6 207.21 157.26 106.47

365.5 269.77 182.01 115.75

3.1.3 Laboratory short encapsulation pull test results – MMTT flexible bolt, second submission

The results of the tests on the second submission MMTT bolt (light indent) are shown

graphically in Figure 9 and are summarised in Table 3 below:

Table 3: Laboratory short encapsulation pull test results for MMTT flexible bolts, second submission

Test reference Bond strength System stiffness (kN/mm)

number (kN) 40-80 kN 50-150 kN 100-200 kN

CR1 172.22 141.27 91.72 29.72

CR2 117.13 215.07 N/A N/A

CR3 172.44 137.46 88.54 28.43

Mean

Best 3

153.93 164.60 90.13 29.07

153.93 164.60 90.13 29.07

3.1.4 Laboratory short encapsulation pull test results – Bridon flexible strand A 19 wire strand with outer wires indented was originally supplied to the mining industry by

Exchem, manufactured by Bridon. Although no longer supplied, this strand was widely used,

and it was decided that it should be evaluated. Bridon supplied samples and the results of the

tests on these samples are shown graphically in Figure 10 and are summarised in Table 4 below:

8

Table 4: Laboratory short encapsulation pull test results for Bridon flexible strand

Test reference Bond strength System stiffness (kN/mm)

number (kN) 40-80 kN 50-150 kN 100-200 kN

CR1 285.4 149.28 126.20 84.22

CR2 323.7 158.11 151.19 109.01

CR3 371.4 123.83 158.61 132.03

CR4 343.1 108.42 127.64 110.19

CR5 336.4 99.52 96.96 86.18

CR6

Mean

Best 3

338.6 113.02 125.41 102.00

333.12 125.36 131.00 103.94

351.05 143.74 145.81 117.08

3.1.5 Laboratory short encapsulation pull test results – Megabolt Megastrand flexible strand

Megabolt (UK) Ltd supplied samples of strand consisting of 8 wires featuring a heavy indent

grouped around an integral central steel grouting tube. The results of the tests on the

Megastrand bolt are shown graphically in Figure 11 and are summarised in Table 5 below:

Table 5: Laboratory short encapsulation pull test results for Megabolt Megastrand

Test reference Bond strength System stiffness (kN/mm)

number (kN) 40-80 kN 50-150 kN 100-200 kN

CR1 450.0 303.25 325.30 287.82

CR2 452.0 121.22 189.64 225.54

CR3 457.0 1081.48 824.02 475.20

CR4 460.0 2000.00 1984.77 652.43

CR5

Mean

Best 3

460.0 769.43 1118.77 1011.97

456 855 889 531

459 1283 1309 713

3.2 TEST RESULTS – SYSTEMS BONDED USING CEMENTITIOUS GROUT

A survey of current usage in the mining industry showed that the mini-cage cable is now widely

used. This is a derivative of the Garford bulb cable, originating from Australia, and consists of

seven wire strand processed in a purpose built press which grips a portion of strand and

compresses it axially to form a bulb. The tendon comprises a length of strand bulbed to a

specified diameter and pitch. Two tendons can be clipped together to form a double capacity

system, and it is this version which is used widely in the UK. Since the mini-cage system can be

regarded as the benchmark product, initial tests were carried out using this product together with

a cementitious grout formed from OPC, fly ash and additives. The branded product tested is the

only grout currently used for the application in UK mines. Each batch mixed was sampled and

tested to ensure that it complied to the current BS7861-2:1996 for compressive strength.

3.2.1 Laboratory short encapsulation pull test results – Osborn Mini-cage The test methodology used for the first tests was similar to that developed for flexible systems

embedded in resin. This was a short encapsulation pull test with the candidate materials

embedded in sandstone cores. However, rather than deploy a biaxial pressure cell to prepare and

test the sample, it was decided to use a variant of the method previously used by RMT to

determine particularly the performance of long tendons when embedded in coal. Samples of

coal had been assembled in a steel shell and then grouted together, prior to drilling and

installation of the tendon. The stiffness of the steel shell was calculated to provide lateral

confinement as axial load was applied. The practical advantage of this method was that several

9

samples could be prepared and allowed to cure at one time, thus promoting reasonably rapid test

execution, because use of a biaxial cell for housing of the sample during curing would

effectively limit sample preparation to only one or two samples. For the initial tests, a bond

length of 450mm was selected, as this had already proved suitable for resin bonded systems, and

the DETT test for cementitious systems in BS7861 part 2-1996 also used a 450mm bond length.

The rock sample was first housed in a biaxial cell and the borehole drillied to the required depth.

Then the core was removed from the cell, and installation of the core into the steel shell,

followed by grouting of the tendon, carried out with the steel housing placed vertically on the

laboratory floor. Afer curing for 14 days, a hollow ram was set on the top of the test assembly

and then an end fitting comprising a double barrel and wedge assembly located on the

protruding strand and locked in position. Load was applied, and load and displacement at the

end fitting were recorded and plotted.

The test results – for ‘mini-cage’ cables housed in 45mm diameter holes and grouted with

cementitious grout – are shown in Figure 12. The results show a flaw in the method used in that

the ‘bond’ yielded unexpectedly early – in load terms – although examination of the samples

post-testing showed very little evidence of shear at either bond interface. The sectioning of the

samples also showed, unfortunately, that the core was fractured, mainly axially. The conclusion

from this was that the shells were not providing the confinement expected, allowing the

sandstone core to fail under lateral stresses induced by axial loading of the tendon.

It was then necessary to determine whether, if reversion to testing in the biaxial cell was

required, it was necessary to retain the core within the cell during curing. Such a requirement

would dramatically slow progress. Tests were carried out on samples retained in the cell and

compared with samples left to cure in free air. The results comparing single tests where curing

was carried out when confined or not confined are also shown Figure 12. The results show close

agreement indicating that curing while confined is not required. However, they also show that

the bond was sufficiently strong that yield of the tendon material occurred before bond failure.

This is unacceptable for a meaningful comparison of products and it was concluded that a

shorter bond length was needed.

Tests on birdcaged cables were carried out in parallel with the mini-cage tests and also with the

samples housed in steel shells. The results are also given in Figure 12, and were significantly

poorer than the mini-cage results. This was unexpected since birdcaged systems tested using the

DETT performed well. It was concluded that the geometry of the birdcaged system – where the

cage transition to a straight tale was protracted and occurred beyond the end of the bond –

caused premature failure starting at the mouth of the hole. It was therefore necessary to extend

the bond beyond the sandstone sample, and it was decided this should be done by housing a

section of strand above the sandstone sample in a double embedment tube.

The next tests were carried on mini-cage cables with:

a) curing while unconfined and using a biaxial cell to confine the sample during the test only,

b) using a bond length of 325mm, and

c) using a 450mm long embedment tube to bond the tail and to provide a reaction to the load

applied by the hollow ram.

Earlier tests were carried out using a 600kN capacity hydraulic ram. Incorporation of an

embedment tube to embed the section of strand external to the sandstone sample required a a

larger hollow ram, and a 950kN ram with consequently larger diameter centre hole was used for

the new tests. The results are given in Figure 13. Although a consistent series of results was

obtained, measurement of the position of the strands protruding beyond the steel embedment

tubes showed that some displacement occurred in the embedment tube, and since this is

reflected in the overall measured displacement, such movement, of any significance, is

unacceptable. Additionally, two tests were carried out with bird caged cables, and these are also

10

shown in Figure 13. The results show collectively, an initial high stiffness, followed by a partial

yielding of the bond, and then a gradual reduction in stiffness. The results indicate that the bond

length tested may be satisfactory, but it was decided to carry out further tests with two bond

lengths and with the steel embedment tube length increased.

The next tests were carried out on mini-cage cables as described above, but using two 450mm

long embedment tubes in series (900mm in all) to bond the tail and to provide a reaction to

load, and with bond lengths of 325mm and 450mm. The results are shown in Figure 14. They

confirm that an embedment length of 450mm is too long for this design of reinforcement in that

yield of the bond does not take place in the elastic range of the steel characteristic. They also

show that even doubling the embedment tube length did not prevent displacement within that

length, and in fact the additional length of tube introduced practical difficulties in succesfully

encapsulating such a long total length of embedment.

Another method of anchoring the end of the tendon while still providing encapsulation similar

to the in-situ application was required, and further tests were carried out on mini-cage cables

reverting back to a 450mm embedment tube but also utilising barrel / wedge asemblies above

the tube to minimise displacement outside the test embedment length. The arrangement is

shown in Figure 15. The results, for an embedment length of 325mm, are given in Table 6 and

shown graphically in Figure 16. They indicate consistent bond performance and data which can

be used to establish benchmarks for comparison testing of products intended for a similar

application.

Table 6: Laboratory short encapsulation pull test results for Mini-cage cables embedded in CBG grout – 325mm encapsulation

Test Reference Number Bond Strength (kN) System Stiffness (kN/mm)

150 - 300 kN

CR1 439.45 114.65

CR2 512.70 98.00

CR3 521.95 86.04

CR4 510.01 106.67

CR5 523.45 90.16

Mean

Best 3

501.51 99.10

519.37 106.44

The foregoing tests were carried out with a section of breather tube (of the type specified by

suppliers) included in the length of strand bonded into the core – as would be the case in-situ.

To determine and quantify the effect of the breather tube on bond performance, additional tests

were carried out with no breather present. Results are shown graphically in Figure 17, and key

results tabulated in Table 7. It will be seen that, within the limits of experimental error, the

breather had no effect on bond performance.

Table 7: Laboratory short encapsulation pull test results for Mini-cage cables embedded in CBG grout – 325mm encapsulation no breather tube

Test reference number Bond strength (kN) System stiffness (kN/mm)

150 - 300 kN

CR1 478.8 97.22

CR2 505.4 116.07

CR3 505.4 89.70

CR4 505.4 111.98

CR5 505.4 88.70

Mean

Best 3

500.08 100.74

505.4 108.42

11

3.2.2 Laboratory short encapsulation pull test results – Dywidag Nut-cage Dywidag Systems supplied samples of nut-cage strand which is similar to the mini-cage in that

it comprises two seven wire compact strands laid side by side with bulbs formed at intervals

along the length of each strand. Unlike the mini-cage, the bulbs are formed by rewinding the

strand over a spacing ring placed at a required pitch along the king wire. Originally the spacers

were hexagonal nuts – hence the name – but these have been replaced by non-metallic circular

rings. The tests were carried out at the bond length finalised in the mini-cage test series –

325mm – and the results are shown graphically in Figure 18, and key results tabulated in Table

8.

Table 8: Laboratory short encapsulation pull test results for Nut-cage cables embedded in CBG grout – 325mm encapsulation

Test reference number Bond Strength (kN) System Stiffness (kN/mm)

150 - 300 kN

CR1 445.58 97.22

CR2 395.60 116.07

CR3 416.45 89.70

CR4 420.40 111.98

CR5 433.50 88.70

Mean

Best 3

422.31 100.74

433.16 150.41

3.2.3 Laboratory short encapsulation pull test results – Megabolt Megastrand flexible strand The Megastrand system was included in both test groups since this system is normally resin

anchored at the distal end to enable pre-tensioning, and then post grouted via the integral

grouting tube. The cementitious grout tests were carried out with a bond length of 325mm; the

results are shown graphically in Figure 19, and tabulated in Table 9.

Table 9: Laboratory short encapsulation pull test results for Megastrand cables embedded in CBG grout – 325mm encapsulation

Test reference number Bond strength (kN) System stiffness (kN/mm)

150 - 300 kN

CR1 455.82 97.22

CR2 450.77 116.07

CR3 440.20 89.70

CR4 459.09 111.98

CR5 464.07 88.70

Mean

Best 3

453.99 100.74

459.66 136.41

3.3 DOUBLE EMBEDMENT TESTS WITH PUR

UK Coal Mining Ltd is considering use of polyurethane resin (PUR) for encapsulation of long

tendons installed in underground roadways. Tests were carried out on Megastrand flexible

tendons when encapsulated with PUR materials supplied by the French company A Weber, and

by Carbotech Fosroc of Germany. The polyurethane resin system supplied by Weber was a two-

part resin / catalyst system with a mixing ratio of 1:1. Initial tests using hand-mixing showed

that gel time was too rapid to allow preparation of cube or embedment samples. The company

then supplied a mixing / delivery kit comprising a twin barrel syringe and mixing lance for use

with a compressed air operated gun. This system allowed samples to be prepared successfully.

12

Two resin systems were supplied by Carbotech Fosroc – a PUR known as Bevedol / Bevedan

WT, and a silicate known as Geothix. For the purpose of the tests, the company provided and

operated the same mixing / pumping equipment as used underground for installation of these

products. The purpose of the tests was to assess the load capacity and stiffness characteristics of

the Megastrand / PUR system with reference to the criteria prescribed in the British Standard

BS7861: Parts 1 and 2 (references 1 and 2). Tests were carried out with total embedment lengths

of 250 and 900mm with Weber PUR. Tests on the Carbotech materials were undertaken at an

embedment length of 250mm only.

All tests failed to meet the requirements of the relevant standards by a considerable margin.

Previous tests with Megastrand using ‘AT’ polyester resins and the approved grout were

satisfactory and complied with standards. It is likely that a PUR formulation having a

compressive strength and elastic modulus similar to the approved polyester resin will be

required in order for double embedment test results to meet the required standards.

13

4 RESULTS OF SHEAR EMBEDMENT TESTS

A review of available data from shear tests on resin and cementitious grout bonded systems,

carried out on commencement of the project, showed that

a) sufficient data exists to allow a considered review of test procedures and benchmarks

b) the bond length used for cementitious grout bonded systems is already optimised, and

existing data is sufficient for a review of performance benchmarks, and

c) the bond length for resin bonded systems may not be optimised, and further testing is

required both to optimise bond length and establish performance benchmarks.

The Reflex Bolt was selected for resin bonding optimisation tests due to it being the benchmark

product in the category – as previously described. Tests were carried out with total bond lengths

of 250mm (the recommended length for rockbolts specified in reference 3), 500mm and 900mm

(as specified in reference 1 for cable bolts). All samples were embedded in steel tubes with a

27mm bore using ‘AT’ polyester resin. Test procedure was as described in section 2.2 and the

current standards for rockbolts and cable bolts (references 3 and 1). The test results are shown

graphically in Figures 20, 21 and 22, and tabulated in Table 10.

Table 10: Double embedment shear test results for Osborn Strata Products Reflex flexible bolts

Test reference number Embedment Maximum Mean Std deviation

length shear strength maximum shear about mean

(mm) (kN) strength

(kN)

DEST/0102/BC1 250 410.13

DEST/0102/BC2 250 440.88 414.6 31.4

DEST/0102/BC3 250 392.81

DEST/0102/BC4 500 381.86

DEST/0102/BC5 500 389.42 381.3 15.5

DEST/0102/BC6 500 372.55

DEST/0102/BC7 900 358.4

DEST/0102/BC8 900 360.84 362.2 4.62

DEST/0102/BC9 900 367.37

rockbolts

Ref 3 requirement for 250 250

Ref 1 requirement for

single birdcaged cables

900 200

Ref 1 requirement for

double birdcaged cables

900 350

The results show that all of the tests with 250, 500 and 900mm embedment lengths met the

requirement for maximum shear strength specified in reference 3 (for roofbolts), and reference 1

(for both single and double birdcaged cable bolts). The mode of failure in every case was the

shear of one wire of the strand group, rapidly followed by further individual wire failures until

the assembly was completely sheared. Maximum shear load consistently increased as

embedment length was reduced. This may be due to the ability of a longer embedment length to

stiffen the assembly, during shear, and produce a ‘cleaner’ shear. A shorter embedment length is

more likely to allow failure at the bolt/resin interface during displacement, and allow the strand

to be ‘dragged’ into the shear plane, promoting higher loads.

Displacement at maximum load, and at failure, was similar for all three test embedment lengths.

14

A standard deviation about the mean maximum load indicates improving repeatability with

increasing bond length. It can be concluded from this that optimum test bond length is the

longest evaluated – 900mm. This would be a logical step since the bond length recommended

for cables is already 900mm and these products are similar in load capacity.

Corroborative data for other resin bonded systems was required in order to provide

performance benchmarks. However, at this stage in the project, only one other resin bonded

product was still available for consideration and that was the Megastrand. This was therefore

tested as above, with a 900mm bond length, and results are shown graphically in Figure 23 and

tabulated in Table 11. For comparison previously obtained results with a bond length of 250mm

are also shown.

Table 11: Double embedment shear test results for Megastrand flexible bolts

Test reference number Embedment Maximum shear Mean maximum Std deviation

length strength shear strength about mean

(mm) (kN) (kN)

DEST/1201/CS4 250 383.5

DEST/1201/CS5 250 414.17 407.34 21.27

DEST/1201/CS6 250 424.36

DEST/0102/BC7 900 350.35

DEST/0102/BC8 900 314.3 335.14 18.67

rockbolts

DEST/0102/BC9 900 340.78

Ref 3 requirement for 250 250

Ref 1 requirement for

single birdcaged cables

900 200

Ref 1 requirement for

double birdcaged cables

900 350

15

5 SHEAR TEST DATA – CEMENTITIOUS GROUT BONDED TENDONS

Double embedment shear testing of tendons bonded with cementitious grout have been carried

out by RMT to the procedures required by reference 1 over a number of years so that a database

of results is available. A summary of results in no particular order of significance is given in

Table 12 below:

Table 12: Double embedment shear test results for long tendons

Product Detail Grout DEST

Bond Hole dia Load cap

len (kN)

Megastrand 27.5mm 8 wire MBS8RG CBG (14) 900mm 34mm 447

Sin Birdcage 15mm 7 wire CBG (14) 900mm 43mm 222

Dyform Cable 15mm 7 wire x 2 CBG (14) 900mm 52mm 487

Dble Birdcage 15mm 7 wire x 2 CBG (14) 900mm 52mm 458

Dble Nut-cage 15.2mm 7 wire x 2 275mm spacing CBG (14) 900mm 43mm 383

Dble Birdcage 15mm 7 wire x 2 Lokset CB 900mm 52mm 389

The majority of the tests were carried out using steel tubes with a bore of 52mm and overall

embedment length was 900mm. Average shear strength from these results was 439.8 kN.

16

6 DISCUSSION AND CONCLUSIONS

At the start of the project, a number of flexible bolt type products were available to the UK

mining industry and all of these systems were included in the research programme to evaluate

methods and benchmarks for axial bond performance. Over the period of the programme, some

of these products have been withdrawn by the suppliers and this is reflected in the shear test

programme which was carried out in the later stages. Nevertheless, choice of the industry

benchmark products to act as the control for the core of the research has remained valid in that

these benchmark products have retained their position in terms of usage.

The programme for evaluation of flexible tendons embedded in resin successfully provided a

methodology and data sufficient to provide benchmarks for inclusion in the standard. The

methodology is sufficiently adaptable to allow use of apparatus as specified for the procedure

adopted in the draft revision of reference 1 for rockbolts, or a tensile testing machine with

consequent advantages such as precise control of loading rate. The control product for the resin

bonding research was the Osborn Reflex Bolt and this is now, at the time of writing, the only

flexible bolt used by the UK mining industry. Bond length is a major parameter: it should be

chosen so that load developed during the test matches the typical duty of the product but at the

same time not greater than its yield strength. If that were the case the failure mechanism would

be plastic deformation of the strand rather than bond displacement, and that would defeat the

object. A bond length of 450mm was projected from previous research and this was confirmed

as suitable by the test programme. Data from the programme was sufficiently consistent that

performance benchmarks for recommendation to the committee revising the cable bolt Standard

(reference 1) could be determined, and at the time of writing, methodology statements and

advisory benchmarks had been submitted for inclusion in the draft Standard.

The test programme for products bonded with cementitious grouts was far more problematic,

and considerably more time elapsed before arrival at a satisfactory methodology and bond

length. Initial proposals as to methods and bond length – derived from earlier research – proved

unsatisfactory, and a development process was necessary to arrive at a method where bond

length was satisfactory, displacement took place only within the candidate bond length, and the

method was sufficiently practical to avoid undue cost or inconvenience. A test programme for

the control product – the mini-cage cable – has been completed and from this programme a

bond length of 325mm deduced as suitable. Tests on other candidate products were completed,

and, at the time of writing, benchmark performance figures have been proposed and a

methodology statement is in preparation for submission.

Consideration was given to development of a new procedure for determination of shear strength

performance. The existing double embedment shear test uses a guillotine type apparatus, the test

mechanism of which is unlikely to be duplicated underground. In fact all bolts and tendons

retrieved from failure situations have always shown evidence of tensile failure rather than shear,

although shear forces are usually evident in the deformation characteristics of the bolt or strand

– usually referred to as the ‘crank handle’ effect. Nevertheless, the existing test, is a worst case

scenario and does reveal the true shear properties of the product. It was concluded that the

method should be retained and that research should concentrate on optimisation.

The shear performance of flexible systems bonded with resin, was historically determined using

the method specified in the rockbolt Standard (reference 3) – although these systems were

neither rockbolts nor cable bolts, they were bonded with resin, like rockbolts. A test programme

to optimise the method concentrated on bond length, and tests with the control product with

various bond lengths have shown that a 900mm bond length is the most rigorous and provides

the most consistent data, and this length will be recommended to the revision committee.

17

Further tests on candidate products have been carried out at this bond length, and so a

recommendation on benchmarks can also be made.

Tests on tendons bonded with cementitious grout have historically been carried out with a bond

length of 900mm, and reference to the database and the work described above suggests that this

is still appropriate. Recommendations on benchmarks, based on information from the database,

will be made to the committee.

18

7 REFERENCES

British Standards Institute, 1996. Strata reinforcement support system components used in

coal mines. Part 2. Specification for cable bolts. BS 7861-2:1996.

British Standards Institute, 1980. Specification for high tensile steel wire and strand for the

pre-stressing of concrete. BS 5896:180.

British Standards Institute, 1996. Strata reinforcement support system components used in

coal mines. Part 1. Specification for rockbolting. BS 7861-1:1996.

Rock Mechanics Technology Ltd., 2001. Falls of ground risks in coal mine face roadways.

Contract research report 368/2001, Health and Safety Executive.

Rock Mechanics Technology Ltd., Performance tests for stranded ground reinforcement in

mines. Contract Research report 370/2001, Health and Safety Executive 2001.

Rock Mechanics Technology Ltd., 1999. Stability of long term roadways. Final report on HSE

research project 32.038.

Clifford B, Kent L, Altounyan P, Bigby D, 2001. Systems used in coal mining development

for long tendon reinforcement. 20th Int. Conf on Ground Control in Mining. Morgantown, USA.

19

Figure 3.

Figure 1.

0

50

Internally Threaded

Surface

125

mm

1

25

mm

Chuck Adaptor

‘AT’ Resin

Flexible strand

Joint

DOUBLE EMBEDMENT TENSILE TEST FOR ROCKBOLTS,

SCHEMATIC DIAGRAM

Pull Test Jack

Biaxial Cell

Flexible Strand Rockbolt

Flexible Strand

Rockbolt

Resin

Sandstone Rock

LABORATORY SHORT ENCAPSULATION

PULL TEST, SCHEMATIC DIAGRAM.

Laboratory Pull Tests

Variation of Bond Strength with Bond Length

100

150

200

250

300

350

400

450

100 150 200 250 300 350 400 450 500 550 600

Bond Length (mm)

Bo

nd

Str

en

gth

(kN

)

LSEP Test on Flexible Strand

Bi-axial Cell with

Test Sample

Installed

Bearing Plate

Tendon End

Fitting and

Bearing Plate

Lower M/C Platen

Upper M/C Platen

LVDT Attached

to Tendon

Figure 4.

Figure 2.

Flexible Bolt Seven Wire Systems in 'AT' Resin 20

Figure 5. Figure 6.

Figure 8.Figure 7. 21

Double embedment tube

containing flexible strand

in resin

Hardened steel

bushes interchangeable to

accommodate different

tube sizes

Load applied to upper section of shear frame only. Lower section remains static.

125mm 125mm

DOUBLE EMBEDMENT SHEAR

TEST, SCHEMATIC DIAGRAM

Laboratory Pull Tests

Osborn Reflex Flexible Strand

450mm Encapsulation / 'AT' Resin

0.00

50.00

100.00

150.00

200.00

250.00

300.00

350.00

400.00

450.00

0.00 2.00 4.00 6.00 8.00 10.00

Bond Displacement (mm)

Lo

ad

(k

N)

Laboratory Pull Tests

MMTT 19 Wire Flexible Strand - First Submission

450mm Encapsulation / 'AT' Resin

0.00

50.00

100.00

150.00

200.00

250.00

300.00

350.00

400.00

450.00

0.00 2.00 4.00 6.00 8.00 10.00

Bond Displacement (mm)

Lo

ad

(k

N)

OSBORN REFLEX

BOLT WITH END

FITTING

Lo

ad

(k

N)

Lo

ad

(k

N)

450.00 450.00

400.00 400.00

350.00 350.00

300.00 300.00

250.00 250.00

Lo

ad

(k

N)

Lo

ad

(k

N)

250.00

200.00 200.00

150.00 150.00

100.00 100.00

50.00 50.00

0.00 0.00

0.00 2.00 4.00 6.00 8.00 10.00 0.00 2.00 4.00 6.00 8.00 10.00

Bond Displacement (mm) Bond Displacement (mm)

Laboratory Pull Tests Laboratory Pull Tests MMTT 19 Wire Flexible Strand - Second Submission Bridon 19 Wire Flexible Strand

450mm Encapsulation / 'AT' Resin 450mm Encapsulation / 'AT' Resin Figure 10.Figure 9.

500.00 550.00

500.00450.00

450.00 400.00

400.00

350.00

350.00

300.00

300.00

250.00

200.00

200.00

150.00

150.00

100.00 100.00

50.0050.00

0.00 0.00

0.00 2.00 4.00 6.00 8.00 10.00 12.00

0.00 2.00 4.00 6.00 8.00 10.00

Bond Displacement (mm) Bond Displacement (mm)

Laboratory Pull TestsLaboratory Short Encapsulation Pull Tests

Megastrand Cable Bolt Figure 11. Cable Bolts and Cementitious Grout Figure 12. 450mm Encapsulation / 'AT' Resin

450mm Embedment 22

Figure 13. Figure 14.

Figure 15. Figure 16.

Laboratory Short Encapsulation Pull Tests

Cable Bolts and Cementitious Grout

325mm Embedment

0

50

100

150

200

250

300

350

400

450

500

0 2 4 6 8 10 12 14 16 18 20

Bond Displacement (mm)

Lo

ad

(kN

)

Laboratory Short Encapsulation Pull Tests

Cable Bolts and Cementitious Grouts

325 and 450mm Embedment

0

50

100

150

200

250

300

350

400

450

500

550

0 2 4 6 8 10 12 14 16 18 20

Bond Displacement (mm)

Lo

ad

(k

N)

Minicage 07 ­

325mm embed

Minicage 08 ­

325mm embed

Mini-cage 09 ­

450mm embed

Mini-cage 10 ­

450mm embed

Plastic tube 320mm

long, sealed at both

ends to prevent

ingress of grout

Laboratory Pull Tests - Gauge Results

Minicage Cablebolts with Breather Tube

325mm Encapsulation / CBG Grout

0

100

200

300

400

500

600

0 2 4 6 8 10 12 14 16 18 20

Bond Displacement (mm)

Lo

ad

(kN

)

Sandstone sample –

housed in biaxial cell

Hydraulic ram reacting

between sandstone

and end plate

End

plate

Steel

embedment

tube

Sandstone sample –

housed in biaxial cell

Hydraulic ram reacting

between sandstone

and end plate

End

plate

Steel

embedment

tube

LSEP TEST

ASSEMBLY FOR

CEMENTITIOUS

GROUTED

TENDONS

Single embedment tube + End Fitting 23

300

300

600600 L

oad

(kN

) L

oad

(kN

)

500500

400400

Lo

ad

(kN

)

Sh

ear

Lo

ad

(kN

)

300

200200

100100

00

0 2 4 6 8 10 12 14 16 18 20 0 2 4 6 8 10 12 14 16 18 20

Bond Displacement (mm) Bond Displacement (mm)

Laboratory Pull Tests - Gauge Results Laboratory Pull Tests - Gauge Results

Mini Cage Cablebolts - No Breather Tube Nut-cage Cablebolts

325mm Encapsulation / CBG Grout 325mm Encapsulation / CBG Grout

Single embedment tube + Barrel / Wedge Single embedment tube + End Fitting Figure 17. Figure 18.

600 450

400

500

350

400 300

250

200

200

150

100

100

50

0

0 2 4 6 8 10 12 14 16 18 20 0

0 2 4 6 8 10 12 14 16

Bond Displacement (mm) Displacement (mm)

Laboratory Pull Tests - Gauge Results Results of Shear Tests Megastrand Cablebolts

on Osborn Reflex Bolt Embedded in 'AT' resin 325mm Encapsulation / CBG Grout Figure 19. Figure 20. Single embedment tube + End Fitting / Nut 250mm Embedment

24

Figure 22.

Figure 23.

Figure 21.

Results of Shear Tests

on Osborn Reflex Bolt Embedded in 'AT' resin

500mm Embedment

0

50

100

150

200

250

300

350

400

450

0 2 4 6 8 10 12 14 16 18 20

Displacement (mm)

Sh

ear

Lo

ad

(kN

)

Results of Shear Tests

on Osborn Reflex Bolt Embedded in 'AT' resin

900mm Embedment

0

50

100

150

200

250

300

350

400

450

0 2 4 6 8 10 12 14 16

Displacement (mm)

Sh

ear

Lo

ad

(kN

)

Results of Shear Tests on Megastrand

Flexible Bolts Embedded in 'AT' Resin

0

50

100

150

200

250

300

350

400

450

500

0 2 4 6 8 10 12 14 16 18 20

Displacement (mm)

Sh

ear

Lo

ad

(kN

)

DEST/1201/CS4 - 250mm

Embedment

DEST/1201/CS5 - 250mm

Embedment

DEST/1201/CS6 - 250mm

Embedment

Sample 9002 - 900mm

Embedment

Sample 9003 - 900mm

Embedment

Sample 9004 - 900mm

Embedment

25

Printed and published by the Health and Safety ExecutiveC30 1/98

Published by the Health and Safety Executive 01/06

RR 411