李智 01080142孔庄煤矿1 8mt李智毕业设计hagan11

1、The effect of resin annulus on anchorage performance of fully encapsulated rockboltsPC HaganThe University of New South Wales (UNSW), SydneyA diverse selection of rockbolt designs and resin anchors are available for use inunderground mines. Research in recent years at the UNSW Mining Research Centre

2、 led to the construction of a rockbolt pulltesting facility. This facility has subsequently been upgraded, commissioned and initial test work has been completed to verify the pulltest process.A test program has been completed with the objective to understand the load transfermechanism and improve th

3、e general performance of rockbolts. This paper describes the results of this research.INTRODUCTIONTEST FACILITYDesign objectivesThe desirable attributes of a rockbolt test facility were seen as:Rockbolts are increasingly relied on as a keycomponent in the primary support mechanism of many undergroun

4、d mines. In the Australian coal mining industry, for example, over 5 million rockbolts are installed each year at a cost of over $A35 million.the facility should be capable of examining a widerangeofparametersassociatedwiththePreviousresearchbyUNSW,StrataControlinstallation of rockbolts and of repli

5、cating a widerange of conditions;tests should be carried out under controlled conditions to better ensure the repeatability of results;the facility should be available for use by industry (both suppliers of rockbolt systems and industry endusers) for such purposes as independently assessing the perf

6、ormance of new products or changes in the method of installation.Technology Pty Ltd (SCT) and Powercoal Ltd hasfound that over 30% of rockbolts are not providing optimum performance in coal mining environments (Galvin et al 2001).A research initiative has been launched combining theskills and experi

7、ence of industryand researchdevelopan rockbolts. Theexpertiseintheuniversitytounderstanding of fully encapsulatedbroad objective being to improve the performance ofrockbolt systems and hence improve overall safety in mines. This initiative resulted in the establishment ofThe design of the new test f

8、acility incorporates ahydraulic ram similar to that used in most rockbolt pullout tests. The ram can apply various load conditions to a rockbolt. A biaxial cell is used to hold the test specimen containing a fully encapsulated rockbolt. The test specimen may either be a sample of rock replicating th

9、e conditions in a particular mine or, a manmade material. The advantage of the latter is it mitigates many of the problems that can arise due to the variability in material properties between rock samples.a test facility at UNSW that operates withincontrolled laboratory environment.aAs part of this

10、initiative, the research aimed toquantify the sensitivity to changes in various rockbolt parameters on anchorage performance. This paper outlines the results found to date with regard to the thickness of the resin annulus on anchorage performance of fully encapsulated rockbolts.The effect of resin a

11、nnulus thickness on anchorage performance of fully encapsulated rockboltsFacility featuresThe test facility at the UNSW Mining Research Centre uses a modified workshop lathe as the test platform. The main components of the facility include:toinconsistentresults.Thepoormixingwasexacerbated by the sho

12、rt length of encapsulation.A mixandpour resin was subsequently used in thetest program. After mixing, the resin was injected into the hole into which the spinning rockbolt was rammed. The rockbolt was supported in the chuck while the resin was allowed to set for 10 min. The resin was then left to cu

13、re for a further 48 h with the rockbolt and sample standing vertically.a biaxial cell with an internal diameter of 145 mm,lengthof200 mmandratedmaximumconfinement pressure of 30 MPa mounted to thebed of the lathe;servocontrol hydraulic system used for precisecontrol of the loading rate of a 300 kNho

14、llow core ram during a pullout test;capacityIt was observed that with the change from a cartridgeresin to a mixandpour resin there was a near two fold increase in the maximum pullout load to approximately 200250 kN.computerised system to control the applied loadthrough the hydraulic system and monit

15、oractual load and displacement of the rockbolt.theEXPERIMENTAL PROGRAMTEST SAMPLE PREPARATIONProcedureIn summary, the test procedure involved a load being applied between the rockbolt and end surface of the test sample. This tensile load is intended to simulate the induced load on a rockbolt when se

16、paration occurs between partings in rock strata.Test samplesA cementitous grout (Celtite MG75S) was selected in place of cored rock samples in the test program. The strength of grout was approximately 75 MPa.In order to ensure uniform material properties, asingle batch of over 100 test samples was p

17、repared and cast in plastic moulds. Each core had a diameter of 145 mm and length of 200 mm. The samples were cured for at least 28 days before testing.During each test, the outer surface of the test samplewas subjected to a confinement of 10 MPa within the biaxial cell. Before a pullout test began,

18、 a valve was closed to stop the flow of hydraulic fluid to the cell. The level of confinement simulates in situ field conditions but it was also the minimum level necessary to support the sample in the cell during drilling and pullout test. A pressure transducer monitored any pressure change in the

19、biaxial cell during each test.A hole was drilled in each sample to a depth of175 mm using a drill rod mounted on the lathe. A chisel bit was used for the 26 mm hole and finger bits were used for the larger holes. A constant rotation speed and feed rate was used with water flushing to ensure uniform

20、roughness of the borehole.Rockbolt anchorageA Celtite 24 mm extra high strength CX rockbolt was used in the test program with a basic profile design as shown in Figure 1. The rockbolt has an inner core diameter of 21.7 mm, a diameter across the ribs of22.8 mm and rib spacing of 10 mm. The rockbolt h

21、as an ultimate tensile strength of 344 kN.The tensile load was applied by a hollow corehydraulic ram as shown in Figure 2. A pressure transducer measured the load on the rockbolt. An LVDT measured the displacement of the rockbolt as it was drawn out from the hole by the ram. The data acquisition sys

22、tem recorded the load of the ram and in the biaxial cell and as well as the displacement at a rate of 20 readings/s.Test parametersA combination of the load on the rockbolt and its displacement was used to assess the performance of the rockbolt anchorage system. Using this data, a load/displacement

23、curve was drawn after each test. Based on this curve, the following could be determined.Figure 1. Profile of the rockbolt used in the test program.Resin cartridges were initially used for anchoring,however, problems with poor mixing between the resin and catalyst and with the plastic packaging led2P

24、C Hagan, UNSW Mining Research CentreThe effect of resin annulus thickness on anchorage performance of fully encapsulated rockboltsMaximum pullout load (or MPL), that is the peakresistance sustained by the anchorage system. Stiffness of the system within the elastic region. Displacement to MPL.Stiffn

25、ess in the postfailure region.Residual stiffness of the system.shows the load/displacement curve for the 3 mmannulus test.A different behaviour was observed when the holewas opened out to 32 mm when the resin annulus reached 5 mm as shown in Figure 4.Figure 4 illustrates that the results were againr

26、easonably consistent. However, while initially the stiffness of the anchorage system was similar to that observed at smaller resin annulus, above a load of about 40 kN and in one instance 110 kN, a change occurred that resulted in a much greater displacementChangepointresistance.Load resistance 50 m

27、m.frompostfailuretoresidualat anominal displacement ofbeforemaximumloadwasachieved.Thisdisplacement was of a similar magnitude to therockbolt rib spacing.Figure 2. Test set-up showing the arrangement of the bi- axial cell, hydraulic ram, pressure transducer and LVDT.ResultsThe effect on anchorage pe

28、rformance of increasing hole diameter while maintaining rockbolt diameter was investigated and has been reported (Hagan and Weckert, 2002). Hole diameters of 26, 28 30 and 32 mm with corresponding thickness of the chemical resin annulus of 2, 3, 4 and 5 mm were examined. The test at each resin annul

29、us was replicated up to six times.Figure 4. Load/displacement curve for an anchorage system with a 5 mm annulus.The results from the test program are summarised inTable 1.There was little measurable change observed in the pressure of the biaxial cell during each test. The experimental noise tended t

30、o mask any changes that might have otherwise occurred. It might be expected that some change would occur during a pullout test as the resin dilates and contracts with the movement oftherockboltribs.Unfortunatelythecurrentmonitoring arrangement tended to even out anytransient changes in stress that m

31、ight occur along the length of the test sample. Alternate arrangements to monitor any induced stress changes are being considered in future experiments.AnalysisLittle difference was observed in the curves for resin annulus thicknesses of 2, 3 and 4 mm as indicated in the summary graph in Figure 5. T

32、he performance of the anchorage systems in these instances exhibited a relatively high as well as consistent level of stiffness up to the point of maximum pullout load (MPL); theFigure 3. Load/displacement curve for an anchorage system with a 3 mm annulus.ObservationsReasonable repeatability was obs

33、erved for each level of resin annulus as illustrated in Figure 3. This figure3PC Hagan, UNSW Mining Research CentreLoad (kN)Load (kN)300Test SeriesEC056 250EC053EC058 EC054200EC055 15010050001020304050Displacement (mm)300Test Series250EC068 EC070 EC067200EC069 15010050001020304050Displacement (mm)Th

34、e effect of resin annulus thickness on anchorage performance of fully encapsulated rockboltslatter being the maximum load bearing capacity of theanchorage system.TABLE 1Summary of test resultsat approximately 180 kN and 240 kN respectively. Thelowest MPL and postfailure stiffness were both associate

35、d with the smallest annulus which may indicate the need for a minimum amount of resin to ensure good bonding and load transfer between a rockbolt and rock.Annulus thickness (mm)units2345Limit of elastic behaviour - loadLimit of elastic behaviour - displacementStiffness within elastic regionMaximum P

36、ullout Load (MPL)Displacement at MPLStiffness within post- failure regionResidual load at post- failure/residual inflection pointDisplacement at post- failure/residual inflection pointResidual stiffness Residual load at50 mm displacementThe results indicated that a change in anchoragebehaviour occur

37、red at 5 mm. At this annulus it is possible that the material properties of the resin come into play and the resin no longer was solely a medium to facilitate the transfer of load between the rockbolt and rock.km1.501.801.601.00kN/mm99.485.010040.0kN225245240185mm4.805.104.8013.5kN/mm-1

38、6.9-23.0-26.6-16.3kN12512012590mm11.512.512.023.8kN/mm-1.49-1.42-0.94-1.27kN60709045Figure 5. Superimposed curves showing the average results for each annulus thickness.This initial elastic behaviour reflectedproperties of the rockbolt componentthe materialin the anchorThe impact of too large a resi

39、n annulus was areduction in the MPL. In this test program it was found that a change from 4 to 5 mm led to a near 25% reduction in the load bearing capacity of the anchorage system. Extrapolating this observed behaviour to even larger hole diameters and hence a greater resin annulus, it is possible

40、that at best the MPL for the anchorage system would be maintained at this lower level but it is more likely that it would reduce even further. Followup tests will be required to confirm this trend.system as well as the cohesiveness between therockbolt, resin and rock. As the MPL is less than theUTS

41、of the rockbolt, the MPL isfailure of either the resin/rock interface or both.likely to indicateorresin/rockboltBeyond the MPL, the resistancetothe externallyapplied load fell away with further displacement ofthe rockbolt until a residual resistance level was reached for the anchorage system. It is

42、interesting to note that this residual resistance still represented a reasonably high value equivalent to about 70% of the MPL.Significantly at this large resin thickness there was acorresponding threefold increase in the amount of displacement needed before the peak load was achieved.Consequently e

43、ven after failure of the resin interface,a fully encapsulated rockbolt can still provide an appreciable level of resistance against separation of rock strata.In practical terms this would indicate that for largeresin annulus, a higher degree of relaxation in the bedding, i.e. a greater amount of sep

44、aration between strata, must occur before the same load is achievedIt should be cautioned, however, that the level of thisresidual resistance might be dependent on the nature of material properties of the surrounding rock mass and further testing would be required to confirm paredwithasmalle

45、rannulussystem.Alternatively, the ability of the anchorage system toresist separation reduces with large resin annulus. Hence the anchorage system with an unduly largeIn each case, except for the 5 mm annulus, the limit ofelastic behaviour and the MPL were fairly consistent4PC Hagan, UNSW Mining Res

46、earch CentreLoad (kN)3002502 mmannulus2003 mmannulus4 mm annulus5 mm annulus15010050001020304050Displacement (mm)The effect of resin annulus thickness on anchorage performance of fully encapsulated rockboltsresin annulus is less likely to act as an effective rocksupport mechanism.Hagan, P C and Weck

47、ert, S, 2002. Anchorage andfailure mechanisms of fully encapsulated rockbolts (Stage 2) interim progress report. ACARP Project C10022, April.CONCLUSIONThe test program indicated thatthere was anoptimum range of resin annulus thickness withinwhich there was little change in the performance of a fully

48、 encapsulated rockbolt anchorage system.OriginalversionofmanuscriptpublishedinProceedings of10th International Conference on Rock Mechanics, September, 2003, (South African Institute of Mining and Metallurgy: Johannesburg).Either side of this optimum range there was areduction in the MPL as well as other properties of the anchorage system. For example, it was