Abrasivity of Hawkesbury Sandstone Verhoef

Quarterly Journal of Engineering Geology and HydrogeologyAbrasivity of Hawkesbury Sandstone (Sydney, Australia) in relation to rock dredging Peter N. W. Verhoef Quarterly Journal of Engineering Geology and Hydrogeology 1993; v. 26; p. 5-17 doi:10.1144/GSL.QJEG.1993.026.01.02 Email alerting service click here to receive free email alerts when new articles cite this article Permission request click here to seek permission to re-use all or part of this article Subscribe click here to subscribe to Quarterly Journal of Engineering Geology and Hydrogeology or the Lyell Collection Notes Downloaded by Victoria Roads Library on 6 November 2007 © 1993 Geological Society of London The F-value has shown a tendency to be linearly related to abrasive wear (Schimazek & Knatz 1970. Major tunnelling projects have been carried out in this rock and increasingly use has been made of mechanical excavation methods. O. The Malabar Ocean Outfall Decline passes through Hawkesbury Sandstone and was partially excavated by mechanical means. As rock dredging is a relatively recent development it can profit from the experience gained in mechanical tunnel excavation. W. the rock cuttability and wear tests developed by Roxborough (1987) and the Cerchar test and Goodrich test (Bamford 1984. will always necessitate a trial dredge excavation to calibrate and to check the appropriateness of the abrasivity parameters chosen. Van den Bold & Vermeer 1990). data have been published on the cuttability and abrasivity 1 of the rocks excavated (Lowe & McQueen 1988. For the two recent projects carried out in the Sydney region. This paper compares the available site investigation and laboratory data with the excavation performance of the dredger. are underlain by the Hawkesbury Sandstone. Large parts of the Sydney area. Australia) in relation to rock dredging Peter N. Section of Engineering Geology. In this paper special attention is given to the F-value developed by Schimazek & Knatz (1970). This situation provided an opportunity to compare the available information on tool consumption and abrasivity of both projects. Verhoef. correlations with laboratory cutting and abrasion tests are not always significant. Site investigations for rock dredging projects would be improved if systematic determinations of the F-values were carried out. Experience with tool wear prediction in rock dredging (Verhoef 1988) is limited. 5-17. The Hawkesbury Sandstone is of Triassic age and up to 290m thick. potential tool consumption is a significant factor in the estimation of contractors' costs. Tool wear in rock cutting dredging appears to be related mainly to the abrasivity of the excavated rock in one way or another. as contractors usually consider their tool consumption and production data to be highly confidential. P. The F-value is obtained from a number of easily measured rock parameters (Brazilian tensile strength.50 © 1993 The Geological Society Abrasivity of Hawkesbury Sandstone (Sydney. Accurate prediction. Paschen 1980. cited in Braybrooke 1988) are used in site investigations to assess abrasivity of rock for tunnelling or mining purposes. partially cut in rock of the Hawkesbury Sandstone. The Netherlands Abstract During rock cutter dredging for the trench for the Sydney Harbour Tunnel. Cuttability is influenced by the abrasivity of the rock as it may blunt the tools resulting in an increase of cutting energy required. 1990). however. It appears that while the F-values correlate well with actual tool consumption. On two of the Outfall tunnels. For the Sydney Harbour Tunnel. 1976. 0481-2085/93 $03. a weak to moderately strong quartz-rich rock. Certainly in Europe the F-value is used to assess abrasivity of rock. . During the tendering stage. consisting partly of land tunnels and partly of immersed reinforced concrete tube elements in the harbour. This would help to improve the 'educated guesses' of tool consumption currently practised during the tendering stages of a dredging project. Unusually the contractor made excavation data available for analysis. 1). Verhoef Delft Technological University. Lowe & McQueen (1988) give data on the rock properties and the tool consumption rate and provide an analysis of roadheader performance. 1Cuttability refers to the facility of rock to be excavated by cutting tools. considerable attention has been paid to the abrasivity of the Hawkesbury Sandstone (Fig. In Australia. Box 5028. mineralogical composition and grain size. and with the cutting and abrasive wear rates as determined by the Newcastle-upon-Tyne cuttability tests. Faculty of Mining and Petroleum Engineering. Introduction One of the major problems in rock dredging projects is the correct prediction of tool consumption.) Use of the F-value is considered advantageous compared to laboratory tests which measure the abrasivity of rock directly because it is difficult to perform sufficient abrasivity tests to cover the variability inherent in a rock mass and it is impossible to perform laboratory tests that are truly representative of the actual cutting and abrasion mechanisms operating.Quarterly Journal of Engineering Geology. the Sydney Harbour Tunnel and the Sydney Ocean Outfalls. the trench dredged for the tube elements was excavated partially in rock. using a rock cutter suction dredger. tool consumption data were obtained and compared with the wear value F developed by Schimazek. 2600 GA Delft. 26. including the Harbour. Values of F can be obtained from rock samples using the Brazilian tensile strength test (on saturated specimens for dredging projects) and by studying thin sections of the same sample under the microscope to obtain information on mineralogy and grain size. Engineering properties of the Hawkesbury Sandstone Pells (1985) has given a comprehensive review of the properties of the Hawkesbury Sandstone in the Sydney area.. The data on the Malabar project came from Lowe & McQueen (1988) and data on the dredging project were compiled by Watson (1990). Hardness of minerals other than quartz may be accounted for by expressing their hardness relative to that of quartz..). Thus. Voest-Alpine Bergtechnik uses graphs containing the F-value and unconfined compressive strength to predict the consumption of several types of tungsten carbide chisels (K. Eq Qtz is the equivalent quartz volume percentage and ¢ is the grain size (mm).6 P. pers. Locally mudstone or shale is . comm. F=Eq Qtz x 0 x BTS 100 (N/mm) (1) where F is Schimazek's wear factor. VERHOEF SUBURBAN SYDNEY (J 0 TH HEAD OUTFALL SYDNEY HARBOUR BONDI OUTFALL SYDNEY HARBOUR TUNNEL MALABAR OUTFALL N BAY (J . t KM ~ FIG... As the Schimazek method was not used during the site investigation programme of both projects. tool consumption data of projects for which the F-value was determined are unknown to the author. Only tool replacement data considered representative of normal rock cutting dredging operation were used.. L o c a t i o n m a p ... W. especially in coal mining and tunnelling. The rock abrasivity data were compared with tool replacement data. Braybrooke (1988) shows graphs published by Voest-Alpine on pick-usage of Voest-Alpine's AM 100 roadheader using Schimazek's F-value. Gehring 1991. The mass structure is typically mega crossbedded which has been described by Herbert (1976) to be the result of braided river deposition in a Triassic environment comparable to the present River Bramaputra in Bangladesh.. The rock mass consists dominantly of massive sandstone beds. 5 LUCAS HEIGHTS Q. N. 1. However. the necessary parameters were not readily obtainable and had to be partially inferred. typically 2-5 m thick. but locally up to 15m. CV 22%). with UCSdry values also occurring in the strong (50-100MPa) range. Two main groups of rock types were present: sandstones and siltstone-shale laminites. Table 2 shows that in ten instances the F-values could be calculated for samples collected from the over-water boreholes and relevant for the rock dredging.1 8.0 3. 27 samples obtained from cores of ten over-water boreholes for the Sydney Harbour project were examined in thin section. . which is rather high for sandstones (a value of 20% is common.5 24. rock mass properties. The data have not been included in Table 2 because the cores had suffered from ageing which would influence the test results. UCS/BTS. The data fit the range of properties as described by Pells (1985) although the ductility number ~ (UCS/BTS) seems lower.% (range 71-89%. Table 1 gives the mineralogical composition as assembled by Robson (1978) and cited with other data by Pells (1985). with some siderite.5 (1.5-50MPa). In each case saturated BTS mineralogy and grain size were determined on one sample and reported in the site investigation report. Most unconfined compressive strength values fall in the moderately strong group (12. The major minerals present were quartz and clay with subordinate iron hydroxides and carbonate (possibly siderite.8 7. is an indicator for the mode of cutting.4 Dry bulk density (Mg/m 3) Porosity (%) 2. feldspar and silt size particles) Matrix clay (kaolinite. UCSsa t values being only 30-67% of the dry strength 7 values measured.32 mm (range 0.25--0. expressed by the coefficient of variation (CV) is somewhat more than 20% according to the data given in Pells' paper. TABLE 1. 9 15 is average and greater than 15 indicates brittle behaviour. mixed layer clay) Secondary silicates 58.1 0.37 16.3 to 1. usually interbedded with the sandstone.4 4. The sandstone is composed of subangular quartz grains in an argillaceous matrix. Mineralogical composition of the Hawkesbury Sandstone (average of 42 samples from 16 locations in Sydney basin) Mineral Fractional (%) Standard deviation Quartz (sand size) Others (rock fragments. Cuttability and abrasivity of Hawkesbury Sandstone To be able to make predictions on the performance of a rock cutting machine excavating a rock mass. The results of these tests will be discussed in a later section of this paper.ABRASIVITY OF HAWKESBURY SANDSTONE present in layers up to 2 m thick. Disregarding the siltstone-shale laminites.5 (%) Data from Robson (1978). a value less than 9 indicates ductile cutting behaviour. The mega cross-bedded structure results in a spatial variability of the rock material distribution on outcrop scale. 1The ductility number or brittleness ratio. range: 12 to 15 BTS). cutter head operation.4 13. Unfortunately no correlations between I s and UCS or BTS could be derived from the site investigation reports. being in the range 7-12. Pells gives correlations between axial point load strength Is axia~ and UCS and also between the Brazilian tensile strength (BTS) and UCS.6. The compilation of data on strength variation in the Hawkesbury Sandstone in the Sydney area given by Pells (1985) is relevant to the present study. iron hydroxides stain the rock through thin layers or laminae and may act as cement. CV 34%). Roxborough 1987). the factors that affect the performance of mechanical rock excavation systems can be grouped under the following headings: cutter head design. Based on data from Ferry (1983) he concluded the UCS was 20 times the Is axi~ and UCS = 13 BTS (modal values. The variability of the quartz content.7) S axial" Table 2 gives a summary of the data on engineering geological properties of the Hawkesbury Sandstone at the site of Sydney Harbour Tunnel. From these data the correlation between point load strength and Brazilian tensile strength (necessary for this study to estimate F-values from the borehole records) has been derived as: BTS = 1.5-17. the modal quartz content of the 19 sandstone samples estimated with the use of density diagrams was 74 vol. Accessory minerals present are tourmaline and zircon. The test results of Roxborough (1982) on Hawkesbury Sandstone from the Sydney Outfall project for 16 data pairs gave an average of 9 and a range of 5. White mica grains occur in minor amounts and occasionally microcline feldspar is found. In certain zones. illite. According to Gehring (1987). CV 14%). from Pells (1985) As part of the present study. cf. For the present study additional tests on cores from the over-water boreholes have been performed.46mm.2 2. The variability of unconfined compressive strength values of the Hawkesbury Sandstone is about 35%. it is necessary to understand the excavation process.13 3. in some samples dolomite crystals have been observed). Mean grain size was 0. According to Roxborough (1987). Moisture has a pronounced effect on strength. The modal clay content was 13% by volume (range 5-20%. 6 (1.03-1. The cutter head operation refers to the applied energy input.3) Over-water boreholes No (n) Mean (Range) -26 -26 6 13 13 -4 4 -6 --10 22. V E R H O E F TABLE 2. If the core has not been broken it may be rotated .4-6. It can also be used to compare the cuttability of different rock types (using a standard cutting test) and from the result it is possible to approximate the potential excavation rate for a particular machine type in a given rock.9) 1./d. The test is standardized to exclude machine design influences and consists of cutting a groove 12. steel for cutting dredgers) per unit cutting distance (mg/m).9) 8.1 mm) Cerchar Abr.8-10. the energy or work required (cutting force F¢ times distance travelled L) to cut a unit volume of rock (V). T h e core c u t t i n g t e s t In the late 1960s a cutting test was developed by Roxborough and co-workers at the Mining Engineering Department of the University of Newcastle-uponTyne (UK).6) 3.83-4. (mg/m) Cerchar Abr. (mg/m) Abr. information on which can be obtained from the following rock properties (Roxborough 1987. (MPa) Ductility number UCS/BTS Qtz (%) Qtz eq (%) SE dry (MJ/m 3) SE sat.87 (0.1 mm) F-value sat. The environment refers to dry or wet excavation conditions and encompasses the external physical variables such as ambient temperature and pressure.7) 4.3-13.9 (16.2) 60 (19-82) 62 (24-83) 11.25 (3. According to Roxborough (1987).8 (2. measured as the weight loss of tool material (usually tungsten carbide.4-13.2-93) 22.14 (0.11) 1.6 (8. see also Fig. The machine characteristics needed for a certain type of rock are governed mainly by its cuttability.8 (4-46) 4.07) Sources: Pells (1990).5-9. (4) Cutting tool wear rate: the rate at which a cutting tool wears in a given rock. (3) Specific energy: SE = F. dry (0. The core is then rotated by 180 ° to make a similar parallel cut.0-5. (0.0-6. From the specific cutting force the torque and power required to cut a rock at a specified rate can be determined while the force that must be provided by a machine's thrusting system to achieve and maintain the required depth of cut can be calculated from the specific normal force.6 (29-67) 21.8 P. This parameter may be used to measure the efficiency of a rock cutting system within a given rock.13 (1. Roxborough (1987) points out that the question of cuttability of rock is largely determined by the rock mass properties at the site. The choice requires the selection of a type of machine and then adapting it to the site conditions. The cutting test was developed to determine the four machine performance parameters on core samples. wear dry (mg/m) Abr.15) 0.6 (10.0-12.44-2. the mean force acting on a pick or chisel in its cutting direction (F¢) per unit depth of cut (d).2 (7.70 (1. (MJ/m 3) Cutting wear dry (mg/m) Cutting wear sat.L/V.11-1.8-10.0 (2.5 (6.7) Southern Tunnels No (n) Mean (Range) 18 14 16 --10 -10 ---9 -6 6 -- 42.0) 76 (66-80) 11.61 (0. (MPa) BTS dry (MPa) BTS sat.0 (8-40) 3. sat.2) 4.0-34.3 (1. (N/mm) Northern Tunnels No (n) Mean (Range) 70 55 45 --10 -10 3 4 -9 -19 --- 42.80) 4.0-1.3) 4. with lower values indicating higher efficiencies.7mm wide and 5 mm deep along the surface length of a rock core sample parallel to its long axis (Fig.6 (1. (2) Specific normal force: F. Coffey & Partners SI reports (1987). the mean force acting on a cutting tool normal to its cutting direction per unit depth of cut (d).57-1. Cutter head design refers to the geometry and the material properties of the cutting tools. F-values calculated from data SI report.8) 70 (40-82) 10.8-8. W.4) 9.6 (9. specific energy and tool wear rate provide the most useful basis on which to relate machine potential to rock properties. the forces and velocities involved and the environment in which the cutting operation takes place. N.98) 0. Both specific forces are known to increase linearly with depth of cut. wear sat. Summary of geotechnical properties of the Hawkesbury Sandstone at the Sydney Harbour Tunnel site Test UCS dry (MPa) UCS sat.0 (2. 2): (1) Specific cutting force: F¢/d.7) 1.4-5. This test aimed to assemble information on the relevant parameters which might describe the performance of an excavation machine in a rock mass. 2).3 (10. 7 mm insert: tungsten carbide 12. TABLE 3.7 .7 mm wide with a front rake angle of 0 ° and a back clearance angle of 5°. Specifications for rock cutting test (UNSW. Roxborough and co-workers have performed a suite of index tests on the rock materials used.~" rnm e" CORE SAMPLE FIG. placed in a lathe rotating at . Attempts were made to relate relevant index tests and the rock cutting parameters to the actual performance of tunnelling machines. WC 90.7mm wide. For each rock core tested a new tungsten carbide chisel-shaped cutter insert is used. The amount of rock cut from each groove is measured and used to calculate the specific energy. porosity). The execution of the test is straightforward.. The specifications of this cutting test are given in Table 3. considerable amounts of rock core are required to obtain a good impression of the variation in rock cutting characteristics for a certain SANDSTONE 9 rock mass.. 12.. Roxborough (1987) points out that. The test arrangement is placed on a shaper. Significant chipping relates to the magnitude of the peak component forces measured during the test. physical properties (density..6 Mg/m 3.25 UCS + C(N/m 2) (2) where SE = specific energy. This relationship allows cutting tests to be used and advantage taken of the more numerous data on UCS to make an analysis of the variability of strength in the rock mass to be excavated.. From the beginning of the development of the cutting test. density I4. again to make a third and fourth cut. Roxborough found: SE = 0. the major drawback of the method is the difficulty of performing sufficient tests for the results to become representative. grain size and shape. UCS. Roxborough considers the wear of the carbide inserts in the cutting test to be attributable to two sources. Grain size 6 ~tm..59 _+ 0. hardness HV2o = 1225kgf/mm 2. Hence relationships of cutting parameters with index tests are important..5%. However. UCS = unconfined compressive strength and C is a constant found by linear regression and dependent on rock type. BTS... which can be applied to the excavation performance prediction. including petrographic examination (mineralogy... back clearance angle 5° Material properties: grade B23. The tungsten carbide insert is weighed before and after the set of up to four cuts and its weight loss is used to determine cutting wear. The latter mainly occurs when rock of high strength is tested. Shore hardness. namely abrasion and brittle chipping of the metal. The insert is 12. The core abrasion test The abrasion test was developed to investigate the contribution of abrasive wear. length preferably 200250 mm.. front rake angle 0°. The impact chipping usually takes place at the cutting edge and corners of the inserts in the cutting test. A limiting minimum diameter of 50 mm for the rock core is required because the breakout angle of rock chips is dependent on the radius of the core. McFeat-Smith & Fowell (1977) found linear correlations between laboratory specific energy and in situ specific energy and between laboratory cutting wear and pick replacement rate for a Dosco road header in relatively massive rock (no significant discontinuities). ~ . probably more importantly. In addition a relation between SE and field cutting rate was found (see also Speight & Fowell 1987). Results of these index tests have been correlated with the parameters obtained from the cutting test by means of multiple linear regression techniques (McFeat-Smith & Fowell 1977).. If the core is 250 mm long a maximum length of 1 m can be tested. but the equipment necessary is quite exclusive and. NCB cone indenter and Schmidt hammer rebound. The principal forces acting on the chisel are measured by means of a triaxial dynamometer to which the cutting tool is attached. although these relationships look promising. The forces are measured continuously during the cut and logged on computer. Composition: Co 9. rock core: diameter larger than 50 mm. According to Roxborough (1987). 2.5%. but would apply only to machines which have a constant depth of cut. This is performed on a core of the same rock. cementation). Test arrangement of the Newcastle-upon-Tyne cutting test.ABRASIVITY OF H A W K E S B U R Y DYNAMOMETER[~ PICK HOLDER ~ IDIRECTION CARBIDE INSERTa-~--~ OF CUTTING . equation (2) is basically sound. For the laboratory cutting test. Sydney) cutting speed 105 mm/s cutting depth 5 mm cutting width 12.. with small diameter cores the rock yield is reIatively lower and the specific energy higher than for a larger core of the same rock. (--) Talc Gypsum Calcite Fluorite Apatite Window glass Orthoclase Quartz Topaz Corundum 1 2 3 4 5 5. Schimazek used the following methods to obtain the necessary parameters for the F-value: Petrographic examination. In October and November 1990 the author undertook further tests on old rock cores from .4 15 31 100 146 833 Feldspars Clay & micas Carbonates ---- ---- 3l 4 3 An abrasivity index: Schimazek's F-value Another method of assessing abrasivity was developed by Schimazek (Schimazek & Knatz 1970. Brazilian strength data were available and for the rocks tested the mineralogical composition could be inferred from petrographically similar samples taken near-by so that F-values could be calculated. Relative hardness of minerals with respect to quartz was determined using Rosiwal's hardness scale (Table 4). which rather surprisingly shows no apparent relationship between the F-value and the results of both cutting wear and abrasive wear rates.5 (Paschen 1980). but the more complicated formulae do not seem to apply to general situations (Bisschop 1990). Both Paschen (1980) and Verhoef et al. such as grain angularity.m. 3). using similar testing procedures. using point The following adaption has been made with respect to the standard practice of determining the F-value. The forward feed is taken at 0. which influence abrasive wear (Verhoef et al. with the shallow depth of cut and the very low forces applied ensuring that virtually all wear is the result of abrasion. Test arrangement of the Newcastle-upon-Tyne abrasion test. Mohs' H. Cutting and abrasion testing of Hawkesbury Sandstone Cutting and abrasion test results were available from the Sydney Outfall Tunnels and the Sydney Harbour Tunnel projects. The abrasive wear can be expressed in weight loss of carbide divided by cutting length (mg/m). Extensive multiple linear regression analyses undertaken by Paschen (1980) resulted in improved correlations. The results of pin-on-disc abrasivity testing applied to artificial and sedimentary rocks appeared to correlate linearly with a wear factor F.1 to 0. 1976). (kgf/mm 2) Rosiwal H. it is necessary that these are obtained in a standardized way. to appreciate the relative contribution of abrasive wear. counting techniques.2 mm per revolution. The mineral contents were obtained from thin section study. The average grain size was estimated by multiplying the average intercept length by 1. To be able to use and compare data. Tensile strength was determined using the Brazilian split test on dry specimens. Considering its simplicity and referring in advance to additional complications due to the dependence of abrasion on the 'tribological system' (see discussion) it seems preferable to use the F-value as defined by Schimazek (equation (l)). Also.2 5. W. which has been given as equation (1) in this paper. and feeding the tungsten carbide insert (identical to the cutting test) at an angle of about 45 ° axially along the outer surface of the core (Fig. 1990). the Schimazek factor does not include microfabric factors. This implies that the Fvalue data used in this paper may not be compared directly with F-values cited elsewhere but should be corrected for the strength test sample condition. For dredging projects the use of dry tensile strengths was considered not relevant and from the beginning of the application of the F-value to rock dredging saturated Brazilian tensile strengths were used to determine the wear factor. (1990) re-examined this method by performing pin-on-disc tests and studying correlations with mineralogical and rock mechanical parameters.10 P. TABLE 4. In this way lengths of 25 m to 100 m of rock surface may be abraded. N.0 3. VERHOEF 50r. 3. Grain size was determined using the line intercept method under the microscope.8 4. Table 2 shows the mean results of the cutting and abrasion tests carried out on the over-water boreholes. This figure may be compared with the cutting wear loss determined by the cutting test. Rosiwal's (1916) Mineral Hardness Scale Mineral LATHE CHUCK DIRECTION OF FEED TOOLHOLDER CARBIDE INSERT CORE SAMPLE TAILSTOCK FIG. 4.5 6 7 8 9 20 50 125 130 550 600 750 1000 1850 2300 0.25 1.p. The results are given in Fig. (--) Vicker's H. 57 0.00 0. Results of the cutting and abrasion tests carried out on samples obtained from the over-water boreholes for the Sydney Harbour Tunnel project.:t Ec~ 3.23 43 14 0. SST fine gr.63 -- 0.15 0.5 0. . Additional cores were taken from a block of Hawkesbury Sandstone obtained from the domestic waste disposal site at Lucas Heights.75 0.27 0.w.37 0.00 -0.40 0.55 0. = slightly weathered.12 0.38 0. 4.89 0.39 0.43 --2 0.80 1. SST med.gr.39 -2.w. As the cuttability and abrasivity of the rock were studied in relation to the rock cutting dredging done for the Sydney H a r b o u r Tunnel.3 1.68 0. 5.06 21 14 0.29 0.13 0.61 1.0 0. South Sydney. This may reflect the deterioration of the quality of the cores during storage.51 Cutting wear v 3 ¸ 2.13 0. The samples tested were taken from the over-water boreholes in the H a r b o u r in order to gather additional data relevant to the rock cutting dredging.3 1.26 0.69 0.w.gr.3 29 14 0.83 0.04 34 14 0. SST med.59 0. Coffey Partners Pty Ltd.58 0.00 0.09 3.41 0. discs were cut for the Brazilian tensile strength test (saturated) and thin sections made for microscopic study.77 0.53 10.65 -- 1.43 0.10 0.08 1.16 2. It should be noted that these cores had been stored in metal boxes in the open air for more than two years which may have had a detrimental influence on their quality. the conclusion can be drawn that there is no clear relationship between F-value and laboratory wear rates as measured with the cutting and abrasion test.13 0.52 9. SST SST SST sl. where rock excavation by ripping was taking place.19 0.4 2.35 0.03 0.gr.28 4.79 0. of variation (CV) (%) number of tests (n) 0. Results of cutting and abrasion tests and F-value determination on aged samples from the over-water boreholes of Sydney Harbour and from a block sample taken at Lucas Heights disposal site Specific Cutting Abrasive BTS Cutting force Normal force energy wear wear F-value (MPa) Mean (kN) Peak (kN) Mean (kN) Peak (kN) (MJ/m 3) (mg/m) (mg/m) (N/mm) Core Number Description 3001 3002 3201 3211 3212 3213 3233 3241 3252 3261 3262 3281 sl.gr.40 -0. The results of the laboratory tests are given in Table 5 and Fig.65 0.36 -0.36 0.9 0.32 1.gr.11 0.88 0. strength and cutting wear are generally lower than those measured during the site investigation on fresh cores.55 3.08 22 14 0.29 0.16 0.27 0.6 0. SST SST Siltstone Lucas Heights block average (x) standard deviation (s) coeff.12 0.12 0.09 0.13 8.5 o 1 0 0 Abrasive wear 0.7 2. Again.18 0.84 1.07 0.52 0.37 1.3 0.07 0.79 4. Both the cutting and abrasion tests have been performed on these rock cores.5 ~ 0 Q 0 0.0 0.12 0.06 0.54 0.10 0.08 0. SST med.17 0.72 24 12 2.8 Estimated F-value (N/mm) 1 FIG.49 1. with the aim of determining the wear factor F of Schimazek.5- 1.23 2.53 1. med.07 0.32 0.27 0.3 0.05 30 14 3.50 0.gr. The samples were provided by the geotechnical consultants to the Sydney H a r b o u r Tunnel project.4 0.67 0.20 0.20 0.4 2. SST = sandstone the Sydney H a r b o u r Tunnel project.27 0.61 2.40 0.36 0.51 0. From each core tested. achieved by immersion in water for 24 hours. SST sl.57 0.w.46 1.09 48 13 sl.ABRASIVITY OF H A W K E S B U R Y 11 SANDSTONE TABLE 5.28 0. 6 4. compared with estimates of the F-value for the tested samples.56 0.43 0.2 0.55 0. These latter tests were performed in Professor Roxborough's Laboratory in the Department of Mining Engineering at the University of New South Wales. = medium grained.0 3. med.9 2.52 2.25 0. all cores were tested in a water saturated condition. SST med.79 1.05 0. A comparison of Figs 4 and 5 shows that the values of cutting forces.31 0. 50 extremely weathered rock 77 0.3 0.4 0.8 4.3 0. Results of the additional cutting and abrasion tests carried out on (aged) samples from the over-water boreholes of the Sydney Harbour Tunnel project.60 67 0. % Size (ram) F-mass N/mm) 65 0. Only data that were considered representative of normal dredging operation at the site were used. the Brazilian and the point load strength for Hawkesbury sandstone.0 0.5E E Length (m) Is (MPa) BTS(est) (MPa) 7.50 0.10 60 0.4 0.35 68 0.1 0'.2 0.5 1.0 2. not included in regression analysis l Sydney Harbour Tunnel rock dredging Sydney Harbour is an old river valley partially filled with Quaternary sediments.40 71 0. while for Devonian sandstone they found that BTS equals about three times TS. 5.6 0.5- 1t • I. VERHOEF TABLE 6.2 0. To protect the interests of the dredging contractor the real tool consumption data are not published.69 0. Alternatively an estimate of Brazilian strength can be made from the uniaxial compressive strength test. . The central part of the trench excavation for the Sydney Harbour Tunnel was therefore in soft sediments.7 2.2 2.06 0. but it is well known that BTS commonly over-estimates true uniaxial tensile strength.07 0.37 estimates from other tensile strength tests or index tests is not a straightforward matter.9 4.3 0. From these it may be derived that on average the BTS is about 1. Shulin Xu. other tests which also give an indication of tensile strength were used such as the uniaxial (or true) tensile strength and the point load test.8 0'.10 70 0.3 0. t Q.18 0. compared with Fvalues determined on the samples.3 0.35 80 0.5 0.5 times the I s value. I0 60 0.N.7 F-value (N/mm) o'.1 0. Cutting wear Ii i: Abrasivewearli 0 o o'.12 0. Estimate of average strength.4 ols o16 o2~ o18 Fmass estimate (N/mm) FIG.6 13.02 0.9 i Quartz vot.2 013 014 015 o'.60 60 0. Only at the sides of the ancient valley had partially weathered Hawkesbury Sandstone to be excavated.W.6 0'. De Freitas & Clark (1988) found for Penrith sandstone that BTS was about four times direct tensile strength (TS). In the ISRM Suggested Method for Point Load Strength determination (1985) it is mentioned that I s values equal about 0.5 5. In some instances where no Brazilian strength data were available. to determine a characteristic F-mass BH no.0 0. Estimates of F-value have been made from the site investigation reports and the over-water borehole records.02 0.7 1. i FIG..0 0. quartz content and grain size for the length of borehole actually excavated for the trench. Fortunately Pells (1985) gives correlation data of UCS. 6. F-mass estimates were only made where boreholes were sufficiently close to the excavation zone.4 0.9 0. 302 (N) 330 (N) 300 (N) 12 (N) 320 (S) 321 (S) 322 (S) 323A (S) 324 (S) 325A (S) 326A (S) 2.0 1.12 P. The derivation of BTS o o.1 gg 2 "~ 1.3 0.5 1.8 1. Comparison of the tool consumption of the rock cutter dredger with an estimate of the average F-value for the rock mass excavated.1 1.48 0.2 1.50 0.8 tensile or Brazilian strength.2 5. the unconfined compressive strength considered characteristic by Lowe & McQueen is 55 MPa (Table 7). 5 m . 7. r \~ 1~ r" ~ "" " " " ~ X %X -5 " .qu'wai~N'~ . They have divided the Hawkesbury Sandstone into five types. The conclusions of this survey are: (1) The laboratory cutting and abrasion wear rates do not correlate with the F-value for the Hawkesbury Sandstone. . 7). together with an estimate of average quartz content and grain size. . 8. With respect to excavation volume. ( I ~ //~ • 329 TRENCH " ' " .%. while the strength measured by Roxborough on the sample used for the cutting test was 26 MPa. The typical daily dredging excavation zones from which tool consumption numbers were available are numbered in working order. This was done by considering the variation in the I s value and petrography recorded in the relevant section of the borehole. Lucas Heights block. If no boreholes were close.. an F-value of 0. carbonate cemented.'=~ zo~ 30rn . Type 3: medium to coarse grained. The tool consumption data were compiled by Watson (1990). . Lowe & McQueen (1988) give an extensive description of the engineering geological properties of these rocks. Extremely weathered rock was discarded. The F-mass estimates were made as follows.%. If this value is used for the calculation of F. 57 vol. Table 7 gives the average wear values derived from the cutting and abrasion test of Roxborough (1987) ~ and the pick Considering the variability of the quartz content (CV = 20%) and compression strength (CV = 35%) and the high variability of F-value within one rock ]Note that the cuttability test has also been carried out on these samples in Newcastle-upon-Tyne (England). quartz content 76 vol. FXG. (3) The cutting and abrasive wear rates as determined by the cutting and abrasion tests do not correlate with actual tool consumption in this case. as close to natural moisture content as possible. Only reliable tool consumption data were used and only F-mass estimates of boreholes sufficiently close to the excavated rock zone. .. 5 13 block (Table 5. based on petrographic characteristics: Type 1: fine to medium grained sandstone.ABRASIVITY OF HAWKESBURY SANDSTONE An attempt was made to estimate an average F-value (F-mass) for the section of the borehole actually excavated by the dredger. Simplified map showing part of the trench near the northern shore. quartz content 78 vol. which consists mainly of siltstone and sandstone units. Only cutting wear rate was determined. which would give the SST 4 a more logical position in the graph of Fig. The problem with tool consumption data is that these are not always related to 'normal practice' rock cutting dredging. (2) The F-value correlates with tool consumption (and thus abrasive wear of the pick-points). The results are given in Table 6. As regards the strength of Type 4. • a0.. 7 the height contours show the approximate distribution of rock head. quartz content 78 vol.. Then the daily excavation reports were examined and it was determined which boreholes were close to the excavated zone (Fig.% quartz. the data were discarded.. The trench has been excavated to a depth of . Figure 6 shows plots of estimated F-values considered representative of the excavation zone as encountered in the boreholes and the tool consumption recorded near to the boreholes. All the reported tests were carried out in the saturated condition. Care was taken that the data on tool consumption were representative of normal practice and not biased by dredging operator factors or exceptional dredgiiag conditions. Type 5: fine to coarse. Average data necessary to estimate the F-value are given in Table 7. or~ d a y ~ eoce.. EZ~] N • 329 ~'~ ='~¢e '"5'" .2 0 . 6) shows a good linear trend. First an average strength (Is) was estimated for the section of the borehole which was in the excavation zone (Table 6). Type 2: fine to medium grained. the density of borehole data is very small. average quartz content 63 vol. o'. the result of the estimated means of F-mass with the tool consumption (Fig. Type 4: medium coarse grained to conglomerate. Note the distribution of boreholes. CV = 48%). In Fig.%.91 is obtained.%. Malabar Outfall Decline Tunnel (Lowe & M cOueen 1988) This decline tunnel traverses two sedimentary rock formations: the Hawkesbury Sandstone and the underlying Newport Formation. as were data from the head-on dredging performed at the harbour sides. following Pells (1985) as the Newport (Nwp) rocks. Pick consumption data were given and these have been included. W.13 4.302 1. VERHOEF TABLE 7.26 AM75 (pps/m 3) AM100 (pps/m 3) 0.8 FIG. Estimated F-values of the typical Hawkesbury Sandstone types (SST 1-4) and Newport Sandstone and Siltstone compared with the wear rates determined with the laboratory cutting and abrasion test.07 1.10 3.47 0.60 0. Type 2 differed from Type 3 mainly in grain size.42 o2~ AM 75 FIG.0 45.8 nwp sst nwp siltst -~ 0.09 2.2 014 016 018 1 1.5 3.0 55.950 --0.0 45. siltstones and sandstones were described as being very similar to type SST 1 Hawkesbury Sandstone.14 P.4 1.6~ i ~ Abrasive wear 0 0 o12 0'.30 0. 8. an increase of tool consumpton with F-value is shown.30 0. Despite the fact that state-of-the art site . N. Tool consumptions of the Voest Alpine roadheaders are plotted against the F-value in Fig.30 2.93 3. As no tensile strength test results were reported. For both. 0'.35 0. BTS is estimated to be 1/13 of UCS.535 0.206 2.189 ----- 0.4 • • ~2 ~3 m A • Cutting wear (Nc) i 1- 1.16 3. Summary of geotechnical data for the Malabar Decline Tunnel (from Lowe & McQueen 1988) SSST type 1 2 3 4 5 Nwp.189 1. This should be borne in mind when examining Figs 8 and 9.93 -0. 9.% mass 39 * * 7 1.0 60. Figure 8 shows how the estimated average F-value relates to the relevant wear data available.950 0. Considering the manner in which the data have been obtained.2 Estimated F-value (N/mm) 1.09 UCS (MPa) 63 78 78 76 57 60 45 BTS est.2 -2. 9.45 1. Discussion This study has attempted to relate laboratory or in situ derived rock parameters to actual excavation performance. Comparison of tool consumption data of Voest Alpine Roadheaders AM 75 and AM 100 with the F-values considered representative for the rock types excavated in the Malabar Outfall Decline.23 0.siltst Vol.0 2. boreholes apparently could not be estimated.866 0.30 0.6 1.81 1.6 ~1 8 I 1'. 1.13 0.0 -38. the pick consumptions for both have been combined.35 1.5 23 74 Grain size (mm) Qtz % 0. but this is an important property with regard to abrasivity as can be deduced from their F-values.42 0.19 2.4- A nwp sst ~5- sstl sst2 sst3 SSt4 1. In the tunnel type SST 3 could not be distinguished from type SST 2 (data from Lowe & McQueen 1988).2~ E I nwp siltst 4" ~3- E m o8~ • Cutting wear E 0.5 4.6 0'. See text for discussion. they could not be distinguished in the tunnel consumption data of the two roadheader types used (Alpine Voest AM75 and AM100) are given. As no distinction could be made between Type 2 and Type 3 sandstone in the tunnel and in view of the fact that the relative abundance of these two types in the 0 0.4 Estimated F-value (N/mm) 1'.2 1'. any conclusions can only be tentative.92 * Type 2 & 3 make up 50% of the rock mass excavated. Malabar Outfall Decline (Lowe & McQueen 1988).8 i 1'.5 3. F est Abrasive Cutting (MPa) (N/mm) wear (mg/m) wear (mg/m) 32. In this case it is suggested simply that the F-value and the laboratory cutting and abrasive wear rates relate to actual tool consumption.40 0. There appears to be a relationship with the cutting wear and abrasive wear rates determined in the laboratory tests.19 1.50 0.9 4.6 0.sst Nwp. Both methods also relate to pick consumption. it is notable that the estimated F-mass value shows an apparently linear correlation with actual pick consumption. using the same environmental conditions and simulating the proper temperatures and forces etc. the laboratory cutting and abrasion wear rates are not related to both F-value and pick consumption (Figs 4--6). The system of a dredger cutting rock may be approached experimentally by the scheme shown in Fig.ABRASIVITY OF HAWKESBURY SANDSTONE investigation reports were available for the Sydney Harbour project (containing much more geotechnical data than usual for dredging projects). The F-value as such is a wear . Very often new designs of tools were immediately tested on a purposely built machine. For each case the method of estimating F has been consistent and efforts were made to obtain representative values. When a reliable guess of mineralogy could be made (Fig. Uetz 1986. This is why the specially designed cutting and abrasion tests which are developed for the Dutch dredging industry use steel chisels instead of tungsten carbide ones (Bisschop 1991. Cutting tool 15 geometry and the tool material both influence the result. 4) or the BTS could be assessed from other strength tests (Figs 6 and 8). In the case of the rock cutter dredging operation. an F-value considered to be representative of a section of a bore core was used for a huge volume of rock. on which most attention has been placed up to now. For the estimate of F-mass (Fig. This type of development has not always been the practice. Van der Sman 1988). In tribology it is attempted to simulate as well as possible the particular aspects of the process under study. the results obtained by this survey are not surprising. Zum Gahr 1987). Tribological testing categories for a rock cutter suction dredger. however. the F-value was estimated. Vl Model test with simple testbodies mml FIG. both internal and external. The interaction between cutter head and rock is dependent on many variables. Simple laboratory tests like the pin-on-disc test (Category VI in Fig. In tribology it is stressed that wear (and thus pick consumption) is a system dependent process. 10. This has proved to be too expensive a method. One reason was the difficulty of performing many cutting and abrasion tests on rock cores. 6) many more assumptions had to be made. Dredgers commonly use high quality steel (sometimes with tungsten carbide coating or inserts). In the case of Malabar. 10 (Verhoef 1990). Tests in Category VI or V are carried out to obtain an indication of the relative performance of different types of cutting steel for example. It is considered that the results as presented are the best that could be derived. but in the assessment of the properties of the rock mass with its inherent variability of properties. From what is known about wear problems using the science of tribology (e. the data show that the Fvalue and the cutting and abrasive wear rates derived from the cutting and abrasion tests are related. 10) or the cutting test (Category V) are very remote from the actual process taking place when dredging rock.g. which are too numerous to be scaled down and simulated by simple laboratory tests. In as far as the geometry of the cutting tool determines the cutting and wear mechanisms operating. Davids & Adrichem 1990. The tools undergo tests with increasingly complicated equipment and finally the prototypes are tested on the real machines. The major problem in the case of rock cutting no longer lies in the tool development. The above also explains why results of different types of wear tests could diverge. the amount of data related to abrasivity was poor. In most cases the F-value had to be estimated because one of the necessary parameters was lacking at a particular sampling point. I Field testing during normal working practise II Full scale test of complete test machine lrnu III Test with full size part of machine IV Test with odginal part of machine V Test on testbody under similar loading conditions 4. this is a factor which can be used in tool design. The limited number of cutting or abrasion tests which can be performed for a project is one problem. The Analysis of a Laboratory Cutting and Abrasion Test to be applied in Rock Cutting Dredging. In site investigation practice. August 1988. In site investigation practice for dredging projects thin section examination is frequently neglected. . ISRM 1985. 13~42. Rock Testing Procedures at VA's Geotechnical Laboratory in Zeltweg. Kevin Green and John Watson of the Westham Dredging Company Pry Ltd. Joe Shonhardt. I benefited very much from the happy support received from the staff and personnel of the Mining Engineering (Paul Hagan. I s. Michael de Mol. Faculty of Mining and Petroleum Engineering. The Testing of a Classification Apparatus for the Wear of Cutter Heads during Cutting of Rock (in Dutch). use should be made of rock index tests which relate to cutting performance and abrasive wear. MJ/m 3) F c = specific cutting force (N/m) /7. Delft University of Technology. John Braybrooke is thanked for the critical interest shown during the course of the study. The results of this paper indicate that further study into the use of wear factors combining index tests. 1990. 1988. C. Aldert van Hemmen (Stapel Shipyard) and Harry Steeghs (Delft Hydraulics Laboratory) and two anonymous reviewers are thanked for their comments on the first draft of this paper. W. is warranted. List of notations CV = coefficient of variation = s/x x 100 (%) s = standard deviation x = average (weighted mean) UCS = Unconfined compressive strength (MPa) BTS = Brazilian tensile strength (MPa) Is a~ial = axial Point load strength (MPa) TS = Tensile strength (MPa) F = Schimazek's wear factor (N/mm. K. Civil Engineering (Fiona MacGregor. Emodulus and so on. Patrick Wong) supported the work and provided rock samples. Professor David Price (Delft University). In this case the wear factor F derived by Schimazek. I s and thin section examination. Faculty of Mechanical and Marine Engineering. Sydney. J. such as the F-value. Carol Vallance). & ADRICHEM. Both F-value and the cutting and abrasion wear rates were related to the tool consumption of the roadheaders used to excavate the Malabar Outfall Decline in Sydney. grain shape. N. The Netherlands). Greg McNally). Contractors will then be able to estimate to a much higher level of accuracy the tool replacement rate to be expected for a project. BTS. thin section examination (mineralogy. Red Flossman. the cutting wear and abrasive wear rates derived from the Newcastle-upon-Tyne cutting and abrasion tests. Andr6 Veldstra. Such tests include UCS. Sue Howard. W. VERHOEF factor which is potentially very useful. = grain size (mm) SE = specific energy (N/m2. For wear prediction. equation (1)) Eq Qtz = Equivalent quartz volume percentage (%). Suggested method for determining point load strength. DAVIDS. Delft University of Technology. Mining Science & Geomechanical Abstracts. Proceedings of the Fifth Australian-New Zealand Conference on Geomechanics. related reasonably well with tool consumption. Internal report TZU 41. Sydney are thanked for the confidence and enthusiasm with which the experience and reports on the Sydney Harbour dredging with the Kunara rock cutter suction dredger were entrusted to me. The state of the art of rock cuttability and rippability prediction. therefore. BTS. it is necessary to calibrate the results of abrasion tests or wear factors against a trial excavation with a real cutting machine at the site. grain size). Coffey Partners International Pty Ltd (Philip Pells. This research is supported by the Technology Foundation (STW. F. 1987. ACKNOWLEDGEMENTS. Conclusion For the first time relatively accurate tool consumption data of a rock cutter suction dredger could be studied.16 P. did not correlate with the tool consumption of the rock cutting dredger. because it is based on parameters which can be obtained easily and in much larger quantities. S. microscopic structure. Austria. Classified internal report. GEHRING. International Journal of Rock Mechanics. Emodulus. this is determined by adding the Rosiwal hardness with respect to quartz ( = 100) of the minerals comprising the rock. Professor Frank Roxborough was a very generous host during my three months stay at the University of New South Wales. 22. Likewise. These data should then be used to calibrate the results of more complicated wear or cutting tests in the laboratory and by a trail dredging operation on the real scale (Verhoef 1990). Classified internal report. BRAYBROOKE. Another method commonly applied in rock tunnelling. Drago Panich. Voest Alpine Zeltweg. The amount of cutting or abrasion tests which can be performed on rock cores will always be limited. using index tests like UCS. considering the volume percentage taken by those minerals ¢. P. 1991. 61-70. Paul Gwynne) and Applied Geology Departments (Larissa Smith. The mineralogical and microscopic properties of the soils and rocks should be determined in a geostatistically justified way and it is possible to undertake laboratory index tests on a number of samples. The approach to wear prediction and cuttability performance in site investigations should therefore be to obtain as many rock parameters as possible. = specific normal force (N/m) Rsq = regression coefficient squared References BisscnoP. R. Sydney. Internal report Westham Dredging Company Pty. VERHOEE. In: ROMANA (ed. 1987. H. M. The role of some basic rock properties in assessing cuttability. Proceedings of International Society of Rock Mechanics Symposium.) Engineering Geology of the Sydney Region. UETZ. 1988. M. Proceedings of Conference on Rock Engineering. 1980. R. J. J. Ltd. Petrographische und geomechanische Charakterisierung yon Ruhrkarbongesteinen zur Bestimmung ihres Verschleissverhaltens. ROXBOROUGH. & -1990.A B R A S I V I T Y OF H A W K E S B U R Y HERBERT. C. 1987. F. 1988. 307-320. --. MCFEAT-SM1TH. I. WATSON. ZUM GAHR. Ground conditions and construction methods in the Malabar Ocean Outfall Decline and observations on rock cuttability. 1986. Faculty of Mechanical and Marine Engineering. April. Delft University of Technology. In: PELLS. P. Amsterdam. & MCQUEEN. IE Australia.D. 1982. Gliickauf. SCHIMAZEK J. Discussion Volume. revised typescript accepted 5 November 1992 . Engineering properties of the Hawkesbury Sandstone. VAN DEN BOLD. The measurement of tensile strength of rock. Construction of the North Head Ocean Outfall Tunnel. 1990. 1987. B. Proceedings of the Australian Underground Construction and Tunnelling Association Seminar on Cost Effective Tunnelling in the Sydney Basin. Dissertation.und Rollenbohrwerkzeuge. 1976. Der Einfluss des Gestein- - - - 17 saufbaus auf die Schnittgeschwindigkeit und den Meisselverschleiss yon Streckenvortriebsmachinen. Roadheader performance studies using a full scale laboratory research facility. F. H. 587-602. A. R. J. J. PELLS. Delft Progress Report. 159-172. Unisearch Limited Report for The Metropolian Water Sewerage and Drainage Board. 1990. Amsterdam. An Assessment of the Cuttability of Rock Formations Associated with the Sydney' M W S & DB Submarine Outfall Tunnels. Th. 1988. 5-38. H. D. 29. 1977. P. H. Balkema. E. Mfinchen. IE Australia. & KNATZ H. Proceedings of the 28th US Symposium on Rock Mechanics. Madrid. Classified internal report. et al. Ertzmetall. Towards a prediction of the abrasive wear of cutting tools in rock dredging. 1988. Rotterdam. 495-504. N. Rotterdam. & VERMEER. W. & -1976.) Rock Mechanics and Power Plants. Canberra. P. 1970.. 179-197. Balkema. VAN DER SMAN. Proceedings Seminar "Tunnels--Wholly Engineered Structures". 165203. Balkema. N. PASCHEN. L. M. Technische Universit/it Claustahl. Die Beurteiling der Bearbeitkarkeit von Gesteinen durch Schneid. - - SANDSTONE - - Received 28 October 1991. 125-132. Results of a First Series of Wear Tests on Chisels with the Shaper (in Dutch). 1985. 6th International IAEG Congress. T. & FOWELL. B. Science Press. & CLARK. DE FREITAS. Tuscon. The depositional development of the basin. Proceedings of VII Australian Tunnelling Conference. P. Canberra. IE Australia. Amsterdam. 90/8. University of Newcastle upon Tyne. Rotterdam. SPEIGHT. In: BRANAGAN. 1990. 274-278. K. J. Correlation of rock properties and the cutting performance of tunnelling machines. N. LOWE. 13. The Underground Domain. SHULIN XU. & FOWELL. F. Balkema. Rotterdam. 973-980. W. J. H. Microstructure and wear of materials. (ed. 113-119. Influence of microscopic structure on the abrasivity of rock as determined by the pin-on-disc test". Elsevier. 106. Abrasion und Erosion Carl Hauser Verlag. Proceedings of the 6th International full Congress of the IAEG. An Outline of the Geology and Geomorphology of the Sydney' Basin. Wear testing categories for rock dredging projects.