Repeated-load response of aggregates in relation to

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Repeated-load response of aggregates in relation to track q'dality'index 2

GERALDP. RAYMOND Civil Engineering Department, Queen's University, Kingston, ON K7L 3N6, Canada

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AND

RICHARD J. BATHURST Civil Engineering Department, Royal Military College of Canada, Kingston, ON K7K 5L0, Canada Received July 15, 1993 Accepted March 29, 1994 Track quality rating systems are briefly introduced as a background for undertaking a study of the repeated-load response of ballast aggregates. The results from a number of different laboratory investigations are reviewed and this data interpreted in terms of track quality behaviour. The paper reviews selected results from repeated-load triaxial tests used to investigate the repeated-loading response of different granular railway ballasts at stress levels comparable with those below North America heavy freight axle loads. These results are used to establish an aggregate index to predict deformation and breakdown of ballast under repeated loading. Large-scale test programs are reviewed that relate aggregate quality to simulated ballasted track formation response using a 0.9 m long by 250 mm wide tie to represent a typical loaded rail seat. The large-scale testing was restricted to one aggregate that was subjected to a range of load levels and artificial subgrade stiffness. Similar related work on coarse, single-sized aggregates recommended for drainage layers in highway pavements is reviewed to illustrate the trade-offs between support compressibility and quality of aggregate defined by the aggregate index value. The laboratory tests and model performance are compared with published data to establish a laboratory performance rating in the form of an aggr~egateindex for prediction of those track quality indices that relate to deformation as a function of aggregate type. :. Key words: ballast, aggregate, hardness, toughness, railway, track quality. Les systbmes de classification en fonction de la qualit6 de la voie sont introduits bribvement car ils sont B l'origine de 1'Ctude entreprise sur la rCponse des agrCgats de ballast au chagement rCpCtC. Les rCsultats de plusieurs recherches diffkrentes en laboratoire sont examines et ces donnCes sont interprCtCes en terme de comportement de qualit6 de voie. L'article examine des rCsultats choisis parmi des essais triaxiaux B chargement rCpCtC utilisCs dans 1'Ctude de la rCponse de divers ballasts granulaires pour voie ferrCe, B des niveaux de contrainte comparables B ceux qui existent sous les charges axiales de trafic lourd rencontrCes en AmCrique du Nord. On utilise ces rCsultats pour Ctablir un indice d'agrCgat qui prCdit la dCformation et la dCsintCgration du ballast sous charge rCpCtCe. On examine des programmes d'essais B grande Cchelle reliant la qualit6 de 1'agrCgat B la rCponse d'une voie ballastie simulCe, ceci en utilisant une poutre de 0,9 m de long par 250 mm de large pour reprksenter une assise typique de voie ferrCe en charge. L'expCrimentation B grande Cchelle a CtC limitCe B une sorte d7agrCgat qui a CtC soumis B une plage de valeurs de chargement et B des raideurs de rCaction artificielles. Des travaux semblables effectuCs sur des agrCgats grossiers uniformes recommandCs pour les couches de drainage dans les chaussCes d'autoroutes sont examinks pour illustrer le compromis nCcessaire entre la compressibilitC du support et la qualit6 de l'agrCgat dCfinie par la valeur de I'indice d7agrCgat.Les essais de laboratoire et le comportement des modkles sont comparCs aux donnCes publiCes, afin d7Ctablir une classification du comportement en laboratoire sous la forme d'un indice d7agrCgatpermettant de prCdire les indices de qualit6 de voie qui associent la dCformation au type d'agrdgat. Mots cle's : ballast, agrigat, duretC, rCsistance, voie ferrCe, qualit6 de voie. Can. Geotech. J. 31, 547-554 (1994)

Introduction One of the major operating expenses of ballasted railway or transit (urban passenger) track is that of the maintenance of way. For effective and efficient operation the funds for track maintenance, which form part of the total maintenance of way budget, should be spent productively so as to minimize the chance of accidents or train delays and maximize the quality of track consistent with minimizing expenditures. Such an undertaking requires quantitative data on track conditions to ensure that maintenance is planned and executed as effectively as possible. Although track-geometry cars have been available to collect such data for more than a century, their widespread and effective use has only been prevalent since the mid-1970s in response to cheaper and more reliable instrumentation, computer technology, and data-processing software. The three main uses of trackgeometry data are (i) location of exceptions to track standards, Prtnrcd in Canada I Imprirnd su Canada

(ii) characterization of present conditions, and, (iii) prediction of future deterioration. A schematic of a typical track-geometry car is shown in Fig. 1. The four basic parameters collected electronically by modern track-geometry cars are both rail profiles and rail alignments; gauge (perpendicular distance between the rails); and cross level (or cant), which is the difference in elevation between the rails at the same chainage. In addition, the position along the track may be recorded electronically by placing magnets or other devices on the track that are sensed by the geometry car or by manual input. The above parameters are generally digitized f o r analysis and compared against track plans or with previously obtained values to establish appropriate maintenance. In general, current geometry cars d o not collect any data relating to the ballast or subgrade conditions. An obvious question arises as to whether the track support affects the track geometry and, if so, what is its magnitude?

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CAN. GEOTECH. J . VOL. 31, 1094

GU IDE

RIGHT

LEFT M E A S U R I N G WHEEL

PARAMETER P R O F I L E LEFT PROFILE RIGHT GAUGE S U P E R E L E V A T I O N OR C R O S S L E V E L A L I G N M E N T LEFT A L I G N M E N T RIGHT SURFACE I R R E G U L A R I T I E S LEFT SURFACE I R R E G U L A R I T I E S R I G H T

FIG. 1. Schematic of a track-geometry car. 1973, 1975, 1976). Settlement data from European railways are illustrated in Fig. 2. The trends are similar to North American experience. Field settlement data from the ORE (1975) show that for the first approximately 30 X lo6 t of traffic the settlement of the tracks may be fairly well represented by the semilogarithmic law

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European studies on track optimization Track-quality indices (TQIs) have been used by European railways to study the optimum adaptation of the conventional track to future traffic (Office for Research and Experiments of the International Union of Railways (ORE) 1971,

where S,(t) is the mean settlement over the unit length, t, is the reference tonnage taken as 2 X lo6 t, a, is the settlement at the reference tonnage, a , is the slope of the semilogarithmic relation, and t is the tonnage since discretionary (mechanized) maintenance. This mean settlement unfortunately was not uniform. If it was, there would be less need for this study. Of more concern are the differences from the mean. The standard deviation of the settlement differences from the mean was found to increase according to a similar relationship, such that

[2]

o,(t)=b,+b,log

where o,(t) is the standard deviation of the settlement differences at time, t, and b, and 0, are constants of similar form to a , and a".

549

R A Y M O N D A N D BATI-IURST

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It should be noted that the standard deviation of the point settlement differences from the mean settlement is not a characteristic of the track, but a variation of numerous different point settlement differences from the mean settlement involving two successive measurements for any one of the numerous points. Track defects, on the other hand, involve comparisons of the movements of different points. Again, the standard deviation of numerous different point values of defects involving two successive measurements for any one comparison of points was found to follow the relationship

0.601 0.80

[3]

o,(t)=C,+C,log

where o,(t) represents the standard deviation of the measurement under consideration, and C, and C, are the constants. The defects found to be capable of being expressed by the above relationship were established as (i) standard deviation of longitudinal level, (ii) standard deviation of cant or cross level, and, (iii) standard deviation of track twist. On competent slab track such deviations would not occur, thus it seems reasonable to conclude that these defects, which all follow similar relationships to that of ballast settlement, must be related to the ballast and subgrade settlement characteristics. The European studies unfort~inatelydid not study the ballast aggregate as a variable, but within a given test zone other parameters were varied even though different zones may have had different ballasts. Despite the fact that the same ballast was used within any one test zone the major parameters affecting the rate at which defects developed were stated to be related to the ballast conditions (compaction, elasticity, longitudinal and transverse inhomogeneities, etc.) as well as the initial quality of the tracks. They stated that the above parameters were the principal contributors to increased ballast stresses in track structures. In regard to assessing the effect of any variation, it should be noted that both types of maintenance are related to a given magnitude of defect. This means that if the contact pressure is halved because of an above-track variable (i.e., axle load), it can be anticipated, based on the European observations, that the defect would be halved after the passage of the same tonnage. Any maintenance that is controlled by observing a limiting defect, whose rate of growth is controlled by the semilogarithmic relationships, is clearly more than halved. For example, halving the ballast pressure would theoretically mean an exponential increase in tonnage prior to the limiting defect being achieved. In practice, ballast is also subject to weathering and other degradation factors. Nevertheless, it is to be expected that better quality ballast should resist these other factors better, and thus give longer time cycles between required maintenance for reduction in ballast pressures. With this in mind, a major study of ballast response to repeated loading was undertaken at Queen's University and the Royal Military College (RMC) of Canada.

Queen's University and RMC research Although the research work undertaken was broadly based, the work presented here is focused on aspects of load ranking of ballasts to resist repeated loading. The influence of

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weathering and other phenomena'that would be necessary in a true selection procedure are not considered in this discussion. Repeated-load triaxial testing Of interest to the track engineer is the behaviour of ballast at low confining pressures. Vertical stresses at the tie-ballast interface under static wheel load only average 140 kPa, and depths of ballast above the tie base on the side and end of the tie are rarely more than 150 mm. Initial testing was carried out in a 229 mm diameter triaxial cell at a confining pressure of 35 kPa using a stage 1 stress difference of 140 kPa and a stage 2 stress difference of 210 kPa, each applied for 500 000 cycles, and in a 250 mm diameter consolidorneter where no lateral strain was permitted. The consolidometer cycled stress was 544 kPa. All of the above tests were carried out at a loading frequency of 1 Hz. Timmerman and Wu (1969) report the results of cyclic load tests carried out on a granular material at different frequencies. Based on their work, it is reasonable to expect that the 1 Hz frequency used in the current investigation will not influence the repeated load-deformation response of the ballast specimens that would have occurred had the load been applied at (predominant) higher frequencies anticipated in track ballast (say 15 Hz). Seven ballasts were selected from the 21 ballasts supplied for research purposes by Canadian National (CN) and Canadian Pacific (CP) rail. A nonballast (Grenville marble) was added to these materials for a study of load ranking. The ballasts were selected on the basis of their mineral hardness and aggregate toughness to provide as wide a range of characteristics as was available. All ballasts were given the same initial grading, with percent passing as follows: 38 mm, 100%; 25 mm, 75%; 19 mm, 62%; 13 mm, 46%; 9 mm, 36%; 4.8 mm (No. 4 sieve), 16%; 2.4 mm (No. 8 sieve), 0%. Figure 3 shows the variation of plastic axial strain with the logarithm of the number of cycles for the first stage test results. The characteristic trends in deformation d o not become clear until after about 10 000 cycles, illustrating the

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CAN. GEOTECH. J. VOL. 31. 1994

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i FIG.6. Correlation of laboratory aggregate breakdown and aggregate index. Symbols as in Fig. 3.

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FIG.5. Plastic strain per logarithmic cycle of loading vs. aggregate index. Symbols as in Fig. 3. importance of continuing the test to at least 500 000 cycles. The order of deformation of the various materials remained the same under the stage 2 loading, as will be apparent below. Influence of hardness-toughness ballast characteristics on track deformations The longevity of ballast aggregates under repeated loading can be expected to be dependent on resistance to mechanical degradation. Selected laboratory test methods can be used to quantify aggregate hardness (e.g., mill abrasion test) and toughness (e.g., Los Angeles abrasion). Los Angeles abrasion (LAA) The LAA test (ASTM C131, C535, 1989) gives a relative measure of particle resistance to fracturing. The test is

considered to simulate the effect of high contact forces on aggregate particles, including those generated by impact loading. High impact forces on railway ballast aggregates will occur at rail discontinuities such as those found at grade crossings and transitions. In addition, high impact forces can develop at any location on track when wheel flats exceed "condemnable" limits. The ability of a ballast to survive high contact forces is dependent on the toughness of the aggregate (i.e., particle resistance to fracturing). A low LAA value indicates a material with a high resistance to fracturing under high contact forces. Mill abrasion (MA) The MA test is a nonstandard laboratory test method that measures the relative resistance to abrasion or hardness of aggregate materials as a result of the autogenous grinding of the aggregate particles. Abrasion of ballast aggregate particles will result from the constant movement of aggregate particles against each other. The abrasion mechanism is simulated by the autogenous grinding process in the MA test. The specifications for the MA test can be found in the current CP Rail test protocols (CP Rail 1984). In some of the test data reported in this paper, the CP Rail method of test was modified for samples having a smaller top size than that designated in the original specification (Bathurst and Raymond 1990a, 1990b). Aggregate index Experience with railway ballasts (Raymond 1979; Raymond et al. 1979) has shown that aggregates that are tough with respect to fracture resistance are not necessarily highly abra-

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Aggregate index as an indicator of plastic defortnation and ballast breakdown The influence of aggregate quality on permanent deformations under repeated loading can be seen in Fig. 5 . The straight-line approximation was established by first fitting the results of a first-order regression analysis to the semilogarithmic slopes of the plastic axial strain results shown in Fig. 3. The slopes obtained from this analysis were then plotted against aggregate index and regression analysis used to obtain the correlation coefficients given in Fig. 5 . One regression was carried out using seven ballasts alone, and the other for all eight materials. In either case the approximations are statistically significant equations. Figure 6 shows the change in gradings expressed as a change in the grading modulus (e.g., Hudson and Waller 1969) or by the percent passing the No. 8 sieve. The data for this plot are taken from one-dimensional loading tests on ballast at a Canadian National Railways test site and have been reported in detail by Gaskin and Raymond (1976). Although the trend in the data is visually appyent, it is less convincing based on a goodness of fit test ( r - ) . The plots for stage 1 alone, stages I and 2 together, and stage 2 alone all established significant relationships. The correlations are significant for the triaxial data and mildly so for the particles generated passing the No. 8 sieve in the onedimensional test. The one-dimensional test data were probably less significant because of the use of such a high repeated loading. Finally, results obtained from 10 ballasts placed in adjacent quarter-mile sections of C N Rail track are plotted in Fig. 7. A subjective field breakdown rating

C

TONNAGE

FIG.7. Correlation of field breakdown assessment and aggregate index. Results from CN Rail test track. FBR from Gaskin and Raymond 1976. sion resistant. The data from a number of sources shown in Fig. 4 illustrate the range of LAA and MA values for a wide range of aggregates. The figure also illustrates the poor correlation of these parameters. However, the data presented below support the hypothesis that the same longevity of ballast under cumulative tonnage can be obtained by aggregates having different combinations of hardness and toughness values as defined by the results of LAA and MA tests. A parameter that reflects the contribution of both mechanisms to aggregate durability in track is the aggregate index (I,),where [4] I, = LAA + 5MA

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FIG.9. Ballast maintenance cycle model used by CP Rail (CP Rail 1984). established by Gaskin and Raymond (1976) and based on maintenance requirements was noted to be mildly significant, whereas breakdown as reported by Dalton (1973) of particle grading curves of extracted samples resulted in disappointing results. The latter, however, is not surprising, as initial gradings in any mass-produced stockpile are highly variable. In addition, breakdown was produced by more than the load environment with several of the aggregates showing considerable weathering. After considerable analysis of these laboratory data and some field data, the load-classification diagram shown in Fig. 8 was proposed "as an initial starting point for further refinement as field data may become available" (Raymond

C A N GEOTECH J VOL 31, 1994 \

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FIG. 11. Load deformation response of coarse single-sized aggregates. 1979). Since this initial work, research by CP Rail has led to a model that is used to relate aggregate index (or abrasion number according to C P Rail terminology) to the observed breakdown life of ballast from the loading environment alone (Klassen et al. 1987; C P Rail 1984). The relationship is illustrated in Fig. 9. Ballasts that weathered or were badly fouled from foreign sources were eliminated from the CP Rail study. In addition, the subgrade support was relatively good.

AGGREGATE INDEX NUMBER ( I,) FIG. 12. Deformation rate vs. aggregate index. Large-scale repeated-load testing In addition to the triaxial tests and to verify the general trends deduced from the work by the European railways, several sets of ballast box tests were performed using a 305 mm depth of Sunbury ballast on subgrades having a range of compressibilities (Raymond and Bathurst 1987; Bathurst and Raymond 1987). Sunbury ballast has an aggregate index of 69.5. The box test set-up consisted of a 914 mm long footing, 250 mm wide, representing the rail seat of a tie, that was centrally loaded in a box 1.5 X 1.5 m in plan. The

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R A Y M O N D A N D BATHURST

TRAFFIC

LOADING

(TONNES)

FIG. 13. Estimated defect growths for transit track based on information for typical freight defect growth.

results from one of these sets of tests are shown in Fig. 10. Also illustrated in the figure is the empirical formulation of rate of settlement and amount of settlement, which, after the same tonnage, is proportional to the load, provided subgrade compressibility remains constant. It may be seen that this for~nulationgives excellent results provided the magnitude of the cycled load is not excessive. That is, the formulation is valid provided s o m e threshold load is not exceeded. On subgrades of different compressibility it was found that softer subgrades caused a faster rate of settlement and lower threshold load, other factors being equal. The influence of aggregate quality and ballast support compressibility is illustrated in more recent related work reported by Bathurst and Raymond (19900, 1990b). The focus of this work was on the mechanical stability of essentially single-sized aggregates used as permeable drainage layers below the wearing surface of highway pavements. Similar to railway ballast materials, these materials must have high permeability, which is in conflict with the requirement that they must also be stable under repeated loading (i.e., broadly graded coarse-sized aggregate with binder). The aggregates investigated had a range of aggregate index. The coarsest size aggregates tested (gradation 1) were typical of the top size in many railway ballast specifications but were slightly broader (i.e., coefficient of uniformity C,, = 2.5-4.4 versus 1.5-3 for the ballast materials reported earlier). The tests were carried out in a 1 m square box and subjected to up to 2.5 million load applications. The magnitude of peak plate load was 244 kPa. The accumulation of permanent vertical deformation is illustrated in Fig. 11 and follows an essentially linear trend with the logarithm of the number of load applications. The slopes of the curves have been plotted in Fig. 12 to show the influence of support compressibility and aggregate quality on deformation rate. Taken together, the results of the investigation illustrate the trade-offs between aggregate layer support stiffness and quality of aggregate defined by the aggregate index. For example, the poorer the aggregate quality, the greater the need to minimize aggregate mobility, which is derived in part from underlying support compliance.

Discussion Based on the reviewed data and (he tests reported herein, and because seven of the ballast materials are in use on freight-oriented wood crosstie mainline tracks, it is possible to estimate the typical approximate maintenance-cycle life of these materials. The ballast-cycle life (as opposed to breakdown life studied by C P Rail) may be associated with the dynamic ballast pressure calculated from typical mainline wood crosstie construction (track modulus assumed as 14 ~ N . m - ' . m - ' of rail) subject to two coupled G-75 trucks (bogies) with 30 t axle loads travelling at 5 0 k d h . Most of the European d a t a reviewed by t h e writers may be extended to similar zero values at l o 4 t of traffic. Using this tonnage threshold and Southern Railway's 12.5 mm twist limit for freight leads to a first estimate of ballastcycle life based on different aggregate indices as shown by the solid lines in Fig. 13. Similar estimates of rate of defect growth may be made for passenger (transit) track. Assuming a limiting twist of 5 mm for passenger comfort ride quality, as used by European Railway studies referenced earlier, and estimating the dynamic ballast-crosstie pressure for a track modulus of 56 ~ N . m - ' . m - ' of rail using 290 mm wide concrete ties at 876 mm spacing with 56 kg.m-l rail and a typical transit truck as 115 kPa, then aggregate maintenance cycles for a typical transit loading have been estimated as shown by the broken lines in Fig. 13. These results show considerable savings in maintenance by selecting better quality ballast even for transit traffic. Furthermore, if as indicated, European railways, for economic reasons, are using even lower defect limits today than shown in Fig. 13, then quality ballast is a prerequisite to minimizing maintenance of ballasted track. Practical applications In addition to the C P Rail model that is used to predict ballast life based on aggregate index and abrasion number (Fig. 9), the concepts expressed in this paper have been applied to track owned by other railways. For example, the concept expressed by Fig. 13 has been used to select a highquality ballast by the first author (Raymond 1991) for a

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CAN. GEOTECH. J. VOL. 31, 1994 \

mainline United States railroad. Excellent results were reported. It was also used to select ballast for the GO Transit extension to Whitby, Ontario, also with excellent results (Raymond 1986). The TQI measurements by CN Rail for this stretch of track were reported to be the highest ever achieved on their line (CN, personal communications, 1989).

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Conclusions A review of track-quality indices (TQIs) used to rate track geometry f o r track maintenance has been undertaken. Although there are many variations, it is evident that track maintenance is based on three main philosophies: (i) obtaining a standard deviation of a defect (or some limit minus the defect) and basing maintenance on such justification or by legislated jurisdiction; (ii) analysis of economic or financial considerations, such as balancing derailments and slow order costs with maintenance costs; and (iii) limits set by vehicle ride characteristics that tend to vary with speed, as truck construction, within limits, tends to be relatively uniform; such a method is typical f o r passenger-related rail corporations. Since slab track is not subject to rapid growth of trackgeometry defects, unless the slab fails it is apparent that the growth of defects on ballasted track is dependent on both the subgrade and the ballast. For like subgrades, the ballast aggregate index is likely to be the controlling factor for defect growth, whereas for the same ballast the subgrade variability is likely to be the controlling factor. On railway lines with different dynamic axle loading, the loading will play an important part. The results so far suggest that the rate of defect growth resulting from a constant axle load of magnitude less than the threshold load is (i) proportional to the logarithm of gross tonnage, (ii) proportional to the axle load at the same tonnage, (iii) proportional to the aggregate index of the ballast, ( i v ) slower for greater granular cover on clay and silt subgrades and (v) slower on stiffer subgrades. The results of research reported here have been applied with proven success, as demonstrated by the C P Rail ballast life prediction model and two case studies.

Acknowledgements This work reported here was funded in part by Canadian Pacific Rail, Canadian National Rail, Via Rail, and the Transport Canadian Research and Development Centre through the Canadian Institute of Guided Ground Transport, and by the Natural Sciences and Engineering Research Council of Canada. The large-scale box tests were funded in part by the Tensar Corporation under a contract awarded to G.P. Raymond of Queen's University and P.M. Jarrett and R.J. Bathurst of the Royal Military College of Canada. Additional s u p p o r t was provided by t h e Ministry of Transportation of Ontario and the Academic Research Program at RMC (Department of National Defence). ASTM 19890. Test method for resistance to degradation of smallsize coarse aggregate by abrasion and impact in the Los Angeles machine (C131-89). In Annual Book of ASTM Standards. vol. 04.02. ASTM, Philadelphia. ASTM 19890. Test method for resistance to degradation of largesize coarse aggregate by abrasion and impact in the Los Angeles

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machine. In ~ n * u a l~ b b k - ' b f~fandards.vol. 04.02. ASTM, bb Philadelphia. Bathurst, R.J., and Raymond, G.P. 1987. Geogrid reinforcement of ballasted track. Transportation Research Record No. 1153, pp. 8-14. Bathurst, R.J., and Raymond, G.P. 1990n. Stability of unbound open-graded aggregate layers. Ministry of Transportation of Ontario, Report PAV-90-0 1. Bathurst, R.J., and Raymond, G.P. 1990b. Dynamic response of open-graded highway aggregates. Transportation Research Record No. 1278, pp. 35-42. Boucher D.L., and Selig, E.T. 1987. Application of petrographic analysis to ballast performance evaluation. Transportation Research Record No. 1131, pp. 15-25. CP Rail. 1984. Specifications for railway ballast. CP Rail. Dalton, C.J. 1973. Field durability tests on ballast samples as a guide to the significance of the specification requirements. Canadian National Railways Technical Research Centre, St. Laurent, PQ. Gaskin, P.N., and Raymond, G.P. 1976. Contribution to selection of railroad ballast. ASCE Transportation Engineering Journal, 102(TE2): 377-394. Hudson, S.B., and Waller, H.F. 1969. Evaluation of construction control procedures-aggregate gradation variations and effects. National Cooperative.Mighway Research Program Report 69. Klassen, M.J., Clifton, A.W., and Watters, B.R. 1987. Track evaluation and ballast specifications. Transportation Research Record No 113 1, pp. 35-44. Office for Research and Experiments of the International Union of Railways (ORE). -1971. Description of research methods, definitions. Question Dl 17, Report RPI. ORE, Utrecht, Belgium. Office for Research and Experiments of the International Union of Railways (ORE). 1973. Study of the change in the track level as a function of the traffic and the track components (first results of laboratory and site tests). Question D117, Report RP2. ORE, Utrecht, Belgium. Office for Research and Experiments of the International Union of Railways (ORE). 1975. Study of the change in the track geometry as a function of traffic. Additional results. Question D117, Report RP7. ORE, Utrecht, Bel,'oium. Office for Research and Experiments of the International Union of Railways (ORE). 1976. Investigation of the maintenance work contributions for different types of track superstructure. Question Dl 17, Report RP9. ORE, Utrecht, Be],.oium. Raymond, G.P. 1979. Ballast properties that affect ballast performance. American Railway Engineering Association Bulletin, 8(NO. 673): 428-449. Raymond, G.P. 1985. Research on railroad ballast specification and evaluation. Transportation Research Record No. 1006, PP. 1-8. Raymond, G.P. 1986. Aggregate assessment of two sources for use as railway ballast, for GO-Transit. Private Consulting Report 53860. Raymond, G.P. 1991. ATSF 1980 El Dorado line change failure rehabilitation. ASCE Journal of Geotechnical Engineering, 107(GT8): 1191-1207. Raymond, G.P., and Bathurst, R.J. 1987. Performance of largescale model single tie-ballast systems. Transportation Research Record No. 1131, pp. 7-14. Raymond, G.P., Boon, C.J., and Lake, R.W. 1979. Ballast selection and grading. Canadian Institute of Guided Ground Transport, Report 79-4, Queen's University, Kingston, Ont. Timmerman, D.H., and Wu, T.H. 1969. Behavior of sand under cyclic loading. ASCE Journal of the Soil Mechanics and Foundations Division, 95(SM4): 1097-1 112. Watters, B.R., Klassen, M.J., and Clifton, A.W. 1987. Evaluation of ballast materials using petrographic criteria. Transportation Research Record No. 1131, pp. 45-58.