permanent way track ballast in austria: part 1

In the first part of a comprehensivearticle, Dipl.-Ing. Christoph Kuttelwascher,

Track Expert, ÖBB-Infrastruktur AG, Vienna,Austria and Dipl.-Ing. Michael Zuzic, formerHead of Track Division, ÖBB, Vienna, Austria,describe how track ballast can affect the wholerail infrastructure. Literary references (thebracketed numbers) will be detailed in theconcluding part of the article.

Regarding cost-effectiveness and longevityof the rail infrastructure, the ÖBB’s closecooperation with Austrian and other Europeanuniversities, as well as civil engineers, has a longtradition. This enables an efficient utilisation ofknowledge resources and their combination withpractical experience and the prevailingknowledge [1, 2] is complemented by newaspects. Examples given in this article comefrom references and extracts from investigationsthat were carried out on the topic of track ballastby Graz University of Technology, MunichUniversity of Technology, Innsbruck University orHTL (technical college) Saalfelden at the requestof Austrian Federal Railways (ÖBB).

1. Functions and requirementsIn combination with other track components,subsoil, drainage and elastic components, thetrack ballast is a significant component thathas a great influence on the quality anddurability of the track. The main functions oftrack ballast and ballast bed can besummarised as follows:n Load distribution and triaxial loadtransfer.n Resistance against sleeper displacementin all directions.n Simple restoration of the original trackgeometry.n Drainage and maintenance of the load-bearing capacity of the subsoil.n Retention of rainwater.n Ventilation.

From these functions, there is a range ofrequirements to be met by the quality of theballast itself. In view of the rising stressesdue to higher axle loads, and numbers oftrains and travelling speeds on the main lines,the aim is to improve the resistance of thetrack components to the influences and toincrease their service life.

An increase of the resistance is achievedusually by improving the material quality andby technological advances in themanufacturing process. With trackcomponents such as wooden sleepers ortrack ballast, the railway has to rely primarilyon natural resources and/or geologicallydeveloped structures. Track ballast isproduced by blasting, breaking-down andscreening of solid rock and can generally onlybe mined where the rock deposits are notcovered over by loose sediments such assand or gravel. The rock deposits that can befound in Austria are listed in section 2.

Solid rock for producing track ballast shouldfulfil the following conditions:

n Resistance to weathering and lowcrack formationThe resistance to weathering must be verified byappropriate expert reports. Numbers, spacingand widths of cracks in the rock have a greatinfluence on the fatigue strength of the rock.

When blasting solid rock by explosives, therewill be crack formation in various forms andsizes. If micro fissures are not completelyeliminated in the further reconditioning process,this can reduce the strength and resistance ofthe track ballast. For the highest quality andproductivity, the extraction and processing ofraw materials must, therefore, be adapted tothe respective rock and its place of occurrence.

n Toughness, hardness and lowcleavabilityThe toughness is the resistance to breaking orexpansion of cracks and can be expressed byload-deformation graphs. Crack deflection, crackbranching or crack stop ability are influencingfactors here [3, 4]. The hardness of a rock is theresistance to mechanical penetration and is theresult of mineral hardness, grain binding andhardness of the binding agent between theminerals. The minerals are arranged accordingto the size of their Ritz hardness using the Mohshardness test.

For minerals, the cleavability refers to thetendency to break at certain parallel planes inthe crystal lattice. The strength of a rock isenhanced by mineral constituents of low orlacking cleavability. Biaxial or triaxial cleavableminerals have a negative effect on thestrength [5].

n No additions of loam, earth or fine particlesAfter rainfall, the ballast bed must dry out asquickly as possible and this is onlyguaranteed ideally when there is a high levelof air permeability. Larger quantities of fineparticles hinder the drainage capacity of theballast which in the long term can have anegative effect on the load-bearing strength ofthe subsoil. In addition, fine particles, whichin wet condition encase the load-distributingparticles like a lubricant, reduce the frictionangle and thus lower the shearing strength(see 6.2).

n Good breaking behaviour (e.g.sharp edges)The better the breaking behaviour, the greaterthe interlocking of the ballast stones to eachother and to the sleepers which, in turn,produces more favourable load transferproperties and higher resistances to longitudinaland lateral displacements of the track.

2. Geology and rock deposits in Austria

The following types of rock are used in Austriafor the production of track ballast.

n GraniteThe greater part of the Bohemian Massif liesto the nor th of the Danube andaccommodates large deposits of granite fromwhich track ballast is produced. Granites aredeep-seated magmatic rocks which areformed under high pressure and at hightemperatures. They are medium to coarsegrained and usually their crystals can berecognised with the naked eye. Their highcolour variability is usually determined by thecontent of feldspar and the colour spectrumranges from light grey to bluish, and reddish-pink and orange to yellow.

The yellow colours of granite can alsooccur due to weathering of ferriferousminerals (e.g. haematite) to limonite orthrough weathering of feldspars to clayminerals (kaolinisation). Yellow granites areusually technically poorer than grey granites.Selective mining and regular checks of theweathering indicators are of great significancehere. However, discolouration processes canalso occur due to ore minerals contained inthe rock without the technical propertiesbeing altered detrimentally.

Due to their origin, quartz-rich rocks canshow a higher susceptibility to impact (quartzcrack). However, in carbonate rocks the additionof quartz increases the compressive strength. Ahigh proportion of larger feldspars and mica canhave a negative influence on the strengthproperties due to their complete cleavability [5].

n Granite porphyrIn Austria, in the transition between theBohemian Massif and the Molasse zone,there are deposits of granite porphyr whichare also suitable for track ballast production.Granite porphyr is a kind of granite but ofporphyric structure. In the fine-grained todense basic mass, there are greater lightfeldspar crystals or brown biotite platesstored which can be seen with the naked eye.Due to the dense structure, there will often bea metallic sound when struck by a hammer.

n GranuliteGranulite deposits occur in the old primary rockmassifs such as in the Moldanubicum of theBohemian Massif in the north of Austria(Waldviertel). Granulites are metamorphosicstones that have occurred under mediumpressure and high temperatures. Their maincomponents are feldspar and quartz,sometimes containing (brown-red) garnets thatcan be recognised with the naked eye in theoften white to dark grey or brownish granulites.Granulite obtained its name from the Latingranulum which means grain. This refers to theusually fine-grained to medium-grained structure(finer than granite) and the uniform texture.

Granulites are suitable for use as trackballast due to their high compressive strengthand very high resistance to wear. Thegranulite deposits in the Dunkelstein Forestare partly veined with serpentinites. However,these are easy to recognise visually and canbe eliminated by selective mining.

n DiabaseDiabase occurs due to metamorphosis(transformation processes under the influence ofpressure and temperature) of basalts. Only fewdiabase deposits in Austria fulfil the stringentsuitability criteria for track ballast (e.g. northernGrauwacken zone and Bleiberg Hochtal). Thedark green to black-green colour is producedfrom the first stages of metamorphosis which isthe reason why earlier diabase was often calledgreen stone. The proportion of chlorite occurringdue to chloritization is decisive for the strengthbehaviour. In the vicinity of the Bleiberg Hochtaland the Gailtal, diabase with a reddish colour ismined and this colouring is due to minerals suchas haematite or magnetite. No detrimentaleffects on the strength properties havebeen noted.

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Track ballast in Austria: Part 1.

RAIL INFRASTRUCTURE 63

Diabase is dense to medium-grainedand sometimes the rock develops a

porphyric texture due to embedded feldspar.

n BasaltBasalt is a basic volcanic igneous rockoccurring as watery lava when it erupts at theearth’s surface. It consists primarily of amixture of iron and magnesium silicates witholivine and pyroxene and calcium-richfeldspar. It is normally dark grey to black,whilst brownish, reddish or grey-greennuances are also possible, and consists forthe most part of a fine-grained elementarymatter. Due to its very high resistance topressure and wear, basalt is generally verywell suited for track ballast production.

Excepted from this are basalts with atendency to sunburn. Sunburned basalt isextremely susceptible to weathering,disintegrates easily and is, therefore, notsuitable for many technical applications.Sunburn endangered basalt is excluded fromdelivery to the ÖBB.

In Austria, basalts only occur in the eastand south-east (Burgenland, Styria andCarinthia) and here the occurrence cameabout in three volcanic phases. The mostprofuse phase is found in the south-eastStyrian vulcano region [4].

n Dunite, peridodite and bronziteIn the middle Austro-AlpineGrundgebirgsdecke of Styria, there areultrabasic and ultramafic rocks with variousdegrees of serpentinisation. Rocks classed asultrabasic are those with a SiO2-content ofunder 45%. Ultramafic is a term given toportions of rocks with over 90% dark mineralsof the magmatic rocks [7].

At least 90% volume of dunites consist ofolivine, in comparison to the peridotites thatconsist to 40% to 90% by volume of olivine. Asfar as the technical utilisation is concerned,the degree of serpentinisation is of decisivesignificance. Dunites and perdidotites havegood strength properties as long as theserpentinisation is not too far advanced,whereby high contents of hornblende andaugite raise the toughness of the stone.

Serpentinised dunites are mainly darkgreen to black-blue, whereas serpentinites arebrown and brown-grey to black.

Bronzites are very tough, medium

to coarse-grained rocks with greenish brown colouring.

n Limestone (dolomite)Limestone is a sedimentary rock usually ofbiogenous origin. However, it can also beseparated from water by chemical processesand consists mainly of calcium carbonate. Inportions, other minerals are also presentsuch as clay minerals, dolomite, quartz andgypsum. If the dolomite portion predominates,then it is generally regarded as dolomite ordolomite stone.

The stone properties and, therefore, alsothe technical utilisation of limestone can varygreatly. Whereas dolomites and limestonesare often classed as medium-hard rocks,there are silicious limestones that arecategorised among the hard rocks. Thesilicification improves the mechanicalresistance which is expressed in the fact thatthe compressive strength is up to twice ashigh (compared to limestone). Gravellimestone deposits in Switzerland are usedthere for the production of track ballast.

In Austria, the northern Limestone Alpsstretch from Vorarlberg to Lower Austria andconsist mainly of limestone or dolomite. For theproduction of track ballast, these rocks are onlypartly suitable due to their strength properties.

3. ÖBB conditions of deliveryTrack ballast is a natural product and is,therefore, subject to fluctuations in quality. Toguarantee the durability of track ballast over along service life, only hard rocks are used inthe Austrian core network. For a long time,rocks were allocated to this group through thedefinition of cube compressive strength, thecontent of hard minerals (hardness scaleaccording to Mohs) or the suitability for use asdouble-broken chippings. The criteria forsuitability as track ballast material are giventoday from the requirements of the ÖBBSupply Conditions [8] on the basis of theEuropean standard EN 13450 [9].

In 2011, the ÖBB drew up a testingsystem concerning the ‘production and supplyof track ballast grain size I and II’ [10]. Thisoffers the possibility to test the suitability ofthe quarries even without a firm order. Thenthe qualified suppliers can be called directly to submit offers. Basically, a distinction ismade between geometrical, physical and

chemical requirements.

3.1 Geometrical requirementsThe chosen grain size distribution mustguarantee a suitable load dispersion, loadtransfer and drainage. Close-grained aggregateshave a positive effect on the drainage capabilityand the elastic properties. However, withincreasingly narrower grading, the shearingresistance also drops which is accompanied bythe more unfavourable load transfer propertiesof lower ballast bed stability.

It is here that the particle shape hasspecial significance (due to its equalisingfunction). It can equalise the above mentionednegative aspects of a narrow grading and,therefore, due to the interlocking of theballast stones, the stability is retained even inthe case of close-grained material. However,there will inevitably be peak pressures andconsequently the edges of the stones will bebroken or chipped off.

Dynamic track stabilisation anticipatesstone rearrangement processes and leads tosettlements during operation. This raises the number of contact points between theballast stones and, therefore, reduces thepeak pressure.

The granulation K1 (31.5/63) used inAustria, seen in Figure 1, tends towards (inthe same way as the granulation for trackballast in Germany) the category Gc RB B(formerly category D) of EN 13450 [9]. Forreasons of worker protection, track ballast ofgranulation K2 (16/31.5) is used whereverthe workers have to enter the track regularly inorder to carry out work on the vehicles (e.g.parking and marshalling areas).

The proportion of fine particles (< 0.5mm)and finest grain (< 0.063mm) is limited to amaximum of 1.0M% because fine particles inlarger quantities can hinder the drainage andalso reduce the shearing strength of the ballastbed (see 6.2). Despite correct screening, onopen storage depots fine grain fractions fromthe upper and middle piles may be washed intothe lower sections of the pile of material andcollect there due to precipitation. In the case offunnel discharge or transport using wheelloaders, it is possible that these areas, inparticular, are loaded in a concentrated way.Therefore, in Austria, it is mandatory to performa screening of the entire ballast materialimmediately before the loading process. In mostcases, the product will be washed at the sametime for additional reduction of the fineparticles, whereby it is necessary to adapt theflow of water to the material throughput at thevibrating screen. If low-dust ballast is requiredfor special applications (e.g. tunnels), thecontent of finest grain must not exceed 0.5% inweight and at all times only washed ballastshould be used.

To avoid any possible grain fragmentationand demixing during loading, transport andunloading, it is stipulated that when takingspecimens on the worksite the undersizeportion must be < 22.4 mm or a maximum 5%in weight (maximum 3% in weight in the quarry).

The particle shape is determined incompliance with EN 933-4 [11] and the resultis given as the particle shape index. Theproportion of stones with a ratio length:width> 3:1 must be between 5 and 30% in weight,carrying out the test on particle groups

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64 RAIL INFRASTRUCTURE

Left: Figure 1: Grading curve of thegranulation K1 (31.5/63 mm) (Source: [8])

31.5/50mm and/or 16/31.5mm.The length of the stone is verified by

measuring using appropriate particle shapecaliper gauges. On a specimen of more than40kg delivery granulation (31.5/63mm), themass portion of grains with a length ≥ 100mm shall be 6% at the most.

3.2 Physical requirementsn Impact-attrition strength (LosAngeles coefficient)The impact-attrition strength is determinedaccording to the Los Angeles testing methodin compliance with EN 13450 [9] and EN1097-2 [12].

To carry out the test, a specimen of 10kg(grain size 31.5/50) following washing anddrying is placed in a steel drum(approximately 70cm diameter), together with12 steel balls (total weight approximately5.2kg) and rotated 1,000 times around itsaxis. The speed of rotation is around 30revolutions per minute. During rotation, thetest material is lifted by a ridge on the innerside of the drum and thrown down again. Themechanical stress on the rock is by bothimpact and attrition through the interactionsof steel balls, stones and drum wall. Figure 2shows a stone specimen before and aftercarrying out the test, Figure 3 shows a cross-section through the Los Angeles drum.

The Los Angeles coefficient LARB is

obtained after screening through a 1.6mmsieve according to the formula:

LARB= 10.000 - m100

Note: m = material passing through the1.6mm sieve.

The lower the Los Angeles coefficient, themore resistant the rock is to impact andattrition stress. Generally, only rock with LosAngeles coefficients of a maximum of 22% inweight are utilised as track ballast in Austria.Typical LARB values of different track ballastrocks in Austria are shown in Figure 8.

n Impact strength (impactfragmentation value)The resistance to fragmentation is determinedin compliance with EN 13450 and EN 1097-2[12]. The impact fragmentation coefficient SZRBis obtained from the mean value of threeseparate operations. In each case, a mass ofaround 2.8kg (grain size 31.5/40) is placed ina mortar (17cm inside diameter) after washingand drying and stressed by twenty blows of adrop hammer. The hammer has a mass of 50kgand falls from a height of 42cm. The rockfragmented when this test is carried out is thenpassed through the 8mm sieve.

The stress on the rock has an impactcharacter and the resulting fractured stone isobtained from the striking energy of the drophammer on to the specimen. Figure 4 shows

a stone specimen before and after carryingout the test. Figure 5 shows a typical impacttesting device.

The impact fragmentation value iscalculated according to the formula:

SZRB= M1

MNote: M = mass of the single measuringspecimen before the test; M1 = materialpassing through the 8mm sieve.

The lower the impact fragmentationvalue, the more resistant the rock is to impactstresses. Generally, only rock with impactfragmentation values of maximum 22% inweight are utilised as track ballast in Austria.Typical SZRB values of different track ballaststones in Austria can be seen in Figure 8.

n Resistance to wear (Micro-Devalcoefficient)The resistance to wear is determined incompliance with EN 13450 and EN 1097-1 [13].The Micro-Deval coefficient is produced from themean value of two separate operations.

Each separate measuring specimenconsists of a mass of 10kg of washed anddried fractured stone 31.5/50. This is placedin a drum (20cm diameter) filled with 2.0 l ofwater and stressed at a speed of 100revolutions per minute through friction on theinside wall of the drum. After 14,000revolutions, the specimen is screened


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Above: Figure 2: Stone sample before and after a Los Angeles test asper [12] (Source: ÖBB). Above: Figure 3: Typical Los Angeles test machine (Source: [12]).

Above: Figure 4: Stone sample before and after an impactfragmentation test as per [12] (Source: ÖBB).

Right: Figure 5: Typical impact testing device (Source: [12]).

through a 1.6mm sieve. The Micro-Deval coefficient is

calculated according to the formula:MDERB= 10.000 - m

100Note: m = mass of the material retained onthe 1.6mm sieve, in grams.

In the Micro-Deval test, the rock is onlystressed by friction. The rock is more resistantto wear the lower the Micro-Deval coefficientand, therefore, the greater the materialretained on the 1.6mm sieve. Figure 6 shows arock specimen before and after testing, Figure7 shows a normal testing apparatus.

Typical MDERB values of various trackballast stones in Austria can also be seen inFigure 8.

n Gross densityGross density is determined in accordancewith EN 1097-6 [14]. This is the density of theraw stone as a ratio of mass to volume. Themass is determined by weighing the specimenin water-saturated and surface-dried conditionand then again in oven-dried condition. Thevolume contains all pores and cavitiesspecific to the rock. No test value is laid downfor the gross density but generally high grossdensities are required.

In contrast to the gross density, the bulkdensity describes the ratio of mass to volume ofan unconsolidated, dry stone granulation (loosematerial). It is equivalent to the lowestcompactness including all bulk and bedrockpores. We know from experience that it is roughlyequivalent to half the gross density and is,therefore, around 1.3-1.5 t/m³ for track ballast.

The vibration density is that density of aheap of material that is achieved by vibration.

This is equivalent to the maximum achievabledry density in close-grained, coarse aggregates.

n Resistance to weatheringThe stone used as track ballast must beresistant to weathering. Weathering is aprocess of stone disintegration due tophysical, chemical or biogenous influencesand their combinations (e.g. temperaturefluctuations, frost, ice, salt, acids).

The evaluation of the resistance toweathering can be made in many differentways - by visual inspection (in the deposit andfrom broken material), by petrographicexpertise and by undertaking a number oflaboratory tests. The laboratory tests includethe identification of water absorption [14], theresistance to freezing and thawing [15] or theresistance to magnesium sulphate [16]. Ifthere is a suspicion of sunburn in basalt rock,the volume stability must be confirmed incompliance with EN 1367-3 [17].

3.3 Chemical requirementsThe chemical requirements assure theecological acceptance of the rock material andare based on the national regulations concerningrecycling and waste dumping. In Austria, theseare primarily the Waste Management Act,Federal Waste Management Plan and LandfillOrdinance. At the end of its technical lifespan,the used ballast should then be recycled or bedisposed of, if necessary, at low cost.

3.4 Alternative testing methodsApart from the mandatory testing methodsconcerning wear and impact strength of trackballast [cp. 18], alternative methods are, inprinciple, also conceivable. On behalf of

Austrian Federal Railways (ÖBB), studies offive alternatives testing methods were carriedout at Graz University of Technology and atHTL Saalfelden (cp. [19]).

The test to determine the compressivestrength in the excavated material [20] is alarge-scale pressure test using a containersimilar to an odometer.

Two other testing methods, namely thetest to determine grindability of rock by meansof a scratch test (Cerchar test) and the grindingand milling test for granulates (Abroy test),were developed to estimate the wearing rate onmining tools, but also enable conclusions to bereached regarding the abrasiveness as ameasure of resistance to wear.

Using an adapted triaxial test unit with aconstant displacement, the point load test [21]applies a force until the track ballast grainbreaks. This also enables conclusionsregarding the cleavability and the loaddeformation behaviour of the rock being tested.

In the course of a modified impactfragmentation test [21], a dynamic load wasexerted on the excavated material with ballastgranulation K1 (31.5/63mm) using a dropweight under an initial load of 70kg. Bydefinition, the fine grain enrichment is dividedinto fragmentation (percentage by mass <22.4mm) and content of fine par ticles(percentage by mass < 4mm).

All testing methods were carried out in anexemplary way with specimens of rockssuitable for use as track ballast andcorrelations were investigated with resultsfrom the established methods. Some of theresults have been published and furtherdevelopments in the field of standardisedquality controls can be expected.


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Left: Figure 6: Stone sample before and after a Micro-Deval test asper [13] (Source: ÖBB).

Below: Figure 7: Usual test device for Micro-Deval test (Source: [13]).

Above: Figure 8: Test results of important track ballast stones in Austria, detailing mean values and a scattering of the mechanicalcharacteristics (2004-2011) as per EN 13450.

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In the second part of their article, Dipl.-Ing. Christoph Kuttelwascher, Track

Expert, ÖBB-Infrastruktur AG, Vienna, Austriaand Dipl.-Ing. Michael Zuzic, former Head ofTrack Division, ÖBB, Vienna, Austria, describehow track ballast can affect the whole railinfrastructure. Literary references (thebracketed numbers) will be detailed in theconcluding part of the article.

4. Stone mining and selective exploitation

In past years, the ÖBB needed around onemillion tonnes of track ballast annually(fluctuating above and below this figure) inorder to implement all worksites (renewal andmaintenance). Depending upon the wagonsused (loading quantity), this is equivalent tothe figure of around 25,000 to 35,000wagonloads per year. Unlike other trackcomponents, a high proportion of the price ofballast is incurred by transport of the materialto the worksite. Besides technical and qualityassurance aspects, high demands are placedon daily loading capacities, weekly productioncapacities and long-term availability in orderto guarantee a reliable worksite supply.

The mechanical requirements to be metby track ballast are the highest of all rockproducts which automatically limits thenumber of effective suppliers. Deposits of rawmaterial occur homogeneously or are veinedwith rock zones of lower quality, depending onthe geological formation processes. Thesezones can be excluded from the track ballast production with the help of geologicalsurveys for thorough underground exploration,exact mining planning and selectiveexploitation - a precondition for consistentlyhigh-quality material.

Usually the mining and rock processing forthe production of track ballast is carried out inthe following main stages: clearing, boring,blasting, transportation, separation, rough-crushing, mineral processing, breaking-down,screening, storing, post-screening and loading.

Normally, the rock is removed from thequarry by large borehole blasting which cancause cracks in different sizes. Optimisedborehole spacing and explosive chargesminimise the occurrence of micro-cracks. Therequired K1 granulation is normally producedafter the second breaking stage by screeningusing square-mesh screening on steel orsynthetic sieves. Considerations are beingmade to break up all micro-cracks completely inthe reconditioning process because anyremaining micro-cracks in the end product havea negative influence on the strength properties.

5. Quality assuranceThe ÖBB uses a multi-stage quality assurancesystem. All suppliers of railway ballast musthave CE conformity certification and pursue acertified, regular, internal production controlsystem as per EN 13450 [9].

5.1 Qualification test, inspectiontests, intermediate tests

The qualification test (initial test) enables astatement to be made whether the materialbeing mined meets the specifiedrequirements and takes into account all majorparameters of EN 13450 [9]. Geological,

petrographic and tectonic expert appraisalsgive information about medium and longerterm rock properties in the mining region andenable an estimation of the qualitydevelopment in the future.

The operational assessment itself isperformed by the ÖBB. Expert opinions andtest results are referred to in the course of theoperational assessment. Ballast specimensare taken on location for a further round oftests and the technical and commercialefficiency of the supplier is assessed.

Inspections (conformity tests) are carriedout by ÖBB officials in every supply quarry atleast twice a year. They establish whether thequality properties meet the contractualrequirements and serve as a conformitycertificate of internal monitoring by themanufacturer. The ballast specimens taken atthe quarry provide test data that is collected in acentral system. Figure 8 (see part 1 of thearticle) shows examples of time series oftypically achieved mechanical characteristics ofvarious types of rock in Austria.

In trade literature there is often mentionof the good correlation between LA value andimpact fragmentation value. In Austria, such acorrelation applies only for a few types of rock(e.g. basalt) whereas other rocks (e.g.granulite) have no correlation (cp. [19]). Forthis reason, both testing methods are used inthe round of tests in Austria.

Intermediate tests (identity tests) serve tomonitor the ballast quality at the laying site andcan be performed by the ÖBB at any time. Whenthe quantity delivered is over 1,000 tonnes, atleast one intermediate test must be carried outon the respective worksite. For worksites withdelivery quantities of over 5,000 tonnes at leastone intermediate test must be carried out per1,000 tonnes of material. Normally the grainsize distribution is checked, but other stoneparameters can be investigated if required.

5.2 Loading Before ballast is loaded by the supplier, everywagon must be checked so that it is empty inorder to avoid incorrect loading or mixing withany possible residue in the ballast wagon. Thiscan be done by visual inspection or by usingautomatic video surveillance systems. If thelatter is chosen, it is possible for the customerto check the loading process in real time.

Figure 9 shows an example of the loadingcontrol of an ÖBB track ballast supplier usingautomatic video surveillance (start-up in 2011).One image is generated at times of predefinedstages of loading. Documentation of the wagonnumber and the wagon in an empty state ismade by two images before loading, thedocumentation of loading by one image duringactual loading and another one afterwards.

The automatic recording process iscontrolled by an interface with the (officiallycalibrated) belt weigher and documents thecurrent loading quantity. All loading data andphoto information are stored in real time onthe server to which the customer (scheduling)has direct access.

6. Load transfer anddimensioning of the ballast bed

6.1 Hertz’s contact pressure at the rail

One of the most important functions of theballast bed is to absorb and distribute thestatic and dynamic wheel loads and totransmit them to the subsoil. The wheel-railcontact patch is only 1-3cm2, dependent ontheir lateral position, the wheel loads appliedand the contact geometry (rail wear). HeinrichHertz’s theory enables a calculation of thestresses and their distribution to the contactsurfaces of elastic bodies.

For the calculation of the shearingstress occurring at the wheel-rail contact


Above: Figure 9: Images from the automatic loading control of an ÖBB track ballast suppliershowing the video surveillance at various stages of loading - documentation of wagonnumber, wagon empty, loading process and load weight. (Source: ÖBB).


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surface, the following formulae applyaccording to Hertz’s theory with the

assumption of a roller contact: F•r 2a=3,04•2•b•E

(mm)

Note: F = effective wheel force (N).r = wheel radius (mm).b = half width of rolling surface (mm).E = modulus of elasticity of the rail steel (2.1 • 105 N/mm2).PRS = contact pressure (N/mm

2).Under the simplified assumption (only

valid for r ≥ 300 mm) F F• 2•b•E PRS=2a•2b

= 3,04• F•r•2b (N/mm2)

With E = 2.1•105 N/mm2 and 2b = 12mm(width of rolling surface) it applies:

FPRS= 43,5• r (N/mm2)The maximum shearing stress �Tmax, that

occurs at a depth of 4mm to 7mm iscalculated according to the half-space theory.

Tmax = C•PRSC is a factor that lies between 0.31 and

0.33 with constant sur face pressuredepending on the type of touch surface.

For the maximum shearing stress �Tperm

it, therefore, applies by approximation:FTmax=0.3•PRS=13,05• r

6.2 Load dispersion in the ballast bed

With an assumed contact surface of 3cm2 andwheelset loads of 225 kN this producespressures of around 42.000 N/cm2 at the railsurface. With other contact geometries, thesepressures can rise even higher and must becontinuously assimilated and distributed by theindividual track components. With a theoreticalsleeper supporting surface of around 2,400cm2

there will still be pressures, for example on theunderside of the sleeper of around 37 N/cm2

[23]. However, according to investigations byMunich University of Technology, the effectivesleeper supporting surface for uncoatedsleepers after consolidation, depending on thenumber of load alterations, is only around 1-2%of the total sleeper underside area. On theAustrian pre-tensioned concrete sleeper K1 thisis equivalent to around 100cm and wouldindicate very high contact stresses (up toapproximately 2,000 N/cm2) [24].

A sufficiently large ballast bed isnecessary to distribute the traffic loads over anadequately large area of the substructureand/or subsoil and not exceed its load-bearingcapacity. Due to the rail depressions, elasticelements and irregular support conditions, aninitial settlement is necessary to distribute thewheel load over several sleepers and toactivate the underlying resistance force of theballast bed even under the adjacent sleepers.The larger the flexural strength of the rail andthe lower the stiffness of the trackbed, themore sleepers will be needed for the loadtransfer. The skeleton track itself is a floatingconstruction in the loose pile of ballast and thetraffic loads can be dispersed uniformly intothe subsoil only when there are homogeneoussupport conditions.

The load transfer in the ballast bed iscarried out via the contact surfaces of ballaststones to each other, primarily throughcompressive forces and secondarily throughshearing forces. The assumption of a linear

distribution of pressure according to Fröhlich[25] applies only for isotrope andhomogeneous materials. In reality, loadtransfer occurs through randomly formedforce paths (Figure 10).

Depending upon load intensity and depthof the ballast bed, individual force paths reachas far as the subgrade even outside theassumed load dispersion angle. To take intoaccount anisotropy and inhomogeneity,Fröhlich used the concentration factor VK.

The surface pressure on the formationdepends on the assumed load dispersion angleof the ballast bed. To ideally utilise the load-bearing capacity, the subsoil (subgrade) and toachieve a uniform course of pressure on theformation, the depth of the ballast bed shouldtheoretically be large enough that the pressuredispersion lines of adjacent sleepers intersectover the formation [1] is produced from:

n a =2*tan

Whereby a is the ballast bed depth underthe sleeper, n the sleeper spacing and theload dispersion angle.

Practical experience shows substantialdeviations from a homogeneous support due toscattering in the initial consolidation, grainfragmentation as a result of traffic loads or grainsize distributions altered by entry of foreignmaterial (e.g. airborne dispersal, spillage). Whenlaying new track, it is especially important toproduce a ballast structure in the form of a high-quality, homogeneously compacted ballast bed.

When considering the defined target heights, theneed for a uniform granular structure as regardsdepth and grain size distribution should not beneglected (e.g. grain fragmentation due tounacceptably high consolidating energies). In thecase of cavities under the sleepers, there arestiffness fluctuations in the ballast bed whichresult in a concentration of stresses on somelocalised parts in the granular structure [27].

In the shearing graph, the rise of theshearing strength is determined by the angle offriction φ. Large angles of friction favour the


Above: Figure 10: Discontinuous loadtransfer of the ballast bed (Source: [25]).

Above: Figure 11: Rail depressions, rail foot tensions and supporting point force with variousballast bed moduli, spring characteristics and elastic length and a wheelset load of 100 kN(Source [23]).

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ballast bed stability and ensure good loaddistribution, activation of large quantities ofballast and a reduction of the strain on thesubsoil. The friction angle is determined mainlyby the grain size distribution (irregularity,density) as well as shape, roughness, sharpedges and edge stability of the grains. Many ofthese parameters are not influenced by stoneprocessing and are basically defined by rockproperties and mineralogy. To measureadditional geometrical influencing parameters,such as sphericity (shaped like a ball) anddegree of roundness, tests were carried out bythe ÖBB in 2012 on all types of rock suitablefor track ballast using the Petroscope at GrazUniversity of Technology. For this, a quantity ofseparate stones is scanned by a laser beamwhich enables the degree of roundness and theshape index to be identified.

When wet, fine particles in large quantitiesact like a lubricant, reduce the friction angleand, therefore, lower the shearing strength.This results in unfavourable load transferproperties and high stress peaks. They alsobind water through capillarity action, delay thedrying out of the subsoil and can, therefore, inthe long-term reduce the load-bearing strengthwhich leads to settlements.

In various literature the load dispersionangle of new track ballast in the ballast bed isstated at times with up to 45°. Studies atInnsbruck University commissioned by the ÖBBproduced in laboratory tests far lower values ofaround 20° (at 90% load quantiles) for newballast. To evaluate the conditions on the openline, tests on load dispersion were carried outon various kinds of rock and stone shapesduring innovation measuring runs in 2012 onreal track on the new western main line Vienna-St. Pölten in the vicinity of Tullnerfeld.

6.3. Track calculation and stress on the ballast

The stress on the ballast is normally expressedin terms of the ballast pressure. This results fromthe load on a sleeper in relation to the effectivesupporting surface of the sleeper in the ballast.The greatest loads in the ballast bed, whichdestroy the ballast stones, are primarilyquasistatic and dynamic vertical loads.Discontinuities in the track (e.g. switch points,joint gaps) or on the vehicle (e.g. flat spots)produce localised, dynamic force peaks. Abruptdifferences of stiffness in the subsoil (e.g. bridgetransitions) and non-uniform layer densities of theballast bed react in turn on the load transfer(foundation soil-framework interaction).

Zimmermann’s method on the basis of

considerations by Winkler [28] is applied toevaluate the stress on the track components.Although not accepted unconditionally indetail, Zimmermann’s method [29] producesreliable results for the purposes of measuringand is applied at ÖBB in the form ofRegulation B 50-Part 3 [22]. Here the rails areregarded as bearers on an elastic foundationwith the ballast bed modulus C. The ballastbed modulus C describes the relationshipbetween the sur face pressure of thesupporting point and the depression and,therefore, also contains the elasticity of theballast bed and the subsoil. The formulae is:

PC = y

C = ballast bed modulus (N/mm3).P = surface pressure between sleeper andballast (N/mm2).y = depression of the rail (mm).

Elastic elements such as rail pads,elastic coating on the underside of sleepers or sub-ballast mats can be taken into accountby superposition.

The rail deformations are dependent uponwheel load, rail stiffness, stiffness of thesupports and sleeper spacing. As illustrated inFigure 11, there are greater deformations onsoft subsoil and, therefore, greater stress onthe rails. On the other hand, hard subsoil leadsto high supporting point forces and theassociated higher stresses on the ballast. Theuse of elastic coatings on the underside ofsleepers and sub-ballast mats, for example, canhelp to reduce these stresses [31].

In the ÖBB Regulation B 50-Part 3 [22],the ballast bed moduli illustrated in Figure 12are applied. The ballast bed modulus can bedetermined by depression measurements, railfoot tensions or knowledge of the bendingwave at a given vertical load using the

following formulae:n From the rail foot tension:

4•E•I•a F C =A

• 4•σf•Wu (N/mm3)

n From the depression of the rail: F•a 3 F C =4•y•A

• E•I•y (N/mm3)

n From the length of the bending wavebetween the points a and b (Figure 13):

4 4•E•I•a E•I•aL=A•C (mm) &

C= 2000•A•D4 (N/mm3)

Calculated ballast pressure under the sleeper

The basis of the calculation according toZimmermann is the conversion depicted inFigure 14 of the cross-sleeper support surfacein equal surface longitudinal sleepers.a = sleeper spacing.b = width of the assumed longitudinal beam.ü = sleeper overhang.2ü = sleeper length minus wheel contact pointdistance (1,500mm on standard gauge,805mm on narrow gauge).A1=A2=AA1=2•ü•b1A2=b•a

2•ü•b1 A1b = a = a

The ballast pressure p under the sleeperresults from p=C•y, the depression yaccording to the formula:

F•a y=2•A•C•L

•η

L describes the fictive sleeper lengthand produces

4 4•E•I•aL=A•C

A = half supporting sleeper surface (mm²).a = sleeper spacing (mm).C = ballast bed modulus (N/mm³).p = surface pressure between sleeper andballast (N/mm²).y = depression of the rail (mm).E = modulus of elasticity of the rail steel (2.1•105 N/mm2).F = effective wheel force (N) in compliancewith EN 15528.L = fictive sleeper length as a basic value ofthe longitudinal sleeper track.Ix = moment of inertia of the rail (mm4).η = Zimmermann’s influencing factor.φ = speed factor.n = stress reversals.

The effective wheel force F is producedfrom the static wheel force and an addition (10to 20%) for the wheel force displacementwhen travelling through curves.

Above: Figure 12: Ballast bed modulusdepending upon type of subsoil (Source: [22]).

Above: Figure 13: Bending line between the points a and b (Source: [22]).

Right: Figure 14: Conversion of the cross-sleeper track in atheoretical long-sleeper track (Source: [22]).

b1: Slanting edges andnarrowings in the middle of thesleeper should be taken intoaccount for concrete sleepers.


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In the final part of their article, Dipl.-Ing.Christoph Kuttelwascher, Track Expert,

ÖBB-Infrastruktur AG, Vienna, Austria, andDipl.-Ing. Michael Zuzic, former Head of TrackDivision, ÖBB, Vienna, Austria, describe howtrack ballast can affect the whole railinfrastructure. Literary references (thebracketed numbers) are detailed at the end ofthe article.

Zimmermann’s influencing factor η takesinto account the influence of several vehicleaxles and is contained in the ÖBB regulationB50-Part 3 in spreadsheet form. It is set at 1.0for a single load in the middle of the sleeper.

The scatterings of the effects (quasi-static and dynamic stresses) and resistances(ballast, cavities, subsoil) are taken intoaccount by additions for speed and state ofrepair and summarised in the factor s (s=n•φ). The speed factor φ is obtainedfrom the maximum line speed and is between1 and 1.5. The factor n lies between 0.15 and0.25 and is obtained from the line categoryand track classification.

6.4. Resistances to lateral displacement

The resistance to lateral displacement is adecisive parameter for measuring the stabilityof the track to buckling and depends on alarge number of factors (sleeper geometry,contact surfaces, grain size distribution, grainshapes, angularity, amount of ballast aroundthe sleeper edges). It is that reaction forcethat counteracts a displacement of the trackperpendicular to the centre line of the track(normally after a 2mm displacement path).

The resistance to lateral displacement iscomposed of the following resistances: n Sleeper underside friction. Resistancesat the sleeper underside dependent on load,contact sur face and interlocking and/orcoefficient of friction. According to [24] adistinction is made between primary andsecondary sleeper underside resistance.n Shoulder resistance. Active soil pressure

as per soil pressure theory dependent oncoefficient of friction, height of layer andmaterial characteristics.n Sleeper-end resistance. Passive soilpressure as per soil pressure theory becomeseffective only from a certain movement.

After ballast bed cleaning or tamping, theresistances to lateral displacement arereduced by between 40 and 50%. Thedynamic track stabilisation increases theresistance to lateral displacement by between30 and 40% [23]. The percentages of the partresistances given in trade literature fluctuatedepending upon the measuring method used.However, all in all, approximately half of thetotal resistance to lateral displacement isdetermined by sleeper underside friction andon elastic-coated sleepers up to around 60%.

To establish the influence of differenttypes of ballast (granite and dunite), elasticcoatings and safety caps on the resistance to

lateral displacement, tests werecommissioned by ÖBB in 2010 and carriedout by Munich University of Technology usingthe single-sleeper method and have beenpublished in [24].

To perform the measurements a skeletontrack with two uncoated K1 pre-tensionedconcrete sleepers was set up in the test rig.The depth of the ballast bed was 45cm whichis equivalent to a ballast depth of 23cm belowthe lower edge of the sleeper. Sub-ballastmats of varying stiffness (Cstat = 0.045N/mm³ and 0.28 N/mm³) were used tosimulate the subsoil. Ballast bedconsolidation was performed using a vibratingplate and a manual packing device. The testset-up can be seen in Figure 15.

Depression, stiffness, ballast bed modulus

The depressions under static and dynamicload were measured using inductivetransducers. After a simulation of three millionload alternations with an upper load of 225 kN, the static and dynamic ballast bedmoduli, the settlement behaviour and theresistance to lateral displacement of theindividual sleepers were established.

When the consolidation condition isreached after around 250,000 loadalternations, the oscillation amplitude (declineof elastic deformations) drops, whereas theplastic deformations continue to increase.

With the same grading curve the duniteshowed during the fatigue level test,compared to granite, a lower static anddynamic stiffness combined with greaterplastic deformations. After three million loadalternations the plastic deformation of thegranite ballast on stiff subsoil (Cstat = 0.28N/mm³) was around 6mm, whereas that ofthe dunite was around 9mm. After a load of 3million load alternations the static ballast bedmodulus was on average around 0.155N/mm³ and the dynamic ballast bed moduluswas around 0.195 N/mm³.

For the test the sleeper-end ballastwas 0.50m horizontal and the adjoining



Above: Figure 15: Test rig during the fatigue level test. (Source: ÖBB).

Above: Figure 16: Resistance to lateral displacement graph of a single sleeper measurementwith safety caps. (Source: ÖBB).

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embankment slope was 1:1.5. After theentire loading cycle the rails were

uncoupled from the sleepers to measure theresistances to lateral displacement. Then, theindividual sleepers were displaced crosswise tothe centre line of the track, without a verticalload. The horizontal load was commenced in theneutral axis of the sleeper, the force occurring atthe 2mm deformation path (transition staticfriction - sliding friction) was taken as a rulingresistance force. The calculation was madethrough the relation to the sleeper spacing of600mm in the unit N/mm.

Figure 16 shows a typical force-deformation curve of a resistance to lateraldisplacement measurement with safety caps.

Figure 17 shows with dunite ballast onsoft subsoil a lateral resistance increased by27% (compared to hard subsoil), which is dueto a higher density through the largeroscillation amplitude and greater plasticdeformation due to the rearrangementprocesses. On hard subsoil, the resistance tolateral displacement to granite ballast isslightly reduced due to the lower stability ofthe edges.

Due to temperature expansions, highforces act to the outer side of the curve,especially in very tight curves, which withoutadditional measures would produceunacceptably high deformations. Here safetycaps are applied as a means to increase theresistance to lateral displacement. Theresistances to lateral displacement were alsomeasured with safety caps installed in orderto check their effectiveness. Here theincrease of the resistance to lateraldisplacement was on average around 30%(Figures 16 and 17). With ballast bed depthsover 45cm a further increase can be expecteddue to the additionally activated pressurecone downwards.

7. Reduction of the mechanical track ballast loadsUniform consolidation and homogeneity of theballast bed are important requirements toreduce the loads on the ballast structure.Immediately after mechanised ballast bedcleaning and tamping, the ballast is onlycompacted in the influencing zone of thetamping tines. A homogeneous consolidationin the entire cross-section is aimed at throughthe application of dynamic track stabilisation.Irregular settlements due to traffic loads arereduced and anticipated in a uniform way,increasing the resistance to longitudinal andlateral displacements and reducing cavitiesunder the sleepers. The dynamic trackstabilizer exerts a vertical load on the trackand places it in horizontal oscillations of 30-37 Hz. Due to the low ballast pressure ofapproximately 8 N/cm², this is also referredto as ‘force-free spatial consolidation’ [31].

Another course of action to extend theservice life of the ballast bed is the specificapplication of elastic elements such as elasticcoating on the undersides of sleepers and sub-ballast mats. The resulting lower mechanical

stresses on the ballast stones result from themore uniform support conditions on the onehand and from a dampening of the dynamicpulses from the traffic loads on the other. Dueto the use of elastic undercoating, the contactsurfaces between sleeper and ballast can bemultiplied [24].

An increase of the contact surfaces isalso obtained through modified sleeperdimensioning, for example frame sleepers(Figure 18) or HD sleepers.

8. OutlookThe quality of the track ballast used in the linenetwork of Austrian Federal Railways isregulated by the ‘Production and Supply ofTrack Ballast’ and by the technical conditionsof delivery for track ballast (BH 700). TheEuropean standard EN 13450 serves as abasis for the requirements.

All suppliers of railway ballast must haveCE conformity certification and pursue acertified, regular, internal production controlsystem. Typically, the quality is guaranteed by initial testing, conformity testing andidentity testing.

In the EN 13450, the Los Angeles testingmethod has been laid down as a Europeanreference method to determine the resistanceof track ballast to fragmentation. The foundationwas tests carried out by the European RailResearch Institute (ERRI) in 1991 and 1992.Practical experience shows that a singlereferencing on the Los Angeles coefficient (LAvalue) does not completely reflect theexperience of the Austrian rail network.Therefore, Austrian Federal Railways also usesthe impact fragmentation coefficient and theMicro-Deval coefficient as additional qualitycriteria. In addition, over past years, alternativetesting methods have been investigated, further

developed and in some cases published [19].Some of these testing methods are suitable forroutine application and may lead to furtherdevelopment in this sector.

In order to correctly evaluate the behaviourof the Austrian track ballast in the rail networkof Austrian Federal Railways, and to drawconclusions about quality figures, a greatnumber of investigations were carried out in theÖBB rail network in the years 2010 to 2012 inthe course of a project on the systematicobservation of the subject of track ballast.Taking into account the framework conditionssuch as track components, drainage, subsoilstiffness, etc, ballast samples were taken andmaterial tests were performed by accreditedtest institutes and universities.

It is evident that only a systematic view (intechnical, organisational and commercial terms)will be effective. For example, modifications oftechnical requirements automatically haveeffects on supplier structure, transport costsand worksite logistics. On a technical basis allcomponents of the track must be compatible. Asa part of this system, the track ballast usedplays an important role. When there isinsufficient drainage, poor subsoil or dynamicstresses due to discontinuities in the trackstructure, even the highest quality track ballastcannot compensate for the deficiencies in theoverall system.

An important commercial difference oftrack ballast to other track components is that the transport costs make up a highproportion of the overall costs for supplyingballast to the worksite. The requirement ofmaximum track ballast quality at a low price,with the best possible assurance of supplyand minimum transport distances, shows thenecessity of regarding the subject of trackballast systematically.

Right: Figure 17: Calculated resistances tolateral displacement of individual sleepersafter the fatigue level test with three millionload alternations. (Source: ÖBB).

Right: Figure 18: Visible ballast stone contactsurfaces of an elastic-coated frame sleeper inthe St. Pölten area. (Source: ÖBB).


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Literary references[1] Klotzinger, E. (2008): Track ballast. Part1: Requirements and stress. In: ETR, 01-02/2008.[2] Klotzinger, E. (2008): Track ballast. Part2: How quality develops over time andthresholds for action In: ETR, 03/2008.[3] Issler, L./Ruoß, H./Häfele, P. (2003): Science of material strength -Fundamentals.[4] Dietrich, H. (1994): Mechanical Testing of Materials: Foundations, TestingMethods, Applications.[5] Anthes, G. (2006): Study Fundamentalinquir y into deposits of granite stone in Austria.[6] http://www.volcanodiscover y.com/de/vulkane/lexikon/basalt.html[7] http://www.wikipedia.org[8] Technical conditions of delivery for trackballast BH 700; ÖBB Infrastructure AG,1. Aug. 2007.[9] ÖNORM EN 13450 Aggregates for trackballast; Austrian Standards Institute in theapplicable version.[10] ÖBB Infrastruktur AG (March 2011):Testing system as per Ar ticle 53 RL2004/17/EG in the applicable versionconcerning the ‘production and supply of trackballast of particle size I and II’.[11] ÖNORM EN 933-4 Tests for geometricalproper ties of aggregates, Par t 4:Determination of particle shape - Shapeindex. Austrian Standards Institute in theapplicable version.[12] ÖNORM EN 1097-2 Tests for mechanicaland physical properties of aggregates. Part 2:Methods for determination of resistance to

fragmentation. Austrian Standards Institute inthe applicable version.[13] ÖNORM EN 1097-1 Tests for mechanical and physical proper ties ofaggregates. Par t 1: Methods fordetermination of resistance to wear (Micro-Deval). Austrian Standards Institute in theapplicable version.[14] ÖNORM EN 1097-6 Tests for mechanicaland physical properties of aggregates. Part 6:Determination of particle density and waterabsorption. Austrian Standards Institute in theapplicable version.[15] ÖNORM EN 1367-1 Tests for thermaland weathering properties of aggregates. Part1: Determination of resistance to freezingand thawing. Austrian Standards Institute inthe applicable version.[16] ÖNORM EN 1367-2 Tests for thermaland weathering properties of aggregates. Part2: Magnesium sulphate test. AustrianStandards Institute in the applicable version.[17] Austrian standard EN 1367-3 Tests forthermal and weathering proper ties ofaggregates. Part 3: Boiling test for sunburnedbasalt. Austrian Standards Institute in theapplicable version.[18] ORE (1991): Uniform assessmentcriteria of ballast quality and evaluationmethods of ballast condition in the track.Question D 128. Report No. 2.[19] Bach, H./Kuttelwascher, C./Latal, C.(2012): Alternative testing methods for qualityassurance of track ballast. In: ZEVrail,3/2012.[20] Swiss Association of Road and TrafficSpecialists (February 2008): SN 670 830bTest procedure for mechanical and physical

proper ties of aggregates - method for determining the compressive strength oftrack ballast.[21] Breymann, H. (2011): Mechanicalcriteria for the track ballast - point load test,fragmentation. Repor t to the ÖBB(unpublished).[22] B 50-Teil 3 (März 2012): Permanent waycalculation. ÖBB Infrastruktur AG.[23] Lichtberger, B. (2003): TrackCompendium.[24] Iliev, D. (2012): The horizontal trackgeometry stability of the ballasted track withconventional and elastic coated sleepers. In:Munich University of Technology, RoadConstruction Department and Testing Office,Publications: Brochure 86.[25] Fröhlich, O. K. (1934): Pressuredistribution in the foundation soil.[26] Kruse, H. (2002): Model-assistedinvestigations of track dynamics and thebehaviour of railway ballast. Dissertationsubmitted to Hanover University.[27] Holtzendorff, K. (2003): Investigationinto the settlement behaviour of railwayballast and the development of cavities onballasted tracks; Dissertation submitted toBerlin University of Technology.[28] Winkler, E. (1867): The science ofelasticity and stability. [29] Zimmermann, H. (1941): Calculation ofrailway permanent way. [30] Auer, F./Schilder, R. (2009): Technicaland commercial aspects on the topic of soledsleepers - Part 1: long-term experience in theÖBB network. In: ZEVrail. April 2009.[31] Lichtberger, B. (2007): The LateralResistance of the Track. In: EIK 2007.

permanent way track ballast in austria: part 1

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