Permanent Way LJ

Track formation improvement - problems,development and implementation: Part 1.

In the first of a two-part article, Prof. Dr.Ing. Klaus Lieberenz, em. Professor HTW

Dresden, GEPRO Engineering SocietyDresden, Germany, and Franz Pierede, formerHead of Track Maintenance MachineOperations, ÖBB Head Office, Linz~ Austria,describe how the foundations and formationof the trackbed can affect the actual trackquality and per formance. Literary references(the bracketed numbers) will be detailed in theconcluding Part of the article.

ProblemsThe railway substructure is subjected to:• Static and dynamic stresses resultingfrom rau traffic.• Various climatic influences.

Under the influence of these stresses,the entire trackbed System and its individuallayers, i.e. the substructure and the subsoll,is subjected to stresses and deformation [1].Stresses must be assimilated by the givenmechanical properties whereas deformationsmust not exceed certain iimits. The elementsof the trackbed system must be dimensionedso that the stresses acting on them canbe absorbed without destruction ordamaging deformations.

The deformations depend on thestresses acting on, and the resistancesoccurring in, the subsoil and the substructurewhich.are determined by the layer densitiesand the deformation modulus ofthe soils andon the deformation modulus and thicknessesof the bearing layers installed [2]. Thedeformation modulus of the soils isdependent upon the water content and can,therefore, be influenced by drainage Systems.

lt 5 typical of railway lines that both theeffects as weil as the resistances fluctuategreatly and are dependent on the passingtrains, on the speed, condition of the trackand condition of the substructure influencedby weather and drainage. Damage occurs onthe substructure when deformations areexceeded due to a lack of density, badbearing strength, insulation against frost andfilter stability. Soll failure often begins in thespring thawing period when there is a greatrush of water and minimum load-bearingstrength of criticai soils.

The existing line network was built mainlyin the l9th century under the limited technicalcapability of that time. Many problems thathave to be solved today concerningmaintenance and upgrading are aconsequence of the earthworks 100 to 180years ago and of the increase in loads thathave developed since then. The only reactionto the rising loads and higher requirements,due to higher speeds and wheelset loads,has been through measures in the track.Under the action of its own bad and trafficboads, the earthworks were usuallycompacted in the pressure area of the trackand/or a consolidation or partialconsolidation occurred so that a state ofequilibrium came about.

In order to fully appreciate this, lt isuseful to have some knowledge of theconditions prevailing when the ines and

earthworks were built in the l9th century.Informative sources used here wereespecially the books published in Vienna in1876 by W. Heyne ‘Der Erdbau in seinerAnwendung‘ [3] and by F. Rziha ‘Eisenbahn-Unter- und Oberbau‘ [4]. The three bookSby Rziha give an interesting overview of theexhibits relating to railway engineering shownat the Vienna World Exhibition in 1873.

The history of trackand earthwork construction

The major Part of the existing railway lines inEurope is built on earthworks onembankments, in cuttings or cuttings on ahillside or laid out to follow the topography. Inthe existing line network these tracks are upto 97% of the line length depending on thelayout as level line or mountain railway. Onmountain railways the track was laid with theaim of mass equalisation and on fiat groundwith a slight embankment to ensure adequatedrainage. Earthworks were described as‘structures composed of natural materials,without special treatment, produced byordinary labourers‘. The goal was defined asfollows ‘to lift a clod of earth from one spot

and lay it down on another‘ [3]. Nevertheless,the earthwork had great importance from thebeginning, because lt was recognised early onthat lt incurs considerable costs for lineconstruction (up to 65% of the total costs) andan irrational layout and design cancompromise the entire construction.

There are different constructions of anearthwork:• Reclaiming or producing earth.• Securing the earth structure.• Shifting or displacement of soll.• Supply of soll masses or filling.

The cross-sections in Figure 2 illustratethe geometry of the earthworks from thebeginnings of the railway. The formation widthof a double track line was around 6.80 metres,the embankment slope 1:1.25 to 1:1.5 and theditch depth around 0.56 metres.

Loosening and loading of the solls wasdone by hand, using spades, shovels, picks,hammers and chisels in various regionaldesigns as tools (Figure 3). Solid sections ofrock were blasted. The loosened soils wereloaded using projection. For the removal ofsoils when working in cuttings, a Systemevolved on the continent to apply from

Problems in the substructure

- Overloading ~ 2 + ~ ~

- Reduced load-bearing capacity o~< 0p 2

(inadequate drainage,loss of formation crossfall)

.4.

1>higher elastic andplastic deformations

IIloss of formation crossfall

increased water contentmixed zoneloss of load-bearing capacity

FIg. 1: Loss of load-bearlng capacity In the track at a wet bed.

Fig,.1.

-. ‘SOIaQ .~?Ube2~(i4~ .

• Bottom of ditch — deptti of ditch -1

FIg. 2: Railway earthwork profiles (embankments and cuttings) on the Leipzig-DresdenRallway, 1836 to 1838. Taken from: CIvIl Engineer 1889.

RAIL INFRASTRUCTURE

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Above: FIg. 3: Work tools for separatingtransportable and manageable sizes.

the starting and/or end point to achievelayered, lateral or head structures.Transportation to the insertion area was

initially carried out using wheelbarrows orcarts (Figure 4) pushed or pulled by workerson the ground or on timber roadways. Figure 5shows how such work was performed during

preliminary excavations to the Oberau Tunnelon the Leipzig—Dresden line dose to Dresden.Later, horses were used for transport by horsecarts and carriages on wooden tracks or raus.For rationalisation, tracks and locomotiveswere soon used for rolling wagon transport.

Placement of the earth masses for

constructing embankments was carried out inlayered segment construction, headconstruction or scaffold construction (Figure 6)and the soll was usually placed directly afterexcavation without any regulation. Frequently,wooden filling scaffolds were used, like on theWeimar-Gera line in 1875 (Figure 7), leavingthesupports in the embankment.

From today‘s point of view, theconsolidation of the installed soils wascompletely inadequate although the goal wasto implement the filling in such a way that theembankment obtains the greatest possiblefirmness‘ [3]. No consolidation was possibleat all in the case of head construction andscaffold construction. With layered segmentconstruction this was achieved by manualpounding and by the work machine traffic.When using coarse construction material, thecavities were spedifically filled with finerearth. With cohesive types of soil, the lumpswere broken down at the place of insertion,installed with a small layer depth of up to30cm and compacted by manual poundingperformed by strong labourers using woodentampers. The advantage of alternating fromloam or dlay with sand layers was soonrecognised. A slight over-pounding wasintended primarily to push some of the sandinto the empty cavities. Due to the manualpounding, less permeable layers wereproduced in the construction so this methodwas widely abandoned after some cases ofdamage. In order to reduce the settlementsunder traffic, time was often allowed fornatural settlement of the embankmentsand/or accelerated through a superimposedearth fill due to the dead weight of the soll(Figure 8). However, the decisive consolidationwas left to the factor time and this occurredduring construction Operations and under trainbad after resumption of services. Inthe course of time the bad settlements led toan increase in the structural density of thesoils installed.

Work on the track substructure wascompleted with the construction of theconsolidated formation with crossfall. A fittingstatement on the formation crossfall is given in

1 1

Mattock or pick for firmer 50VGerman digging shovel

Lower Hungarian digging ahovel

Pick or cramp iran with blunt end or point Hammer amt chiselfor separating

earth material from the ground and making into

Below: Fig. 4: Means of transport for material on soil, wooden tracks and rail tracks, usingworkers, horses and locomotives.

.- -—~Ä JL

LTransport by wheelbarrow Transport by cart Transport by waggon

—

- ~. 1- ——-. ~ ..‚..~ — 11 —~

.‘-.-.—- — .. .-. ..~ 1

— 1 ‘- - -. ‚. .•

— :~- - ‘‘4 ~ ~‘ ‚~l~-.

-- ..‚.- •.• •~ —.. .~. ‚.i~ ‚. - ‘ ..~‘ - —ø. .

~‘~1 ~ - 1 = ‘~ -. - 4‘

- :~.. . •._ . .

— ~. -. ..~• . jI__ ~

‘~ ~ ‚ •;•-‘ . . -~: — •-~ -

--~-~

Fig. 5: Earth transport on wooden tracks during the construction of the first rallway tunnelnear Oberau whlch was bullt by Freiberg mlners between 1837-1839.

6.1 Layered segment canstruction

— ~

•~:~

6.2 Head construction

6.3 Scaffold construction

111

II

- ~ -

ii‘

Fig. 6: Earthwork constructlon methods.

RAIL INFRASTRUCTURE

Permanent Way fl[5}: A dry railway crown is of the greatestimportance for good construction andmaintenance of the track. The surface waterpenetrating the ballast bed must be kept awayfrom the substructure in order to preventsoftening and freezing spots (frost heaves).Therefore, the formation on open lines is givena lateral slope of 1:20 to 1:30.‘ The trackditches on both sides should serve to dramaway the surface water, to remove thegroundwater and source water and, therefore,to keep the subgrade dry‘.

Normally, the ballast bed materials werelaid directly on the earth formation of theembankment or the cutting. Initially, thesleepers were bedded directly in gravels andsands, but it was soon recognised that thebedding should be as water permeable,resistant and elastic as possible. Later, thepreferred ballast bed materials were goodgravels such as river gravels or broken stoneballast, such as coarse crushed slag made ofbasalt, quartzite, diorite, gray wacke andporphyry were used. Depending on loadingand type of line, the ballast thickness underthe lower edge of the sleeper was between10cm and 20cm, later up to 30cm. Onyielding, wet subsoil, the thickness of theballast bed had to be increased or a hard corereinforcement inserted to ensure a firmsubsoil. Ballast bed and hard corereinforcement should be weil drained to thesides and below.

If weak soils were adjoining, e.g. in loamor clay cuttings, the subsoil was strengthenedwith a hard core base made of broken stoneor using gravel, river ballast or pit ballast. Forthe hard core base, the broken stones werelaid manually on the high side with the widesurface downwards and with the point turnedupwards. The surface had to be Ievelled,pressing out the cavities. Figure 9 showstypes of construction and an example ofinstallation on the Brenner railway line. Eventoday, sections of hard core reinforcement arestill found in good quality during constructionwork and soll probing.

For the main part, construction wascarried out over the subsoil withoutimprovement. In special cases extraordinarysubstructures‘ were built using woodenstakes, stone fillings or fascines.Mechanisation of the earth construction worksbecame possible from around 1860 with thedevelopment of mechanical engineering. In1870, mechanical digging work was stillirrelevant. However, when wages began to rise,the development of machine Operationbecame economical and of interest.

lnitially, ploughs were used to loosen theearth, whilst from 1860 the first machines fortaking up and lifting the soils were used. In

1871 the first excavator operated by Rzihaworked in earthwork construction on a railwayIine in Hungary. To consolidate the solls, firstlyhorse-drawn smoothing rollers andsheepsfoot rollers were used, whilst from1862 the first steamrollers were available andfrom 1902 the first motorised rollers.

Load increase andoperating experience

At first, the insufficient consolidation was notvery problematic and the engineers learned tocope with the necessary bad settlements atthe 10w speeds. In earlier times, packing hoesand tamping picks made of wood and steelwere used to perform the necessary tampingof the sleepers to correct and restore thetrack geometry. Due to the increasing demandfor transport, many ines were upgraded todouble-track ines by laying a second track bymechanical operation. This can often berecognised due to the very differentsubstructure conditions in the cross-sectionof double-track and multiple-track lines.

In the following years, travelling speedsand wheelset loads rose continually. Figure 10from [1] shows that from 1835 to 1910wheelset loads rose from 2 tonnes to 14

Fig. 9: Eariy formation strengthenlng.

~;~

•~•~ ta....

•1. ~-‚ - 4..‘~~• •~‘•~ •.

_~:~l ‚.

II . 1~~ •~:—. ‘~~‘

~ ~;!‚~. .‚- ~ •~-~-iJ‘ ~

~ ~

- -‘ -~ -

~ -. — —~ .. .‚ — ~-

‘~~ ~ - ‚~ ‘

Above: Fig. 7: Scaffoid construction of an embankment on the Weimar to Gera line around 1875.

Beiow: Fig. 8: Consolidation by earth fiu.

/1

1/

1Abb. 293.

4-“)~Types of design ~

Ir

Formation otrengiheniog on Brenner railway ~‚

~ b

~

Cuct~,ro~it bFr ~rFnnerbat)n.Crnoo-sectiss of Brenner railway

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[~] Permanent Way

the track substructure and the subsoil. Theplastic deformations as bad settlementscaused a subsequent consolidation in thepressure area of the track up to around 1.50

metres below the lower edge of the rail and apartial consolidation with a limited sufficientstate of equilibrium. Under the elasticdeformations and with critical saturation,small hollows formed in the formation withbordering cohesive soil in which watercollected. The pumping action as vehiclespassed over then produces mud whichpenetrates into the ballast and leads to mudciogging in the ballast bed. The bearing-loadcapacity damage as frost damage wasrecognised as particularly critical on soils withrising capillary water. Figure 11 from [6]shows the occurrence of mud spots and theirremedy in characteristic situations andrecognises waterlogging as critical. Theresponse to problems in thefoundation/subsoil was logically to applymeasures to dram, but also to reinforce thetrack. In 1911, details were given in [5] under‘maintenance/improvement‘ about theimprovement and reinforcement of the track.Also under ‘ballast bed‘ the drainage wasincluded and implemented so that‘maintenance of the ballast bed alsoextended to maintenance of the drainage,cleaning of the culverts and seepagechannels, removal of the muddied section ofthe ballast bed and clearance of thevegetation‘. Therefore, proper drainage wasrecognised as decisive for the load-bearingstrength and frost protection of the soils andalways demanded but only implemented inpart. With larger problems the ballastthickness was increased, an additional lowerlayer was built of broken stones or a seepagechannel was installed under the ballast bedinitially as a remedy crossways and/orlongitudinally. lt was only much later that alayer of sand, gravel-sand or coke ash wastried out as a filter.

Figure 12 shows the drainage in a cuttingsituation using a seepage channel incombination with a filter layer made of cokeash. This was the beginning of theimprovement and strengthening of thesubstructure using separate trackbed layersand/or formation protective layers.

Additionally, modified clearance gaugesarising from the development of vehicles forgreater transport tasks led to modified andabove all wider line cross-sections. In 1904,the formation width of a double-track line was9.28 metres (Figure 13) compared to around6.80 metres as shown in Figure 2. In manycases the formation was widened not incompliance with the requirements using onlyuncontrolled fillings, therefore restricting thecesses and the drainage systems. This led tothe hindrance of water drainage andconsequently to critical hydrological conditionswith a further increase in bearing-loadcapacity problems and frost problems.

Maximum wheelset loads in Germany(t]

:L~012~

1835 1840 1850 1860 1870 1880 1890 1900 1910 1920 1930 1940 1950 1980 1970 1950 1990 2000

Year

Maximum travelling speeds in Germany[kmlh]

320

250 300280 Passenger trains240 — — Freight trains

100 1201 120140 i~SQl—

80_3~Q~~_ ..‚~40 25 ~°25

0 II

1835 1840 1850 1860 1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

Year

Above: Fig. 10: Increase of wheelset Ioads and travelling speeds.

Below: Fig. 11: The process in the development of wet beds.

kWammelka.mod beda

UackieIIit

‘,~ ~1

.. ..

®~

1. Sleeper not loaded — in normal position

2. DepressIon of the aleepers from Sie normal position due to Siewheel bad. nils causes presaure on Sie material beneath Sie sleeper and resulto in any water and soll particies (mud) present tobeforced upwards.An upwardn owelling of Sie formation agalnsttheballast bed preveots weter flowing oulwards to Sie rallway dltch ortu Sie olope 01 Sie embankment.

3. Due to Sie upwards and downwards pumping action of Sie oleepers Sie dloplaced muddy water retumo to Sie underside 01 Sieoleepers in a cycllc mollon.11110 proceso in repeated an Sie trab moveo over Sie track. Wiren ltraino, additbonal woter flowo lnto Sie wet bedo which leado ta ooftening, olurrying and muddying 01 Sie ballast bed.

Während unter der&frieb,lasf einige Schwelten eingedrückt kersten,weiden enocl,l,esse,rd daran einige von ihren Lagern abgehoben.

1 5chweh‘e unbelastet - in Ruhelage.2 Absinken der Schivelen aus der Ruhelage infolge der Raddrücke Des

Wasser wird mit Schhemmassen aus dem Pwnpensumpf qep,ei3tu. Irochse.&ückt. Aufwulstung gegen den Schslerbetrand hin rerhlnderl die Eiri.4,.serung der0ber/iär.Jie des Plenums nach außen zum Behiignsben bzw. zurEismmd®Eiutrhlnflestunq undAWiebung der Schweden Luftverdünnung,Rück

flutung des verdrängten schlamrnheifiqen Wassers.Dieser Vorgang wiederholt sich bei alten folgenden Raddrtkken. Bei Re

gen fIie,~t den finsackunqen noch zusätzliclr Wasser zu, wodurch Aufwei.chunq~ Breibiwung und llerschlämmung der B4ung Weiter gefördert weiden.

der Schlemmpwnpen:Entwässerung des Pumpensumpfes an den tiefsten Stellen und tb,flu1~

schaffung bei den Schwelenköpfeir. Bei Belastung hinauoqepressles Wasserkommt im eingeteachten durchläsagen ld,slerial nach außen zum Abflu,8.Deich Abstufung werden bei Verdrudtung Auflreibung,Troqb,ldung des Untergrundes und Qlickfluten des Wassers verhindert Erneuerung der verschhf‚weltenBeliwrq.

Schlammpumgen führen infolge Einsinkens zu erhöhten dijnemischen Benns,ovuchungen des Oberbeueo,zurAofhebunq der Elastizität der Bettunp,Lockeivngdes Gefüges des Gleises, zu rascherer Alelülzung des (Jbe,baues,verminderlerBetriebssicherheit verkOhlen Ustezhaltungskoslen

4. Ellminatinn cl Sie wet bedoDralsage 05 Sie wet bodo atSielr deepest opots and crestbon 05water run-off at Sie sleeper endo. Under bad Sie exceoo watercomes Sirough Sie newly plsced, permeable material to the ostside of Sie ballast lied sed lnto Sie dram. The formatIon ot stepaprevests swelllng, trough formation In Sie subsoll and retum 515wof water when bad 10 applied. Repbocement 01 Sie muddled ballastlied.

Wet bedo lead to bncressed dynamic streooeo an Sie track, boa bsuof elaotlclty 01 the ballast lied, loooenbng 01 Sie track otructure, tofast weor of Sie track, reduced operating oafety and hlgher rnabntenance cooto.

tonnes and travelling speeds from 25 tolOOkm/h. This led to greater stresses in

the trackbed system and especially todeformations and bearing strength damage in

Coke ash ..... — L~ —

Koksosche

erschlitz‚irohr

6efälle 1:300Longitudinal seepagechannel with dram pipe Longitudinal seepage

channel with dram pipeslope 1:300

Transverse seepage channel

FIg. 12: Filter Iayer and dralnage channel from 1890.

main-line railwa50a~ptb~hn.

T~ -I 1,7-:;:X_ 1,75—~ft 1,6S—~

7I— 2,70 0,~0 2,70

1:25 1:25

4,299,28

a.ead. atrecke. straight Im

Fig. 13: Ballast bed cross-section for double-track Ilnes In 1904.

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Permanent Way

Track formation improvement - problems,development and implementation: Part 2.

This article is continued from F?aillnfrastructure lssue No: 86. Prof. Dr.-lng.

Klaus Lieberenz, em. Professor HTW Dresden,GEPRO Engineering Society Dresden,Germany, and Franz Pierede, Former Head ofTrack Maintenance Machine Operations, OBBHead Office, Linz, Austria, describe how thefoundations and formation of the trackbed canaffect the actual track quality andper formance. Literary references (thebracketed numbers) are detailed at the end ofthe article.

Development of trackformation improvement

By the end of the l9th century deficiencies inthe substructure were already starting to showand they were attributed mainly to the effect ofwater and frost. The regulations ofthe BavarianMinistry from 1907 for the construction andmaintenance of the railway track [8] can serveas a summary ofthe experience made in thosetimes. They recommend for maintenance to digthe railway ditches deeper, to reinforce theballast bed, to place a Iayer of sand under theballast bed orto use a double Iayer ballast bedwith the lower Iayer consisting of brokenstones. Usually, thin Iayers of separating andfilter Iayer sand, differing from region to region,were placed under the ballast bed consisting ofuniform grain sands with a particle size of 0.06to 2mm. The measures were carried out insections by very arduous manual labour,piacing the sand on the existing ballast bedand, byforkingthe ballast, the sand fell throughon to the formation and was distributed.

In 1935, it was ascertained by K.Gunther (quoted in [7]) that a good subsoilwith a functioning draining improves thequality and efficiency of the track threefold.

Fig. 14: Formation improvement accordingto Pfahnl [6].

The formation can be kept dry ... by properdrainage of the surface water by means ofseepage und drainage systems, by preventingthe rising of ground water and swelling of softsoil by the Installation of insulating layers.These serve to break the capillarity andprevent any rising of water during frost andalso, due to their heat insulation, they make ltdifficult for frost to penetrate.‘ Materials usedfor insulating layers were sand, brushwood,peat, tar, bitumen, cement and metal. Thelatter were prone to cracks and, therefore, didnot ach ieve the desired effect.

In Austria, K. Pfahnl was a visionary inthe field of substructure and track. In theperiod from 1940 to 1945, he published atrack maintenance guide ‘Die Bahnerhaltung‘[6] with many illustrations. Based on fittinganalyses of the deficiencies and types ofdamage (Figure 11), he demonstrated manypracticable solutions. These include thepreferrecl drainage in the sleeper-end andcess area (Figure 14), the installation oflayers consisting of sand, coal siag,brushwood and fascines as weil as thedrainage of ballast sacks (Figure 11). Thesejobs still had to be performed by arduousmanual work and in the track in service. Therewas also a lack of sufficient consolidation andsuitable stone mixtures. Due to insufficientfilter stability, the dram pipes and drainagesystems were clogged up with mud after a fewyears and needed cleaning which was adifficult job.

R. Raab summarises in [7] that theinstallation of hard core layers, stones, gritlayers, sands, coarse coal slags as weil asbrushwood and peat did not bring theexpected success because these materialshad ‘too many cavities that were too big‘.More by accident, it was recognised that oldballast bed gravel-sand, which was initiallymainly used as ballast bed material, slightly

mixed with loamy soil from the subsoil and/orso-called ‘dirty ballast‘ made up of ballastparticles, stone fines and loam had a weilsuited particle composition. If these oldballast bed layers and/or old sand layers wereleft in the track and the track was liftedappropriately, the formation improvement wassuccessful in combination with weilfunctioning drainage systems.

During the Second World War and in thefollowing years, scant attention was paid tospecific maintenance, especially on thesubstructure, and later there was more focuson the further development of track designs.As a result there was a rise in deficienciesand damage, so increasingly the substructurewas given more attention and from 1954progressive experiences with measuresundertaken on the substructure werepublished again [7]. Recommendations weregiven for the type and composition ofprotective layers between formation andballast bed and their grain distribution. R.Raab formulated the following conditions for aso-called Formation Protective Layer (FPL):~ lt must prevent fine particles of loamyand clay earth from rising up.• lt must prevent precipitation water fromseeping on to the subgrade.

lt must achieve inner stability and frictionto form a strong bearing plate that remairissealed and cioses cracks when there ismovement of the subsoil.• lt must not have any capillary propertiesin order to prevent frost damage.

In 1957 the following intensiveinvestigation of the topics of drainage andprotective layers led to the publication of theEarthworks Guideline DV 836 [8]. Thispresented the protective layer as afundamental element for the assurance of badbearing capacity and frost protection, forthe prevention of mixing and for the

Design of substructure crown on water-retaining cohesive soilsdouble-track line

.‘,.... .~—.=‘ ~.-—. ~ .. ~

coalslag ‘~,.‘ ~. ~ ~ ~~

coarse san

lmprovement of ballast bed subsoil on swelling cohesive soils

~

.~ •~ ~C —07. •~ ~. od ~ ‚ 1, o c. .v— c. ~‚_ ‚~_ 0~~ 0 ‘, ‘~ ~ b

0.20 ~‘rnflK.

With ballastsack drainage

coal slagfrost protection needed

:.~°-:*~. ~ —;•—----~ ~---~

hill side — — ~ - -~ 1 -~ -

~ ~ -~-- ~ ::i~: .~- ~•- ... —- ~ !en,,chlack4 ~ ~ t.‘~3c~oti~ts~ck- ~

- -..‘~ .. .

seepage pipeslongitudinal deep ditch with drainage

1:50

ballast sack

RAIL INFRASTRUCTURE

Permanent Way 1Fig. 15: Cross section of a trackbedformation with dralnage and protective Iayer.

draining-off of surface water on the FPLand named lt as a standard solution. The

stone composition of the protective Iayermaterial is laid down in tIght limits in Annex 1of DV 836. The continuation of the Guidelinewas made after further basic work in stages upto the DS 836, the regulation for earthworksdated 01.01.1985 [9]. This wascomplemented with additional Technical Termsof Supply (TL 918 062) for the qualityrequirements to be met by mineral mixtures tobe used as protective layer material. Thismeant that at DB a protective layer materialwas preferred which has a lower waterpermeability due to an increased Proportion offine grains and should, therefore, guarantee toa large extent the flow-off of the surface wateron its surface. This concept led to high-qualityprotective layers, but also to an over-emphasisof the protective Iayer and, therefore, to lessattention being given to the drainage systems.

At OBB, based on the experience madeby K. Pfahnl, a more water permeable FPL waspreferred and greater attention was given tothe drainage which was recognised to bedecisive for the Ioad-bearing capacity andfrost protection. This also corresponded withthe development at Deutsche Reichsbahn(East German Railways) up to 1990 which waslaid down in the FachbereichsstandardEisenbahnunterbau [10]. After the politicalchangeover lt was then permitted, under theterms of implementation (ABest) to the DS836 [111 and the Guideline 836 dated20.12.1999 [12], that besides the less waterimpermeable grain mixture 1 to also use themore water impermeable grain mixture 2 sothat lt was now possible to choose moreselectively according to the Iocally availablehydrological and geological conditions.

Today‘s state-of-the-art for trackformation improvement is a combination ofmeasures for drainage and the Installation oftrackbed layers and/or protective layers(Figure 15). Drainage measures are a reliable

means of preventing the retention of waterdue to water accumulation in the soll and,therefore, a critical rise in the water contentwith changes in consistency and loss of badbearing capacity. On the track formation, thecrossfall, open railway ditches, catchmentchannels and associated draining Systemsperform the tasks of collecting and drawing0ff the surface water.

Subsurface drainage systems areinstalled as an underground drainage systemto collect and draw 0ff unbound water from thesoll and stratum water. Given their delayedeffect, drainage Systems should always beconstructed before the Installation of protectivebayers and/or before track renewal work.

Trackbed Iayers and/or protective layersare a Iayer system placed on the formationthat protects the bordering soll fromdetrimental deformations and the effects offrost. They are Iaid as a trackbed Iayer, frostprotective layer, separating layer, filter Iayerand sealing Iayer. They are made up of grainmixtures and can be added to or improved intheir effectiveness by additional measuressuch as geotextile layers, transition layers orsoil improvement layers. The Iayers can beinstalled when there is no track or using ontrack machines.

Laying technologies forformation protective Iayers

The initial manual Insertion of formationprotective layers consisting of gravel sands,using the block method without removal of thetrack or in open construction with removal ofthe track, was very labour-intensive and costintensive. The increasing use of constructionmachines and vehicles for Installation withouttrack soon replaced the manual labour. Toperform this work, the section of track iscbosed in order to remove track, ballast bedand damaged subsoil and then place the newformation protective layer and ballast bed.

These additional measures such asgeosynthetics, sealing blankets, insulatingslabs, sub-ballast mats and binding additives[1] were deveboped from 1973 so that lt ispossible to react in a more variable way tolocal conditions. These methods can achieveadditional or increased separating, filtering,draining, reinforcing, sealing or dampeningeffects (Figure 16). In the meantime, trackbedsystems have been deveboped which canperform many other tasks (see later).

FIg. 16: Examples of protective Iayers by theuse of geosynthetics.

Protective Iayers with geosynthetics

a) with 1 Iayer of separating and filter geotextile

b) with 1 Iayer of geogrid

c) with 1 layer of composite

d) with several geosynthetic layers

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1 Permanent Way 1

Above: Fig. 17: Diagram of a RM 61 machine used for iaying gravei and sand.

Beiow: Fig. 18: Cross-sectlon diagrams of the track formation showing the RM 61 stages of work.

The technologies became more and moresophisticated, the construction machines hadgreater output and the recycling proportionfrom the ballast became even larger. Fromaround 1960, based on existing examples,track maintenance machines and Systemswere developed that could install formationprotective layers without removing the track.

At the end of 1960, a System developedby Plasser & Theurer, in conjunction with theRM 61 ballast bed cleaning machine, wasable to place in two working passes a layer ofgravel-sand around 15cm thick withoutremoval of the track. Figures 17 and 18 showthe machine and the stages of work. After theballast cleaning, the gravel was distributed on

the ballast bed and, during the second passof the machine, gravel and ballast was pickedup, separated through screens and installedin layers. The layered structure of a FPLinstalled in this way around 1970 can be seenin Figure 19 after 35 years in service.

From 1983, the PM 200-1 was the firstautonomous formation rehabilitation machineto go into service that removed the damagedsubsoil and the ballast using an excavatingcham, placed gravel brought in separately, asweil as cleaned old ballast and new ballast andconsolidated the FPL and ballast. This began amechanical and constructional developmentwhich led to an increasingly sophisticatedmechanisation, an increase in material

recycling and a rise in the quality of installation[13]. lnitially, up to five stages of work usingfive different track maintenance machines werenecessary to produce a multi-layer formationimprovement without removal of the track, buttoday this can be done in one pass by onemachine (Figure 20). The relaying outputs wereraised continually and, at the same time, spoll,transport, construction time and the influenceon traffic was clearly reduced. The materialrecycling and the quality of ballast and stonemixtures were further improved. The stages ofdevelopment are explained in detail in [13].

Today, it is possible to select and applythe most suitable technical and mechanicalsolution depending upon the localgeohydrological, geometric, ecological andoperational conditions.

From the different technologies of roadbased and track-based methods, there arevarying conditions and requirements forinstallation, consolidation and quality controlof the protective layer. Generally, lt appliesthat both methods have to achieve and verifythe same level of quality (density and badbearing capacity) and the same serviceproperties for the protective layer. But both

~ methods of installation have very different• characteristics with regard to the

technobogical, scheduling and operationalconditions [1, 14] that arise, particularlyfrom the utilisation of the track under repairas the working and transporting path. Nolongitudinal construction of the track isneeded and the weather factors are excludedduring machine operation when using theon-track method.

FIg. 19: Photograph showing an excavationduring track renewal in 2005.

ballast sand baffle plate ballast plough pmfihing device distributing device

Before cbeaning After cleaning (ist pass)

-~jjjjz~After placement of the sand (2nd pass)

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Outlook - developmenttowards trackbed systems

ln-depth investigations into the practicalsuitability [15], making special allowance fordynamic excitations, have shown that reinforcedtrackbed Systems consisting of stone mixturesand geosynthetics have a higher stiffness and abetter load-distributing effect and, therefore,reduce and equalise possible settlements.Track geometry and ride comfort are clearlyimproved even at higher travelling speeds.Additionally, thanks to their damping effect, thedynamic stresses under these reinforcedtrackbed Systems are reduced. Therefore, thepreviously applied deeper earthwork measuresfor subsoll strengthening in the substructureand subsoil can in future be complemented andoptimised by reinforced trackbed systems. Thisapplies especially in combination with theinstallation of a higher elasticity in the trackwhich shows a higher effect as a spring anddamping element on stiffer trackbed Systems.

These trackbed systems that reducedynamic stresses can also be installed byroad-based or track-based methods. Figure 21shows a practical example of a trackbedsystem on a railway line with a soft layer in thesubsoil fitted with linear transducers to verifythe effect. Figure 22 gives a view of a geogridlayer being inserted by the PM 1000 whichcan install in one pass a four-layer trackbedsystem consisting of a compositegeosynthetic on the bottom, a mechanicallyimproved trackbed layer made up of recycledballast and subsoil, on top of which a geogridand a stone mixture are laid.

Literary references[1] Göbel, C./Lieberenz, K.: HandbuchErdbauwerke der Bahnen, Eurailpress,Hamburg, 2004.[2] Kipper, R./Lieberenz, K.: lnfluence ofthe substructure and the trackbed system onthe track position, in: Railway TechnicalReview 3/2011, pp. 26-29.[3] Heyne, W.: Der Erdbau in seinerAnwendung auf Eisenbahnen und Strassen,Alfred Hölder, Vienna 1876.[4] Rziha, F.: Eisenbahn-Unter- und Oberbau,first to third volume, Druck und Verlag der K.-K.Hof- und Staatsbücherei, Vienna 1876.[5] Schau, A.: Der Eisenbahnbau, Verlag

von B. G. Teubner, Leipzig/Berlin 1911.[6] Pfahnl, K.: Die Bahnerhaltung,Osterreichische Bundesbahnen, Linz 1944.

Fig. 20: Overview of the processes of aformation rehabilitation machine.

[7] Raab, R.: Erinnerung an die Entwicklungdes Gleisunterbaues — Wege und lrrwege, in:Eisenbahntechnische Praxis 4/1980, pp. 34-37, 2/1981, pp. 33-38, 4/1981, pp. 34-37.[8] Richtlinien für die Entwässerung undFestigung der Erdbauten (Erdbaurichtlinien),DV 836, DB, 1.4.1957.[9] Vorschrift für Erdbauwerke (VE), DS 836,DB, 1.1.1985.[10] Fachbereichstandard Eisenbahnunterbau,TGL 24756, draft September 1990.[11] Ausführungsbestimmungen (ABest) zurVorschrift für Erdbauwerke DS 836, DR,1.7.1991.[12] Erdbauwerke planen, bauen und instandhalten, Ril 836, DB, 20.12.1999.[13] Riebold, K./Piereder, F.: GleisgebundeneUnterbausanierungstechnologien, in: EIK2010, pp. 31-44.[14] Hillig, J. et. al: Anforderungen an dengleisgebundenen Einbau von Schutzschichten,in: EIK 2004, pp. 109-123.[15] Kipper, R./Weisemann, U.: Wirkungsweisevon mehrfach bewehrten Tragschichten - einErfahrungsbericht, presentation at Bautex2010,Chemnitz, 28.10.2010.

On-track installation of protective layers

- Excavation of mixed zone and soil- Completion of soil formation in height,

crossfall and width- Placement and consolidation

of the trackbed Iayer- Combination of trackbed layer

with geosynthetics possible

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Track cross-section with in-situ measuring technoiogy and earthwork Iayers

Truck2 TracklLudwigshafen — Homburg Homburg — Ludwigshafen

protectlve layer of KG 1, d = 0.20 mgeosynthetic (geogrld)protective Iayer of KG 2, d = 0.40 mgeosynthetic (composite)

Scaffold for sensorsapprox. km 24,930

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soff Iayer, peat HN, HZ

aubsoll SU, SO

Above: Fig. 21: The reinforced trackbed system in cross section.

Below: Fig. 22: Installation of a trackbed layer with a geogrid.

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