This paper deals with problems of increasing the axle load on Czech Railways (ED) tracks to 250 kN or 300 kN, respectively. The results of a numerical analysis of the effects of increased axle loads on the track bed structure were verified by experimental measurements carried out on track bed construction models in an experimental box on a 1:1 scale. The results of the research are applicable for routine use on ED.

Horníček, L.

Krejčiříková, H.

Lidmila, M.

Tyc, P.

English

CTU Open Journal Systems (Czech Technical University, Prague / České vysoké učení technické v Praze)

1 IntroductionIn 2005 and 2006, as part of a grant-founded project ofthe Ministry of Transport of the Czech Republic, the Depart-ment of Railway Structures of the Faculty of Civil EngineeringCTU in Prague was engaged in research on project No.1F52H/052/130 “Methodology of Transitional Parametersfor the Construction of the Substructure on Tracks of theConventional Trans-European System”. The objective of thisresearch project was to elaborate the structural layout princi-ples for the permanent way and the substructure to enable anincrease in axle loads to 250 kN and 300 kN.The passage of railway carriages on the rail tracks in theCzech Republic depends basically on the load-bearing ca-pacity of the bridge structures. However, problems of theload-bearing capacity of bridge structures exposed to an in-creased load acting on the axle did not form part of the speci-fications for the research to carried out in the framework ofthis Ministry of Transport project.In order to fulfil the research objective, a detailed numeri-cal analysis of the effect of an increased axle load on thepermanent way and track bed structure was selected, com-plemented with experimental measurements on four trackbed models. The effect of an increased axle load was deter-mined by measuring the sleeper deflection and the track bedstructure.2 Materials and methods2.1 Numerical analysis of the effects of anincreased axle load on track bed structuresThe first step was to assess the rail load-bearing capacityusing the methodology specified in the Instruction ČD S3“Permanent way”. This proved that with an increase of:1. Axle load to 250 kN and 300 kN, the requirements aremet by rail shapes of S46, UIC 60 and R65 type in spliced©  Czech Technical University Publishing House http://ctn.cvut.cz/ap/ 15Acta Polytechnica Vol. 48  No. 6/2008Prerequisites for Increasing the AxleLoad on Railway Tracks in the CzechRepublicM. Lidmila, L. Horníček, H. Krejčiříková, P. TycThis paper deals with problems of increasing the axle load on Czech Railways (ČD) tracks to 250 kN or 300 kN, respectively. The results ofa numerical analysis of the effects of increased axle loads on the track bed structure were verified by experimental measurements carried outon track bed construction models in an experimental box on a 1:1 scale. The results of the research are applicable for routine use on ČD.Keywords: axle load, permanent way, track bed, model measurement, substructure.deflection (mm)22.5 t y (mm)25.0 t y (mm)30.0 t y (mm)0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7deflection (mm)0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.70.00.20.40.60.81.01.21.41.61.82.02.22.42.6depthbelowthebaseofthesleeper(m)Fig. 1: Track bed deflection pattern due to permanent way loading with an axle load of 22.5 t–25.0 t–30.0 t (gravel Edef  100 MPa)rail even in the case of poor track bed quality (loadingcapacity coefficient C  20–50 MPam1).2. Axle load to 250 kN, the requirements are met by UICrails in long-welded rail even in the case of poor track bedquality (loading capacity coefficient C  20–50 MPam1).For loading by 300 kN, the requirements are met onlyby track beds with loading capacity coefficients of100 MPam1 and more.3. Axle load to 250 kN, S49 rails may be used only for ver-tical rail head wear of up to 20 mm in track beds withloading capacity coefficients of 100 MPa1 and more.For loading by 300 kN, the use of S49 rail shape inlong-welded rail is not advisable.The use of concrete sleepers in the permanent bed con-struction depends on the design of the sleeper structure.The sleepers in use on ČD B 91 S corridor tracks are di-mensioned for loading by an axle force of 250 kN. For loadingby 300 kN, an assessment of the sleeper reinforcement wouldbe necessary.The effect of an increased axle load on the track bed struc-ture was determined by means of numerical analysis forcalculating the deflections and stresses using the finite-ele-ment method. In calculations of deflections of longitudinalstructures, simpler two-dimensional models are commonlyused. This solution can be made on the assumption that theload is constant in the longitudinal axis of the structure, or isat least sufficiently long. However, this assumption is not ful-filled, because the changing load for 7 consecutive sleeperswith a distance of 600 mm between the axes is required.For this reason, three-dimensional models of a railway tracksegment were created in Plaxis Tunnel 3D software. Withinthe next period of the solution it turned out to be necessaryto carry out a parametric study, because calculations of three--dimensional models were excessively time-consuming.The computations were made with software developed bya.s. Stavební geologie – Geotechnika Praha. Fig. 1 shows thetrack bed deflection pattern for permanent bed loading withaxle loads of 22.5 t–25.0 t–30.0 t. Fig. 2 displays the stresspattern in the track bed for loading of the permanent waywith axle loads of 22.5 t–25.0 t–30.0 t.Fig. 1 implies that when the weight acting on the axle is in-creased from 22.5 t to 25.0 t, the substructure subgrade, i.e. ata depth of 35 cm below the sleeper loading area, is exposed toa 16 % increase in deflection, and when the weight is in-creased from 22.5 t to 30.0 t the substructure subgrade showsa 52 % increase in deflection.2.2 Model measurements in an experimentalboxThe effect of an increased axle load on increased deflec-tion of the track bed was determined on four models of trackbed structures on a 1:1 scale placed in an experimental boxwith inside dimensions of 2100×990×800 mm (Fig. 3).16 ©  Czech Technical University Publishing House http://ctn.cvut.cz/ap/Acta Polytechnica Vol. 48  No. 6/2008strain (kPa)22.5 t y (kPa)25.0 t y (kPa)30.0 t y (kPa)0 10 20 30 40 50 60 70 80 90 100 110 120 130 140strain (kPa)0 10 20 30 40 50 60 70 80 90 100 110 120 130 1400.00.20.40.60.81.01.21.41.61.82.02.22.42.6depth(m)Fig. 2: Stress pattern in the track bed due to permanent way loading with an axle load of 22.5 t–25.0 t–30.0 t (gravel Edef  100 MPa)Model specification Granulated gravel layer thickness in mm Ballast bed thickness in mm15SD E10 150 35030SD E10 300 35015SD E25 150 35030SD E25 300 350Table 1: Specification of track bed construction models and their characteristicsThe main characteristics of the track bed model structuresare specified in Table 1. The model specifications include thegranulated gravel thickness in cm and the value of the modu-lus of deformation of the subgrade, simulated by rubberplates (e.g. model 15SD E10 implies a model with a layer ofgranulated gravel 15 cm in thickness and the load bearingcapacity of rubber plates Er 109. MPa). Individual modelswere selected so as to characterize different load-bearing ca-pacities (moduli of deformation values) on the substructuresubgrade Epl (see Table 2).Track bed model structures of Type 2 were composed ofone half of a sleeper mounted on a ballast bed 350 mm inthickness. The ballast bed was laid on a layer of granulatedgravel 150 mm or 300 mm in thickness. The structural layerof granulated gravel was placed on rubber plates laid at thebottom of the experimental box. The rubber plates simulatedthe subgrade with a load-bearing capacity of 10.9 MPa and25.0 MPa (see Table 2).The structural layer of granulated gravel graded 0/32 mmwas compacted with a special manual vibratory compactingunit with a compacting area of 174×174 mm. The granulatedgravel layer was compacted in layers 150 mm in thickness.The time for compacting one layer was set to 30 minutes toachieve perfect compaction along the whole surface of the©  Czech Technical University Publishing House http://ctn.cvut.cz/ap/ 17Acta Polytechnica Vol. 48  No. 6/2008a) b)c)Fig. 3: Basic dimensions of the experimental box: a) side view, b) cross section, c) ground planModel specificationModuli of deformation in MPaEr Epl Epp15SD E10 10.9 26.1 63.830SD E10 10.9 53.3 79.415SD E25 25.0 50.1 90.030SD E25 25.0 82.9 103.9Table 2: Values of moduli of deformation on structural layers of model constructionslayer. Compaction of the granulated gravel was checked bymeasuring the modulus of deformation. The values of themoduli of deformation are given in Table 2.On top of the structural layer of granulated gravel, aballast bed of gravel graded 32/63 mm with a thickness of350 mm was laid. The ballast bed structure was divided intotwo layers, each cca 175 mm in thickness. Each layer of grav-el was again compacted for 30 minutes running uniformlyalong the whole surface of the experimental box. The totalballast bed thickness under the sleeper loading area aftercompaction reached the value of 350 mm specified for con-crete sleepers. The measured values of the moduli of defor-mation Epp are given in Table 2.The ballast bed surface served for mounting one half of aninstrumented concrete sleeper B 91 S/1 with a piece of rail ofUIC 60 type. The arrangement of model 15SD E10 in theexperimental box showing the position of the rigid circularplate during plate load tests is displayed in Fig. 4. In order tomeasure the deflection, the track bed was fitted with bardisplacement indicators with a loading area of 100×100 mmwith a protected measurement axis. The deflection was mea-sured at depths of 175 mm and 350 mm under the sleeperloading area. At each depth, four displacement indicatorswere placed at identical positions. The deflection values weremeasured by mechanical and digital path indicators with aprecision of 0.01 mm. The location of the displacement indi-cators is shown in Fig. 5.The measurements further included sleeper deflectiondue to rail load. For an axle load of 22.5 t the maximum forceacting on the rail was calculated as P  50kN, for an axle loadof 25.0 t P  60 kN, and for an axle load of 30.0 t P  70 kN.The deflection measurements in the experimental box areillustrated in Fig. 6. Sleeper deflection and deflection valuesat individual track bed depths were measured following 30×repeated loading with force P acting in three measurementcycles composed of loading and unloading phases. An exam-ple of the deflection results measured on model 30SD E25 isgiven in Table 3.In the rail head loading process, it must be consideredthat by increasing the rail head load from P  50kN to 60 kNor 75 kN respectively, the load increase at P  60kN amountsto 120 % or to 150 % at P  75 kN.3 ResultsThe deflection measurements on model 30SD E25 dis-played in Table 3 provide the following results:1. The deflection measurement method applying simpledisplacement indicators was suitable for determining thedeflection values at various track bed depths, and thedisplacement indicators showed sensitivity in registeringdeflection values due to the changing rail head load.2. A comparison of the deflection values for P  50 kN at adepth of 175 mm with those for P  60 kN or 75 kN, re-18 ©  Czech Technical University Publishing House http://ctn.cvut.cz/ap/Acta Polytechnica Vol. 48  No. 6/2008b)a)Fig. 5 Arrangement and position of individual displacement indicators a) ground plan, b) cross sectionb)a)Fig. 4: Model 15 SD E10 in the experimental box: a) longitudinal section, b) cross sectionspectively shows that the increase in the deflection valuesis 118 % or 143 % respectively, which roughly correspondsto the increased load acting on the rail head.3. A comparison of the deflection values for P  50 kN at adepth of 350 mm with those for P  60 kN or 75 kN,respectively, shows that the increase in the deflection val-ues is 117 % or 150 % respectively, which again roughlycorresponds to the increased load acting on the rail head.4. The deflection measurement results obtained on themodels are in close accordance with the results of thenumerical analysis.Similar results were provided for other track bed structuremodels.3.1 Passage of carriages with an axle load of22.5 t on railway tracks in the CzechRepublicThe passage of carriages with axle loads of 22.5 t (pres-ent-day maximum axle load) on railway tracks in the CzechRepublic is regulated by Instruction ČD S66 “Basic instruc-tion for spatial passage and transition of carriages on railwaytracks in the Czech Republic”. The permitted axle load of©  Czech Technical University Publishing House http://ctn.cvut.cz/ap/ 19Acta Polytechnica Vol. 48  No. 6/2008Fig. 6: Deflection measurement due to rail head loadRail head loadingin kNMean deflection under sleeper loading areain mmDeflection increasein %at depth of 175 mm at depth of 350 mm at depth of 175 mm at depth of 350 mm50 0.28 0.12 100 % 100 %60 0.33 0.14 118 % 117 %75 0.40 0.18 143 % 150 %Table 3: Results of deflection measurements on track bed model 30SD E2522.5 t corresponds to track load classes D3 and D4. The allow-able load per linear meter for track load class D3 is 7.2 tm1,and for track load class D4 the allowable load per linear meteris 8.0 tm1. Instruction ČD S66 enumerates individual rail-way track sections, specifying the track load class permitted.The technical condition of railway tracks in the Czech Repub-lic is specified in the “Outline of property management inSŽDC s.o. for 2004”, ref. No. 559/05/GŘ-013, May 2005.Out of the total length of tracks of 9505.140 km, an axleload of 22.5 t is permitted only on 3454.785 km, i.e. on36.34 %. On all-national corridor tracks with a total length of1460.068 km, an axle load of 22.5 t (track load class D4) ispermitted on 1359.612 km, i.e. on 93.11 %. The axle loadpermitted on the remaining corridor tracks is 20.0 t.On other all-national tracks with a total length of4872.816 km, the axle load of 22.5 t is permitted only on1836.812 km, i.e. 37.69 %. On the prevailing length of otherall-national tracks, the permitted axle load of 20.0 t applies toa length of 2843.108 km, i.e. 58.43 %.On regional tracks with a total length of 3170.640 km, i.e.on 8.14%, the permitted axle load of 20.0 t applies to a lengthof 2051.487 km, i.e. to 64.70 %. Only the remaining regionaltracks have permitted axle loads of 16.0 t to 18.0 t.An analysis of the passage of carriages on the railwaytracks in the Czech Republic shows that the corridor tracks,which have been recently modernized or optimized (the per-manent way and substructure being reconstructed to achieveso-called optimum condition), are suited for the assessing of apotential increase in axle load. Other railway tracks are notsuitable in this respect, as it would be too expensive.3.2 Assessment of a potential increase in axleload to 25.0 t on corridor tracksThe existing corridor tracks in the railway network of theCzech Republic are in considerably better condition than theother all-national and regional tracks as they have gonethrough gradual modernization or optimization. Their tech-nical condition shows the following characteristics:1. The permanent way on corridor tracks includes: rail shapes of UIC 60 or R 65 type, resilient fixation without baseplates, concrete sleepers for resilient fixation without base-plates (the B 91 S type sleeper is dimensioned for axleloads of 25.0 t and a speed of 160 kmh1), a ballast bed 350 mm in thickness under the sleeperloading area, spacing of sleepers of 600 mm.The permanent way on corridor tracks complies withregulation UIC-KODEX 724 E “Gleisbewehrung für 25Tonnen (250 kN) auf Schotteroberbau” of May 2005.2. The substructure is composed of the stable track body ofthe former all-national railways, whose track bed wasreconstructed during modernization or optimization tocomply with the minimum required load-bearing capacityof substructure subgrade of Epl  50MPa. When consider-ing a potential increase in axle loads from 22.5 t to 25.0 tthe load increase acting on the track bed amounts to11.1 %. For this reason, it would also be in place to con-sider an increase in the minimum load-bearing capacityvalue Epl   50 0111 555. . MPa. We may presume thatdue to modernization or optimization during which thetrack bed load-bearing capacity has been increased byapplying non-cemented layers or layers of stabilized soil,increased substructure subgrade loading may be allowed.3. On corridor tracks with a modernized permanent bedand substructure constructions railway operation with theaxle load increased to 25.0 t may be allowed.3.3 Assessment of a potential increase in axleload to 30.0 t on corridor tracksAn analysis of the technical condition of corridor tracksprovides the following conclusions for a potential increase inaxle loads to 30.0 t on corridor tracks:1. The design parameters for permanent way constructionfor an axle load of 30.0 t have not yet been defined. Thepermanent way structure would have to be improved bydesigning a new concrete sleeper for loading by 30.0 t po-tentially increasing the ballast bed thickness under thesleeper loading area.2. The substructure would have to be designed for a trackbed load increased by 50 % (i.e. min. Epl  50 15. 75 MPa). In order to reveal the current condition of thesubtructure, a detailed geotechnical survey of the trackbed would be necessary together with a reconstructiondesign.3. An increase in axle loads to 30.0 t on corridor tracks istherefore presently not feasible.4 Discussion and SummaryA numerical analysis of the effect of increased axle loads to25.0 t or 30.0 t and also experimental measurements on trackbed models lead to the following conclusions:1. An axle load increase to 25.0 t is possible only on corridortracks with current axle load 22.5 t. The load-bearingcapacity of the substructure subgrade must be increasedat least by 11 %.2. An axle load increase to 30.0 t on railway tracks in theCzech Republic is presently not feasible.5 AcknowledgmentThis paper was written within research project No.1F52H/052/130, funded by the Ministry of Transport of theCzech Republic.References[1] Krejčiříková, H., Tyc, P., Lidmila, M., Horníček, L.,Voříšek, P., et al.: Methodology of Transitional Parametersfor the Construction of Substructure on Tracks of the Conven-tional Trans-European System. Research reports of project1F52H/052/130, Faculty of Civil Engineering, CTU inPrague, Department of Railway Structures, 2005 and2006.[2] Instruction ČD S4 Substructure, 1997 (in force since1. 7. 1998).[3] Instruction ČD S3 Permanent Way.20 ©  Czech Technical University Publishing House http://ctn.cvut.cz/ap/Acta Polytechnica Vol. 48  No. 6/2008[4] Instruction ČD S66 Basic Instruction for Spatial Passageand Transition of Carriages on Railway Tracks in the CzechRepublic.[5] Outline of Property Management in SŽDC s.o. for 2004, ref.No. 559/05/GŘ-013, May 2005.[6] UIC-KODEX 724 E Gleisbewehrung für 25 Tonnen(250 kN) auf Schotteroberbau, 1. Ausgabe, Mai 2005.Ing. Martin Lidmila, Ph.D.e-mail: lidmila@fsv.cvut.czIng. Leoš Horníček, Ph.D.e-mail: hornicek@fsv.cvut.czDoc. Ing. Hana Krejčiříková, CSc.phone: +420 224 354 756e-mail: krejcirikova@fsv.cvut.czProf. Ing. Petr Tyc, DrSc.e-mail: petr.tyc@fsv.cvut.czDepartment of Railway StructuresCzech Technical University in PragueFaculty of Civil EngineeringThákurova 7166 29 Praha 6, Czech Republic©  Czech Technical University Publishing House http://ctn.cvut.cz/ap/ 21Acta Polytechnica Vol. 48  No. 6/2008

Prerequisites for Increasing the Axle Load on Railway Tracks in the Czech Republic

Abstract

Similar works

Full text

Available Versions

CTU Open Journal Systems (Czech Technical University, Prague / České vysoké učení technické v Praze)

Directory of Open Access Journals