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ROAD AND RAILWAY CONSTRUCTION

MSC COURSE

2016/2017 AUTUMN SEMESTER

RAILWAY SUBSTRUCTURE

SZÉCHENYI ISTVÁN UNIVERSITY Dr. Ferenc HORVÁT professor

1. SET-UP OF RAILWAY TRACK SUBGRADE

1.1 Railway track cross section – single track S

up

ers

tru

ctu

re

Su

bg

rad

e


Single track just after renewal

Single track in operation

Substructure: Generally each part of the railway track belongs to substructure, which has to fulfil

the tasks as below:

- to implement of the railway track position in space,

- to tolerate the forces generated by traffic,

- to give protection against weather influences, meteoric water and groundwater,

- to ensure transition over / under natural and artificial hindrances,

- to ensure connection conditions of level crossing,

- to help to fulfil the tasks of railway service and track maintenance.

Railway track earthwork: The platform upon which the track superstructure is constructed. Mostly

made out of soil material. Task: to distribute the dead weight of railway track and traffic loads.

Top of subgrade: Top level of the compacted earthwork on planned level and with planned

inclination.

Subsoil: Natural soil under earthwork.

Retaining structure: Structure designed to restrain soil to unnatural slopes.

Groundwater level (m): the level of the water table, the upper surface or top of the saturated portion

of the soil or bedrock layer that indicates the uppermost extent of groundwater. It can be expressed

as a height above a datum, such as sea level, or a depth from the surface.

Standard level of groundwater: the measured maximum height + 0,5 m.

Soil replacement: Unacceptable soils (e.g. organic soils, frost sensitive soils) must be removed and

replaced by an acceptable soil.

1.2 Basic definitions


Subgrade improvement: In cases where the subgrade is too weak or has to low stiffness, the

resulting high cost of track maintenance may dictate the need to improve the subgrade conditions.

Alternatives are as below:

o modification of the subgrade properties without removal or disturbance (e.g. grouting),

o modification of properties by reconstruction (e.g. compaction, replacement, admixture

stabilization),

o strengthening of subgrade (e.g. with asphalt concrete layer).


Railway earthwork has to be designed and constructed on the basis of following principles:

- it has to fulfil his task during his lifespan with safety,

- it has to be stable during the construction period and in his final condition as well,

- it can be used for the planed goals economically,

- it has to be avoided the appearance of unacceptable deformations on earthwork surface,

- it has to be resistant against influences of weather, meteoric water and groundwater,

- it has to be technically harmonized with the other constructed adjacent facilities of railway track

(e.g. electric cable conduit, catenary supports),

- it needs only few maintenance and/or repair works in operation,

- it must comply with the environmental and esthetic aspects.

In plan of railway track earthwork has to be determined the requirements of load bearing capacity

and usability correctly.

In support layer of ballasted track has to be avoided or compensated the sharp change in stiffness

(e.g. section between ballasted and ballastless (e.g. mass spring system = MSS) track.

1.3 Formation


2. IMPACTS ON RAILWAY SUBGRADE

2.1 Basic definitions

Action (F)

a) Set of forces (loads) applied to the structure (direct action);

b) Set of imposed deformations or accelerations caused for example, by temperature changes,

moisture variation, uneven settlement or earthquakes (indirect action).

Effect of action (E)

Effect of actions (or action effect) on structural members, (e.g. internal force, moment, stress, strain)

or on the whole structure (e.g. deflection, rotation).

Permanent action (G)

Action that is likely to act throughout a given reference period and for which the variation in

magnitude with time is negligible, or for which the variation is always in the same direction

(monotonic) until the action attains a certain limit value.

Variable action (Q)

Action for which the variation in magnitude with time is neither negligible nor monotonic.

Accidental action (A)

Action, usually of short duration but of significant magnitude, that is unlikely to occur on a given

structure during the design working life.

Geotechnical action

Action transmitted to the structure by the ground, fill or groundwater.

Static action

Action that does not cause significant acceleration of the structure or structural members.

Dynamic action

Action that causes significant acceleration of the structure or structural members.

Quasi-static action

Dynamic action represented by an equivalent static action in a static model.

Load arrangement

identification of the position, magnitude and direction of a free action.

Load case

compatible load arrangements, sets of deformations and imperfections considered simultaneously

with fixed variable actions and permanent actions for a particular verification.

Limit states

States beyond which the structure no longer fulfils the relevant design criteria.

Ultimate limit states

States associated with collapse or with other similar forms of structural failure.

Resistance

Capacity of a member or component, or a cross-section of a member or component of a structure, to

withstand actions without mechanical failure e.g. bending resistance, buckling resistance, tension resistance.


Strength

Mechanical property of a material indicating its ability to resist actions, usually given in units of

stress.

Reliability

Ability of a structure or a structural member to fulfil the specified requirements, including the design

working life, for which it has been designed. Reliability is usually expressed in probabilistic terms.

Serviceability limit states

States that correspond to conditions beyond which specified service requirements for a structure or

structural member are no longer met.

Characteristic value of an action (Fk)

Principal representative value of an action.

Representative value of an action (Frep)

Value used for the verification of a limit state. A representative value may be the characteristic value

(Fk) or an accompanying value (Fk)

Design value of an action (Fd)

Value obtained by multiplying the representative value by the partial factor f.

Combination of actions

Set of design values used for the verification of the structural reliability for a limit state under the

simultaneous influence of different actions.


Stress

Effect of action in a part of supporting structure (e.g. inner force, moment, strain, deformation) or in a

whole structure (e.g. inclination, turning-off).

Zone under pressure

Part of subgrade / natural ground / foundation, attacked by loads originated from railway traffic.

Maintenance

Set of activities performed during the working life of the structure in order to enable it to fulfil the

requirements for reliability.

Repair

Activities performed to preserve or to restore the function of a structure that fall outside the definition

of maintenance.


2.2 Permanent, variable and accidental actions

2.2.1 Permanent load (dead load)

Dead load of railway track has to put on the loaded surface as like an evenly-distributed load.

Dead load in case of ballasted track, if Vd 200 km/h (Vd = design load):

- single track 12,5 kN/m2, in a width of 4,5 m,

- double track 12,5 kN/m2, in a width of 8,5 m.

Load width has to set symmetrically to the track axle (single track) or line axle (double track).

In case of mass spring system the dead load has to be calculated from data of structural geometry

and density of materials used.


2.2.2 Load of vehicle

Static design load signed LM 71 (above)

and equivalent load (below),

parallel with the longitudinal axis of the

track

Equivalent evenly-distributed load,

perpendicular to the longitudinal axis

of the track

Connected line load 80 kN/m can be changed

on a surface load 26,7 kN/m2, with a width of 3

m.


2.2.3 Extraordinary load

Extraordinary loads is the seismic load in case of high earthwork and retaining structure.

2.2.4 Extras

In normal condition in case of geotechnical facilities it isn’t necessary to take account the

temperature effects.

But in case of retaining structures we have to take account the temperature effects, if the harmful

temperature stresses can’t be avoided.

The effect of the longitudinal loads generated by railway vehicles (e.g. breaking) can be neglected,

except supporting and retaining structures (e.g. abutment).


2.2.5 Calculation of dynamic load

Qdyn = (1 + t·s)·Qstat

s = n ·

n = 0,1 … 0,3 (depends on condition of track)

= 1 + (v-60)/140 (velocity factor)

t = 3 (distribution factor, calculation accuracy 99,7%)


2.3 Propagation of vehicle loads

Source material: Lichtberger: Track Compendium

2.3.1. Loaded surfaces and compressive stresses


2.3.2 Vertical stresses in layer construction under the sleeper

Source material: Lichtberger: Track Compendium


2.3.3 Vertical stresses in layer construction under the sleeper, taking account the adjacent

sleepers as well

Material source: Göbel: Der Eisenbahnunterbau


Vertical stresses on plane of ballast and on plane of subgrade


Compressive stress on the subgrade is generated by vehicles (track’s dead load can be negligible).

Function of compressive stress against the depth can be calculated according to C. Esveld with

formula as below:

2421

12

)21(

2

zb

zb

z

barctg

pz

p = compressive strength on the bottom plane of sleeper (N/mm2),

b1 = width of sleeper on the bottom plane (mm),

z = depth under the bottom plane of sleeper (mm).

Parameters in calculations:

rail 54E1,

static axle load: 225 – 250 kN,

sleeper type LM, b1 = 280 mm,

k = 770 mm,

C = 0,1 N/mm3,

track condition: very good – good – bad.


Standard compressive stress on subgrade,

axle load Q = 225 kN

Standard compressive stress on subgrade,

axle load Q = 240 kN


Deformations on plane of subgrade under the sleepers


2.3.4 Spreading of stresses generated by railway vehicle in track

Approximate assumption


Regulation at DB (German Railways)

At strength calculation the loads have to be taken in account

- in inner zone under pressure: dynamic loads,

- in outer zone under pressure: quasi-static loads.


3. SERVICEABILITY LIMIT STATE OF SUBGRADE

Railway subgrade is suitable in regard of serviceability limit, if

- it can take the deformations generated by railway traffic,

- the geometrical inaccuracy of the rails caused by these deformations can be repaired by main-

tenance works,

- it can take the vibrations caused by railway traffic,

- don’t occur vibrations threating the safety of railway traffic,

- vibrations don’t cause damages in superstructure (e.g. fracture in elements of fastenings).

Acceptable deformation in one renewal cycle, in case of ballasted track

4. SET-UP OF RAILWAY EARTHWORK

Set-up of railway earthwork: shape and dimensions according to standards

Materials and qualities

Construction technologies

Quality supervisions

4.1 Set-up of cross section

With the cross sectional set-up of earthwork all shape and dimension requirements have to be

ensured, which are necessary for its stability, for the safety of railway traffic, and for the suitable

behaviour of track in operation.

Determining factors of cross sectional dimensions:

- planning velocity of the track (e.g. width of track bench depends on velocity),

- dimensions of clearance chart,

- number of tracks and distance between track centres,

- horizontal track geometry (e.g. curve radius),

- height of superelevation,

- track characteristic (fishplated or CWR),

- set-up of superstructure (e.g. type of rail, length of sleepers, etc.),

- dimension of efficient ballast thickness,

- width of ballast shoulder and inclination of ballast slope,

- requirements of protection layer (e.g. thickness),

- cross inclination of plane of subgrade,

- dewatering requirements (e.g. ditches),

- set-up of connecting facilities (e.g. platform),

- place demand of maintenance works (e.g. ballast material storage on track bench),

- placement requirements of facilities along the track (e.g. catenary masts).


sk = top of rail

v1 and v2 = width of ballast shoulder (in curv can be different)

p = width of track bench

e% = cross inclination of protection layer

m = superelevation

a = efficient thickness of ballast

kv = thickness of protection layer

k1 and k2 = side widths on subgrade

k = total width of subgrade

1:n = inclination of slope

am = depth of ditch

asz = width of ditch

T = distance between track centres

Cross section, fill and cut, single ballasted track,

straight, no superelevation


Inclination of plane of subgrade / protection layer is 4-5%.

In case of single track the direction of inclination of subgrade plane has to be (as far as possible)

equal with direction of superelavation. Change in inclination direction can be executed at bridge or

level crossing. Length of transition section is 5 m.

Inaccuracy of the plane of subgrade / protection layer can be not greater than 20 mm, on a base with

length of 4 m.

Inaccuracy of slope surfaces can be maximum 50 mm.

Inaccuracy of height of subgrade can be ±30 mm, in case of height of protection layer can be not

greater than ±20 mm.


Constant length of sleeper at design is 2,60 m.


Cross section, fill and cut, single ballasted track,

in curve with superelevation


Cross section, fill and cut, double ballasted track,

straight, no superelevation

Cross section, fill and cut, double ballasted track,

in curve with superelevation

Condition after more years operation


Layer structure of railway track

Thickness „kv” of protection layer has to be calculated based on geotechnical report. Minimum

thickness is 15 cm.


Differences among ballasted and ballastless (mass spring system) tracks


Cross section at ÖBB (Austrian Railways), single track with higher speed

(„Hochleistungsstrecke”)


Bevágásoknál/töltéseknél:

ak 3,00 m nem kötött talajoknál

5,00 kötött talajoknál

h >2,00 m: t = 1,5 h 0,20 m

h > 2,00 m: t = 3,00 m

1) 0,40 m v 160 km/h

2) acél vezetéktartó oszlopoknál 0,95 m

3) az adatok B70 típusú betonaljakra

és a tervezett sk. értékre vonatkoznak

4) építési tűrés 0,05 m

5) a zárójeles értékek helyszűke esetére vonatkoznak,

és ha a kábeleket a padkán kívül helyezik el

3,80 (3,50)

Ív belső

oldal

Ív külső

oldal

Ív belső

oldal

Ív külső

oldal

Ív belső

oldal

Ív külső

oldal

Vágánytengely - koronaél

távolsága

a5), m

Vágánytengely - alaptest

legkisebb távolsága

b5), m

Padkaszélesség

(kerekített értékek)

c5), mKorona-

szélesség

bPI5), m

Túlemelés

u, mm

3,80 (3,50)

3,80 (3,50)

3,80 (3,50)

3,80(3,50)

3,90 (3,60)

4,00 (3,70)

4,10 (3,80)

0-20

25-50

55-100

105-160

3,65 (3,50) 0,95 (0,65)

1,00 (0,70)

1,10 (0,80)

1,15 (0,85)

0,95 (0,65)

0,90 (0,60)

0,90 (0,60)

0,85 (0,55)

3,75 (3,60)

3,85 (3,70)

3,95 (3,80)

3,65 (3,50)

3,65 (3,50)

3,65 (3,50)

3,65 (3,50)

11,60 (11,00)

11,70 (11,10)

11,80 (11,20)

11,90 (11,30)

2,502,202,202,50

2,80 2,80

c

b

a a

b

4,70

bpit

Kábelcsatorna

vasúti pályatesten

kívüli elhelyezésnél

h

sk

~ 1,05)

Kisajátítási határ

ak

t

1:n h

0,20

0,051)0,051)

1,202)

0,45

1:n

Kábelcsatorna

0,731:201:20

0,35

1,202) 0,051)

Cross section at DB (German Railways), V ≤ 200 km,

double (reconstructed) track


2,502,202,202,50

2,80 2,80

cc

a

b b

a

4,70

bpit

Kábelcsatorna

vasúti pályatesten

kívüli elhelyezésnél

h

sk

~ 1,0

Kisajátítási határ

ak

t

1:n h

0,20

0,052)0,052)

0,751)

0,45

Bevágásoknál/töltéseknél:

ak 3,00 m nem kötött talajoknál

5,00 kötött talajoknál

h >2,00 m: t = 1,5 h 0,20 m

h > 2,00 m: t = 3,00 m

1) 0,75 m = beton feszítőoszlopok esetén,

tartóoszlopoknál 0,55 m

2) építési tűrés 0,05 m

3) zárójeles értékek, ha a kábeleket

a padkán kívül fektetik

3,65 (3,50)

Ív belső

oldal

Ív külső

oldal

Ív belső

oldal

Ív külső

oldal

Ív belső

oldal

Ív külső

oldal

Vágánytengely - alaptest

legkisebb távolsága

a3), m

Vágánytengely - koronaél

távolság

b, m

Padkaszélesség

(kerekített értékek)

c, mKorona-

szélesség

bPI, m

Túlemelés

u, mm

3,65 (3,50)

3,65 (3,50)

3,65 (3,50)

3,65 (3,50)

3,75 (3,50)

3,90 (3,75)

4,05 (3,90)

0-20

25-50

55-100

105-160

13,30

13,40

13,55

13,70

4,30

4,30

4,30

4,30

4,30

4,40

4,55

4,70

1,30-1,35

1,35-1,40

1,40-1,45

1,45-1,50

1,30-1,25

1,30-1,25

1,40-1,25

1,40-1,25

1:n

Kábelcsatorna

0,731:201:20

0,35

Cross section at DB (German Railways), V = 250 km,

double track, new construction


Cross section at station


4.2 Density and load bearing capacity of railway earthwork

4.2.1 Density of railway earthwork


Requested density values (according to Hungarian regulation):

- in protection layer Tr = 98%,

- in barrier layer Tr = 96%,

- below the barrier layer Tr = 94%,

- in backfill of engineering structures Tr = 98%,

- other places Tr = 92%.

4.2.2 Control of load bearing capacity

Measurement of load bearing capacity


Static measurement and evaluation

according to Hungarian Standard

2

5,67

2

3,0300

43

243

24

)21(

2 sssDp

sDpstatE

= Poisson’s ratio

p = loading stress (kPa)

D = diameter of loading plate (m)

s2 = measured setting in second loading (mm)


Static measurement and evaluation

according to German Standard DIN 18 134

Calculation of Ev2

modulus: (Poisson’s

ratio = 0,21)

Ev2 = (1,5 r ) / s

German EV2 ≠ Hungarian E2 stat


Measurement of density and load bearing capacity

by light falling weight deflectometer


The small-plate light falling weight deflectometer

measures

- the conventional dynamic modulus, as the bearing

capacity;

- and it is able to calculate the degree of compactness

from the compaction curve generated as the result of the

drops.

Tool is allowed to use only in case of coarse-grained soils

for purpose of qualification.

Correlation between values of static and dynamic modulus

Results of comparison measurements

Material source: Mérnök Újság, 2003/4


Correlation between requested values of EV2 and EVd

according to German regulation of Ril 836

y = 0,2344x + 21,719

R2 = 0,9844

0

10

20

30

40

50

60

0 20 40 60 80 100 120 140

EV2

EV

d

Quotient EV2 / EVd is not constant. In case of fine-grained changes between 1,5 and 3,5. It

depends sharply on water content and compactness.

Numerous comparison measurement proved that the rate in case of coarse-grained soils used

for protection layer is EV2 / EVd ≈ 2. Conditions of validity:

- thickness of protection layer 30…50 cm,

- compactness correspond to Ril 836,

- dynamic measurement is executed after compaction with minimum 6 hours.

Material source: Göbel – Lieberenz: Handbuch Erdbauwerke


Modulus

Velocity (km/h)

V 40 40 - 80 81 - 120 121 - 160 161 - 250

E2stat

(MPa) 50 60 80 100 120

Edin

(MPa) 35 35 40 45 50

Requested values of E2 stat and Ed modulus in Hungarian regulation

Negative deviation is prohibited.

Values regard on upper plane of protection layer and in absence of it for the upper plane of the

subgrade.

Pairs of values of E2stat and Edin summarized in table above are not allowed to get pairs of values

with correlation! There is a great difference between two measuring methods: static plate test and

light falling weight test. During static loading the pore-water pressure has stopped partly. In dynamic

measurement pore-water can cause significant increase in load bearing capacity.


Geotechnical cross section in German regulation Ril 836


Requested values in Ril 836 (DB)


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