¸ ucjan Siewczyƒski

Poznaƒ University of Technology

MODERNISATION OF RAILROAD SUBGRADE AIMING AT IT’S

ELASTICITY DECREASE

Summary

The paper will be based on a statistical analysis of second modulus of elasticity, done as a

basis for a project, during reconstruction, and for finishing check-up. The analysis were done for

modernisation of E-20, E-30, and E-59 railways.

1. INTRODUCTION

Main railroad lines in Poland are required after modernisations to handle speeds of at least

160 km/h and axle loads of 225 kN. The modernisations have to deal also with roadbed, which,

constructed long ago, does not meet current geotechnical requirements. Therefore in the course of

modernisation of E-20, E-30, and E-59 lines mainly the upper layer of roadbed is strengthened,

mainly by incorporating protective layers [5]. This allows to meet minimal moduluses of

elasticity and a maximal concentration of aggregate and soil used in strengthening structures,

required by construction codes. Attaining those parameters as a result of the reconstruction

means at the same time acquiring new conditions for track structure - top roadbed layer

cooperation [7]. Check-up investigation results show, however, that, in spite of the

reconstruction being made in accordance with results of geotechnical survey, both the existing and

the modernised roadbed are strongly nonhomogeneous. The nonhomogeneity is reflected by

physical and mechanical features, varying between measurement points.

In planning and realisation of the geotechnical roadbed survey a positive understanding of

their need is noticeable, showing on the other hand some methodological restrictions. Roadbed of

E-20 line was preliminarily checked in 1993, with a detailed survey of reconstructed parts of the

line following. For E-59 line the preliminary survey was done in 1995, and the influenced by

flood of 1997 roadbed of E-30 line is surveyed since 1999, in this case with full investigation

programme aiming at it’s reconstruction, begun in year 2000. Railroad Division of Poznaƒ

University of Technology made part of the geotechnical survey for the modernised roadbed (E-

20, E-59) and carries on check-up research during the reconstruction of E-20 and E-30 lines.

2. GEOTECHNICAL ROADBED INVESTIGATIONS

The modernisation of E-20 railway was based on outcomes of existing roadbed

geotechnical investigations, done in two stages. The investigations were used in the

reconstruction project; results were identified during check tests on the construction site.

Research for design included identifying type of roadbed soil with its properties and investigation

of water relations first in places along the line 300 m apart, later 100 m apart. In research made

on the site protective sublayer deflection was determined at track structure level below

breakstone ballast around sleepers’ ends. In a course of construction, deflection of roadbed or

protective sublayers was checked every 50 meters. On construction sites a 30 cm diameter plate

for test loading was being placed on an axis of a future track on a surface ready for a protective

layer to be constructed over it or on gravel sublayer surface, and on a surface of a new track

(surface of key aggregate sublayer). A secondary modulus of elasticity Ev2 was calculated from an

interval 0,05-0,15 MPa for test loadings to 0,20 MPa, according to a flexible plate equation

[2][15]:

E D py

r py

2 (Equation 1)

where: D = 2*r - plate diameter

p - range of load accepted for modulus calculations

y - settlement of the plate in the accepted load range

In modulus value analyses one has to take into account that in current road building

methodology the values of deflection moduluses are determined from the real roadbed load sector

on a basis of the rigid plate equation, proposed also for Polish roadbeds [1][8]:

E r py

1 5, (Equation 2)

In order to evaluate roadbed state of E-59 line (currently not modernised) geotechnical

research was made following the preliminary survey rule of E-20 line. The survey and test loads

were done every 300 m in sequence under one track and afterwards under the second. On the

basis of experience from E-20 and E-59 modernisations and aiming at reduction of time spent for

geotechnical preparation of E-30 line roadbed reconstruction, the soil drilling and loading was

done every 100 m on benches along both tracks and on intertrack space. An important difference

in the survey concept was a requirement of placing the plate for preliminary loading 80 cm below

rail head level of the old track - on the conventional roadbed top layer - not taking into account

deflection caused by the flood. In most parts the load was placed in the lower part of breakstone

ballast, which caused the results to be unreliable and have no value for the roadbed strengthening

projects [16]. Therefore for the projects normalised relationships of soil state and deflection

moduluses are used [3].

3. EVALUATION OF ROADBED STATE BEFORE RECONSTRUCTION

An important element of roadbed deflection research is a contrast of calculated values of

secondary modulus of elasticity with required values Emin ,aiming at roadbed state and repair need

evaluation. For chosen places on the railroad an assumption is made [10]:

Eproj = wg * Emin (Equation 3),

where Emin - minimal value of the modulus (for subgrade of main lines 120 MPa),

wg = 0,8, 0,9 or 1,0 - coefficient taking into account soil and water conditions, varying

along the road. In every place of the railroad an obvious requirement should be met:

Ev2 Eproj (Equation 4).

The roadbed has to be rebuilt if this inequality is not obtained. The easiest and most

commonly used method of roadbed strengthening is incorporation a protective layer or a system

of sublayers constituting a soil roadbed surface - on such basis rail track is laid. Apart from the

bearing capacity requirement (4) a layer must meet graining criterions: grain diversification, water

permeability, stability on sublayer boundaries, freeze resistance [2], [6].

An overall evaluation and contrast of railway roadbed states for E-20 (1274 tests) and E-

59 (488 tests) lines is given in figure 1.

Fig. 1. Cumulative distribution function of roadbed’s secondary deflection modulus Ev2 from

preliminary loading done by VSS plate. A, B, C, U - roadbed state according to deflection values

with A-very good state and U-mortal fault state.

15% of roadbed of the E-20 line required reconstruction at first rate (mortal fault state),

and only 25% of the total investigated distance had a roadbed meeting condition (4). Similarly,

27% of roadbed of the E-59 line was in defect state with condition (4) being met on only 5% of

the line’s length.

In contrast with the background given above the flooded roadbed of E-30 Wroc aw -

Opole line (738 survey points under track number 1) on 15% of it’s length had mortal fault state

(U) (fig. 1), with another 60% having sufficient (but not good - C) state. These results were

obtained from survey mentioned above, therefore to be used with reservation due to the plate

placement method. A significance of this reservation can be appreciated after a distribution of

summed value analysis, shown on fig. 2.

Fig. 2. Cumulative distribution function of roadbed’s secondary deflection modulus Ev2 of Opole

Zachodnie - Dàbrowa line’s track number 2: 1-measured by VSS plate; 2-acquired from polish

standards; 3-measured by VSS plate on the construction site

Of 96 modulus values, calculated from preliminary loading under track number 1 on 9,5

km of Opole Zachodnie - Dàbrowa sector of E-30 line, 10% was smaller than 30 MPa, and 70%

was smaller than 60 MPa. A significantly worse state of the railway is documented by

cumulative distribution function of secondary deflection modulus at protective layer level,

obtained from normalised relationships basing on measured state of soil. According to these

calculations 45% of the modulus values were 30 MPa or less, and 83% of all modulus values did

not exceed 60 MPa. The way of the preliminary measurements conveyance has therefore a

significant effect on the evaluation, project and on the whole roadbed modernisation process.

Examples of stretches with weak roadbed (fig. 3) include Bar ogi - Ko o and Pal´ dzie -

Buk (E-20 line) and Mi´ dzylesie - Lichkov (E-59 line) sectors.

Fig. 3. Cumulative distribution function of roadbed’s secondary deflection modulus Ev2 of

following lines: 1-Mi´ dzylesie-Lichkov (E-59); 2-Bar ogi-Ko o (E-20); 3-Pal´ dzie-Buk (E-30);

4-Rydzyna-Leszno (E-59); 5-Opole Zachodnie - Dàbrowa (E-30); 6-Dàbrowa-Przecza (E-30) .

A, B, C, U - roadbed state according to deflection values with A-very good state and U-mortal

fault state.

On the other hand, roadbed on Rydzyna - Leszno (E-59 line) sector is an example of good

roadbed without defect states. The flooded roadbed of Opole Zachodnie - Dàbrowa and

Dàbrowa - Przecza E-30 line sectors should be classified as weak with high deflectability, even

without verification of preliminary loading results, shown on fig. 2. Roadbed reconstruction of

the two mentioned sectors was done in the first half of year 2001.

4. SUBGRADE REBUILDING AND INSPECTION MEASUREMENTS

On prevalent length of up-to-date modernised sectors of E-20, E-30, and E-59 lines, apart

from places where track’s vertical or horizontal geometry was changed, a protective layer was

built on the existing roadbed. This layer is built mainly from two sublayers - key aggregate and

gravel (E-20) or from unsized stones and key aggregate (E-30) (fig. 4) on existing subgrade after

road breakstone and ground removal in old track-way zone.

Fig. 4. Top roadbed layer of modernised railways E-20 and E-30. Shown are equivalent

moduluses Ee at track sublayer borders and sublayer’s material moduluses E

This system of sublayers is applied in the course of traditional works made by earth

movers. In transverse and longitudinal section formed subgrade to protecting layer building is

strengthened by soil compacting and stabilisation. Subgrade surface preparing for sublayers

building is checked in geometrical and strength respect. Roadbed deflection is checked every 50

meters along track axis or in places of weak grounds.

Subgrade strengthening is characterised on fig. 2 by secondary modulus of elasticity

distribution function values (3) on Opole Zachodnie-Dàbrowa Niemodliƒska sectors.

Distribution function (1) shows subgrade strengthening as result building processes in relation to

its elasticity before modernisation according to geotechnical roadbed investigations made for

project. Distribution function (2) shows subgrade strengthening in relation to its elasticity before

modernisation on the basis of geotechnical standards and grounds state.

Layer thickness is projected according equivalent modulus method based mainly upon

modulus of elasticity. The modulus values are determined on old track-way grounds or on depth

of protecting layer during detailed subgrade researches every 50-100 m along a track. Getting

values are checked according estimated standard dependencies included in geotechnical norms (fig.

2). Equivalent modulus (Ee2) of subgrade-protecting layer system (fig. 4) should satisfy

inequality: Ee2 Eproj.

Protecting layer from gravel or unsized stones and key aggregate sublayers is not built

only both on subgrade of using points and also at rebuilt subgrade of track sections. At remaining

length of track are made practised drainage treatments mainly as shearing of track-way bench,

cleaning and side-ditch rebuilding, resurfacing and regulation of slopes. These treatments improve

water conditions in roadbed and reduce elasticity of track-way [14].

In cases of small value of roadbed modulus from cohesive grounds is made soils liming or

cementing of roadbed upper zone for its drying and strengthening. Inspection measurements

values on building site are helpful in course of building process estimation and gained results [11].

On fig. 5 in bar diagrams form secondary modulus of roadbed elasticity values are shown.

These values are obtained on track-way before EVSS2 , measured on strengthened roadbed, and after

E 2 its roadbed modernisation for Jastrz´ bsko stop, track nr 1.

Fig. 5. Deflection modulus diagrams for Jastrz´ bsko stop (E-20)

Roadbed investigations history for project and on subgrade rebuilding for segment of track Opole

Zachodnie - Dàbrowa is shown on fig. 6.

Fig. 6. Diagrams of a roadbed’s secondary deflection modulus values acquired from a sector of

Opole Zachodnie - Dàbrowa line’s track number 1. 1-from a survey done by VSS plate along the

track; 2-computed according to polish standards; 3-from a survey done by VSS plate on

construction site; 4-from a survey done by VSS plate on a new track; 5-required level of

parameters Eproj. Results shown for every 100 m.

Elasticity research of conventional track-way E VSS2 of operating railway track, subgrade

grounds elasticity analysis under projected protecting layer E s2 , subgrade secondary modulus of

elasticity values strengthened during reconstruction E VSS2 allow to gain values E 2 on protecting

layer which are required by standard specification Eproj .

Since 1999 in cases of adopting AHM-800R machine for track roadbed modernisation (E-

20, E-59, E-30) protecting layer is built as singular layer from all-in aggregate (E-20) or from

unsized stones (E-59, E-30). This protecting layer is projected on the basis of elasticity results

from geotechnical subgrade investigations and complements according to standard dependencies.

Constructional essential bound of machine and certain defects associate with data updating of

geotechnical subgrade measurements E-20 line gave rise to obtain only incomplete results of

experimental rebuilding of subgrade upper zone on Rzepin-Kunowice track (fig. 7) [13].

Fig. 7. Diagrams of secondary deflection modulus values acquired from preliminary loadings on

protective layer of Rzepin-Kunowice line’s (E-30) track number 1 roadbed

Following AHM-800R machine using during subgrade rebuilding (E-59, E-30) on Polish

railway track shows only fragmentary effects in relation to expected results Eproj .

5. NONHOMOGENEITY OF SUBGRADE PROPERTIES

Described subgrade cases included elasticity investigations results from all stages its

modernisation allow for its nonhomogeneity analysis based upon statistical research of ranges of

secondary modulus of elasticity values E 2 .

During researches one can use coefficient of nonhomogeneity [6][12]:

wE

EE

2

(Equation 5)

where:

E - standard deviation of modulus of elasticity values,

E 2 - arithmetic mean of roadbed modulus of elasticity

From a short statistical analysis of the roadbed deflection survey, covering all phases of

modernisation on chosen places, one can conclude the following:

nonhomogeneity of the roadbed deflection before modernisation is high - around 50%

after preparation to be covered by the protective layer (strengthening by compacting and soil

stabilisation), roadbed made from uncohesive soil yields smaller deflection and deflection

nonhomogeneity values, while roadbed made from different cohesive and uncohesive soil

types does the opposite.

after construction of protective layer deflection decisively drops; deflection nonhomogeneity

is also smaller

it can be concluded that nonhomogeneity of deflection is caused primarily by

nonhomogeneity of roadbed below the protective layer

nonhomogeneity of roadbed after modernisation is also influenced by impossibility of full

adaptation of protective layer’s properties to changing properties of the roadbed’s soil

structure along the line, as well as by used materials and methods of compacting

deflectability and nonhomogeneity of deflection of roadbed reconstructed with AHM 800R

train does not meet awaited parameters

Table 1. Statistical subgrade deflection modulus values survey results for selected line

sectors

Place with track existing subgrade modernised subgrade track after modernisation Commentsnumber E 2 E

w E 2 Ew E 2 E

w about subgrade

MPa MPa MPa MPa MPa MPa

E-20Jastrz bskostop

1

267,27 33,42 0,50

124,82

105,90

39,03

17,64

0,31

0,17

158,01

136,20

28,45

14,76

0,18

0,11

native sands

E-30 Opole - VSS

52,51 24,78 0,47 native and built-

Dàbrowa sector(track nr 1)

ns* 39,59 19,18 0,48 75,23 60,90 0,81 133,31

21,10 0,16 in cohesive anduncohesive

E-20 Rzepin -Kunowice sect.AHM 800R

1

2

68,08

69,90

17,48

16,87

0,26

0,24

native and built-in cohesive anduncohesive

* results acquired from VSS plate measurements and from national standards (ns) on a basis of soil condition

6. CONCLUSIONS:

1. A roadbed modernisation process requires geotechnical support on all it’s stages

2. Specially important in modernisation are results of deflection surveys and their statistical

analysis

3. Protective layers allow to reach anticipated deflection of upper part of the reconstructed

roadbed, only lowering the deflection’s nonhomogeneity

4. Results of existing roadbed’s deflection survey are used for evaluation of it’s state. The

protective layer should be planned basing on deflection values of the layer below.

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