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¸ 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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podatnych i pod o˝ a przez obcià˝ enie p ytà.
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oznaczania. WPP, Poznaƒ 1995.
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[5] PKP: Instrukcja o utrzymaniu podtorza kolejowego D-4, Warszawa 1993.
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Materia y seminarium ZDK PKr, Kraków-Zakopane1995.
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Mi´ dzynarodowej Konferencji „Linie dla du˝ ych pr´ dkoÊci”, ilina XI 1996.
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kolejowej, Materia y konferencji mechaniki gruntów i fundamentowania, Gdaƒsk 1997, tom
I, p. 147-154.
[12] Siewczyƒski ¸ .: Warunki wspó pracy nawierzchni kolejowej z podtorzem
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pod o˝ em gruntowym”, Bia ystok-Wigry 1998, p. 271-280.
[13] Siewczyƒski ¸ .: DoÊwiadczalna naprawa podtorza maszynà AHM 800R. Materia y
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Recommended