Welcome to
Presentation on
Dedicated Freight Corridors –
Geotechnical Considerations in
Design and Construction
by – Nand
Kishore, RDSO, LKO
Foundation Day Celebrations of
IRICEN, Pune on 20.03.2006
1
INTRODUCTION
• Quantum jump in originating Railway freight traffic from
390 million ton in 2001-02 to 602 million ton in 2004-05.
• Indian Railway is facing challenge to increase throughput
commensurate with high growth in GDP of 8.5 %.
• Railway has taken up a ‘Mission 700’ to carry 700 million
ton of traffic. For this, dedicated freight corridors are to be
constructed.
• Dedicated Freight Corridors need to be designed and
constructed for specific requirements of axle load, speed
and GMT.
2
GEOTECHNICAL ASPECTS
• A sound and stable formation plays a vital role in overall
performance of track.
• Earlier, tracks were constructed without any geo-technical
considerations which served the purpose for lighter axle
load & slow speed traffic.
• With increase in axle load and speed of freight traffic,
considerable length of track has developed weak/unstable
formation in due course of time.
• Permanent as well as temporary speed restrictions exist
over a length of about 650 km and 2000 km respectively
on account of weak formations.
• With further increase of heavier axle loads, high speed &
GMT, length of weak formation is likely to increase many
fold.
3
LOSSES DUE TO WEAK FORMATION
Direct losses:
• Frequent track attention
• Additional manpower
• Heavy loss of ballast due to puncturing
• Accelerated shallow & deep screening due to mud
pumping etc.
• Reduced life of track structures viz. rails, sleepers,
fastenings etc.
Indirect losses:
• Excess fuel consumption
• Safety hazard
• Reduction in line capacity
• Extra supervision
• Wear and tear of rolling stock
• Social cost: increased travel time, passenger
discomfort, railway’s image, pollution.
4
COST IMPLICATIONS OF WEAK FORMATION
Additional recurring expenditure on
unstable formation per year /km
track maintenance due to
• Cost of additional maintenance : Rs. 4.00 lakh
• Cost of premature track renewal : Rs. 1.50 lakh
• Cost of addl. deep screening
: Rs. 0.11 lakh
Total
Rs. 5.61 lakh
• Cost on account of ballast penetration (once during life cycle of
track) = 0.7 x1 .0 x 3.5 x 500 = Rs12.25 lakh/km
• Cost of blanketing using Al Girder in SC Rly in 1999 - Rs 31.38
lakh/km.
• Therefore, cost of rehabilitation gets recovered in about 4 to 5
years.
• Rehabilitation of weak formation is costly as well as difficult.
• For DFC, strong and durable formation is required from
beginning to avoid rehabilitation later on. Adequate efforts are
required to design and construct the formation.
5
GEOTECHNICAL REQUIREMENTS
• Formation is a permanent asset and can not be replaced
& difficult to upgrade.
• It should be designed for traffic requirements of very long
duration say 50 to 100 years.
• IR decided to introduced CC+8+2 T for BOXN in selected
iron ore routes.
•
In future, 30 t axle load is planned to be introduced.
• Keeping in view of future developments, the design of
formation for DFC should be done for 30 t axle load, 100
kmph speed and 35 to 50 GMT .
6
UIC DESIGN OF FORMATION FOR HIGH AXLE LOAD
• Design of formation mainly include thickness of track
bed layer i.e. ballast and blanket layer.
• As per UIC code 719 R, 1994 minimum thickness (e)
of track bed is given by e=E+a+b+c+d+f+g,
7
UIC DESIGN OF FORMATION FOR HIGH AXLE LOAD
Where,
• e = Total depth of ballast & blanket in meter
• E= Bearing capacity factors based on class of soil
• a= Factor depending on UIC group of routes based
on GMT
• b= Factor depending on type of sleeper
• c= Factor depending on different working conditions
on existing lines
• d= Factor depending on axle load of hauled vehicle
• f= Factor depend on speed of train
• g= Factor depend on inclusion of geo-textile based
on quality class of prepared sub-grade.
The values of the above factors are given in the UIC-719R,
1994 code.
8
Provision of ballast & blanket thickness as per UIC code
S.
No
Soil as per
IS
classificati
on
Quality class of
the soil as per
UIC code
Thickness of
prepared subgrade
of QS3 class soil
(GW, SW, GP & SP)
For 22.5t
For 25t
For 30t
(extrapolated)
1
GW
QS3
NIL
8cm
15cm
35cm
2
SW
QS3
NIL
8cm
15cm
35cm
3
GP
QS3
NIL
8cm
15cm
35cm
4
SP
QS3
NIL
8cm
15cm
35cm
5
GM
QS1
0.50m
53cm
65cm
85cm
6
GM-GC
QS2
0.35m
43cm
50cm
70cm
7
GC
QS1
0.50m
53cm
65cm
85cm
8
SM
QS1
0.50m
53cm
65cm
85cm
9
SC
QS1
0.50m
53cm
65cm
85cm
10
SM-SC
QS2
0.35m
43cm
50cm
70cm
11
ML-CL
QS1
0.50m
53cm
65cm
85cm
12
ML
QS1
0.50m
53cm
65cm
85cm
13
CL
QS1
0.50m
53cm
65cm
85cm
14
MI
QS1
0.50m
53cm
65cm
85cm
15
CI
QS1
0.50m
53cm
65cm
85cm
Note: 1. QS1 and QS2 require provision of geo-textile in addition to blanket layer.
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2. QS3 class of soil used in prepared subgrade is almost similar to blanket material.
STUDY OF FORMATION STRESSES
ON TEST TRACK PANEL
In January 1999,
RDSO
had
conducted
a
simulated study to
assess
vertical
stress distribution
in Railway formation
on full scale test
track panel in TM
Dte.
10
OBSERVATIONS IN TRACK PANEL STUDY
Longitudinal variation of stress in formation – Effect of
axle load is felt upto 4th sleepers on either side from the
loading sleeper.
11
OBSERVATIONS IN TRACK PANEL STUDY
Variation of stress with axle load at 60 cm depth – Vertical
stresses at a depth increases linearly with axle load. 12
OBSERVATIONS IN TRACK PANEL STUDY
Variation of induced stress with depth & axle load – Variation of
Stress beyond 1.3 m is nominal with axle load.
13
.
Conclusions of the track panel study
•
Induced stresses inside formation increase linearly with
increase in axle load and reduce with depth. However,
below one meter depth, induced stress varies only
nominally with increase in axle load.
• Subgrade soil in top one meter layer of railway formation
truly governs its axle load carrying capacity. Therefore,
to strengthen the existing formation for introduction of
heavier axle loads, soil in this portion is to be replaced
with proper blanket material.
• Reinforcement of blanket layer with bi- axially oriented
geogrid can substantially reduce stresses on subgrade
soil thereby reducing depth of blanket layer required.
14
Existing Provisions in Guidelines of
Earthwork for higher axle load
•
•
•
•
•
No blanket on rocky subgrade, GW, SW soils
45 cm thick blanket for GP, SP, GM & GM-GC soils
60 cm thick blanket for GC, SC, SM, SM-SC
100 cm CL, ML, CI, MI, CL-ML soils
CH, MH soils – Unsuitable for use in top 3 m of bank
• For heavier axle load traffic above 22.5t and upto 25t &
above 25t upto 30t, additional blanket thickness of
30cm & 45cm respectively, over and above as given
above of superior quality material, shown as upper
blanket layer in enveloping curves.
15
16
GENERAL DESIGN CONSIDERATIONS
• Adequate soil survey & exploration should be done for
deciding the alignment for freight corridor to avoid
troublesome spots, unstable hill slopes, swampy & soft soils,
peat lands, etc.
• Ground improvement and slope stabilization measures etc.
may be planned in advance for troublesome spots.
•
Adequate thickness of blanket with or without geogrids based
on soil type, axle load, speed, GMT to be provided.
• Side slopes of embankment/cuttings should be designed with
realistic soil parameters and drainage conditions using
standard methods of slope stability analysis/ software rather
than adopting thumb rules.
17
GENERAL DESIGN CONSIDERATIONS
Contd…
It is desirable to increase formation width of BG
embankment for proposed DFC say upto 8.5 m for ballast
side slope of 2 H:1 V and cess width of 120 cm against
existing 6.85 m width & ballast slope of 1 H:1 V and cess
width of 90 cm.
Drainage Improvement • Water is the enemy of soil and poor drainage is most of
the time the main cause of trouble in formation.
• Adequate cross-slope should be provided at the subgrade
top
• In cuttings, adequate catch water drains and side drains
should be planned.
18
GE CONSIDERATIONS IN CONSTRUCTION OF DFC
Construction Material:
• Unsuitable soils such as CH, MH, organic soils etc.
should not be used in construction of embankment.
• If bank has to be constructed with cohesive subgrade,
sandwich construction (provision of intermediate sand
layers ) may be adopted.
• If suitable blanket material is not available naturally,
mechanized production of blanket material should be
planned. Details of mechanical production given in RDSO
document GE: IRS-2, July 2005.
19
GE CONSIDERATIONS IN CONSTRUCTION OF DFC
•
•
•
•
•
Construction Machinery:
Manual methods of construction cannot achieve the desired
quality and progress of earthwork.
Modern construction equipments viz.
vibratory rollers,
earthmover, motor graders, scraper, dumpers, mobile water
sprinklers, etc. should be deployed.
For construction of formation over soft soil, methods such as
stage construction, pre - loading, sand drains, prefabricated
vertical PVC drains may be used for expediting consolidation.
For monitoring quality of construction, a well equipped &
properly manned GE laboratory should be established in field.
It would be desirable to have separate staff for quality control
from those involved in construction.
20
GE CONSIDERATIONS IN CONSTRUCTION OF DFC
• Rate of earthwork paid in railways is generally much
less
vis-a-vis
other organizations such as NHAI,
CPWD etc. while rate of blanket material is
comparatively higher.
• It is very difficult to achieve desirable quality of
earthwork at low rate of earthwork.
• Detailed realistic analysis of earthwork commensurate
with the desired quality of earthwork including quality
control set up etc. is required to be done.
21
CONSIDERATIONS FOR DFC ON EXISTING TRACK
• Before introduction of higher axle load, it is necessary to
investigate the condition of existing formation and rehabilitate &
strengthen weak formation.
• Methods of rehabilitation tried in past such as lime treatment,
ballast piling, cement grouting, vinyl drains, open cross drains
filled with coarse grained material, sall balli/ sleeper/ rail piling,
layer of laterite block, polyethylene etc. have not shown the
desired improvement.
• Provision of blanket in full width of formation is proven solution
for rehabilitating weak formation the world over. Geo-grid can
also be provided to reduce the thickness of blanket.
• General drainage arrangement of embankment/cuttings should
be improved by providing cross drains, side drains, catch water
drains etc.
22
CONSIDERATIONS FOR DFC ON EXISTING TRACK
• Various methods for provision of blanket on existing
track are detailed in RDSO report No. GE-39, March2003. These are:
- With Aluminium Alloy Girder
- Track Dismantling Method
- With manually operated portals
- With CC crib & rail clusters (SE Railway Method)
- With rail Clusters (Eastern Railway Method)
- Lifting of track with deep screening
- Fully mechanized methods – Formation
Rehabilitation Train
• Choice of method depends on several factors like
extent of problem, projected traffic, axle loads,
availability of traffic blocks, accessibility of site,
availability of labour and material etc.
• Formation rehabilitation train is commonly being used
23
in foreign railways. It requires long block (about 8 hrs).
CONCLUSIONS
• To meet growing need of freight traffic, it is imperative to
construct dedicated freight corridors.
• These freight corridors must be designed for heavy axle
load, higher speed & high GMT keeping in view of future
traffic demands.
• Construction of freight corridors will require use of
modern machineries, strict quality control in execution of
earthwork & blanketing and proper drainage.
• Ground improvement in case of soft subsoil will have to
be ensured for construction of new dedicated freight
corridors.
• Existing track, if planned to be used as dedicated freight
corridor, will require to be investigated & strengthened by
providing adequate thickness of blanket by any
24
suggested methods.
25