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For official use only

GOVERNMENT OF INDIAMINISTRY OF RAILWAYS

GUIDELINES ON

TEMPORARY AND PERMANENT RESTORATION

OF EMBANKMENT

AFTER BREACHES/ WASHOUTS

Report No. GE: G-7

JULY-2005

Geotechnical Engineering Directorate

RESEARCH DESIGNS & STANDARDS ORGANISATION

LUCKNOW-226011

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PREFACE

This report has been prepared on the basis of field experience &

literature survey. The views expressed are subject to modification from

time to time in the light of future developments on the subject. The views,

as such, do not represent the views of Ministry of Railways (Railway

Board), Government of India.

This report is the property of RDSO and is meant essentially for

official use. It may not be loaned, reproduced in part, or in full, or quoted as

an authority without the permission of Director General, RDSO.

(Nand Kishore)Executive Director/GE

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CONTENTS

S.No. Description Page No.

1. Introduction 1

2. Scope 1

3. Reasons for washouts/breaches/slips 1

4. Type of damages 2

5. Materials available for restoration work 4

6. Temporary repair methods 8

7. Permanent repair methods 11

8. Conclusion 13

9. References 15

10. Annexure 17

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GUIDELINES ON TEMPORARY AND PERMANENT

RESTORATION OF BANK AFTER BREACHES/WASHOUTS

1.0 INTRODUCTION

Washouts/breaches of railway embankment during floods is a

commonly occurring phenomenon, especially in monsoons. There arevarious direct and indirect losses due to washouts or breaches of the

embankments. Main reasons behind the washouts/breaches are

detailed in para 3.0 below.

2.0 SCOPE

This report contains a theoretical study on temporary and permanent

repair methods for washouts/breaches of railway embankments. The

report is based on field experience, previous studies done by RDSO

& literature survey. The recommendations of this report will help in

quick restoration of traffic on a washed out railway formation.

3.0 REASONS FOR WAHSOUTS/BREACHES/SLIPS

Main reasons for washouts/breaches are enumerated below-

i) Continuous Rains- Banks situated in heavy rainfall areas are

subjected to slips and breaches. When there is a continuous rain or

continual interceptive rain for prolonged period, there is lot of

infiltration of rainwater into the bank. This leads to decrease in

cohesion of soil and drop in the shear strength. Further, it increases

the gravitational forces acting on the bank & leading to slips in the

bank.

In the year 2004, many washouts/breaches of bank took place on

account of heavy rainfall in Lummding-Badarpur hill section of NFRailway.

ii) Floods and Receding Water-Floods are natural phenomenon causedby rains. Flash floods in hilly terrain result in washouts. Plain areasare also subjected to rapid flow of water due to heavy floods. During

major floods, the water carries a lot of debris and it either erodes,

scours, leads to submergence of bank and/or even overtops it,

resulting in washouts. Slips occur in banks when flood water recedes.

Such floods occur mainly in delta region & alluvial plains, where therivers are wide, shallow and meandering type.

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Primary cause ofmeandering is excess discharge during floods, due

to which high turbulence is developed. Basic factors controlling

process of meandering are:-

a) Dischargeb) Stream loadc) Valley sloped) Bed and side resistanceDoab area between river Ganga and Son is heavily flooded in

monsoon causing formation breaches in Eastern and EC Railway.

iii) Vertical Sag (Bad Bank)- Many a time during the rains, vertical sagsoccur in railway track. Such sags develop due to inadequate/poor

bearing capacity of soil. Vertical sags are quite common where a

good portion of bank is made of ash, cinder or black cotton soils etc.Poor or inadequate compaction of newly made banks may also lead

to vertical sags.

iv) Inadequate Openings- Railway banks act as a barrier to the natural

flow of water in plains especially, where such plains acts as drainagepath for wide spread catchments areas lying many miles away. Whenheavy rain occurs in the catchment areas, water gushes out to the

plains all of a sudden.

At times, openings provided in railway banks may prove inadequate

to bear this excess amount of water, resulting in washouts. A clear

difference in height of water level on either side of opening is seen insuch cases. To get over the problem, additional openings across the

track could provide a solution.

v) Scouring Damages- Scouring may cause damage to bridgefoundation as well as to other nearby structures such as end

embankment, retaining walls etc.. If scouring exceeds a certain level,it can result in collapse of bank.

4.0 TYPES ON DAMAGES

Washouts/breaches may result in following types of damages:

i) When the damage is limited to cess of embankment.2

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DAMAGE IS LIMITED TO CESS

ii) When the damage is extended to center of track.

DAMAGE IS EXTENDED TO CENTER OF TRACK

iii) Rupture extends to foundation subsoil and original shapeof embankment is not maintained.

ORIGINAL SHAPE OF EMBANKMENT DISTURBED

iv) Embankment is deformed in a way generally similar touniform settlement.

UNIFORM SETTLEMENT

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v) Embankment behind bridge abutment is settled and cracked.

EMBANKMENT SETTLED AND CRACKED BEHIND BRIDGE

5.0 MATERIALS FOR RESTORATION WORK

i) Cinder

ii) Boulders

iii) Sand bags

iv) Local earthv) Stone dustvi) Fly ash and Bottom ashvii) Sal balli/released rails

i) Cinder- Cinder used to be easily available in the past when steamlocomotives were in vogue. Therefore, it was used in restoration work

in an extensive manner on railways. Now, with the progressive

decline in steam locos over the years and currently no more in use,availability of cinder has become scarce. Hence, the option to use this

material is no longer available.

ii) Boulders- Boulders can be procured from nearby stone quarry/river

bed. Use of boulders in embankment may require heavy compaction

machinery, which is generally not used in our country. Therefore, inabsence of heavy compaction machinery, use of boulders for

restoration purpose may not be advisable except for pitching theslopes at later stages of restoration.

iii) Sand- Sand is easily available in most of the areas and it can serve asa useful restoration material. Ordinary river sand filled in cement

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bags can be stored in advance at convenient points for quick restoration

of traffic. Embankment restored with sand may require erosion control

measures later on.

iv) Local earth- Utilization of local earth offers the simplest and fastest

method for restoration of embankment. However, the following soils

must be avoided:

Peat and Organic soils Chalk etc. which are likely to disintegrate Poorly graded sands with Cu less than 2. Clay and silts of high plasticity (CH & MH) in top 3 m of

embankment.

For this purpose, it would be better if borrow pits within railway area are

identified well in advance.

v) Stone dust- Stone dust is normally available in ballast quarries as a

byproduct. It can also serve as a good blanket material, if due attention is

paid during manufacturing of ballast. Stone dust may be stored in advance

at convenient locations.

vi) Fly ash and Bottom ash - About 1000 million tonnes ash is produced in

India every year by thermal power plants and is available free of cost

from the plants. In most of the power plants, bottom ash and fly ash are

mixed in slurry form and is disposed of to ash ponds in slurry form.

Fly ash is a waste product of thermal power plant where it poses

problem of disposal. Generally, both ashes are available in huge

quantities in thermal power stations.

Fly ash is a finely divided residue resulting from the combustion of

pulverized coal in the boiler and collected from electrostatic precipitation.

It is a pozzolanic material which in the presence of water reacts with lime

and form cementitious materials.

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Typical geo-technical properties of Fly ash

Parameters Range

Specific gravity, G 1.90- 2.55

Plasticity Non-plastic

M.D.D (gm/cc) 0.9-1.6

O.M.C (%) 18.0-38.0

Cohesion (KN/m2) Negligible

Angle of Internal Friction, 30-40

Coefficient of Consolidation,

Cv(cm2/sec) 1.75 10

5 2.01

10

3

Compression index, Cc 0.05 0.4Permeability, k (cm/sec)

8 106 7

10

4

Particle Size Distribution (% of

materials)

Clay size fraction

Silt size fraction

Sand size fraction

Gravel size fraction

1 10

8 85

7 90

0 10

Coefficient of Uniformity, Cu 3.1 10.7

Bottom ash is collected at the bottom of boiler furnace as a resultant

of coal burning activity. This is comparatively coarser materialcharacterized by better geo-technical properties and therefore,

promises to be an excellent material for fill embankment.

Test results of bottom ash from NTPC Ltd. Ramgundam, Jyothinagar,

Andhra Pradesh, as obtained in GE lab, RDSO are tabulated below:

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Gravel

(%)

Sand

(%)

Silt

(%)

Clay

(%)

%

Passing

Classification P.I. Cu Cc

05 89 06 00 06 SP-SM NP 3.78 1.31

03 80 17 00 17 SM NP 4.00 0.74

Physical properties of bottom ash as supplied by NTPC for its various

units are tabulated below-

Physical properties of Bottom ash

S.No Material Sp.Gravity Clay(%) Silt(%) Sand(%) Gravel(%) Cu Cc L.L.

1 Unchahar 1.66 1.0 12.0 87.0 0 7.8 3.7 92.6

2 Korba 2.15 0.5 8.0 91.0 0.5 4.7 2.1 77.0

3 Vijayawa

da

1.82 - 22.0 71.0 7.0 9.4 1.1 53.5

4 Badarpur 1.95 1.0 12.0 87.0 0 9.1 1.0 47.4

5 Dadri 2.01 1.0 40.0 59.0 0 7.5 1.4 48.0

6 Ramagun

dam

2.08 1.0 12.5 76.5 10 8.0 1.6 65.1

7 Neyveli 2.08 3.0 5.5 91.5 0 5.2 2.1 104.1

8 Farakka 2.16 2.5 8.0 78.5 11.1 14 1.5 70.9

9 Kahalgoa

n

2.17 1.0 14.8 65.9 18.3 8.8 1.3 45.0

10 Rihand 2.19 - 13.6 75.8 10.6 6.5 1.2 57.0

Bottom ash is non-plastic with silty sand material. Its particles are

spherical in shape and uniform in size. Due to this property, it is 5 to 10

times more permeable than soil having the some effective grain size. The

permeability coefficient, k is in the order of 8.3 x 10-5

cm/sec. Bottom

ash is predominantly granular in nature, it behaves much the same as a

cohesive soil with respect to consolidation. However, a notable

difference between them is that, the bottom ash consolidates much more

quickly then a clay soil because it is more permeable.

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Compacted bottom ash achieves its most of shear strength from its

interlocking of particles, expressed in terms of angle of internal

friction. It also exhibits some apparent cohesion when moist due to

surface tension in the pore water.

Density of bottom ash fill is an important parameter which determines

the strength, compressibility and permeability characteristics of the

fill. M.D.D. of bottom ash is on the higher side upto 1.88 gm/cc.

As compared to fly ash, bottom ash is a coarse grained material (high

%age of sand), has high value of MDD and specific gravity. Due to

these properties, bottom ash is superior material to fly ash.

vii) Sal balli/Released rails - Though these materials are readilyavailable in plenty with the railways, however, they have a limited

use in restoration work when used alone.

6.0 TEMPORARY REPAIR METHODS

Various methods for temporary restoration of bank are as follows-

i)

Ballah/Rail pilingii) Filling with cinderiii) Filling with sand bagsiv) Filling with Fly ash and Bottom ashv) Filling with local earth

Temporary repairs methods are described below:

i) Ballah/Rail Piling - In railway banks, where there is likelihood of

slip occurring, ballah/rail piling offers the best solution in the short

term. No other solution will serve the purpose at that moment of time.Ballah/ rail piling proves to be effective solution in following cases-

(a) Where the movement of trains must not stop or even if it stops,it should be for minimum possible time.

(b) Where equipments and ballah/rail piling can be mobilized invery short period of time.

(c) Where the banks are very high and there is slope failure and notthe toe failure.

(d) where the minor slips have already occurred and immediatelyrestoration of track is required.

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It supports the slipped/ disturbed soil and immediately takes up

the load and stabilizes the disturbed area. It also removes the chances

of any further slip in this disturbed region and provides stability to thesoil.

ii) Filling with cinder - The washed out bank can be rebuilt with puttingthe cinder into the bank. However, these days cinder is not easily

available in railways which was collected in the past from steam

locomotives.

iii) Filling with sand bags - The washed out bank can be rebuilt bydumping sand bags already stored in advance along the bank. Thesand bags should be half filled to minimize void spaces in between

the sand bags.

iv) Filling with Fly ash and Bottom ash - The washed out banks can be

rebuilt with fly ash or bottom ash, the latter being preferable

material. Fly ash is a cohesionless material and is highly erodible innature. Liquefaction generally occurs when fly ash is deposited under

loose saturated condition during construction of embankment. Inview of this and properties earlier discussed, special procedure suchas Sandwich Construction or by Earth Cover is required for

construction of embankment with fly ash.

Sandwich Construction:

Intermediate soil layers are often provided in the fly ash

embankment for ease of construction, to facilitate compaction of

ash and to provide adequate confinement. Such layers minimize

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liquefaction potential also. Embankment with intermediate soil layers

can be adopted in case height of the

Typical cross section of embankment showing sandwich Construction

embankment is more than 3 m, otherwise Earth Cover method

can be adopted. The compacted thickness of intermediate soil

layers shall not be less than 200 mm. One or more layers shall beconstructed depending upon the design requirements. The vertical

distance between such layers may vary from 1.5 to 3 m. The top 1

m of embankment should be constructed using selected earth to

form the subgrade.

Earth Cover:

The fly ash embankment should be covered on the sides and top

by soil to prevent erosion of ash. Good earth suitable for

embankment construction can be adopted as cover material for flyash embankment.

For successful compaction of fly ash, self-propelled, pneumatic-tired rollers and self- propelled or towed vibratory rollers can be

used.

v) Filling with local earth - The washed out bank can be rebuilt by

putting the soil from borrow pits which should be at a minimum

distance of H+3 m from the toe of the bank, where H is the heightof embankment. Proper compaction of the soil should be ensured.

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7.0 PERMANENT REPAIR METHODS

Permanent repair methods for bank restoration are as follows-

i) Provision of blanketii) Provision of culvert/bridge etc.iii) Boulder pitchingiv) Toe wallv) Slope flatteningvi) Retaining wallvii) Provision of sand layerviii) TurfingPermanent restoration methods are described below:

i) Provision of blanket- If it is not possible to provide blanket duringtemporary restoration of embankment, then blanket layer of adequate

thickness conforming to stipulated specification must be provided a

the time of permanent restoration. For this purpose, any method asdescribed in RDSO Report no. GE-39 can be used for laying of

blanket.

ii) Provision of culvert/bridge etc- If damage or washout ofembankment occurs due to level difference in water level on both side

of embankment as already discussed, suitably designed culverts /bridges at appropriate locations should be constructed.

iii) Boulder Pitching - In situations where railway banks remainsubmerged in water for considerable period during rainy season or

otherwise, boulder pitching should be carried out upto appropriate

level.

iv) Toe Wall - When bank is high, soil is plastic in nature, slope are

inadequate and water remains in borrow pits by the side of toe of

banks, such banks are prone to slips. Cross level variations and

difficulty in maintenance of track are regular feature of such banks

during the monsoon. Toe wall of boulder crates with re-profiling of

slopes/sub banks can be probable solution at such places for

stabilization of banks up to 6 m.

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When bank height is more than 6 m and bank slope profile

shows signs of bulging, distorting or flattening with passage of

time, cross level variation, movement of TP post and trees away

from the centerline of track with every passing year, duringrains, severe slips may occur in such banks. In such type of

banks, toe wall with Ballah/ Rail piling at toe of sub-bank could

be good solution.

v) Slope flattening Slope stability analysis should be carried out

and if existing slopes are found to be steep, then flatter slope

should be provided with or without berms/sub-bank in keeping

with the results of analysis.

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vi) Retaining wall If adequate slopes as determined from slope

stability analysis can not be provided at site due to various

constraints, retaining wall may be constructed at toe of the

embankment.

vii) Provision of sand layer In case, water table remains high at the

breach site, 30 cm thick sand layer may be provided at bottom of sub

bank when slope of embankment has to be stabilized by constructing

a sub-bank. In such cases, it will be preferable to provide sand layer

below main bank also at the time of temporary repairs. Sand layer

will facilitate a lowering of water table and in quick dissipation of

pore water pressure.

viii) Turfing - Turfing is suited for soil with some clay friction. Methodconsists of preparing slope area by grading it for sowing seeds or

planting root strips of locally available creeping grass. Its root goes

up to 50 to 75 mm deep into the slopes serving as a soil anchor andoffering added resistance to erosion. Some typical species of grass

which develop good network of roots and considered suitable are

listed below:

-

Doob grass- Chloris gyne- Iponea gorneas (Bacharum Booti)- Casuariva and goat foot creepers etc.- Vetiver grass (vetiveria zizanioides)

8.0 CONCLUSION

8.1 Material for repair of embankment should be chosen keeping in viewthe availability of same in the near by area.

8.2 Depending on past history and experience, vulnerable stretches ofembankment can be identified and approximate quantity of material

may be worked out.

8.3 As far as possible, estimated quantity of material may be stored atconvenient locations. If this is not possible, then reliable sources for

material procurement should be identified well in advance. Possible

borrow pit area in railway land may be identified and demarcated.

8.4 If damage is large and permanent repair requires a long time,temporary repairs to a satisfactory level for restoration of traffic

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should be made immediately and permanent repairs made

subsequently.

8.5 If damage is small and permanent repair is not difficult, repairsdone initially should be of the permanent repair type. If

possible all of the permanent repairs should be completed

during the temporary repair period.

8.6 The selection of temporary repair method for embankment willdepend on conditions of the damaged embankment. In

selecting the temporary repair method, it is necessary to

consider the outline of the permanent repair so as to avoid the

repetition of the same work during the permanent repair.

8.7 The repair level at the temporary repair stage will depend on

the overall level of damage in the area and the time allowed forthe repair work. The general procedure will depend on thedegree of damage.

Factors to be considered for temporary repair include the extentof damage, the work schedule, the level to which the formation

will be restored, the scope and process of the work and its

priority.

Crack, swelling, movements, and other signs of instability ofslopes or cut slopes should be watched carefully in this periodand until permanent repair is made, because of the danger that

delayed effects may cause another disaster.

8.8 In selecting proper permanent repair methods, the originalstructure of the embankment, the scale and mechanism of the

damage and the possibility of secondary damage should be

considered. This selection can be made with use of theinformation on patterns and level of damage, damage

mechanism and ground conditions that may be obtained in the

investigation for temporary repair.8.9 At thetime of permanent repair of damaged bank, slope

stability analysis should be carried out and new slope should be

provided as per results of slope stability analysis.

-----------------------

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9.0 REFERENCE :-

1. Guide lines for Earthwork in Railway Projects, GE:G-1, July2003.

2. Slope Stability and formation treatment of Malda Division.IPWE Seminar Dec. 2001, Secunderabad,

3. Comprehensive Report on Natural Disaster Reduction forroads, - Permanent International Association of Road Congress

1995.

4. Technical paper title Design and Construction of easternapproach embankment using fly ash for second NizamuddinBridge, New Delhi , CRRI, New Delhi- 110020 in 2nd

International Conference on Fly ash Disposal and Utilization.

5. Guidelines for use of fly ash in road embankments- IRCspecification publication, New Delhi 2001, IRC: SP: 58-2001.

6. A report on Caol Ash- An environment friendly material for filland embankment construction, NTPC, Lodhi road, New Delhi,July,2002, Part I.

7.

Guidelines for use of fly ash in Railway embankmentsPublished by NTPC, Lodhi Road, New Delhi March 2003

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ACKNOWLEDGEMENT

The Guidelines has been prepared by

1. Shri A. K. Singh, Director/GE2. Shri G. Nageswara Rao, Director/GE

under guidance of Shri Nand Kishore, Executive Director/GE with

assistance of

1. Shri S.K Ojha, SRE/GE

2. Shri R.S Meena, SRE/GE.

3. Shri Susheel Kumar, JE-II (Design)

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ANNEXURE

List of NTPCs Coal Based Thermal Power Stations

1. Singrauli super Thermal

Power station

P.O. Shaktinagar Distt Sonebhadra,

U.P. 231222

2. Korba super Thermal Power

station

P.O. Pragati Nagar, Korba (West)

Distt. Korba, CH.-495450

3. Ramagundam Super Thermal

Power Station.

P.O. Jyoti Nagar Distt. Karim Nagar,

A.P.-5052154. Faraka Super Thermal Power

station

P.O. Nabarun, Distt. Murshidabad,

W.B. 742236

5. Vindhyachal super Thermal

Power station

P.O. Vidhya Nagar Distt. Sindhi, M.P.

- 486885

6. Rihand super Thermal Power

station

P.O. Rihand Nagar Distt. Sonebhadra

U.P. - 321223

7. National Capital Power

station

P.O. Vidyut Nagar Dadri Dhaulana

Road Distt.Gautam Budha Nagar U.P.

2010088. Feroz Ghandhi Unchahar

Thermal Power station

P.O. Unchahar, Distt. Rae Bareilly,

U.P. 229406

9. Badarpur Thermal Power

station

P.O. Badarpur New Delhi 110044

10. Kahalgaon super Thermal

Power station

P.O. Deeptinagar, Kahalgaon Distt.

Bhagalpur, Bihar 813203

11. Talcher-Kaniha superThermal Power station

P.O. Kaniha, Distt. Angul, Orissa-759147

12. Talcher- Thermal Powerstation P.O. Talcher Thermal Distt.Angul,Orissa 759101

13. Tanda Thermal Power station P.O. Tanda Distt. Ambedkarnagar,

U.P.

14. Simhadri super Thermal

Power station

P.O. Simhadri, Distt. Vishakhapatnam

A.P. 531020