IRC SP 058: Guidelines for Use of Fly Ash in Road - QuestIn

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Indian Roads Congress Special Publication 58

GUIDELINES FOR USE OF FLY ASH IN

ROAD EMBANKMENTS

NEW DELHI 2001

cigitized by the Internet Archive in

2014

http://archive.org/details/govlawircy1999sp58_0

IRC:SP:58-1999

Indian Roads Congress Special Publication 58

GUIDELINES FOR USE OF FLY ASH IN ROAD

EMBANKMENTS

Published by

THE INDIAN ROADS CONGRESS

Copies can be had from

The Secretary, Indian Roads Congress Jamnagar House, Shahjahan Road,

New Delhi-110011

NEW DELHI 2001

Price Rs. 120.00 (plus packing

postage)

and

IRC:SP:58-2001

First

Published

:

March, 2001

Reprinted

:

December, 2003

Reprinted

:

June, 2006

Reprinted

:

August, 2009 (Incorporated

Amendment

- March, 2009)

(Rights of Publication

and Translation are reserved)

Printed at India Offset Press,

New

(500 copies)

Delhi- 1 10064

IRC:SP:58-2001

GUIDELINES FOR USE OF FLY ASH IN ROAD

EMBANKMENTS CONTENTS Page Personnel of Highways Specifications

(i)

to (v)

& Standards Committee Background

-

1

1.

Introduction

-

3

2.

Scope

-

4

3.

Design Considerations

-

4

4.

Construction of Fly Ash Embankments

-

13

5.

Quality Control

-

21

References

-

22

IRC:SP:58-2001

PERSONNEL OF HIGHWAYS SPECIFICATIONS AND STANDARDS COMMITTEE (As on 22.8.2000)

1.

Prafulla

Kumar

Director General (Road Dev.)

(Convenor)

Road Transport

&

Bha van, New DelhiS.C.

&

Addl.

Secretary to the Govt, of India, Ministry of

Highways, Transport 1 1

Chief Engineer,

Sharma

Transport

(Co-Convenor)

000

Ministry

of Road

& Highways, Transport Bhavan,

New Delhi- 110001 3.

The Chief Engineer (R) (

Member-Secretary)

S&R

Ministry

Bhattacharya),

(C.C.

Road Transport

&

New Delhi-

Bhavan,

of

Highways, Transport 1 1

000

Members 4.

M.K. Agarwal

Engineer- in-Chief (Retd.), House No. 40, Sector

5.

P.

Balakrishnan

1

6,

Panchkula- 134113

Chief Engineer (ReU.), Highways

& Rural

Works Department., No. 7, Ashoka Avenue, Kodambakkam, Chennai-600024 6.

Dr. R.K. Bhandari

Head,International

S&T Affairs Directorate,

Council of Scientific

& Industrial Research,

Anusandhan Bhavan,

2,

Rafi Marg,

New Delhi- 110001 7.

P.R. Dutta

Chief Engineer (Mech.), Ministry of Road, Transport

& Highways,

Transport Bhavan,

New Delhi-1 10001 8.

D.P. Gupta

DG(RD) (Retd.), E-44, Greater Kailash Part-I Enclave,

9.

RamBabu Gupta

New Delhi-1 10048

Chief Engineer-cum-Officer on Spl. Duty with Public

Works

Minister, 9 Hathoii

Market, Ajmer Road, Jaipur-302001

ADG(R) being not in position, the meeting was presided by Shri Prafulla Kumar, DG(RD) & Addl. Secretary to the Govt, of India, MORT&H (i)

IRC:SP:58-2001

10.

Dr. L.R. Kadiyali

Chief Executive, L.R. Kadiyali

& Associates,

C-6/7, Safdarjung Dev. Area, Opp. IIT Main Gate,

Mathur

11. J.B.

New Delhi- 110016

Chief Engineer, Ministry of Road Transport

&

Highways,

New Delhi12.

H.L.

Meena

1

Transport

Bhavan,

10001

Chief Engineer-cum-Addl. Secy, to the Govt,

of Rajasthan, P.W.D., Jacob Road, Jaipur-302006

Momin

13. S.S.

Chief Engineer, Maharashtra State Road

Dev. Corpn. Ltd., Nappean Sea Road, Mumbai-400036 14.

Jagdish Panda

Engineer-in-Chief-cum-Secy. to the Govt, of

Works

Orissa,

Department,

Bhubaneswar-751001 15. S.I,

Patel

Chief General Manager, National Highways

Authority of India,

1,

Eastern Avenue,

Maharani Bagh, New Delhi- 1 1 0065 16.

M.V.

Patil

Secretary

(Roads), Maharashtra P.W.D.,

Mantralaya, Mumbai-400032 17.

K.B. Rajoria

Engineer-in-Chief, Delhi P.W.D. (Retd.), C-II/32,

18.

Dr.

Gopal Ranjan

Moti Bagh, New Delhi- 1 1003

Director, College of Engg. Roorkee, 27th

KM

Roorkee-Hardwar Road, Vardhman Puram, Roorkee-247667 19.

S.S. Rathore

Spl. Secretary

& Chief Engineer (SP), R&B,

Block No. 14/1 Sardar Bhavan, Sachivalaya, ,

Gandhinagar-382010 20.

K.K. Sarin

21. Dr.

S.M. Sarin

DG(RD) & AS, MOST (Retd.), S-108, Panchsheel Park, New Delhi-1 10017 Dy. Director, CRRI (Retd.), 2295, Hudson Lines, G.T.B. Nagar, Delhi-1 10009

(»)

IRC:SP:58-2001

22.

H.R. Sharnia

Associate

(Highways),

Director

Intercontinental Consultants

Pvt.

Green

A-ll,

Ltd.,

& Technocrats Park,

New Delhi-1 10016 C.K. Singh

23. Dr.

Engineer-in-Chief-cum-Addl. Commissioner-cum-Spl. Secy., Road Constn.

Department, Ranchi (Jharkhand) 24.

Nirmal

Jit

Singh

Chief Engineer Transport

Ministry of Road

(Pig.),

& Highways, Transport Bhavan,

New Delhi-1 10001 25.

Prabhash Singh

Chief Enginer, Zone-Ill, Delhi P.W.D., Building, LP. Estate,

26. Dr.

Geetam Tiwan

Tiansortation Res.

Programme, Institute

27.

K.B. Uppal

Mohan

&

Injury Prevention

MS 808 Main Building,

of Technology,

Director,

MSO

New Delhi-1 10002

Indian

New Delhi-1 10016

AIMIL Ltd., Naimex House, A-8,

Co-operative Indl. Estate, Mathura

Road, New Delhi- 11 0044 28. V.C.

Veima

Executive Director, Oriental Structural Engrs.Ltd., 2 1

Marg,

,

Commercial Complex, Malcha

Diplomatic

Enclave,

New Delhi- 11 0021 29. P.D.

30.

Wani

The Engineer-in-Chief

Member, Maharashtra Public Service Commission, 3rd Floor, Bank of India Building, M.G. Road, Mumbai-400001 (S.S. Juneja) H.P. Public

Works Department,

U.S.Club,Shimla-171001 31.

The Chief Engineer (B)S&R

(V. Velayutham), Ministry of Transport

Road

& Highways, Transport Bhavan,

New Delhi- 110001 32.

The

Principal Secy, to the

Govt, of Gujarat

(H.P.

Jamdar),

R&B

Department,

Sardar Bhavan, Block No. 14, Sachivalaya,

Gandhinagar-382010

(iii)

IRC:SP:58-2001

R&B Department, A&E AP, Errum Manzil, Hyderabad-5 00082

33.

The Engineer-in-Chief

(V. Murahari Reddy),

34.

The Engineer-in-Chief

(R.R. Sheoran), Haryana Public

B&R,

Deptt.,

Works

Sector

19-B,

Chandigarh- 1600 19 35.

The Member

(R.L. Koul), National

of India,

1,

Highways Authority

Eastern Avenue, Maharani Bagh,

New Delhi- 110065 36.

The Director & Head

(S.K. Jain), Civil Engg. Department, Bureau

of Indian Standards,

Bahadur

Manak Bhavan,

Shah.

9,

Marg,

Zafar

New Delhi- 110002 37. B.L.

Tikoo

Addl. Director General, Dte. General Border

Roads, Seema Sadak Bhavan, Ring Road, Delhi Cantt, 38.

The Director (R&D)

(Dr.

New Delhi-

1 1

00 1

A.K. Bhatnagar), Indian Oil Corporation

R&D

Ltd.,

Centre,

Sector

13,

Faridabad-121007 39.

The

Director,

HRS

(V. Elango)

,

Highways Research

Station,

P.B. No. 2371, 76, Sardar Patel Road,

Chennai-600025 40.

The Director General of Works Engineer-in-Chief s Branch, AHQ, Kashmir House, Rajaji Marg,

Ex-Officio 41. President,

Indian Roads Congress

New Delhi-

1

1001

Members M.V.

Patil

Secretary (Roads),

Maharashtra P.W.D., Mantralaya, 42.

Mumbai-400032

Kumar

Hon. Treasurer,

Prafulla

Indian Roads Congress

Director General (Road Dev.)

&

Addl.

Secretary to the Govt, of Irdia, Ministry of

Road Transport New Delhi

(iv)

&

Highways,

IRC:SP:58-2001

G. Sharan

43. Secretary,

Indian Roads Congress

Chief Engineer, Ministry of Road Transport

&

Highways,

New Delhi Correspond ing

1.

Prof.

C.E.G. Justo

Members

Emeritus Fellow, 334, 25th Cross, 14thMain,

Banashankari 2nd Stage, Bangalore-560070 2.

I.J.

Mamtani

Chief Engineer, Lajpat Nagar-III,

3.

N.V. Merani

MOST

(Retd.), G-58,

New Delhi- 110024

Principal Secretary, Maharashtra (Retd.),

PWD

A-47/1344, Adarsh Nagar, Worli,

Mumbai-400025 4.

Prof.

N. Ranganathan

Head of Deptt. of Transportation Pig., SPA Consultant, 458/C/SFS,

(Retd.),

Sheikh Sarai 5.

Prof.

C.G. Swaminathan

k

Badri\

6,

I,

New Delhi-

1 1

Thiruvengandam

R.A. Puram, Chennai-600028

(v)

00 1 Street,

IRC:SP:58-2001

BACKGROUND The Geotechnical Engineering Committee in its first meeting held on

1

draft for

5.7.97 requested

Use of Fly Ash

in

CRRI (Shri

A.V.S.R. Murty) to prepare

Road Embankments. The draft prepared

by Shri A.V.S.R. Murty was discussed by the Committee in its meeting held on

1

5.5.98.

During the meeting, few corrections/modifications

suggested by the members were carried out. The Committee in

its

meeting held on 22. 1 0.99 formed a Sub-group consisting the following to look into the draft.

The Sub-group held its meeting on 26. 1

1

.99

and

approved the draft for placing before the Geotechnical Engineering

Committee (H-3): 1.

Sanjay Gupta

Member-Secretary/Coordinator

2.

K.N. Agarwal

Member

3.

A.P.S. Sethi

Member

4.

S.K. Soni

Member

5.

Deep Chandra

Member

6.

U.K. GuruVittal

Member

7.

A.K. Mathur

Member

8.

Arun Kumar Sharma

Director (T),

below)

IRC

The Geotechnical Engineering Committee (Personnel given meeting held on 6. 2.99 approved the draft.

in its

1

Dr. Gopal Ranjan

Convenor

Sanjay Gupta

Member-Secretary

Members Dr. U.N. Sinha

Dr. A. Vardarajan

A.V. Sinha

S.I.Patel

Lt.Col.V.K.Ganju

A.K. Chakrabarti

1

IRC:SP:58-2001

Ashok Wasan

S.B.

Sukomal Chakrabarti

Vinod Kumar

Basu

I.C.Goel

P.J.Rao

M.R. Dighe

CE(R) S&R, MORT&H (C.C. Bhattacharya)

Dr.

V.M. Sharma

CE,

Hill

Zone,

Lucknow Ex-Officio

President,

Members

DG(RD) & Addl.

IRC

(K.B. Rajoria)

(Prafulla

Secretary, (S.C.

Secretary,

MORT&H

Kumar)

IRC

Sharma)

Corresponding Members

Dr.

M.R. Madhav

K.B. Rajoria Dr. B.V.S. Viswanathan

the members of the Highways (HSS) Committee in its meeting held on 21.1 2.99. During the meeting, it was decided that the details of some recently completed projects should be removed and then the document be recirculated to this Committee. The draft was discussed in newly constituted HSS Committee members and was discussed during the meeting held on 22.8.2000. After detailed discussions, the draft was approved by the Committee and authorised the Convenor, Geotechnical Engineering Committee to modify the draft in light of the comments of members. The modified draft submitted by Convenor, Geotechnical Engineering Committee was approved by Convenor, HSS Committee and later by the Executive Committee in its meeting held on the 30 August, 2000. The draft was approved by Council in its 160 Meeting held at Kolkata on 4. 1 1 .2000.

The

draft

was discussed by

Specifications and Standards

th

th

The contributions from Central Road Research Institute and Fly

Ash Mission, Department of Science and Technology, Govt, of

India, are

acknowledg 2

IRC:SP:58-2001

1.

INTRODUCTION

Due to industrialisation and rapid economic growth, 1 1 demand for electricity has risen tremendously. To meet this demand, a number of coal based thermal power plants have been set up. At present, in India thermal power plants produce about 90 million .

tonnes of fly ash per annum, and hardly 1 3 per cent of it is utilised. 1

When pulverised

.2

coal

is

burnt in the furnace of the

power stations, about 80 per cent of the ash produced is very fine nature. This part gets carried along with flue gases

by using

and

is

in

collected

either electro-static precipitator or cyclone precipitator.

The remaining ash sinters and falls down at bottom of the furnance. This is known as bottom ash. Fly ash may be disposed in dry form (in ash mounds or through water slurry in a pond. When fly ash and bottom ash are mixed and disposed in the form of water slurry to ash ponds, it is called pond ash. For the purpose of embankment construction either pond ash, bottom ash or mound ash can be used. Fly ash being a very fine material is not recommended for embankment construction. However, it may be noted that the term "fly ash" is commonly used as a generic term to denote any type of coal ash. For the purpose of these guidelines the term fly ash would denote Pond Ash/Bottom Ash/Mound Ash, which are to be used for embankment construction. This

is

called fly ash.

the

causing environmental pollution, creating health hazards and requires large areas of precious land for disposal. Due to increasing concern for environmental protection and growing awareness of the ill effects of pollution, disposal of ash generated at thermal power plants has become an urgent and challenging task. Fly ash can be utilised in many ways as shown through extensive efforts as well as field demonstration. But bulk utilisation is possible in the field of civil engineering applications especially construction of road embankments. Typically, in developed urban and industrial areas, natural borrow sources are scarce, expensive or inaccessible. The environmental degradation caused due to the use of topsoil for embankment 1

.3

Fly ash

is

R&D

construction

is

very high. Moreover,

situated in urban areas,

and therefore,

many power fly

environmentally preferable alternative to natural borrow 3

plants are

ash can provide an soil.

|RC:SP:58-2001

1

coal,

its

The properties of fly ash vary depending upon type of

.4.

pulverisation and combustion techniques, their collection and

disposal systems, etc.

Ash

exhibit different physical

of collection, depth,

collected from the

same ash pond may

and engineering properties depending on point

etc.

Obviously, ash from two different thermal

power plants can be expected to have different properties. These factors can be easily taken care during characterisation, design and quality control operations during construction. In spite of variations in

its

properties, fly ash possesses several desirable characteristics, such as,

lightweight, ease

of compaction,

faster rate

of consolidation, etc. Also,

spreading and compaction of fly ash can be started

comparison to soil for construction

after a rainfall.

1

.

Fly ash would be a preferred material

of embankments over weak subsoil.

2.

2.

much earlier in

SCOPE

These guidelines provide

salient details regarding

design and construction of road embankments using fly ash.

The Indian

Roads Congress (IRC) and Ministry of Road Transport & Highways (M/o.

RT4H) specifications for earthen embankments can be broadly

applied in general for construction of fly ash embankments. In case of

any deviations, these specifications will take precedence.

3.

3.1. to

DESIGN CONSIDERATIONS

The design of fly ash embankments is basically similar

design of soil embankments. The design process for embankments

involves the following steps: •

Site investigations



Characterisation of materials



Detailed design

The design of embankment is an

iterative process.

developing conceptual plans, which satisfy 4

It

involves

site needs, design

IRC:SP:58-2001 requirements pertaining to slope stability, bearing capacity, settlement

and drainage. These conceptual designs are finalised based on the engineering properties of fly ash and specific

site conditions.

Site Invesigations

3.2.

The following information concerning the site and surrounding areas

must be collected:



Topography: The existing configuration of the proposed developments, topographic information determining



fill

site

is

essential for

volumes, surface drainage and overall

site layout.

Hydrology: The nature of existing and potential development of surface water and ground water conditions, flooding



and the

if expected.

Subsoil investigations: The nature and extent of soil and rock strata,

which influence

the design,

and performance of project.

For detailed procedure on carrying out

site investigations,

1RC:36-1970 may be referred. Characterisation of Materials

3.3.

The materials to be used

in

embankment construction should

be characterised to determine their physical and engineering properties. In certain specific situations,

as detailed in sections 3.3.

1

chemical properties

.8 to 3.3.

1

.

1

may be of relevance

0. Suitability

of the material

and design parameters are obtained through characterisation tests.

3.3.1.

Flyash

3.3. 1.1.

The following information on the

should be

made

fly

ash to be used,

available for the Engineer's approval before

5

IRC:SP:58-2001

commencement of work: Particle size analysis

1.

of the material

The maximum dry density (MDD) and optimum moisture content

2.

(OMC)

as per IS

modified proctor

Heavy Compaction test),

moisture content, for

3.3.1.2.

information,

ash

is

1

it

Once

shall

test

(commonly known

as

and the graph of density plotted against

this test

2 .

the Engineer has approved the above

form the basis

The density of fly

for compaction.

considerably lower than density of many types of soils. So, unlike

soils, fly

using

it

ash with low

as a

fill

MDD value should

not be rejected for

material. However, in general, fly ash of density

lower than 0.9 gm/cc may not be suitable for embankment construction.

The design parameters should be rechecked, when densities

is

3.3.

1

.3.

in

accordance with the procedures

IS:2720 (Method of Tests for Soils-relevant •

ash of lower

To determine engineering properties of fly ash, tests

be earned out

shall

fly

encountered.

laid

down in

parts).

Shear strength parameters, for evaluation of the

stability

of proposed

slopes and the bearing capacity of foundations located on the •

Compressibility characteristics, for predicting the magnitude and duration of the



fill.

fill

settlement.

Permeability and capillarity are required to assess seepage and to

design drainage systems.

3.3.1.4. The design analysis of an engineered fill or embankment requires the shear strength of fill material to be determined.

by conducting triaxial shear or direct shear test. Shear strength is affected by sample density and moisture content. To determine shear strength parameters c and This

is

accomplished

in the laboratory

4

1- IS:2720(Part4):1985

2- IS:2720(Part8): 1983

6

IRC:SP:58-2001

laboratory shear strength tests should be conducted on samples

compacted to densities equivalent to those expected to be attained the

in

field.

3.3.

1

.5.

consolidation

is

Fly ash gets consolidated

at

completed very quickly. So

a faster rate and primary

it

has low compressibility

and shows negligible post construction settlements.

3.3.1

.6.

Liquefaction generally occurs when fly ash

is

deposited

under loose saturated condition during construction.There is very little possibility

of liquefaction to occur, when

construction, as the material

optimum moisture content,

is

fly

ash

is

used

in

embankment

compacted to maximum dry density at

i.e.,

under partially saturated condition. In

regions of moderate to high seismic activity, analysis of embankment stability

should consider liquefaction potential of the ash

fill.

To avoid

the possibility of any liquefaction to occur, the following precautions

maybe taken: • Proper compaction of the • In case water table

is

fill

high,

it

material as per specifications

should be lowered by providing

suitable drains or capillary cut-off



By sandwiching

3.3.1

.7.

ash between intermediate horizontal soil layers.

Typical values for different geotechnical properties

of fly ash are given

in

Table

1

properties as given in Table

for guidance. In general fly ash with 1

are acceptable for

construction.

7

embankment

IRC:SP:58-2001

Table

1.

Typical Geotechnical Properties of Pond Ash

Parameter

Range

opccinc vJIavliy

i.yu —z.j j

Mid ct~i r*i"t"\/ \yiQviTYiiifn IVlaXlIIlUIIl

Non-Plastic

Uiy I

i

y\ j

cif\/ L-JCIlMiy I

j/^

t

no

mri/r^r* i ^glll/CC^ i

Optimum Moisture Content (%) Cohesion (kN/m

1

38.0-18.0

2

Negligible

)

Angle of Internal Friction

30°- 40°

(cp)

Coefficient of Consolidation

C

1.75 x 10

v

5

-

2.01 x 10

3

(cmVsec)

Compression index

C

0.05-0.4

c

Permeability (cm/sec) Paritcle Size Distribution

Clay

8xl0"

-7x

10"

4

(% of materials)

size fraction

Silt size fraction

Sand

6

size fraction

Gravel size fraction Coefficient of Uniformity

1-10 8-85 7-90 0-10 3.1- 10.7

3.3.1.8. The chemical characteristics of fly ash, which need be evaluated, are pozzolanic property, leachability and selfhandening characteristics. The pozzolanic property of fly ash would be of importance if stabilisers, like, lime are used. Selfhardening property of bituminous coal ashes is insignificant. Fly ash to be used as fill material should not have soluble sulphate content exceeding 1 .9 gm (expressed as S0 ) per litre when tested

to

3

according to BS: 1377 Test 10 but using a 2:1 water-soil

mm

ratio.

(or other be deposited within 500 distance prescribed by the Engineer) of concrete, cement bound materials and other cementitious material or metallic surface forming part of permanent works. Generally, Indian fly ashes are found to be safer on this parameter. For details, MOST Specifications for Road and Bridge Works, Section 305.2 may be

Otherwise,

it

shall not

referred.

8

IRC:SP:58-2001

The primary environmental concern regarding use of fly ash for embankments would be contamination of ground and surface water due to heavy metal leaching. But it may be noted that most fly 3.3.1.9.

ashes are relatively

inert.

Moreover, coal used

in Indian

thermal power

As a result, enrichment of heavy metals is lower compared to fly ash produced by thermal power plants abroad. Studies have shown that even though constituents in fly ash particle may dissolve initially but retention by weathered fly ash residues reduces plants have high ash content.

the possibility of their migration into ground water.

3.3.1.10.

The leaching problem can be minimised by controlling

the amount ofwater, which infiltrates into fly ash embankment. Normally,

percolation of water into the fly ash core will be

minimum when sides

and top are protected using good earth. Further, by providing impervious wearing course to the pavement constructed over the embankment seepage can be minimised. Side slopes should be properly benched and protected with soil cover with vegetation or soil cover with stone pitching. Monitoring of fly ash embankments has indicated that relatively little water tends to percolate through the complete embankment. Even in such a case, the alkaline nature of the fly ash-water solution

restricts

heavy metal leaching.

The fly ash embankments 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 3.3.2.

Earth cover

material for fly ash

:

embankments. Gravel may be used

to construct

granular cut-off at the bottom. These materials are to be tested as per

MOST Specifications for The soil used 1

.52

for cover

fill

materials used in

should not have

embankment construction.

maximum dry density less than

gm/cc when height of embankment

is

upto 3

subjected to extensive flooding, otherwise the

cover soil should not be

less than

1

.6

m and in areas not

maximum dry density of

gm/cc when

tested according to

IS:2720(Part 8)- 1983. Subgrade/earthen shoulder material should 9

IRC:SP:58-2001

have

minimum compacted dry density of 1 .75 gm/cc when tested

according to IS: 2720 (Part 8)- 1983. Plasticity index of cover should be between 5 to 9 per cent

soil

when tested according to IS: 2720

Chemical analysis or determination of deleterious constituents would be necessary in salt-infested areas or when presence of salts is suspected in the borrow material. Expansive soils should not (Part 5)- 1985.

be used for construction ofcover, unless it is properly stabilised using lime.

Detailed Design

3.4.

The detailed design includes analysis for establishing of the embankment at the selected site. The design of fly ash embankment is similar to earthen embankments. However, 3.4.1.

structural features

special

emphasis

is

required with respect to provision of earth cover

embankments since ash is easily erodable. The thickness of side cover (measured horizontally) would be typically in the range of 1 to 3 m. Height and side slope of the embankment govern the thickness of earth cover. For embankment upto 3 m height, in general, the earth cover thickness of about 1 m would be sufficient. For high embankments and for embankments to be constructed in flood prone areas, the cover thickness may be increased. The side cover should be regarded as a part of embankment for design analysis. The embankment would, for fly ash

therefore,

be designed as a composite structure with

and earth cover on the sides. Well-compacted shear strength so that the horizontal to

1

fly

ash in the core

ash attains sufficient

embankment can be constructed with 2

vertical side slope. This should

stability analysis for

3.4.2.

fly

be confirmed through

each project.

The three most common types of failure ofembankment

are toe failure (occurring

when

foundation soil

material), slope failure (occurring in a layered

is

stronger than

fill

embankment when a

strong layer limits the extent of development of failure surface) and

base failure (occurring when the foundation soils beneath the base of

embankment have low strengths). Regardless of the type of failure, the basic principle of stability analysis is to compare those factors contributing to instability to those resisting a failure. The design methods the

10

IRC:SP:58-2001

use limit equilibrium method for stability analysis of embankment. In this

method,

stability is

considered along a failure surface. Generally in

the slip circle method failure plane is assumed to be circular.

A particular

minimum factor of safety. For more details on stability analysis, IRC:75-1 979 may be referred.

critical circle

gives the

3.4.3.

the critical circle

Calculation of factor of safety of different circles until is

located

is

a very time consuming process. Computer

programme provides quick solution. Using a computer, different types of embankment cross-section can be quickly analysed and proper cross-section can be selected. The software for stability analysis of high embankments available with the Indian Roads Congress, approved by Ministry of Road Transport & Highways, Government of India, can be used for design of fly ash embankments. This computer programme is based on the 'Simplified Bishop Method'. The sliding earth mass is divided into a number of slices. The factor of safety is determined by comparing a sum of activating moments and resisting

moments of all the slices. 3.4.4.

It

is

recommended

that factor

of safety for

embankments constructed using fly ash should not be less than

1

.25

under normal serviceability conditions and when checked for worst combination under seismic and saturated conditions, it should not be less than 1.0.

3.4.5.

ash

Intermediate soil layers are often provided in the fly

embankment for ease of construction, to facilitate compaction of

ash and to provide adequate confinement. Such layers minimise liquefaction potential also.

can be adopted

Embankment with intermediate soil layers of the embankment is more than 3 m.

in case height

The compacted thickness of intermediate soil layers shall not be less than 200 mm. One or more layers shall be constructed depending upon the design requirements. The vertical distance between such layers may vary from 1 .5 to 3 m. The top 0.5 m of embankment should be constructed using selected earth to form the subgrade for the road

pavement. Typical cross-sections of fly ash embankment with and without intermediate soil layers are shown in Figs. 1 and 2 respectively. 11

IRC:SP:58-2001

Ground Level

Fig.

1.

Embankment Layer of Fly Ash and Soil

Typical Cross-Section of Alternate

with

Granular Layer 0.5

Selected Earth Cover

m (minimum) 1

to 3

m

Natural

Ground

level

Fig. 2.

Typical Cross-Section of Embankment with Core of Fly Ash

12

IRC:SP:58-2001

Properly benched and graded slopes prevent the

3.4.6.

erosion of fly ash particles. Fly ash at

4 to 6

embankments should be benched

m vertical intervals to drain surface water run-off to the ends

of the embankment, rather than allowing travel

down

pavement

the face of the

volume of the run-off to

full

embankment

to the toe.

Run-off from

surfaces should be collected and discharged into proper

drainage system. For more details regarding drainage aspects,

IRC:SP: 50-1 999

may be referred.

CONSTRUCTION OF FLY ASH

4.

EMBANKMENTS 4.

1

Clearing and Grubbing

.

This work consists of cutting, removing and disposal of trees, bushes, shrubs, roots, grass, rubbish,

the area of road land drains,

which

will

etc.,

from the alignment and within

accommodate road embankment,

and such other areas as specified on the drawi

lgs.

During clearing

and grubbing, the contractor shall take adequate precautions against soil erosion, fill

water pollution,

etc.

All trees, stumps,

area should be cut to atleast 500

shall

be

filled

etc., falling

within

mm below ground level and pits

with suitable material and compacted thoroughly so as to

make the surface at these points conform to the surrounding area. Stripping and Storing of Top Soil

4.2.

When constructing embankment using fly ash, the top soil from all

areas to be covered

by the embankment foundation should be

stripped to specified depth not exceeding piles

1

50

of height not exceeding 2 m, for use

embankment re-vegetation

slopes, cut slopes

is

desired.

mm and stored in stock

in

covering the

fly

ash

and other disturbed areas where

Top soil should not be unnecessarily trafficked when in stockpiles. Also, these shall not be

either before strippingor

surcharged or otherwise loaded and multiple handling should be kept to

minimum. 13

IRC:SP:58-2001

Out

Setting

4.3.

After the site has been cleared, the limits of embankment should

be

set

out true to lines, curves, slopes, grades and sections as

shown

on the drawings. The limits of the embankment should be marked by fixing batter pegs on both sides at regular intervals as guides before

commencing sufficiently

the construction.

The embankment should be

built

wider than the design dimensions so that surplus material

may be trimmed, ensuring that the remaining material is of the desired density and in position specified, and conforms to the specified slopes.

Bench marks and other stakes should be maintained as long as

in the

opinion of the engineer, they are required for the work.

Dewatering

4.4.

If the foundation

of the embankment is in an area with stagnant

it is feasible to remove it, same should be removed by pumping or any other means as directed by the Engineer, and the area of the embankment foundation should be

water, and in the opinion of the Engineer the

kept dry. Care should be taken to discharge the drained water so as

not to cause

damage

to

works, crops or any other property.

Construction of embankments underwater logged conditions shall be

governed by provisions of IRC:36- 1970. 4.5.

Compacting the Ground Supporting Embankment

4.5.1.

Where

levelled, scarified,

as to achieve (Part 8)- 1 is

necessary, the original ground should be

mixed with water and then compacted by rolling so

minimum 97 percent of MDD determined as per IS:2720

983

high and the

for the foundation soil. soil

At locations where water table

has potential for rapid and relatively great migration

of moisture by capillarity, a granular layer, impervious membrane or a barrier

of approved medium

shall

able to rise to the subgrade level.

over

full

cut-off.

be inserted so that moisture

is

not

Sand blanket of adequate thickness

width of embankment can be adopted as an effective capillary

Medium grained sand can be used

for this purpose. This will

provide a working platfonn for the construction of fly ash 14

fill

and function

IRC:SP:58-2001

Provision of geotextile separating layer

as capillary cut-off.

between drainage blanket and

fly

ash will help the drainage

blanket to function efficiently and prevent intrusion of fly ash into

drainage blanket. Drainage blanket can be nominally compacted

with or without vibration. Bottom ash can also be used for construction of drainage blanket.

Its

grain size distribution

generally compatible with the grain size distribution of

is

medium

grained sand. Further guidance regarding capillary cut off design

and

its

'Recommendations

from IRC:34-1970, Road Construction in Water Logged

can

provision

for

be

obtained

Areas'.

4.5.2.

material

Where

occurring

by the Engineer, any unsuitable the embankment foundation shall be

so directed

in

removed and replaced by approved materials required

degree

specified for

of compaction.

embankment

Any

laid in layers, to the

foundation

especially high

treatment

embankments, resting

on suspect foundations

as revealed by borehole logs should be manner to the depth required. The depth of boreholes should be related to the height of embankment to be

carried out in a suitable

constucted.

4.6

Handling and Transportation of Fly Ash

4.6.1

Pond ash

is

typically delivered to the site in

covered dumper truck to minimize loss of moisture and dusting.

Pond ash generally contains enough moisture and may even contain excess moisture

to prevent dusting

to create

road spillage

during transport. In such cases, periodic inspection and

lifting

ash from relatively dry areas of the pond would be needed.

15

of

IRC:SP:58-2001

The fly ash may require on site temporary stockpiling if the rate at which the ash is supplied to the project site is more than the contractor's demand for an efficient rate of placement. Such cases 4.6.2.

should be avoided to the extent possible, and is

inevitable, adequate precautions should

by spraying water on stockpiles surface of the fly ash stockpile layer

at

in

case stockpiling

be taken

to prevent dusting

regular intervals. Otherwise, the

may be covered with tarpaulins or a thin

of soil or other granular material not subject

to dusting. Traffic

movements may be restricted to those areas which

are kept moist, to

prevent tyres of passing vehicles dispersing ash into the

air.

Spreading and Compaction

4.7.

4.7.

at site

1

.

The side soil cover of required width shall be provided

along with the core and mechanically compacted as the embankment

progresses upwards. The addition of side cover subsequent to the construction of the core

is

prohibited.

The fill

material should be spread

by mechanical means, finished by motor grader. The motor grader blade shall have hydraulic control so as to achieve the speci fied slope

and grade. The most

efficient

lift

thickness

and vibratory energy. Smaller vibratory

is

of roller weight

a function

rollers

with dead weights of

kN perform well on loose layer thickness of the order of 00-1 50 mm. Medium weight vibratory rollers with dead weights in

10 to 15 1

the range 60- 1

00 kN, provide

thickness of about 250 1

00

kN

satisfactory

compaction

are used, loose layer thickness upto

if site trials as

for loose layer

mm. When vibratory roller of dead weight 80-

explained

in section 4.7.3

400

mm can be adopted

show satisfactory compaction.

When compaction is earned out using only static roller of 80- 00 kN weight, loose layer thickness shall not exceed 200 mm. The cover soil 1

and

fly

ash should be laid simultaneously before compaction, to ensure

confinement of fly ash. Clods or hard lumps to

have a maximum

size

of 50 mm.

16

in

cover soil shall be broken

IRC:SP:58-2001

Moisture content of the

4.7.2. at the site

of placement prior

fill

material shall be checked

commencement of compaction.

to

Moisture content of fly ash laid for compaction shall normally vary

from

OMC (determined as per IS: 2720 (Part 8): 1983 to OMC ± 2

The moisture content limits can be varied depending on the weather conditions, by the Engineer-in-charge, provided specified

per cent.

compaction is

is

achieved as revealed through actual

no dust problem.

It

site trials

and there

may be noted that grain shape and particle size

of fly ash make the upper layers

difficult to

compact. At moisture

contents higher than the appropriate range, fly ash

may liquefy and

would be difficult to handle and compact. Moisture content of cover soil shall

be maintained

added to the

fill

material,

at its it

OMC. Where water is required to be

shall

be sprinkled from a water tanker fitted

with a sprinkler capable of applying water uniformly without any flooding.

The water shall be mixed thoroughly by blading, discing or

harrowing or by suitable means until uniform moisture content is obtained

throughout the depth of the layer. If the material delivered to the construction site to sun,

till

too wet,

it

shall

the moisture content

4.7.3. rollers.

is

is

acceptable for compaction.

Fly ash can be compacted using vibratory or static

Towed or self-propelled vibratory rollers are recommended.

Regardless of the equipment used, as possible after spreading. efficacy trials.

be dried by aeration and exposure

fly

ash must be compacted as early

The contractor

shall

demonstrate the

of the equipment he intends to use by carrying out compaction

The procedure to be adopted

for these site trials shall

submitted to the Engineer for approval.

be

first

The use of test strips to develop

compaction method specifications (optimum compaction procedure to satisfy density requirements) for the construction is

of the embankment

advisable. Typically several test areas are developed

of compaction parameter (such

trials

can be conducted. In such

as, lift thickness,

moisture content,

time while the others remain constant. 17

where a series

trials,

usually one

etc.) is

varied at a

IRC:SP:58-2001

4.7.4.

Each layer of fly ash shall be thoroughly compacted to

the specified density.

When vibratory roller is adopted for compaction,

two passes without vibration followed by 5

to 8 passes

with vibration

Mass per metre width of roller is recommended to be 2300-2900 kg/m and frequency range 1 800-2200 rpm. The construction of fly ash core and earth cover on would be sufficient to compact individual

layers.

the sides should proceed simultaneously. 4.7.5.

Each compacted layer shall be finished parallel to the

final cross-section

of the embankment. The following end product

specifications as given in Table 2,

have been suggested for construction

of fly ash embankments. Table

2.

Specifications for Compaction

95%

Minimum dry density after compaction as percentage of

MDD IS:2720 (Part 8)- 1983 100%

Minimum dry density after compaction when used in bridge abutments - for

embankment

times the height of the

embankment

4.7.6.

length equal to

.5

1

At locations where compaction of the ash

impracticable using rollers, such as,

fill

fill/earth is

portions adjacent to

structures/steep abutments or around concrete drainpipes in

embankment, hand held vibratory tampers

shall

masonry

embedded

be used for

compaction. The required moisture contents and compaction requirements shall be same, as for the rest of the embankment, however,

compacted layer thickness should not exceed 100 mm 4.7.7.

in

such cases.

The Engineer may permit measurement of field density

according to agreed procedure. Subsequent layers shall be placed only after the finished layer has

been tested

for

its

density requirements.

The contractor shall maintain record of all such tests. When density neasurements reveal any soft areas in the embankment, further 18

IRC:SP:58-2001

compaction shall be carried out as directed by the Engineer. In spite of that if specified degree

ofcompaction is not achieved, the material

removed and replaced by approved

the soft areas shall be

in

material,

moisture content brought to permissible limits and recompacted to the required density.

Embankment shall be constructed evenly over their full

4.7.8.

width and the contractor

shall control

and

direct construction plant

Damage by the construction plant or other vehicular traffic shall be made good by the and other vehicular traffic uniformly across the width.

contractor with material having the

same characteristics and

strength

as it had before it was damaged. Embankments shall not be constructed

with steeper side slopes or to greater width than those shown drawings.

in the

Whenever embankment construction is to be taken up against

the face of natural slope or sloping earth

embankments,

cuttings,

(Vertical: Horizontal),

and excavations which are steeper than

1

:4

such faces shall be benched immediately before

placing the subsequent

fill.

A less permeable capping layer of selected

earth should be constructed

would form the subgrade

on the top of fly ash embankment, which

for the road

layer should not be less than

pavement. The thickness of this

500 mm.

Precautions Against Corrosion

4.8.

4.8.

works face including

1

.

The sulphate content

limits specified in section 3.3.

1 .8.

in fly

ash should be within the

The sulphate content of fly ash may

sometimes cause concern about possibility of sulphate attack on adjacent concrete structures. While no reported failures have occurred, certain precautions are advisable, in case sulphate attack on concrete structures is

suspected. These consist of painting the adjacent concrete faces

with bitumen or compounds, which offer moisture protection to concrete. Corrosion of cast iron, lead, copper, 19

PVC

or terra cotta

IRC:SP:58-2001

pipes would be

minimum due to contact with fly ash. There have been

reported failure of aluminium conduit materials buried in fly ash. If protection of pipes

is

necessary, polythene sheeting, bituminous coating

or embedding and backfilling with inert materials,

like, suitable soil

of

minimum cushion thickness of 500 mm shall be adequate. 4.8.2.

Where signi ficant volumes of seepage are encountered,

pipes should be used to drain the water out of the Perforated pipe

is

embankment area.

usually placed in the vicinity of seep. One-third solid

wall pipe with two-third slotted portion can be used to drain the water

out of embankment area.

PVC or ABC pipe materials are preferred

because of their long-term performance. Analysis should be perfonned to

confirm that they provide adequate wall strength to support the

expected embankment loads. filter

To prevent the internal erosion of the fill,

protection should be provided around the pipes.

4.9.

Finishing Operations

Finishing operations shall include the

work of shaping and

dressing the shoulders/verge/road bed and side slopes to conform to the alignment, levels, cross-sections and dimensions

shown on

the

drawing or as directed by the Engineer subject to the tolerance. Both upper and lower ends of side slopes

shall

be rounded off to improve

appearance and to merge the embankment with the adjacent In case turfing

is

terrain.

proposed, top soil should be provided so that after

seeding, a dense cover can develop.

The depth of top

soil

should be

sufficient to sustain plant growth, the usual thickness being 75 to

mm.

1

00

Slopes shall be roughened and moistened slightly before the

application of top soil in order to provide satisfactory bond.

Embankments constructed

in flood

prone areas should be protected

by stone pitching as per the provisions of IRC:89-1 985. 20

IRC:SP:58-2001

5.

5.1

QUALITY CONTROL

Quality of compacted material shall be controlled

.

through periodic checks on the compaction process or the end product, singly or in combination as directed. The end product must conform to the specifications.

Control Test on Borrow Material

5.2.

If fly ash from more than one source is being used at monitoring must be done to identify the ash type being placed. The tests required to be conducted on fly ash to be used as borrow material for embankment are indicated below. The frequency

5.2.1.

the project

site,

of testing indicated refers to the minimum number of tests to be conducted. The rate of testing must be stepped up as found necessary, depending on the compaction methods employed at the project. •

IS

Heavy Compaction

3000 •

m

3

Test:

At the

of ash, as per IS:2720 (Part

Moisture Content:

One

test for

rate 8)-

1

of 2

tests

per every

983

every 250

m

3

of ash, as per

IS:2720(Part2)-1973.

5.2.2. The samples collected for testing moisture content should be representative of the material being placed. Because fly ash may air dry relatively rapidly, samples should not be taken from the surface of the lift, but should represent the overall moisture content.

Analysis and Acceptance of Density Results

5.3.

Control shall be exercised on each layer by taking at least one measurement of density for each 1000 square metres of 5.3.

1

.

compacted area, or closer as required to

yield the

minimum number of

evaluating a day's work on statistical basis. The determination of density shall be in accordance with IS:2720 (Part 28)- 1974. Test locations shall be chosen by random sampling technique. The number of tests to be conducted and acceptance criteria shall be as outlined in MOST Specifications for Road and Bridge Works, Section 900. test results for

21

IRC:SP:58-2001

REFERENCES 1.

2.

IS:2720 (Part 2)- 1973, Methods of Test for Soils - Determination of Water Content, Bureau of Indian Standards, New Delhi. IS:2720 (Part 4)- 1 985, Methods of Test for Soils - Grain Size Analysis, Bureau

of Indian Standards, 3.

4.

IS:2720 (Part 5)- 985, Methods of Test for Soils-Determination of Liquid and Plastic Limits, Bureau of Indian Standards, New Delhi. 1

IS:2720 (Part 8)- 1983, Methods of Test for Soils - Determination of Water Content-Dry Density Relation Using Heavy Compaction, Bureau of Indian Standards,

5.

New Delhi.

IS:2720 (Part 28)-1974, Methods of Test for Soils - Determination of Dry Density of Soils in Pace, by Sand Replacement Method, Bureau of Indian Standards,

6.

New Delhi.

New Delhi.

IS:2720 (Part 29)- 1977, Method of Test for Soils - Determination of Dry Density of Soils in Pace, by Core Cutter Method, Bureau of Indian Standards,

New Delhi. 7. 8.

BS: 1377-1975, Methods of Tests for Soils

Engg. Proposes.

IRC:34-1970, Recommendations for Road Construction Areas, Indian Roads Congress,

9.

in Civil

in

Water Logged

New Delhi.

IRC:36-1970, Recommended Practice for the Construction of Earth Embankments for Road Works, Indian Roads Congress, New Delhi.

10.

IRC:75- 1 979, Guidelines for the Design of High Embankments, Indian Roads Congress, New Delhi.

11.

IRC:89-1985, Guidelines for Design and Construction of River Training and Control Works for Road Bridges, Indian Roads Congress, New Delhi.

12.

IRC:SP:50- 1 999, Guidelines on Urban Drainage, Indian Roads Congress,

New Delhi. 13.

14.

IRC Highway Research Board Special Report 16, 'State-of-the-Art: Reinforced Soil Structures Applicable to Road Design and Construction, Indian Roads Congress, New Delhi, 1996. Ministry of Surface Transport, (now Ministry of Road Transport & Highways), Government of India, 'Specifications for Road and Bridge Works', 1995.

15.

Fly

Ash Mission, Department of Science

& Technology,

India, Technical Reports on Characterisation by IISc, Bangalore), 2000. 16.

Government of of Indian Fly Ashes, (Prepared

Electric Power Research Institute, California, 'Fly Ash Design Manual Road and Site Applications'(Prepared by GAI Consultants), 992.

for

1

17.

CRRI

Project Reports on Okhla Flyover Project and Second Nizamuddin Bridge Approach Embankment, Central Road Research Institute,

New Delhi,

1999.

22

HI

i

1

mam

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