Indian Roads Congress Special Publication 58
GUIDELINES FOR USE OF FLY ASH IN
NEW DELHI 2001
cigitized by the Internet Archive in
Indian Roads Congress Special Publication 58
GUIDELINES FOR USE OF FLY ASH IN ROAD
THE INDIAN ROADS CONGRESS
Copies can be had from
The Secretary, Indian Roads Congress Jamnagar House, Shahjahan Road,
NEW DELHI 2001
Price Rs. 120.00 (plus packing
August, 2009 (Incorporated
- March, 2009)
(Rights of Publication
and Translation are reserved)
Printed at India Offset Press,
Delhi- 1 10064
GUIDELINES FOR USE OF FLY ASH IN ROAD
EMBANKMENTS CONTENTS Page Personnel of Highways Specifications
& Standards Committee Background
Construction of Fly Ash Embankments
PERSONNEL OF HIGHWAYS SPECIFICATIONS AND STANDARDS COMMITTEE (As on 22.8.2000)
Director General (Road Dev.)
Bha van, New DelhiS.C.
Secretary to the Govt, of India, Ministry of
Highways, Transport 1 1
& Highways, Transport Bhavan,
New Delhi- 110001 3.
The Chief Engineer (R) (
Highways, Transport 1 1
Engineer- in-Chief (Retd.), House No. 40, Sector
Chief Engineer (ReU.), Highways
Works Department., No. 7, Ashoka Avenue, Kodambakkam, Chennai-600024 6.
Dr. R.K. Bhandari
S&T Affairs Directorate,
Council of Scientific
& Industrial Research,
New Delhi- 110001 7.
Chief Engineer (Mech.), Ministry of Road, Transport
New Delhi-1 10001 8.
DG(RD) (Retd.), E-44, Greater Kailash Part-I Enclave,
New Delhi-1 10048
Chief Engineer-cum-Officer on Spl. Duty with Public
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)
Dr. L.R. Kadiyali
Chief Executive, L.R. Kadiyali
C-6/7, Safdarjung Dev. Area, Opp. IIT Main Gate,
New Delhi- 110016
Chief Engineer, Ministry of Road Transport
Chief Engineer-cum-Addl. Secy, to the Govt,
of Rajasthan, P.W.D., Jacob Road, Jaipur-302006
Chief Engineer, Maharashtra State Road
Dev. Corpn. Ltd., Nappean Sea Road, Mumbai-400036 14.
Engineer-in-Chief-cum-Secy. to the Govt, of
Bhubaneswar-751001 15. S.I,
Chief General Manager, National Highways
Authority of India,
Maharani Bagh, New Delhi- 1 1 0065 16.
(Roads), Maharashtra P.W.D.,
Mantralaya, Mumbai-400032 17.
Engineer-in-Chief, Delhi P.W.D. (Retd.), C-II/32,
Moti Bagh, New Delhi- 1 1003
Director, College of Engg. Roorkee, 27th
Roorkee-Hardwar Road, Vardhman Puram, Roorkee-247667 19.
& Chief Engineer (SP), R&B,
Block No. 14/1 Sardar Bhavan, Sachivalaya, ,
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
& Technocrats Park,
New Delhi-1 10016 C.K. Singh
Engineer-in-Chief-cum-Addl. Commissioner-cum-Spl. Secy., Road Constn.
Department, Ranchi (Jharkhand) 24.
Chief Engineer Transport
Ministry of Road
& Highways, Transport Bhavan,
New Delhi-1 10001 25.
Chief Enginer, Zone-Ill, Delhi P.W.D., Building, LP. Estate,
MS 808 Main Building,
New Delhi-1 10002
New Delhi-1 10016
AIMIL Ltd., Naimex House, A-8,
Co-operative Indl. Estate, Mathura
Road, New Delhi- 11 0044 28. V.C.
Executive Director, Oriental Structural Engrs.Ltd., 2 1
Commercial Complex, Malcha
New Delhi- 11 0021 29. P.D.
Member, Maharashtra Public Service Commission, 3rd Floor, Bank of India Building, M.G. Road, Mumbai-400001 (S.S. Juneja) H.P. Public
The Chief Engineer (B)S&R
(V. Velayutham), Ministry of Transport
& Highways, Transport Bhavan,
New Delhi- 110001 32.
Principal Secy, to the
Govt, of Gujarat
Sardar Bhavan, Block No. 14, Sachivalaya,
R&B Department, A&E AP, Errum Manzil, Hyderabad-5 00082
(V. Murahari Reddy),
(R.R. Sheoran), Haryana Public
Chandigarh- 1600 19 35.
(R.L. Koul), National
Eastern Avenue, Maharani Bagh,
New Delhi- 110065 36.
The Director & Head
(S.K. Jain), Civil Engg. Department, Bureau
of Indian Standards,
New Delhi- 110002 37. B.L.
Addl. Director General, Dte. General Border
Roads, Seema Sadak Bhavan, Ring Road, Delhi Cantt, 38.
The Director (R&D)
A.K. Bhatnagar), Indian Oil Corporation
P.B. No. 2371, 76, Sardar Patel Road,
The Director General of Works Engineer-in-Chief s Branch, AHQ, Kashmir House, Rajaji Marg,
Ex-Officio 41. President,
Indian Roads Congress
Maharashtra P.W.D., Mantralaya, 42.
Indian Roads Congress
Director General (Road Dev.)
Secretary to the Govt, of Irdia, Ministry of
Road Transport New Delhi
Indian Roads Congress
Chief Engineer, Ministry of Road Transport
New Delhi Correspond ing
Emeritus Fellow, 334, 25th Cross, 14thMain,
Banashankari 2nd Stage, Bangalore-560070 2.
Chief Engineer, Lajpat Nagar-III,
New Delhi- 110024
Principal Secretary, Maharashtra (Retd.),
A-47/1344, Adarsh Nagar, Worli,
Head of Deptt. of Transportation Pig., SPA Consultant, 458/C/SFS,
Sheikh Sarai 5.
R.A. Puram, Chennai-600028
00 1 Street,
BACKGROUND The Geotechnical Engineering Committee in its first meeting held on
Use of Fly Ash
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
During the meeting, few corrections/modifications
suggested by the members were carried out. The Committee in
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
approved the draft for placing before the Geotechnical Engineering
Committee (H-3): 1.
Arun Kumar Sharma
The Geotechnical Engineering Committee (Personnel given meeting held on 6. 2.99 approved the draft.
Dr. Gopal Ranjan
Members Dr. U.N. Sinha
Dr. A. Vardarajan
CE(R) S&R, MORT&H (C.C. Bhattacharya)
DG(RD) & Addl.
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.
was discussed by
Specifications and Standards
The contributions from Central Road Research Institute and Fly
Ash Mission, Department of Science and Technology, Govt, of
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
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
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
called fly ash.
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
very high. Moreover,
situated in urban areas,
many power fly
environmentally preferable alternative to natural borrow 3
ash can provide an soil.
The properties of fly ash vary depending upon type of
pulverisation and combustion techniques, their collection and
disposal systems, etc.
exhibit different physical
of collection, depth,
collected from the
same ash pond may
and engineering properties depending on point
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
properties, fly ash possesses several desirable characteristics, such as,
of consolidation, etc. Also,
spreading and compaction of fly ash can be started
comparison to soil for construction
after a rainfall.
Fly ash would be a preferred material
of embankments over weak subsoil.
much earlier in
These guidelines provide
salient details regarding
design and construction of road embankments using fly ash.
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.
The design of fly ash embankments is basically similar
design of soil embankments. The design process for embankments
involves the following steps: •
Characterisation of materials
The design of embankment is an
developing conceptual plans, which satisfy 4
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
The following information concerning the site and surrounding areas
must be collected:
Topography: The existing configuration of the proposed developments, topographic information determining
volumes, surface drainage and overall
Hydrology: The nature of existing and potential development of surface water and ground water conditions, flooding
Subsoil investigations: The nature and extent of soil and rock strata,
and performance of project.
For detailed procedure on carrying out
1RC:36-1970 may be referred. Characterisation of Materials
The materials to be used
embankment construction should
be characterised to determine their physical and engineering properties. In certain specific situations,
as detailed in sections 3.3.
.8 to 3.3.
may be of relevance
of the material
and design parameters are obtained through characterisation tests.
The following information on the
ash to be used,
available for the Engineer's approval before
commencement of work: Particle size analysis
of the material
The maximum dry density (MDD) and optimum moisture content
as per IS
Heavy Compaction test),
moisture content, for
and the graph of density plotted against
the Engineer has approved the above
form the basis
The density of fly
considerably lower than density of many types of soils. So, unlike
ash with low
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
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
Shear strength parameters, for evaluation of the
slopes and the bearing capacity of foundations located on the •
Compressibility characteristics, for predicting the magnitude and duration of the
Permeability and capillarity are required to assess seepage and to
design drainage systems.
220.127.116.11. 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
in the laboratory
2- IS:2720(Part8): 1983
laboratory shear strength tests should be conducted on samples
compacted to densities equivalent to those expected to be attained the
Fly ash gets consolidated
completed very quickly. So
a faster rate and primary
has low compressibility
and shows negligible post construction settlements.
Liquefaction generally occurs when fly ash
under loose saturated condition during construction.There is very little possibility
of liquefaction to occur, when
construction, as the material
optimum moisture content,
compacted to maximum dry density at
under partially saturated condition. In
regions of moderate to high seismic activity, analysis of embankment stability
should consider liquefaction potential of the ash
the possibility of any liquefaction to occur, the following precautions
maybe taken: • Proper compaction of the • In case water table
material as per specifications
should be lowered by providing
suitable drains or capillary cut-off
ash between intermediate horizontal soil layers.
Typical values for different geotechnical properties
of fly ash are given
properties as given in Table
for guidance. In general fly ash with 1
are acceptable for
Typical Geotechnical Properties of Pond Ash
i.yu —z.j j
Mid ct~i r*i"t"\/ \yiQviTYiiifn IVlaXlIIlUIIl
cif\/ L-JCIlMiy I
mri/r^r* i ^glll/CC^ i
Optimum Moisture Content (%) Cohesion (kN/m
Angle of Internal Friction
Coefficient of Consolidation
1.75 x 10
2.01 x 10
Permeability (cm/sec) Paritcle Size Distribution
(% of materials)
Silt size fraction
Gravel size fraction Coefficient of Uniformity
1-10 8-85 7-90 0-10 3.1- 10.7
18.104.22.168. 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
according to BS: 1377 Test 10 but using a 2:1 water-soil
(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
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 22.214.171.124.
ashes are relatively
Moreover, coal used
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.
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
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.
material for fly ash
embankments. Gravel may be used
granular cut-off at the bottom. These materials are to be tested as per
MOST Specifications for The soil used 1
materials used in
should not have
maximum dry density less than
gm/cc when height of embankment
subjected to extensive flooding, otherwise the
cover soil should not be
m and in areas not
maximum dry density of
tested according to
IS:2720(Part 8)- 1983. Subgrade/earthen shoulder material should 9
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
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.
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.
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
be designed as a composite structure with
and earth cover on the sides. Well-compacted shear strength so that the horizontal to
ash in the core
ash attains sufficient
embankment can be constructed with 2
vertical side slope. This should
stability analysis for
be confirmed through
The three most common types of failure ofembankment
are toe failure (occurring
material), slope failure (occurring in a layered
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
use limit equilibrium method for stability analysis of embankment. In this
considered along a failure surface. Generally in
the slip circle method failure plane is assumed to be circular.
minimum factor of safety. For more details on stability analysis, IRC:75-1 979 may be referred.
the critical circle
Calculation of factor of safety of different circles until 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.
of safety for
embankments constructed using fly ash should not be less than
under normal serviceability conditions and when checked for worst combination under seismic and saturated conditions, it should not be less than 1.0.
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
Embankment Layer of Fly Ash and Soil
Typical Cross-Section of Alternate
Granular Layer 0.5
Selected Earth Cover
m (minimum) 1
Typical Cross-Section of Embankment with Core of Fly Ash
Properly benched and graded slopes prevent the
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
the face of the
volume of the run-off to
to the toe.
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
Clearing and Grubbing
This work consists of cutting, removing and disposal of trees, bushes, shrubs, roots, grass, rubbish,
the area of road land drains,
from the alignment and within
accommodate road embankment,
and such other areas as specified on the drawi
and grubbing, the contractor shall take adequate precautions against soil erosion, fill
All trees, stumps,
area should be cut to atleast 500
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
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
of height not exceeding 2 m, for use
slopes, cut slopes
mm and stored in stock
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
After the site has been cleared, the limits of embankment should
out true to lines, curves, slopes, grades and sections as
on the drawings. The limits of the embankment should be marked by fixing batter pegs on both sides at regular intervals as guides before
The embankment should be
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
opinion of the engineer, they are required for the work.
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
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
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
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
able to rise to the subgrade level.
be inserted so that moisture
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
Provision of geotextile separating layer
as capillary cut-off.
between drainage blanket and
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.
grain size distribution
generally compatible with the grain size distribution of
grained sand. Further guidance regarding capillary cut off design
from IRC:34-1970, Road Construction in Water Logged
by the Engineer, any unsuitable the embankment foundation shall be
removed and replaced by approved materials required
laid in layers, to the
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
Handling and Transportation of Fly Ash
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
during transport. In such cases, periodic inspection and
ash from relatively dry areas of the pond would be needed.
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
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
Spreading and Compaction
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
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
and vibratory energy. Smaller vibratory
of roller weight
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
are used, loose layer thickness upto
if site trials as
for loose layer
mm. When vibratory roller of dead weight 80-
in section 4.7.3
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
ash should be laid simultaneously before compaction, to ensure
confinement of fly ash. Clods or hard lumps to
have a maximum
of 50 mm.
cover soil shall be broken
Moisture content of the
4.7.2. at the site
of placement prior
material shall be checked
commencement of compaction.
Moisture content of fly ash laid for compaction shall normally vary
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
achieved as revealed through actual
no dust problem.
may be noted that grain shape and particle size
of fly ash make the upper layers
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
added to the
at its it
OMC. Where water is required to be
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,
the moisture content
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
ash must be compacted as early
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.
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
can be conducted. In such
as, lift thickness,
time while the others remain constant. 17
where a series
varied at a
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
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
the sides should proceed simultaneously. 4.7.5.
Each compacted layer shall be finished parallel to the
of the embankment. The following end product
specifications as given in Table 2,
have been suggested for construction
of fly ash embankments. Table
Specifications for Compaction
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
times the height of the
length equal to
At locations where compaction of the ash
impracticable using rollers, such as,
portions adjacent to
structures/steep abutments or around concrete drainpipes in
embankment, hand held vibratory tampers
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.
The Engineer may permit measurement of field density
according to agreed procedure. Subsequent layers shall be placed only after the finished layer has
The contractor shall maintain record of all such tests. When density neasurements reveal any soft areas in the embankment, further 18
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
moisture content brought to permissible limits and recompacted to the required density.
Embankment shall be constructed evenly over their full
width and the contractor
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
as it had before it was damaged. Embankments shall not be constructed
with steeper side slopes or to greater width than those shown drawings.
Whenever embankment construction is to be taken up against
the face of natural slope or sloping earth
and excavations which are steeper than
such faces shall be benched immediately before
placing the subsequent
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
Precautions Against Corrosion
works face including
The sulphate content
limits specified in section 3.3.
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
or terra cotta
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
necessary, polythene sheeting, bituminous coating
or embedding and backfilling with inert materials,
like, suitable soil
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
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.
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
drawing or as directed by the Engineer subject to the tolerance. Both upper and lower ends of side slopes
be rounded off to improve
appearance and to merge the embankment with the adjacent In case turfing
proposed, top soil should be provided so that after
seeding, a dense cover can develop.
The depth of top
sufficient to sustain plant growth, the usual thickness being 75 to
Slopes shall be roughened and moistened slightly before the
application of top soil in order to provide satisfactory bond.
prone areas should be protected
by stone pitching as per the provisions of IRC:89-1 985. 20
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
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
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. •
of ash, as per IS:2720 (Part
of ash, as per
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
Control shall be exercised on each layer by taking at least one measurement of density for each 1000 square metres of 5.3.
compacted area, or closer as required to
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
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.
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,
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,
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
IRC:34-1970, Recommendations for Road Construction Areas, Indian Roads Congress,
IRC:36-1970, Recommended Practice for the Construction of Earth Embankments for Road Works, Indian Roads Congress, New Delhi.
IRC:75- 1 979, Guidelines for the Design of High Embankments, Indian Roads Congress, New Delhi.
IRC:89-1985, Guidelines for Design and Construction of River Training and Control Works for Road Bridges, Indian Roads Congress, New Delhi.
IRC:SP:50- 1 999, Guidelines on Urban Drainage, Indian Roads Congress,
New Delhi. 13.
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.
Ash Mission, Department of Science
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.
Project Reports on Okhla Flyover Project and Second Nizamuddin Bridge Approach Embankment, Central Road Research Institute,