Grameen Sampark Final April 0... - pmgsy

In this Issue
Editorial 3
Potential Applications of 4
Interlocking Concrete Block Paving in
Rural Roads Construction
Dr. S.D. Sharma, B.M. Sharma and
Dr. P.K. Nanda
Performance Criteria for 15
Design of Low Volume Rural Roads
U. C. Sahoo, M. Amaranatha Reddy and
K. Sudhakar Reddy
Stabilization of Soil Subgrade 22
with Polypropylene Fibres
Dr. I.K.Pateriya and Dr. K. A. Patil
Experiencing Folded Plates in
Roadworks Retaining Structure
Dipankar Chakrabarti and
Shyamalendu Mukherjee
News in Brief 32
th
The National Rural Roads Development Agency (NRRDA) was established on 14 January, 2002 as
the dedicated agency of the Ministry of Rural Development for the operational management of the
rural roads programme - PMGSY
Grameen Sampark is a newsletter of the NRRDA containing items of topical interest. For official text
or detailed information please contact NRRDA or visit the website.
Published by: National Rural Roads Development Agency
th
(NRRDA), 5 Floor, 15, NBCC Tower, Bhikaji Cama Place,
New Delhi-110066
e-mail: nrrda@pmgsy.nic.in Website:www.pmgsy.nic.in
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Note: Accepted articles may be condensed.
27

Editorial
Pradhan Mantri Gram Sadak Yojana
We often preach, but rarely practice, the old adage 'a stitch in time saves nine'. This disconnect also largely
pervades our approaches to the management of the huge network of rural roads which we have built up over the
years with considerable investment of tax payers' money. PMGSY sought to practically address this malady by
embedding 'planned 5 year maintenance of completed roads' in the programme guidelines. However, anecdotal
evidence, buttressed by limited field observations of independent monitors, indicates that this policy has not
achieved substantial success in terms of the intended outcome across States. Sample inspection of 4412 roads by the
National Quality Monitors, during December2007and December 2008 reveal that a very high proportion ( 32%)of
PMGSY roads were not being maintained at all, contrary to the stated policy. Since we have already completed
construction of over 2 lakh km. of rural roads under PMGSY, by investing close to US $ 10 billion, quite obviously,
institutionalizing an efficient maintenance management policy cannot brook any further delay.
Efficient management of rural roads requires not only enhancement in budgetary outlay but even more
importantly change in systems, procedures and processes. One thing is quite clear business as usual will not work.
What is called for essentially is a paradigm shift in our approach to maintenance management. It is in this context that
NRRDA is holding a workshop in collaboration with the Government of Andhra Pradesh to explore the feasibility of
applying principles of Asset Management to rural roads. Asset Management seeks to synergize ideas and principles of
Engineering as well as Management Sciences with a view to developing a decision making framework that helps in
choosing the optimal strategy for managing high value infrastructure assets. At its core, asset management is a
business process which strives to maintain a prescribed level of service at the lowest cost possible. Allocation of
resources on the basis of a well-defined set of policy goals and objectives, evaluation of alternative options in terms of
their impact on relevant policy objectives and monitoring results with reference to measurable performance
benchmarks are some of the core principles of Asset Management.
Adoption of Asset Management principles for rural roads would call for major institutional as well as
attitudinal changes. Challenging the status quo is by no means easy; but it is certainly doable. We can ill afford to let
our precious rural road assets to deteriorate by sheer atrophy and the prevailing culture of niggardliness towards
maintenance.
(J.K. Mohapatra)
Director General, NRRDA
Asset Management: Building a culture of
sustainable maintenance of rural roads.
Grameen Sampark
3

4
Potential Applications of
Interlocking Concrete Block Paving in
Rural Roads Construction
Dr. S.D. Sharma*, B.M. Sharma**, Dr. P.K. Nanda***
Transport Infrastructure development in rural areas is
absolutely essential for soci-economic upliftment of
rural population. An adequate road transport system
improves connectivity to the inaccessible areas and in
turn facilitates smooth flow of goods and services. Rural
roads also help the rural population in terms of
increased mobility to schools, health centers, market
centers and create more employment opportunities.
They also provide accessibility to productive resources
and physical mobility of raw materials, farm produce
and other products, promote industrialization, increase
the size of markets and create enhanced economic
prosperity, etc. Economic developments brought about
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through increased mobility and accessibility turns into
income-generating skills, increased income for rural
workers, positive changes in socio-economic attitude
and reduction in inequalities between different regions,
leading to increased productivity on the whole.
Provision of roads in rural areas is a gigantic task as
about six lakh villages in India are scattered widely over
a vast area of 33 lakh sq. km.
The Government of India has been making sincere
efforts in this direction and has implemented a number
of rural development programmes since 1974, with
development of rural roads as one of the major
objectives. Prominent amongst these are : Minimum
*Scientist, **Head (Pavement Evaluation Division) and ***Director, Central Road Research Institute, New Delhi
nd th
Reprinted from the proceeding of National Conference on Rural Roads (22 to 24 May 07) New Delhi

Needs Programme, National Rural Employment
Programme, Rural Landless Employment Guarantee
Programme, and Jawahar Rozgar Yojana. However,
these programmes lacked science and technology
contents / inputs and were primarily targeted as drought
relief and employment guarantee as their main
objectives. Due to these reasons, they had limited
success in the overall development of rural roads. The
lack of scientific planning and methods in creating rural
infrastructure and the centralized nature of
implementation proved to be impediments in creating
durable rural roads, through such programmes.
In tune with the objectives of Road Development Plan
Vision (1), a national mission popularly known as
“PMGSY” (Pradhan Mantri Gram Sadak Yojna), for
achieving rural connectivity through provisions of allweather
roads to remote villages was initiated in 2000
by the Government of India, with the overall objective
of connecting all villages having population of more
than 500 by the year 2007. This is an ambitious
programme with far-reaching positive returns and
consequences for the nation's economy, in general, and
the rural economy, in particular. It is expected that,
through the implementation of this programme, out of
the 3,50,000 unconnected habitations, 1,60,000
habitations will be benefited, with construction of some
6,00,000 km of new all-weather roads. This will
constitute an addition of 33 per cent to the existing
18,20,000 km of rural roads and 20 per cent to the
existing network of 33,00,000 km of total roads in the
country. The current estimate of total investments
needed for this stupendous task is Rs.60,000 crores. It is
estimated that the effective implementation of PMGSY
would lead to three times increase in the per capita GDP
(Gross Domestic Product) within one decade. Thus, the
fulfillment of this programme will lead to a quantum
jump in the nation's economy (2,3). Since the local selfgovernments
are actively involved in the planning,
designing and implementation of this programme, there
is scope for people's participation at the grassroots
levels and achievement of most of the objectives on the
ground.
Pradhan Mantri Gram Sadak Yojana
The major difficulties being faced in implementation of
this programme are the non-availability of good quality
road building materials particularly the granular subbase
and aggregates. In addition, transportation of other
materials such as bitumen, steel and cement etc. also
affect the cost and timely completion of projects due to
the long haulage of these materials. Non-availability of
skilled manpower in the rural areas is another important
factor affecting the construction quality of rural roads.
Keeping in view these problems, it is felt/ suggested that
alternate techniques such as Interlocking Concrete
Block Paving (ICBP) can have potentially large
applications for construction of rural roads.
It needs to be highlighted at this stage that the Panchayat
Raj Department of Government of Haryana, has taken
up a great initiative and have decided to construct rural
streets within the village areas on a massive scale by
using paving blocks technology. It is planned by the
Govt. of Haryana to develop two villages as Ideal /
Modal villages which will have roads constructed with
paving blocks technology. Gradually, depending upon
the success achieved, construction of rural roads in
many more villages will be done using the technology of
paving blocks.
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6
Interlocking Concrete Block Pavement
Interlocking Concrete Block Pavement (ICBP) has been
extensively used in a number of countries for many
years, as a specialized problem-solving technique, for
providing pavements in areas where conventional types
of construction are not possible and also are less durable
due to many operational and environmental
constraints. ICBP technology found its application in
India, a decade before, for specific requirements viz.
footpaths, fuel stations, parking areas etc. This
technology is now being adopted for different areas /
situations where the construction of conventional
pavements using hot bituminous mix or cement
concrete technology is not feasible/ desirable/
economical.
ICBP has many advantages as listed below:
(i) No need to deploy heavy construction equipments
/ machineries
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(ii) Factory production of paving blocks facilitates
centralized quality control
(iii) Labour intensive construction method
(iv) Instant opening of road to traffic
(v) No thermal expansion and contraction of concrete
(vi) Accommodates higher elastic deflections without
failure
(vii) Pavements are not damaged due to fuel and oil
spillage
(viii) High salvage value almost all blocks can be
recycled / reused
(ix) Least life cycle cost due to low maintenance cost
(x) Environment friendly technology
(xi) Can be used in poor drainage conditions

(xii) Can help in conservation of naturally occurring
materials particularly the soils, gravels and
aggregates
Some of the proven areas where ICBP technology has
been successfully applied are listed below [5&6]:
a) Non-Traffic Areas: building premises, footpaths,
balls, pedestrain plaza, landscapes, monuments
premises, premises, public gardens/ parks,
shopping complexes, bus terminus parking areas
and railway platforms, etc.
b) Light Traffic: car parks, office driveway, housing
colony roads, office/ commercial complexes, rural
roads, residential colony roads, farm houses, etc.
c) Medium Traffic: boulevard, city streets, small
market roads, intersections/ rotaries, low volume
roads, utility cuts on arteries, service/ fuel stations,
etc.
d) Heavy and Very Heavy Traffic: containers/ bus
terminals, ports/ dock yards, mining areas, roads in
industrial complexes, heavy-duty roads on
expansive soils, bulk cargo handling areas, factory
floors and pavements, airport pavements, etc.
There are four generic shapes of paving blocks which
correspond to the four different types of blocks, as stated
below [4&5]:
(a) Group A: Paver blocks with plain vertical faces,
which do not key into each other when paved in
any pattern,
(b) Group B: Paver blocks with alternating plain and
curved/ corrugated vertical faces, which key into
each other along the curve/ corrugated faces,
when paved in any pattern,
(c) Group C: Paver blocks having all faces curved or
corrugated, which key into each other along all the
vertical faces when paved in any pattern, and
(d) Group D: 'L' and 'X' shaped paver blocks which
have all faces curved or corrugated and which key
Pradhan Mantri Gram Sadak Yojana
into each other along all the vertical faces when
paved in any pattern.
The generic shapes and groups of paver blocks
identified into four different types are illustrated in
Figure 1.
Group - A
Group - B
Group - C
Group - D
Figure 1: Typical Shapes of Concrete Paver Blocks
The various aspects dealing with materials, construction
and laying of interlocking concrete block pavement etc.
are described in the following sections.
Materials for Interlocking Concrete Block
Pavement
The quality of materials used, strength of cement
concrete, durability and dimensional tolerance of
paving blocks etc., is of great importance for achieving
the satisfactory quality and performance of block
pavements. All these aspects including the block
manufacturing process, which immensely affect the
quality of paving blocks, have been outlined in the
Indian Roads Congress Special Publication [7]. In
addition, a specification on Precast Concrete Blocks for
Paving, has recently been published by the Bureau of
Indian Standards [8].
Paving Blocks
The recommended thickness of blocks; grades of
concrete for various applications; specifications of
Grameen Sampark 7

8
materials used for production of blocks; physical
requirement, test methods, sampling and acceptance
criteria etc., have already been presented in BIS Code
[8].
Bedding Sand and Joint Filling Sand
It is a well established fact that if proper attention is not
paid to the quality of bedding sand, and if the thickness
of bedding sand layer is not kept uniform, serious
irregularities in surface profile can occur result and
consequently excessive differential deformations and
rutting can early in the service life of block pavement.
The gaps in between the two adjacent paving blocks
(typically about 3 mm wide) need to be filled in with
sand which should relatively be finer than the bedding
sand. The gradations of bedding sand and joint filling
sand are given in Table 1.
It is necessary to restrict the fines (silt and/ or clay,
passing 75 micron sieve) to about 10 percent, since
excessive fines make joint filling very difficult. Similarly,
it is not advisable to use cement in the joint filling sand,
which would not only make difficult to completely fill
the joints, but may also adversely affect the desired
flexibility characteristics of the paving block layer. The
joint filling sand should preferably be as dry as possible;
otherwise complete filling of joints will be difficult [7].
Table 1: Gradations of Bedding Sand and
Joint Filling Sand
IS Sieve Size Bedding Sand Joint Filling Sand
Percent Passing by Weight
9.52 mm 100 -
4.75 mm 95-100 -
2.36 mm 80-100 100
1.18 mm 50-95 90-100
600 micron 25-60 60-90
300 micron 10-30 30-60
150 micron 0-15 15-30
75 micron 0-10 0-10
Grameen Sampark
Base and Sub Base Materials
The main purpose of providing base materials are the
load spreading properties to disperse stresses to the
subgrade level and to provide the desired drainage
characteristics, which would have significant bearing
on performance of a block pavement. Although, local
availability and economics generally dictate the choice
of base materials at the design stage, yet the commonly
used materials considered suitable for base courses are
unbound crushed rock, water-bound macadam, wet
mix macadam, cement bound crushed rock/ granular
materials, and lean cement concrete/ dry lean concrete
etc. In broad terms, wherever the subgrade is weak (CBR
value below 5), the use of bound granular materials,
like, cement treated crushed rock, should be preferred

while for high strength subgrade, unbound crushed
rocks may be used. The climatic and environmental
factors also need to be considered during the choice of
base materials. Sub-base is essential where commercial
traffic is expected. The quality of sub-base materials is
inferior to the base materials and may include natural
gravels, cement treated gravels, sands and stabilized
subgrade materials etc. The quality of sub-base
materials should be in conformance with IRC: 37-2001.
Construction of Interlocking Concrete Block
Pavement
Sequencing of Laying Operations
The sequencing of laying operations (Figure-2) for
construction of block pavement should be as follows
[8]:
(i) Installation of sub-surface drainage structures
Basecourse
compacted
and inspected
Beddind sand
slockpited ahead
of screeding
Edge restraint constructed on
basecourse
Figure 2: Sequencing of Laying Operations
Sand bedding
course
screeded
Laying face
Paving
Units
laid
Pradhan Mantri Gram Sadak Yojana
(ii) Leveling and compaction of subgrade
(iii) Provision and compaction of sub-base course
(where needed)
(iv) Provision and compaction of base-course and
checking for the correct profile
(v) Installation of edge restraints
(vi) Provision and compaction of bedding sand
(vii) Laying of blocks and interlocking
(viii) Application of joint sealing sand and compaction
(ix) Cleaning of surface
(x) Filling any remaining empty portions in the block
layer, especially near edge restraint blocks with in
situ concrete.
Cut infill
units
Paving Joint-filling
Units sand
compacted placed
Pavement
completed
allowing access
Pallets of paving units placed as
close as possible to work-lace
Site access and starting point
Grameen Sampark 9

10
Construction of Sub grade
This is the foundation layer over which the block
pavement is constructed. Like in conventional
pavements, the depth of water table should not be at a
level of 600 mm or higher, below the subgrade level. It
should be compacted in layers of 150 mm thickness.
The prepared subgrade should be graded and surface
dressed to a tolerance of ± 20 mm of the design levels,
and its surface evenness should have a tolerance of
within 15 mm under a 3 m straight edge [7].
Construction of Base and Sub-base Layers
Base course and Sub-base course are constructed in
accordance with the standard procedures contained in
relevant IRC specifications like IRC:37-2001; IRC:50-
1973; IRC:51-1993; IRC:63-1976; IRC:19-1997. When
cement treated bound base is proposed it may be
constructed using rolled dry lean concrete as IRC:SP-
49-1998. The quality control methods, as specified in
IRC: SP-11-1988 shall apply. Constructing these layers
to the proper level and grade is very much essential to
maintain the top surface level and surface regularity of
the block pavement surface.
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Edge Restraint Blocks and Kerbs
Concrete blocks subjected to traffic tend to move
sideways and forward due to braking and maneuvering
of vehicles. The tendency to move sideways has to be
counteracted at edges by provisions of special edge
blocks and kerbs. The edge blocks should be designed
and anchored to the base such that the rotation or
displacement of blocks is resisted [7]. These blocks are
to be made of high strength concrete for withstanding
the traffic wheel-loads without getting damaged. These
members should be manufactured or constructed in-situ
in order to have at least a 28-days characteristic
compressive strength of 30 MPa or flexural strength of
3.8 MPa. As far as possible, the edge blocks should have
vertical face towards the inside blocks. Where the space
does not easily permit the use of plate vibrators,
dhurmut or manual compactor using small size plate
rammer may be used. The road kerbs provided on edges
of roads also serve the purpose of edge blocks. In case
the kerbs are not provided, it has to be replaced by the
edge strips. In case of heavy traffic, 150 mm x 150 mm
(height x width) plain cement concrete (M-25) may also
be provided over dry lean concrete to give further
confinement to the blocks. In-between the edgerestraint
blocks, cement mortar (1: 6, cement: coarse
sand) may be used in place of sand for sealing of blocks.
Placing and Screeding of Bedding Sand
The thickness of sand bedding after compaction should
be in the range of 20-40 mm, whereas, in the loose form,
it should be 25 to 50 mm. It is preferable to restrict the
compacted thickness to about 20-25 mm to reduce the
risk of any localized over-compaction, which would
affect the final block surface level. Bedding sand should
not be used to fill-up local depressions on the surface of
base or sub-base layers. The depressions, if any, should
be repaired with same base or sub-base material in
advance before placing the sand. The sand of specified
gradation, should be uniformly in loose condition, and
should have uniform moisture content. Optimum
moisture content is when sand is neither too wet nor too
dry and has moisture of about 6 to 8 percent.

Requirement of sand for a day's work should be
prepared and stored in advance and covered with
tarpaulin or polythene sheets. The processed sand so
obtained is spread with the help of screed boards to the
specified thickness and levels. The screed boards are
provided with nails at 2-3 m apart which when dragged
gives the required thickness. The length of nail should
take into account the surcharge to be provided in the
uncompacted thickness. Alternatively, the screed can
be dragged on edge strips kept on both sides as guides
[7].
Laying of Paving Blocks
Blocks can be laid generally by manual labour but
mechanical aids like hand-pushed trolleys can expedite
the work. Normally, laying should commence from the
edge strips and proceed towards the central line. When
dentated blocks are used, the laying done at two fronts
will create problem for matching joints in the middle.
Hence, as far as possible, laying should proceed in one
direction only, along the entire width or area to be
paved [8].
Pradhan Mantri Gram Sadak Yojana
While locating the starting line, the following should be
considered:
On a sloping site, start from the lowest point and
proceed to up-slope on a continuous basis, to
avoid down-slope creep in incomplete areas.
In case of irregular shaped edge restraints or strips,
it is better to start from straight string line.
Influence of alignment of edge restraints on
achieving and maintaining the laying bond.
Laying Patterns
The blocks can be placed in different bonds or patterns
depending upon the specific requirements. Some
popular bonds commonly adopted for block paving are:
(i) Stretcher or running bond (ii) Herringbone bond and
(iii) Basket weave or parquet bond etc. The typical
layouts of these bonds are given in Figure 3.
O
(a) Stretcher or Running Bond (b) Parquet or Basket Weave (c) 45 Herringbone Bond
O
(d) 90 Herringbone Bond
(e) Parquet Derivative (f) Double - V
(g) Double Herringbone (h) Herringbone (i) Herringbone Bond
Figure 3: Laying Patterns of Paving Blocks
Grameen Sampark 11

12
Typical Pavement Compositions
Typical compositions normally used in ICBP technology are given in Table-2 with typical cross sections as shown in
Figure 4.
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BLOCK PAVED
SURFACE
BASE COURSE
SUBGRADE
Figure 4: Typical Pavement Structure Drainage
JOINT FILLING FINE SAND
INTERLOCKING CONCRETE BLOCK
COARSE BEDDING SAND
Table 2: Catalogue for Pavement Thickness
EDGE RESTRAINT
SHOULDER
Traffic and Road Type Materials >10
Sub grade CBR (%)
5-10
Thickness (mm)

Block Pavement at Typical Locations
Essentially, there are three important aspects in
detailing. These are: (i) Curves (ii) Intrusions, and (iii)
Changes in alignment
Curves: It is necessary to cut the paving units to fit the
edge restraints. Rectangular blocks of similar or
contrasting colour as an edging have been used to
minimize the visual effects of small errors in block
cutting. To avoid unsightly and potentially weak joints,
it is often preferred to change the laying pattern at the
curves. The curve itself can be installed in Herringbone
bond and yet the pavement can revert to stretcher bond
on the approaches [4 & 5].
Intrusions:
On some pavements, like in city streets,
there could be several intrusions, like, manholes,
drainage gulleys, etc. where coping with these
intrusions with the pavement is desirable. Around
intrusions, it is good practice to lay blocks along both
sides of the intrusion simultaneously so that closure is
made away from the starting workface, rather than
carrying the pavement around the intrusion to return to
the original laying face to avoid accumulation of closing
error [7].
Compaction
For compaction of sand bedding and paving blocks laid
over it, the vibratory plate compactors are used over the
laid paving blocks; at least two passes of the vibratory
plate compactors are needed. Such vibratory
compaction should be continued until the top of each
paving block is in level with the adjacent blocks. It is not
a good practice to leave compaction till the end of the
day, as some blocks may move under construction
traffic, resulting in the widening of joints and corner
contact of blocks, which may cause spalling or cracking
of the blocks. There should not be any delay in the
compaction after paving blocks have been laid. This is
necessary to achieve uniformity of compaction and
retention of the pattern of laying. During compaction of
the blocks laid, some amount of bedding sand may get
filled up into the joints between them; the extent of sand
Pradhan Mantri Gram Sadak Yojana
getting filled up into the joints will depend on the degree
of compaction of sand, i.e. the force applied by the
compactor. Standard compactors may have a weight of
about 90 kg with plate area of about 0.3 m2 and apply a
centrifugal force of about 15 kN. On the other hand,
heavy duty compactors may weigh 300-600 kg, with
plate area of about 0.5-0.6 m2 and apply a centrifugal
force of 30-65 kN. Where the bedding sand is required
to be compacted for heavily trafficed pavements, heavyduty
compactors should be used. After compaction by
vibratory plate compactors, some 2 to 6 passes of
vibratory roller (with rubber coated drums or those of
static weight less than 4 tonne and nominal amplitude of
not more than 0.6 mm) will further help in compaction
of bedding sand and joint filling [7].
Laying and Surface Tolerances
While constructing the block pavement, the surface
toleranes of individual layers may be observed, as
indicated in IRC:SP:63-2004.
Conclusion
ICBP technology is gaining importance and is
becoming more popular day-by-day because it is
user friendly and requires less infrastructure in
terms of construction equipment / machineries, as
compared to the conventional flexible and rigid
pavements.
ICBP technology can provide durable and
sustainable road infrastructure where construction
and maintenance of conventional pavements are
not cost effective.
ICBP is much cheaper than the rigid (concrete)
pavement, designed for identical operating
conditions. Compared to the bituminous
pavement for low traffic volume roads and high
strength subgrade, the initial construction cost of
ICBP is likely to be equal to or marginally higher.
For high traffic volume roads and low strength
subgrade, ICBP will be cheaper than the flexible
pavement.
Grameen Sampark 13

14
Guidelines for the use of Interlocking Concrete
Block Pavement and Precast Blocks for Paving-
Specification are now available in India for
production of better quality paving blocks and
construction of such pavements.
Code of practice for laying and construction of
Interlocking Concrete Block Pavements has been
submitted to Bureau of Indian Standards, which
will be very useful for Indian industries and
highway professions for adoption of block
pavement technology in India, on a large scale.
ICBP technology can help in conservation of
naturally occurring materials like soils, gravels and
aggregates which are now becoming scarce due to
large scale construction activities taking place
throughout the country.
ICBP technology can replace concrete pavements
at least in case of low trafficked roads, to start with.
Road departments and the construction industry
must, therefore, seriously consider ICBP
technology as a potential technology for the
purpose of providing roads in the rural areas.
References
1. Road Development Plan:2001, Ministry of Road
Transport & Highways, Published by Indian Roads
Congress, 2001.
2. Sikdar, P.K., Pradhan Mantri Gram Sadak Yojana A
Mission for Rural Connectivity by All-Weather
Grameen Sampark
Roads, Indian Highways, Vol. 29, No. 5, May
2001.
3. Sikdar, P.K. Pradhan Mantri Gram Sadak Yojana
For the People, By the People, Indian Highways,
Vol. 30, No. 6, June 2002.
4. Sikdar, P.K., Sharma, S.D., Sood, V.K., (2004),
“Interlocking Block Pavement For Sustainable
Road Infrastructure For Cold Region”,
International Conference on Sustainable Habitat
For Cold Climates, Leh, India, September 16-18,
2004.
5. Sharma, S.D., Sikdar, P.K., Rao, Y.V., (2004)
“Interlocking Concrete Block Pavements Its
Prospects”, Seminar on Design, Construction and
Maintenance of Cement Concrete Pavements,
IRC, October, 2004.
6. Muraleedharan, T. and Nanda, P.K., (1992)
“Application and Performance of Interlocking
Concrete Block Pavement An Overview”. The
Indian Concrete Journal, pp 395 -400, July 1992.
7. IRC SP: 63-2004 “Guidelines For Use of
Interlocking Concrete Block Pavement” Indian
Roads Congress.
8. “Indian Standard Specification for Precast
Concrete Paver Blocks”, Bureau of Indian
Standards, Modified 3rd Draft, January 2004.
(Under Publication).

U. C. Sahoo*, M. Amaranatha Reddy** and K. Sudhakar Reddy***
If the selection of pavement layer thickness is dependent
entirely on past experiences gathered about the
performance of in-service pavements, the resulting
design methods are usually termed as empirical
methods. Even in these procedures, there is normally a
distress mode selected (usually rutting) for designing
thickness and will be selected based on the experience
of pavements that have developed acceptable levels of
rutting during their design life period. As these are not
based on any fundamental mechanistic principles that
govern the stress-strain behaviour of the pavement
components, extrapolation of the design procedures
has to be done to situations where new pavement
materials are used, climatic conditions are different
from those prevailing during past experience etc.
Counting efforts are being made for rationalizing the
pavement design procedures by reducing the empirical
content and correlating the performance of the
pavements with load associated behaviour of pavement
Pradhan Mantri Gram Sadak Yojana
Performance Criteria for
Design of Low Volume Rural Roads
components. Analytical tools are used in these methods
to analyze pavement structures subjected to traffic
loads. Hence, these methods are often called Analytical
Design Methods or Mechanistic Methods or even
Theoretical Methods. A more appropriate terminology
would be rational Design Procedures as no design
method can be purely analytical or theoretical, as the
analytically determined parameters have to be
correlated with the performance of the pavements,
which can only come from experience.
In these procedures, some mechanistic parameters
(critical stresses, strains, deflections, etc.) that are
considered to be causative of (or having strong
correlation with) pavement distresses (fatigue cracking,
permanent deformation, etc.) are identified and
correlations are developed between these analytical
parameters and pavement life. The common forms of
structural distresses considered are fatigue cracking of
bound layers and permanent deformation in different
*Research Scholar, Civil Engineering Department, IIT Kharagpur (ucsahoo@civil.iitkgp.ernet.in)
**Assistant Professor, Civil Engineering Department, IIT Kharagpur (manreddy@civil.iitkgp.ernet.in)
***Professor, Civil Engineering Department, IIT Kharagpur (ksreddy@civil.iitkgp.ernet.in)
nd th
Reprinted from the proceedings of National Conference on Rural Roads (22 to 24 May 07) New Delhi
Grameen Sampark 15

16
layers due to repeated application of traffic wheel loads.
Most of the existing analytical design procedures have
performance criteria that give limiting strain (identified
critical strain parameter) values to ensure that the extent
of structural distress during the service life of pavement
will not exceed acceptable levels.
Any rational pavement design method should have the
following main components:
a) Identification of critical distress parameters for
defining the performance of the pavement. These
can be in terms of surface profile parameters such
as roughness (Fifth Wheel Bump Integrator,
International Roughness Index etc.) mostly
reflecting the functional performance of the
pavement. The performance parameters can also
be in terms of structural distresses such as cracking
of bound layers and rutting in different layers or
even a combined index such as the Present
Serviceability (PSI) used by AASTHO.
Grameen Sampark
b) Selection of proper performance criteria
developed by correlating the observed
performance of pavements with carefully chosen
performance parameters. While performance has
to be defined in terms of the traffic that can be
handled by the pavement before excess failures or
distresses occur, the parameters selected for
explaining the performance (distress or failure) can
be a combination of various pavement parameters
(thicknesses, material properties etc.) or a
combination of critical mechanistic parameters
(deflection, stresses and strains).
c) A framework or a list of steps specifying as to how
the parameters can be selected and/or computed.
The rationality of the design procedure can be judged
from the way corresponding performance criteria have
been developed. The criterion is generally developed
considering a failure condition, which may be any
structural or functional failure or both. The rural roads in

India mostly consist of granular pavements with thin
bituminous surfacing, in which rutting is considered as
the only mode of failure. This is attributed to the vertical
compressive strain at the top of subgrade layer.
Several highway organizations have developed their
own failure condition and performance criterion for
design of low-volume roads. In this study, the criteria
developed by AASTHO, AustRoads, Asphalt Institute
TRRL, etc. have been discussed.
Performance and Failure Criteria for
Pavement Design
In mechanistic design methods, the limiting values of
stresses and/or strains at which a given degree of distress
will occur are commonly known as the performance
criteria. The rationality of the design procedure can be
judged from the way the corresponding performance
criteria have been developed. Performance criterion is
generally developed considering a failure condition,
which may be any structural or functional failure or
both. Fatigue cracking of bituminous surfacing and
permanent deformation (rutting) along wheel paths,
mainly due to repeated application of traffic loads, have
been identified as the two major modes of structural
failures that need to be addressed in the structural
design of pavements. Some performance criteria also
use roughness as the mode of failure in terms of present
serviceability index (PSI) [1]. The low-volume rural
Pradhan Mantri Gram Sadak Yojana
roads in India mostly consist of granular pavements with
thin bituminous surfacing, in which rutting is
considered as the only mode of failure, which occurs
due to vertical compressive strain at the top of subgrade.
In this paper, the rutting criteria adopted by different
highway organizations for design of low-volume road
pavements have been presented with the objective of
comparing these criteria with that adopted for design of
Indian roads.
Selection of Critical Performance Parameters
Horizontal tensile strain at the bottom fibre of
bituminous bound layer and vertical compressive strain
on top of subgrade have traditionally been taken to be
causative for the two major modes of failures
considered, i.e., fatigue cracking and rutting. Excessive
strains applied repeatedly have been considered to be
the major factors for the development of the two modes
of failures. Figure 1 shows a typical layered flexibile
pavement system subjected to a dual wheel loading
applied at the surface.
Deformation or rutting provides the principal indication
of deterioration in granular pavements with thin
bituminous surfacing. It develops chiefly in the wheel
tracks,and increases with time or more precisely with
the cumulative application of commercial traffic.
Bituminous Surfacing
Granular Base
Granular Sub-base
Subgrade
Figure 1: Critical mechanistic parameters
ε z
ε E t 1,µ 1
E, 2 µ 2
E, 3 µ 3
E, 4 µ 4
Grameen Sampark 17

18
Subgrade Failure Criterion
The basic design thickness in the case of low-volume
roads is the thickness of unbound granular material,
which will limit the vertical compressive strain on top of
the subgrade to an acceptable level. The strain induced
in the subgrade by moving wheel load is mostly elastic
(recoverable). However, the accumulation of the
irrecoverable part of strain leads to permanent
deformation in subgrade. The permanent deformation
manifests at the surface of the pavement as rutting in the
wheel paths, although due to inherent variability of the
subgrade and pavement materials and the construction
techniques, surface roughness develops along with
rutting.
Performance Criteria Addopted By Different
Organizations
AustRoads Design for granular pavements with thin
bituminous surfacing [2 3]
The limiting strain criterion for the subgrade is given by
Eq. 1. It was derived by applying mechanistic procedure
to a range of pavements.
Where,
7.14
N = [8511/ µ ] (1)
µ
Grameen Sampark
= vertical compressive strain (microstrain)
at the top of the subgrade
N = allowable number of repetitions of the
strain before unacceptable level of
rutting develops.
Implicit in the design procedure for granular pavements
with thin bituminous surfacing, is a terminal condition
which is considered to be unacceptable and hence
signifies the end of life of the pavement. The terminal
condition is considered to be an average rut depth of
about 20mm, and terminal roughness about three times
the initial roughness.
AASHTO Low Volume Road Design Procedure [1]
The low-volume road design procedure used by
AASHTO is based on lower level of reliability (50%)
because of their low usage and associated low level of
risk. Predicted future traffic, seasonal resilient moduli of
roadbed soil, elastic modulus of aggregate base and
subbase layer, design serviceability loss, allowable
rutting and aggregate loss (GL) of surface course are the
main input for the design of low volume roads.
Common values for terminal serviceability index are
Pt=2.0. For minor highways like aggregate surfaced
roads, where funds or economy is the main factor, the
design is done by reducing the traffic or design life rather
than reducing the terminal serviceability to a number
lower than 2.00. Aggregate loss due to traffic and
erosion should be considered in the design and this may
be calculated using any of the following equations 2, 3
and 4.
According to a study by University of Texas at Austin:
Where,
GL = 0.12 + 0.1223 (LT) (2)
GL = Total Aggregate loss in inches;
LT = Number of loaded trucks in
thousands
Another study in Brazil formulated the following
equation:
GL = (B/25.4)/ (0.0045LADT + 3380.6/R +
0.467G) (3)

Where,
GL = Total Aggregate loss in inches during the
period of time being considered;
B = Number of blading during the period of
time being considered;
LADT = Avg. daily traffic in the design lane;
R = Avg. radius of curve, in feet, and;
G = Absolute value of grade, in percent
British study done in Kenya is more applicable to areas
with little truck activity and is given below:
Where,
AGL =
2 2 2
[T /(T + 50] * f (4.2 +0.092T +0.889R +
1.88VC) (4)
AGL = Annual aggregate loss, in inches;
T = Annual traffic volume in both directions,
in thousands of vehicles;
R = Annual rainfall, in inches;
Pradhan Mantri Gram Sadak Yojana
VC = Average percentage gradient of the road,
and
f = 0.037 for lateritic gravels; 0.043 for
quartzite gravels, 0.028 for volcanic
gravels, and 0.059 for coral gravels.
Rutting is bound to occur in average surfaced roads, and
is considered as performance criteria for these roads.
The typical value of allowable rut depth for designing an
aggregate surfaced road falls between 1.00 and 2.00
inches.
Design charts are available to estimate the required
thickness of aggregate surfaced roads for low volume
roads.
Vermont Agency of Transportation [4] procedure for the
design of low-volume pavement structures is based on
the 1993 AASHTO Guide for Design of Pavement
Structures. The following performance indicators in
terms of PSI were used:
For paved roads, initial PSI = 4.0 and terminal PSI = 2.0
and for unpaved roads, initial PSI = 4.0 and terminal PSI
= 1.0
Grameen Sampark 19

20
A maximum of 50mm rut depth was recommended for
the unpaved roads. The reliability adopted is 50%.
Asphalt Institute [5] adopted the following subgrade
strain criteria
Where,
Grameen Sampark
-2 0.223
= 1.05*10 *[1/N] (5)
N = No of 80 kN equivalent single axle loads;
Z
Z
= Vertical subgrade strain ( micro strain) at
top of the subgrade layer
TRRL [6] considers the following relationship to
complete allowable subgrade strains for 85 percent
probability of survival to a design life of N repetitions of
o
80kN axle and a pavement temperature of 20 C.
Log (N) = -7.21-3.95* log ( ) (6)
Z
The failure condition considered for the above criteria is
rutting of 20 mm
The Shell [7] design method uses the following
subgrade strain for different confidence levels:
-2 -0.25
50% confidence = 2.8*10 *N (7)
Z
-2 -0.25
85% confidence = 2.1*10 *N (8)
Z
-2 -0.25
95% confidence = 1.8*10 *N (9)
Z
A terminal value of percent serviceability (PSI) of 2.5
was taken as failure condition.
Indian Road Congress (IRC 37:2001) [8] adopted the
following performance criteria for high volume roads.
N R =
-8 4.5337
4.1656*10 [1/ Z ] (10)
N R = Number of cumulative standard axels to
produce rutting of 20 mm.
Z
= Vertical subgrade strain (micro strain).
Development of an average rut depth of about 20 mm is
considered to be failure in rutting mode.
IRC:SP:20:2002 [9] is for design of low-volume rural
roads in India. The criterion for determining the
thickness of a flexible pavement with a thin bituminous
surfacing is the vertical compressive strain on top of the
subgrade imposed by a standard axle load (80kN). The
maximum rutting allowed is 50mm before any
rehabilitation work is taken up. The design charts have
reportedly been prepared as per Road Note 29 of TRL,
IRC: 37 and other related experiences in India. No
mechanistic rutting criterion has been proposed
correlating the design life with subgrade strain or any
other parameter.
Mohanty et al [10] studied the performance of 59 village
road sections in Orissa and proposed some design
charts for construction of new low-volume rural roads.
The pavement condition data collected on these
sections were correlated with mechanistic response of
the pavement to develop a performance criteria based
on limiting rutting value.

Where,
-11 5.44
N = 3.42 x 10 (1/ ) (11)
N = Number of standard axle repetitions to
cause 50 mm rutting;
V
= Vertical sub grade strain
Performance criterion is the most important aspect
considered in the design of pavements and all rational
design methods must have properly developed
performance criteria. It is seen that most of the design
methods in vogue have design criteria mostly in terms of
subgrade strain and aim to control rutting. The main
concerns with the design practices followed in India are
that either they do not have performance critferia or
even if there is mention of performance criteria there is
not much evidence of the criteria having been
developed on the basis of sufficient data. This
emphasizes the need for collection of data on the
performance of different types of low-volume roads on a
long term basis. The recent initiative taken by NRRDA
for collection of performance data on the recently
constructed PMGSY will go a long way in filling this
major void in the low-volume road design in India.
References
1. American Association of State Highway and
Transportation Officials, “AASHTO Guide for
Design of Pavement Structures 1993, AASHTO,
Washington, D.C.
2. Austroads Pavement Research Group 1998, A
guide to the design of new pavements for light
traffic: a supplement to Astroads pavement design,
APRG Report No. 21, ARRB Transport Research,
Vermont South, Victoria.
3. Austroads, Pavement design a guide to the
structural design of road pavements, AP-17/92,
Austroads, Sydney, 1992.
4. Vermont Agency of Transportation, “Low Volume
Pavement Design Procedure”, Vermont Agency of
Transportation, Montpelier, VT, March 2002
V
Pradhan Mantri Gram Sadak Yojana
5. Ibid. Shook J.F., Finn F. N.., Witczak M. W. and
Monismith C. L., “Thickness Design of Asphalt
Pavements The Asphalt Institute Method, pp. 17-
44.
6. Lister N. W. and Powell W. D., “ Design Practice
for Bituminous Pavements in United Kingdom”
Proc. 6th International Conference on Structural
Design of Asphalt Pavements”, Vol-1, 1987, pp.
220-231.
7. Gerristen A. H. and Koole R. C. “Seven Years'
experience with the structural aspects of the Shell
Pavement Design Manual”, Proc. 6th International
Conference on Structural Design Asphalt
Pavements”, Vol-1 1987, pp. 94-106.
8. Indian Road Congress, IRC:37:2001 Guidelines
for Design of Flexible Pavements, New Delhi,
2001.
9. Indian Road Congress, IRC:SP:20-2002 Rural
Roads Manual, 2002, New Delhi.
10. Mohanty S. K., Reddy K. S. and Pandey B. B..,
“Performance and Design of Village Roads”,
Highway Research Bulletin No. 55, IRC, 1996, pp.
66-84.
Grameen Sampark 21

22
Stabilization of Soil Subgrade
with Polypropylene Fibres
Dr. I.K.Pateriya* and Dr. K. A. Patil**
In India, transportation is mainly by roads. Only roads
can access very small villages, remote areas and hilly
areas. Hence, considerable attention is required
towards the widening of roads, their suitability and
periodic repair works. Most state highways in the
central part of India have problems of foundation for
highway embankments, bridge abutments, retaining
walls and earth dams with steep slopes have been built
using different types of reinforcements. Hoare(1979)
analyzing the results of a series of laboratory
compression and CBR tests on a sandy gravel reinforced
with randomly distributed synthetic fibres less than 2%
by weight, observed that the presence of fibres
increased the apparent angle of internal friction and
ductility of the soil particularly at low confining stress.
A. Boominathan (1999) carried out some tri-axial
compression tests on sand reinforced with randomly
distributed fibres.
*Joint Director (Technical), NRRDA, Delhi
**Lecturer in Civil Engineering; Govt. College of Engineering, Karad (M.S.) 415 124
Grameen Sampark
Fibre reinforcement technique permits use of natural as
well as synthetic fibres for soil reinforcement. In
Maharashtra black cotton soil is found in abundance
which is highly expansive soil. An attempt has been
made to investigate the use of polypropylene fibres for
improving properties of locally available soil. The
comparison of properties of soil with addition of varying
percentages of fibres by dry weight of soil and having
different aspect ratios is also carried out. The addition of
polypropylene fibres resulted in increase in optimum
moisture content and decrease in maximum dry density.
Direct shear tests conducted on soil shows increase in
value of cohesion and decrease in value of angle of
internal friction. With the inclusion of the fibres increase
in C.B.R. value was observed. The crust thickness of
flexible pavement is appreciably reduced, due to
increase in C.B.R.value of soil subgrade.

EXPERIMENTAL WORK
Materials Used
The soil used in the study was collected from 10 km
distance from Jalna. The soil used was black cotton soil.
Table 1 shows geotechnical properties of soils collected
for experimentation. Polypropylene fibres of average
diameter 0.25 mm with aspect ratios of 20, 40 and 80
were used.
Sample Preparation
Fibre reinforced soil samples were prepared at
maximum dry density and optimum moisture content
obtained by conducting standard Proctor test on unreinforced
soil and reinforced soil. The fibre reinforced
specimens were prepared by hand mixing the dry soil,
water and polypropylene fibres. The percentage of fibre
used in samples was 1, 2, and 3 percent by dry weight of
soil. The water was added prior to fibre to prevent
floating problems. fibre reinforced soil samples were
prepared at the maximum dry density and the optimum
Table1: Geotechnical properties of soil
Pradhan Mantri Gram Sadak Yojana
moisture content obtained from standard proctor tests
on reinforced soil. Un-drained direct shear tests were
conducted on reinforced samples with varying
percentages of fibres and aspect ratio. California
bearing ratio (C.B.R) tests were conducted under soaked
conditions. Unconfined compression strength tests
were conducted on cylindrical specimen at Proctors
maximum dry density and optimum moisture content.
Specific Liquid Plastic Plasticity Maximum Dry Cohesion Angle of Internal
Gravity Limit % Limit % Index %
3
Density (gm/cm )
2
(kN/m ) Friction (Degrees)
2.49 56 27 29 1.53 34 16
RESULTS AND DISCUSSION
The influence of aspect ratio and fibre concentration on
the properties of soil were studied. The OMC and dry
density test results on black cotton soil with different
aspect ratio and fibre content are reported in Table 2.
These data indicate that maximum dry density
decreases gradually with increase in the fibre content,
which is due to lower density of the fibre than the soil
particles. An increase in Optimum moisture content
was observed due to adsorption of water particles on the
surface of polypropylene fibres.
Table 2: Proctor's test results for un-reinforced and reinforced soil
Sr. No. Description Aspect Ratio % O.M.C MDD (gm/cm3)
1. Soil without reinforcement - 24.6 1.53
2. Soil with 1 % Polypropylene fibres 20 24.7 1.52
3. Soil with 2 % Polypropylene fibres 20 24.9 1.51
4. Soil with 3 % Polypropylene fibres 20 25.1 1.50
5. Soil with 1 % Polypropylene fibres 40 24.8 1.52
6. Soil with 2 % Polypropylene fibres 40 25.0 1.50
7. Soil with 3% Polypropylene fibres 40 25.3 1.48
8. Soil with 1 % Polypropylene fibres 80 24.9 1.50
9. Soil with 2 % Polypropylene fibres 80 25.2 1.47
10. Soil with 3% Polypropylene fibres 80 25.4 1.44
Grameen Sampark 23

24
Changes in Cohesion and
Direct shear tests were conducted on soil samples in unreinforced
and reinforced conditions. The
Grameen Sampark
reinforcement was added in the range of1%to3%with
varying aspect ratios of 20, 40 and 80. The results
obtained are summarized in Table 3.
Table 3: Effect of reinforcement on shear strength characteristics of soil
Sr. No. Description Aspect Cohesion Increase over
Ratio
2
(kN/m ) % Soil without
Reinforcement
(Degrees)
1. Soil without reinforcement - 34 — 16
2. Soil with 1 % Polypropylene fibres 20 35.4 4.12 15.9
3. Soil with 2 % Polypropylene fibres 20 37.2 9.42 15.6
4. Soil with 3 % Polypropylene fibres 20 36.9 8.53 15.5
5. Soil with 1 % Polypropylene fibres 40 36.3 6.76 16.0
6. Soil with 2 % Polypropylene fibres 40 39.6 16.47 15.8
7. Soil with 3 % Polypropylene fibres 40 38.7 13.82 15.6
8. Soil with 1 % Polypropylene fibres 80 35.8 5.29 15.7
9. Soil with 2 % Polypropylene fibres 80 38.4 12.94 15.4
10. Soil with 3 % Polypropylene fibres 80 37.9 11.47 15.0

From Table 1, it is found that black cotton soil has
2
cohesion (C ) as 34 kN/m and angle of internal friction
( ) as 16 degrees. From Table 3, it is found that due
addition of polypropylene fibres in black cotton soil, for
all aspect ratios of 20, 40 and 80, the cohesion increases
and the angle of internal friction decreases. Due to
addition of 2% polypropylene fibres in black cotton soil,
the cohesion increases by 9.42%, 16.47% and 12.94%
for aspect ratio of 20,40 and 80 respectively. The angle
of internal friction decreases by 2.5%, 1.25% and
3.75% for aspect ratio of 20, 40 and 80 respectively.
Fibre content and aspect ratio governs the shear strength
of fibre reinforced soil. The strength of reinforced soil
increases with an increase in fibre content. The rate of
increase is higher at lower fibre content i.e. less than
2%. At fibre content greater than 2%, the relative gain in
Pradhan Mantri Gram Sadak Yojana
strength is small. This is possibly due to the fact that
fibres of lower specific gravity occupy relatively large
volume in the composite. Thus, with higher fibre
content, the quantity of soil matrix available for holding
the fibres is insufficient to develop an efficient bond
between soil and fibre. above 2% fibre content, the
uniform mixing of soil and fibre is difficult as balling up
of fibre takes place.
Changes in CBR value of soil
Table 4: CBR values for reinforced and un-reinforced soil
The CBR tests were conducted on un-reinforced soil and
soil reinforced with fibre. The tests were carried out after
four days soaking in water. CBR values at different
aspect ratio and varying fibre content are given in table
4 and Fig. 1. The maximum CBR value in present study
was found at aspect ratio of 40 and 2% fibre content.
Sr.No. Description Aspect Ratio Soaked CBR %
Value (%) increase
1. Soil without reinforcement - 3.05 —-
2. Soil with 1 % Polypropylene fibres 20 4.20 37.77
3. Soil with 2 % Polypropylene fibres 20 5.15 68.85
4. Soil with 3 % Polypropylene fibres 20 5.05 65.57
5. Soil with 1 % Polypropylene fibres 40 4.50 47.55
6. Soil with 2 % Polypropylene fibres 40 5.35 75.40
7. Soil with 3 % Polypropylene fibres 40 5.20 70.49
8. Soil with 1 % Polypropylene fibres 80 4.40 44.26
9. Soil with 2 % Polypropylene fibres 80 5.15 68.85
10. Soil with 3 % Polypropylene fibres 80 5.00 63.93
From Table 3, it is found that due addition of 2 %
polypropylene fibres in black cotton soil, the increase in
C.B.R. value is found to be 47.55%, 75.40 % and
70.49 % for aspect ratio of 20, 40 and 80 respectively.
Also, it is observed that on 3% addition of
polypropylene fibres, C.B.R. value is found to be less
than that at 2% fibre content. Hence, 2 % fibre content
with aspect ratio of 40 may be considered as optimum
fibre content.
Grameen Sampark 25

26
Increase in the C.B.R. value is due to compaction
characteristics of polypropylene fibre reinforced soil.
Higher compaction can be achieved by addition of
fibres with higher aspect ratio up to certain limit. The
design of flexible pavement is governed by C.B.R. value
of subgrade soil. Thus, higher value of C.B.R. for
subgrade soil gives lesser pavement thickness and
proves to be the economical solution in pavement
construction.
% Soaked CBR Value
5.5
5
4.5
4
3.5
3
0 1 2 3
Polypropylene fibres Content
Figure 1: Relationship between polypropylene fibres
content and Soaked % C.B.R. value
Grameen Sampark
1 % fibres 2 % fibres 3 % fibres
Reduction in Crust Thickness of Flexible
Pavement
Thickness of flexible pavement is calculated based on
C.B.R. value of soil subgrade and traffic in terms of ESAL
applications as per SP:72-2007. As the C.B.R. value
increased from 3.05 % to 5.35 %, on addition of 2 %
polypropylene fibres with aspect ratio of 40, the crust
thickness reduces appreciably. Table 5 below, illustrates
the reduction in crust thickness for different ESAL
applications (Traffic categories T4 to T 7of SP 72:2007)
From table 5, it is observed that the design crust
thickness reduces by 75 mm for traffic category T4 and
by 100 mm for traffic categories T5 to T7. The reduction
in crust thickness is partly in the thickness of modified
soil with C.B.R. more than 10 % and partly in the
thickness of granular sub base (GSB).
Conclusions
Based on the limited experimental work done in the
laboratory, following conclusions are drawn:
1. On addition of 2 % polypropylene fibres with
aspect ratio of 40, the soaked C.B.R value can be
improved up to 75 % in comparison with the unreinforced
soil.
2. The crust thickness is reduced by 75 to 100 mm for
different ESAL applications.
References
1. Boominathan A. (1999), “Randomly Distributed
fibre Reinforced Sand”, Short term course on
Geosynthetics and reinforced soil structure,
I.I.T.Madras, India, pp. XVI 1 to XVI 10.
2. Meenal Gosavi, K.A.Patil, S.Mittal (2004) Swami
Saran “Improvement of Properties of Soil in
Subgrade by Using Synthetic Reinforcement”
Journal of Institution of Engineers (India), CV, Vol.
84, pp.257-262, February 2004
3. Ranjan Gopal and Charan H.D. (1998) “Randomly
Distributed fibre Reinforced Soil”, IE (I) Journal,
Vol.79, pp. 91-100 .
Table 5: Reduction in Crust Thickness with increase in CBR value
Sr. CBR 1 to 2 Lakhs 2 to 3 Lakhs 3 to 6 Lakhs 6 to 10 Lakhs
No. ESAL (T4 ) ESAL (T5 ) ESAL (T6) ESAL (T7)
1. 3.05 % 375 mm 425 mm 475 mm 525 mm
2. 5.35 % 300 mm 325 mm 375 mm 425 mm

Experiencing Folded Plates in
Roadworks Retaining Structure
Dipankar Chakrabarti*, Shyamalendu Mukherjee**
Road is a high investment sector. The sustainability of
roads results in unobstructed growth. Sustainability of
embankment signifies that its toe does not slip, the slope
is steady and if at all sloped surfaces erode, to some little
extent, the eroded soil particles do not go waste into
ditches/rivulets. In the states like West Bengal, Assam,
Part of Bihar and may be in all other states the rural road
alignments generally follow embankment which had
been previously used as road. The soil of these
embankments was borrowed from close vicinity, some
times even just from areas adjacent to the toe lines. Now
while aiming at widening, raising embankment it is
found that in many stretches the existing mass are under
*Executive Engineer (HQ) WBSRDA,
**Assistant Engineer (Nadia Division) , WBSRDA,West Bengal
Pradhan Mantri Gram Sadak Yojana
threat of slippage into such ditches. The structural
element that we may think about for resisting slippage is
a retaining wall. When it is very low in height and
constructed along the toe line, we may call it as Toe
wall. Cut-off wall is another hidden element, which
plays effective role by resisting moisture entry in the
embankment. A considerable amount of resources is put
in for constructing the retaining walls. Economising this
account shall fetch overall economy. The objective was
to develop a structural system, which would be cost
effective but capable enough to perform as retaining
wall, toe wall or cut-off wall, may be even as Guide
Bank.
Grameen Sampark 27

28
Laboratory Test (Under Vertical Loading)
A set of tests have been carried out in laboratory to
ascertain the ability to sustain vertical load by a paper in
Grameen Sampark
terms of its own weight when folded to different ratios of
length and breadth of folds corresponding to different
heights. The results obtained are as under:
Test Height (H) Length of Breadth of Self weight Slenderness Length of Sustained Ratio of
No. (in mm) Fold (L) Fold (B) of the Paper Ratio Fold/ Breadth weight Load and
(in mm.) (in mm.) (in gms.) of Fold (L/B) (in gms.) Self weight
I 80 75 25.0 2.56 3.20 3.00 454.00 177.34
II 80 55 27.5 2.56 2.90 2.00 543.00 214.06
III 80 30 10.0 1.28 8.00 3.00 170.00 132.81
IV 66 63 42.0 1.60 1.57 1.50 410.00 256.25
V 143 63 42.0 3.33 3.40 1.50 356.67 107.11
VI 100 80 50.0 1.00 2.00 1.60 238.00 238.00
VII 45 75 20.0 4.00 2.25 3.75 1020.00 255.00
VIII 56 60 22.0 8.00 2.54 2.72 1987.00 248.38
IX 180 43 18.0 5.00 10.00 2.39 145.00 29.00
X 150 43 18.0 4.00 8.33 2.39 770.00 197.50
XI 120 43 18.0 4.00 6.67 2.39 947.00 236.75
XII 83 43 18.0 2.00 4.61 2.39 1800.00 750.00
It is found from the laboratory tests that when breadth of
fold (B) = 0.125 times of height (H) and the length of fold
(L) is thrice the breadth of fold the most economical
cross section of the folded plate wall would be adequate
to sustain vertical load upto hundred and thirty three
times (133) that of the self weight of the structure. Which
virtually means that a 3 m. long 250 mm. thick brick
wall of height 3 m., if folded in conformity to the above
parameters of fold, can take load of 580 tons (Self weight
4387 Kgs.). It can sustain load from approximately 800
m2 of roof area. which confirms that if materials of
higher crushing strength could be obtained by
improving quality of material used for folded wall, the
cost for quality improvement might bring much higher
cost benefit ratio.

Laboratory Test on Folded Plate Structure
under Transverse Loading
Structural performance of brick wall is less critical in
compression and more in bending. An attempt was
made for model analysis with cuboids arranged in the
form of Rat Trap Bonded folded structure. Cuboids of
thermocole 12 mm x 20 mm x 40 mm. were made for
the purpose but the attempt was in vain. Since the
thermocole cuboids being very light in weight did not
remain static while the next layers were put in.
Anticipating that wooden cuboids might be better
wooden cuboids are under preparation. About 4500
numbers of wooden cuboids of different dimensions are
needed for a model analysis.
Field Application of Folded Plates
In the district of Nadia in West Bengal a (PMGSY)
Project was initially selected. The road selected was
“Elangi to Lakshmigachha” under Package No.
WB/14/25. There was a pond beside the road at
chainage 5.90 km. It was decided to go for a
performance study of folded plate retaining wall of
Pradhan Mantri Gram Sadak Yojana
height 1.5 m above ground level. The breadth at the
bottom of retaining wall at foundation level was kept 2/3
of the height of retention. A 975 mm wide base plate of
100 mm. thick PCC (1:3:6), was cast. Then a 250 mm
thick brick masonry wall in folded configuration was
constructed. Out of the total length, a stretch was further
enforced with corbelled bricks, five layers (75x5=375
mm) projected to the countryside. The idea was to see
that the mass of earth over the shelf, developed by the
corbelling, would generate a restoring moment which
would minimise the overturning moment.
The folded brick wall was constructed against the
conventional English or Flemish Bond in a new bonding
system called “Rat Trap Bond”. It had been propagated
in India through the efforts of renowned Architect Shri
Laurie Baker .There is a saving of 25% of the total
number of bricks and thus in the cost by using Rat Trap
Bond. Computer simulated test modules have
established that Rat Trap Bond is 25% stronger. The
following comparative statement shows consumption
of basic materials for brick wall by conventional English
Bond and Rat-by-Rat Trap Bond.
Material required
with respect to type of bonding No of Bricks Cement Sand
1 Cum. Brick work 230 th using English Bond 487 62 Kgs. 0.22 Cum.
1 Cum. Brick work using Rat Trap Bond 370 30 Kgs. 0.126 Cum.
Folded Plate Folded Plate as Guide Bank
Grameen Sampark 29

30
Apart from the above, both faces of Rat Trap Bonded
Brick wall are checked with plumb bob, so both the
faces are uniform. As a result there is no necessity to
provide plastering. All that would be required is neat
cement pointing and patching on one edge of the
header course. Hence there will be additional savings in
plastering.
On completion of construction and curing the back
filling was done with, in layers by local earth of
Maximum Dry Density (MDD) 1.70 gms./cc. Then an
earth compactor was employed to roll and compact the
retained earth. The compactor was directed to start
rolling from about 1 m away from the retaining wall and
it came slowly towards the folded wall and went on
rolling moving over the corbelled shelves with full
capacity of vibration, which is equivalent to 36 M.T.
Observations
Through the wall was expected to fail severely, it did
not. The stretches where the relieving shelves were not
in existence, after repetition of about 3-4 cycles of full
vibration rolling the vertical joint at the junction of fold
on the pond side showed a line of crack which
propagated along the line of weakness of brick masonry.
The maximum width of crack was about 35 mm and it
appeared at about 7250 mm from GL i.e. at about at ½ of
height from GL. This clearly signifies that the failure was
due to intensity of rolling load to this enormous extent.
Not by virtue of back filling. The entire operation was
Grameen Sampark
video recorded. A selected portion of video recording is
attached with a soft copy of this document.
Progress of Field Tests
A good number of folded plates were then applied to
different locations of different projects as a cost effective
tool for different height of retentions also. All are
performing satisfactory till date. Some photographs are
attached.
In one instance folded plate has been applied to act as a
guide bank beside a rivulet, which converges and
passes through a narrow vented old culvert at the fag
end of a PMGSY road – Rukunpur Khalshipara to
Bangaljhi Ferry Ghat under Package No. WB/14/27.
The stretch of road at this point would get inundated in
every monsoon. Erosion was a predominant feature in
this stretch. The folded plate brick masonry structure
was used as a guide bank and it performed very well. It is
observed that the fins of the folds acted like small spurs
and the soil started depositing between the fins and
chances of erosion has been reversed.
Analysis of Economics
A cost estimate has been done for three types of
retaining wall 11.45 m. long to retain 1.5 m. high earth.
The types of wall chosen are as under: -
1. Folded plate Rat-Trap Bonded wall.
2. Standard Trapezoidal Brick masonry wall.
3. Standard Trapezoidal Plain Cement Concrete
(1:2:4)
The following table shows the comparative analysis of
the economics of the types of walls.
Type of Wall Cost / running meter
1. Folded plate “Rat-Trap Rs. 1781.25 / m.
bonded wall”
2. Brick masonry retaining Rs. 3498.54 / m.
wall
3. Plain Concrete (1:2;4) Rs. 5104.60 / m.
retaining wall

It shows that the cost of standard brick masonry
retaining wall is almost double and concrete retaining
wall costs 2.865 times more than the folded plate brick
rat-trap bonded retaining wall. Hence, in other words
the savings will be to the tune of 50% and 65 %
respectively.
Structural Analysis
A preliminary analysis shows that the structure is
marginally safe. But from experiment it reveals that the
structure is highly safe. Therefore it can be concluded
that certain parameters are yet to be considered. Further
analysis in this light is being carried out.
Conclusions
Based on the limited experimental work and
observation on some of the structures already
constructed in the field, it can be concluded that:
1. The folded plate structure develops immense
stiffness and sustainability against any and every
kind of loads due to folded configuration.
2. There must be some structural uniqueness
generated within the system, which contributes
additional stiffness.
3. By virtue of this phenomenon the folded plate wall
is found to be more efficient than the degree of
efficiency found out by usual structural
calculations.
4. The folded plate structure is very economical and
can be used safely as retaining walls, cut off walls,
and guide banks.
Pradhan Mantri Gram Sadak Yojana
Figure 1: Typical details for 1.500m. heigh
(G.L. to Top Level) Retaining Wall
SECTIONAL ELEVATION THROUGH XX
PLAN OF RAT TRAP BRICK MASONRY RETAINING WALL
All dimensions are in mm.
Figure 2: Details of Rat Trap Brick Bonding
ODD COURSES EVEN COURSES
PLAN
ODD COURSES EVEN COURSES
L - JUNCTION
ODD COURSES EVEN COURSES
T - JUNCTION
Grameen Sampark 31

News in Brief
General Body Meeting
th
The 10 General Body Meeting under the Chairmanship of Hon'ble Minister of Rural Development and
rd
President NRRDA was held on 3 November 2008. Amongst other items, the General Body approved the
Annual Report for 2007-08 and the audited accounts for the year 2007-08 were adopted.
Executive Meeting
th th
The 17 Executive Committee Meeting was held on 12 January 2009. Apart from the review of the
activities carried out under PMGSY the Executive Meeting approved the appointment of the Statutory
Auditors for 2008-09 and the empanelment of NQMs.
Conference and Workshops
Date Venue Subject
nd rd
22 - 23 Nov, 08 Tawang, National Workshop on Planning and Construction of
Arunachal Pradesh Hill Roads in Rural Areas.
th th
06 - 10 Jan, 09 Ashoka Hotel,
th
16 General Session of Afro-Asian Rural Development
New Delhi Organization (AARDO) Conference.
th th
09 - 10 Feb, 09 NITHE Interactive W/S on performane of NQMs & STAs - GJ,
HR, HP, J&K, PB, MP, RJ, UK & UP
th
27 Feb, 09 Patna, Bihar Inauguration/ Foundation Stone Laying Ceremony at
Patna for PMGSY Works
th
18 Mar, 09 New Delhi Workshop on E-Procurement
th
06 April, 09 NRRDA Presentation on Procurement and Quality. Control for
Delegation from Sri Lanka (30 min)
th
08 April, 09 Krishi Bhawan Meeting with French Delegation
National Rural Roads Development Agency
Ministry of Rural Development, Government of India
th
5 Floor, 15-NBCC Tower, Bhikaji Cama Place, New Delhi-110 066
Ph.: 26716930/ 33, Fax: 51000475 E-mail: nrrda@pmgsy.nic.in
Web: www.pmgsy.org www.pmgsy.nic.in