Design of road pavements , MSA, PCU, WBM

1. 1
ROADS
Water Bound Macadam
Amardeep Singh

2. 2
CATEGORY OF ROADS
• NATIONAL HIGHWAYS – Main highways of India connecting major ports, foreign
highways, capitals of large states. Total length in India 58112 kms
• STATE HIGHWAYS – Alternate roads of state, connecting National Highways and cities
within the state. Total length 137119 kms
• DISTRICT ROADS – Important roads of state serving areas of production and markets.
Total length 470000 kms
• OTHER DISTRICT ROADS – Roads serving rural areas for production and outlet to market
• VILLAGE ROADS – Roads connecting villages. Total length of ODR and VR in India
2650000 kms
– Total length of all type of roads in India is 3315231 kms.

3. 3
TYPICAL ROAD CROSS SECTION

4. 4
GEOMETRIC DESIGN
• Elements of design:
– Sight distance
• The length of road ahead visible to drivers
– Stopping sight distance
– Passing sight distance
– Horizontal alignment
• Super elevation (e=V2/127R)
where, V is velocity (kph) of vehicle and R is radius (mtr) of curve
Super elevation commonly not more than 12 % of the width of road
• Minimum radius
– Vertical alignment
– Pavement design
– Intersection and crossing design

5. 5
Pavement Thickness Design
• Determined by IRC : 37 , two parameters are required –
MSA and CBR
Design Traffic in CVPD (A)
A = P(1 + r ) x
P = No. of commercial vehicles per day (CVPD) as per last count
X = No. of years between last count & the year of completion(Yrs.)
Design traffic in Million Standard Axles (MSA) (N)
N = [ 365 x A x [( 1+r ) n - 1] x F x D] / r
A = Design Traffic in CVPD.
r = annual growth rate of commercial vehicles
n = design life in years
F = vehicle damage factor
D = lane distribution factor
– California Bearing Ratio (CBR) of underlying soil of road
Soaked CBR value ( after 96 hours of submerged in water )
Average traffic of 7 days is computed and only Buses, Trucks and other heavy vehicles
came under commercial vehicles category.

6. 6
Calculation of MSA
Traffic data provided by client
Car/Van/
A rick. Bus Truck
Mcycle/
scooter
Animal
driven Cycle
Others
(Heavy)
3473 334 2726 2467 773 1740 927
Commercial Vehicles per day(Trucks+ Buses + Others heavy) = 3987
Conversion into PCU’s
1 3 3 0.5 6 0.5 3
3473 1002 8178 1233.5 4638 870 2781
Total PCU = 22176
PCU = Passenger Car Unit, it is a conversion factor as per IRC
to convert each vehicle to equivalent to Car. It is required to
determine the width of the road as per designed traffic.

7. 7
Calculation of MSA
CALULATION OF M.S.A. (IRC:37-2001)
Sr. No.
Abservat
ion
Descripti
on Value
1 P
No. of commercial vehs as per last
count 3987
2 x No. of years between last count & the year of completion(Yrs.) 1
3 CARRIAGE WAY LANES 2
4 A Design Traffic in CVPD. A + P(1 +r )^ x 4286
5 r ANNUAL GROWTH RATE OF COMMERCIAL VEHICLES 0.075
6 n DESIGN LIFE IN YEARS 5
5 F VEHICLE DAMAGE FACTOR 4.5
AS PER TABLE NO 5.1 OF IRC
7 D LANE DISTRIBUTION FACTOR 0.75
8 N DESIGN TRAFFIC IN Million Standard Axles 30.67
N = [ 365 x A x [( 1+r ) n - 1] x F x D] / r (Say) 31
After the calculations of MSA
and values of soaked CBR are
known, with reference of
IRC:37-2001 the pavement
thickness is determined.

8. 8
Calculation of MSA
At MSA 30 and soaked CBR
value assumed 5% , with
reference of IRC:37-2001 the
pavement thickness is as per
table.
Total Pavement Thickness : 710 mm
BC : 40 mm
DBM : 120 mm
Base : 250 mm
Sub-Base : 300 mm

9. 9
Carriage Lane widths as per IRC
• Single lane -- 3.75 m
• Two lane, no kerbs -- 7.0 m
• Two lane, raised kerbs -- 7.5 m
• Intermediate carriage way -- 5.5 m
• Multi lane -- 3.5 m x no of lanes

10. 10
Construction of Road - WBM works
• Water bound macadam is most commonly used practice in road
construction in India. It was developed by a Scottish Engineer John
Loudon McAdam.
• The road layer consists of clean crushed aggregates, mechanically
interlocked by rolling and bound together with screenings, filler
material and water laid on a well compacted base course, is called
water bound macadam (W.B.M.). Generally all operations of W.B.M.
is done manually by skilled labor.
• Water Bound Macadam comes under Base / Sub Base Category
• There are commonly three types of aggregate sizes/ Gradings
G1 – 90 to 45 mm
G2 – 63 to 45 mm
G3 – 53 to 22.4 mm

11. 11
Construction of Road - WBM works
Materials
• Coarse aggregates : Coarse aggregates shall be either crushed or broken stone, crushed
slag, over burnt brick aggregates or any other naturally occurring aggregates such as kankar
and laterite of suitable quality. Not less than 90 percent by weight of the gravel/shingle pieces
retained on 4.75 mm sieve shall have at least two fractured faces.
• Screenings : Screenings to fill voids in the coarse aggregate shall generally consist of the
same material (13.2 mm or 11.2 mm crushed stone chips) as the coarse aggregate. However,
where permitted, predominantly non-plastic material such as moorum or gravel (other than
rounded river borne material) may be used for this purpose provided liquid limit and plasticity
index of such material are below 20 and 6 respectively and fraction passing 75 micron sieve
does not exceed 10 percent.
• Binding material : Binding material to be used for water bound macadam as a filler material
meant for preventing raveling shall comprise of a suitable material having a Plasticity Index
(PI) value of less than 6 as determined in accordance with IS:2720 (Part-5).
For Binding material crusher dust, fly ash may also be used because of its non plastic nature if
approved by client.

12. 12
Construction of Road - WBM works
Laying of Aggregates Dry Rolling
Spreading of screenings Water sprinkling and compaction

13. 13
Construction of Road - WBM works
• Construction Operations
1. Preparation of base : The surface of the sub-grade to receive the
water bound macadam course shall be prepared to the specified grade and camber
and cleaned of dust, dirt and other extraneous material.
2. Spreading coarse aggregates : The coarse aggregates shall be spread
uniformly and evenly upon the prepared sub-grade/sub-base in the required
quantities from the stockpiles. The thickness of each compacted layer is not more
than 100 mm for Grading 1 and 75 mm for Grading 2 and 3.
Generally in road works loose thickness of layer is provided 1.33 times to the
desired compacted thickness.
Wooden blocks of desired loose thickness of layer can be used to maintain level.
Wherever possible, approved mechanical devise such as Grader can be used to
spread the aggregates uniformly so as to minimize the need for manual rectification
afterwards. For spreading of aggregates use of JCB of directly by dumper should be restricted.

14. 14
Construction of Road - WBM works
3. Rolling: Immediately following the spreading of the coarse aggregate,
Dry rolling shall be started with three wheeled power rollers of 80 to 100 kN
capacity or tandem or vibratory rollers of 80 to 100 kN static weight.
Rolling shall begin from the edges gradually progressing towards the centre.
First the edges shall be compacted then roller move inward parallel to the centre
line of the road, in successive passes uniformly lapping preceding tracks by at least one half
width at a speed of 10 km/hr.
4. Rolling shall be discontinued when the aggregates are partially
compacted with sufficient void space in them to permit application of screenings.
5. During Dry rolling, slight sprinkling of water may be done, if necessary.
Material which gets crushed excessively during compaction or becomes segregated
shall be removed and replaced with suitable aggregates.

15. 15
Construction of Road - WBM works
6. Application of screenings: After the coarse aggregate has been Dry
rolled, Screenings to completely fill the voids and shall be applied gradually over
the surface. Dry rolling shall be done while the screenings are being spread so that
vibrations of the roller cause them to settle into the voids of the coarse aggregate.
The screenings shall not be dumped in piles but be spread uniformly in successive
thin layers either by the spreading motions of hand shovels or by mechanical spreaders, or
directly from tipper with suitable grit spreading arrangement.
7. Sprinkling of water and grouting: After the screenings have been
applied, the surface shall be copiously sprinkled with water, swept and rolled. Hand
brooms shall be used to sweep the wet screenings into voids and to distribute them
evenly.

16. 16
Construction of Road - WBM works
8. Application of binding material: After the application of screenings
the binding material shall be applied successively in two or more thin layers at a
slow and uniform rate.
After each application, the surface shall be copiously sprinkled with
water, the resulting slurry swept in with hand brooms, or mechanical brooms to fill
the voids properly, and rolled during which water shall be applied to the wheels of
the rollers if necessary to wash down the binding material sticking to them.
These operations shall continue until the resulting slurry after filling of voids, forms
a wave ahead of the wheels of the moving roller.
9. Setting and drying: After the final compaction of water bound
macadam course, the pavement shall be allowed to dry overnight. Next morning
hungry spots shall be filled with screenings or binding material as directed, lightly
sprinkled with water if necessary and rolled. No traffic shall be allowed on the road
until the macadam has set.
The compacted water bound macadam course should be allowed to completely dry
and set before the next pavement course is laid over it.
The water bound macadam work shall not be carried out when the atmospheric
temperature is less than 100C in the shade.

17. 17
Grading Requirements Of Aggregates

18. 18
Quantities of Aggregates and screenings -
10m2 area

19. 19
Quantities of Binding material -10m2 area
• The quantity of binding material required for 75 mm compacted
thickness of water bound macadam will be 0.06-0.09 m3/10m2 and
• 0.08-0.10m3/10m2 for 100 mm compacted thickness.

20. 20
DRAINAGE of WATER
• DRAINAGE is VERY! VERY! VERY! IMPORTANT, both in relation to road pavement
construction and maintenance.
• Good drainage will help to keep the water table (and strength) of the road
pavement in equilibrium.
• Rain water should be drained out through camber provided and should not
collect over the wearing surface in any case.
• Water below the road pavement must be kept low and not be allowed to rise up
into the construction layers
• The road pavement must be constructed so that it will drain in the event of a
failure of the integrity of the surfacing layers, i.e. if water is able to enter the
road pavement there must be a path for it to exit.

21. 21
DRAINAGE SYSTEMS FAILURE

22. 22