Flexible Pavement Design
Pavement is a structure which should enable passage of traffic of different kinds, in different kinds of terrains and seasons
· SAFELY
· EXPEDITIOUSLY
· ECONOMICALLY
· COMFORTABLY
For design of flexible Pavement, the following factors are required.
1. Design traffic in terms of cumulative number of standard axles
2. California Bearing Ratio of the Sub grade in case of new formation or Widening of an existing road.
3. Benkelman Beam deflection value in case of Overlay of an existing pavement.
1.Computation of design traffic (As per IRC-37 – 2001)
Design traffic (N) is considered as the cumulative number of standard axles (8160 Kgs) to be carried during the design life calculated using the equation,
N = 365 x ((1+r) n -1) x A x D X F
r
Where,
N = Cumulative number of standard axles to be catered during
design period in terms of Msa.
design period in terms of Msa.
A = Initial traffic in the year of completion of construction in
terms of CVPD
terms of CVPD
D = Lane distribution factor
F = Vehicle damage factor (Either from the table or from the axle load survey)
n = Design life in years
r = Annual growth rate of commercial vehicles
In order to estimate the design traffic, the following data pertaining to the road for which the pavement design made are required.
Ø Initial traffic after construction in terms of No. Of commercial vehicles per day (CVPD). This shall be based on traffic census.
Ø Traffic growth rate during the design life in percentage
Ø Design life in No. of years
Ø Vehicle damage factor (VDF)
Ø Distribution of commercial traffic over the carriageway (Lane distribution factor)
Traffic Census
2.Computation of Initial Traffic by Traffic census (As per IRC-9-1972)
Traffic data is essential to calculate traffic intensity based on initial prevailing traffic and to project the traffic for the design period. Design traffic shall be calculated based on actual traffic flow. Estimate of initial daily average traffic flow for any road should normally be based on traffic conducted for 7 consecutive days, 24 hours classified traffic counts. Traffic should be counted at least twice every year.
One count should be taken during the peak season of harvesting and marketing and the other during the lean season. Traffic census should not encompass abnormal conditions of traffic like a fair or exhibition. Every subsequent census should be taken at the same locations. New stations could be added as and when needed. The summary of data should essentially consist of the following.
Fast Moving Vehicles
|
Slow Moving Vehicles
|
Two Wheelers
|
Bi-cycles
|
Auto Rickshaws
|
Cycle rickshaws
|
Car, Jeep and Van
|
Animal drawn
|
Light Commercial Vehicles & Mini Bus
|
Tractor trailer
|
Buses
| |
Trucks
| |
Multi axles
|
From traffic survey, two important components are arrived, Viz. Commercial Vehicles Per Day (CVPD) and Passenger Car Unit (PCU). For the pavement design only the number of Commercial Vehicles Per Day (CVPD) of gross weight of 3 tonnes and above is considered. The Commercial Vehicles Per Day is used for arriving the Design Traffic and Passenger Car Unit is used for arriving the required carriageway width.
3.Carriageway Width (As per IRC -64 - 1990 )
The width and lay out of roads depend on many factors, chief amongst them being the classification of the road and traffic volume. The road Carriageway width should be designed to accommodate the design traffic volume. The width of carriageway should be sufficient for the traffic expected on the road in the design year. The width requirement should be assessed on the basis of equivalent passenger car units.
For making capacity computations under mixed traffic conditions, the different types of vehicles should be converted into a common unit known as Passenger car unit. The following table gives equivalency factors for various categories of vehicles for calculation of passenger car units (PCU).
(Table No.PCU1)
S.No.
|
Vehicle type
|
Equivalent multiplication factor
|
1
|
Passenger car, Tempo or Auto rickshaw
|
1.0
|
2.
|
Agriculture tractor or LCV
|
1.5
|
3
|
Cycle, Motor cycle or Scooter
|
0.5
|
4
|
Truck, Bus or Agricultural tractor – trailer unit
|
3.0
|
5
|
Cycle rickshaw
|
1.5
|
6
|
Horse drawn vehicle
|
4.0
|
7
|
Bullock cart (Large)
|
8.0
|
8
|
Bullock cart (Small)
|
6.0
|
Different lane width and Their Design service volumes
S. No.
|
Lane width of Road as per
IRC:64-1990
|
Design service volume in Passenger car unit per day in both directions
|
1
|
Single lane width of 3.75m with earthen shoulders
|
2,000
|
2
|
Intermediate lane width of 5.5m with earthen shoulders
|
6,000
|
3
|
Two lane of 7 m width with earthen shoulders
|
15,000
|
Tentatively, a value of 35,000 PCUs can be adopted for four-lane divided carriageways located in plain terrain . It is assumed for this purpose that reasonable good earthen shoulders exist on the outer side, and a minimum 3.00 M wide central verge exist. In case well designed paved shoulders of 1.50m width are provided, the capacity value of four-lane dual roads can be taken upto 40,000 PCUs.
Recommended Design Service Volume ( PCUs per hour) for Roads in Urban Areas(Table DSV2)
S.No.
|
Type of carriage way
|
Total Design service volumes for different categories of urban roads.
| ||
Arterial
|
Sub Arterial
|
Collector
| ||
1.
|
2-Lane ( One-way)
|
2400
|
1900
|
1400
|
2.
|
2-Lane ( Two-way)
|
1500
|
1200
|
900
|
3.
|
3-Lane ( One-way)
|
3600
|
2900
|
2200
|
4.
|
4-Lane Undivided
( Two -way)
|
3000
|
2400
|
1800
|
5.
|
4-Lane Divided
( Two -way)
|
3600
|
2900
|
---
|
6.
|
6-Lane Undivided
( Two -way)
|
4800
|
3800
|
---
|
7.
|
6-Lane Divided
( Two -way)
|
5400
|
4300
|
---
|
8.
|
8-Lane Divided
( Two -way)
|
7200
|
---
|
---
|
Illustrated example for calculation of PCU is as below:
Vehicle type (a)
|
Average No of vehicles per day (b)
|
Equivalent multiplication factor (c)
|
Total PCU per day (b x c)
|
No of Commercial vehicles with more than
3 t weight
|
Passenger car
|
276
|
1
|
276
|
-
|
Tempo(LCV)
|
360
|
1
|
360
|
360
|
Auto rickshaw
|
63
|
1
|
63
|
-
|
Agriculture tractor
|
99
|
1
|
99
|
99
|
Cycle
|
124
|
0.5
|
62
|
-
|
Motor cycle and Scooter
|
424
|
0.5
|
212
|
-
|
Truck
|
851
|
3
|
2553
|
851
|
Bus
|
259
|
3
|
777
|
259
|
Agricultural tractor – trailer unit
|
519
|
3
|
1557
|
519
|
Cycle rickshaw
|
12
|
1.5
|
18
|
-
|
Horse drawn vehicle
|
5
|
4
|
20
|
-
|
Bullock cart (Large)
|
28
|
8
|
224
|
-
|
Bullock cart (Small)
|
34
|
6
|
204
|
-
|
Total
|
3054
|
6425
|
1691
|
4. Traffic growth rate (r) (As per IRC-37 – 2001)
Traffic growth rate is required to project the prevailing traffic to get the design traffic. Growth rate is obtained by comparing the present day traffic with data of previous years. If adequate data is not available, an average growth rate of 7.5 percent may be adopted. The traffic in the year of work completion from the year of last count is calculated using the following formula:
A = P (1+r) n
Where A = Traffic in the year of work completion
P = Number of commercial vehicles as per last count.
r = Rate of growth of traffic
n = Number of years between last traffic count and year of
completion of Construction.
completion of Construction.
For example, if the traffic is 1691 CVPD in year of last count in 2008, proposed year of completion of work is 2011 and rate of traffic growth is 7.5%, then the traffic at the end of construction period is,
= 1691(1+0.075)3 = 2101
5.Design Life (n) & Stage construction (As per IRC-37 – 2001)
Design life is defined in terms of the cumulative number of standard axles (8160 Kgs) that can be carried by the pavement before strengthening. When it is not possible to provide full thickness of pavement during initial thickness, stage construction is recommended. However stage construction is not permitted for sub base & base and it should be designed for the full life according to the classification of roads as tabulated below.
S. No
|
Road classification
|
Design life in years for Sub base and Base
|
1
|
NH & SH
|
15
|
2
|
MDR & ODR
|
10
|
For Bituminous construction, in all cases the stage construction shall be limited to 5 years design life only.
6.Vehicle damage factor (F) (As per IRC-37 – 2001)
The vehicle damage factor (VDF) is a multiplier to convert the number of commercial vehicles of different axle loads and axle configuration to the number of standard axle load repetitions. The vehicle damage factor is arrived at from axle load surveys. Vehicle damage factor is used for converting different axle load repetitions into equivalent standard axle load repetitions. Guidelines furnished by AASHTO indicate that the vehicle damage factor of 1 is equivalent to 8160 Kgs in case of single axle and to 14968 Kgs in case of Tandem axle. This equivalency load is only considered for the calculation of traffic intensity as vehicle damage factor. Hence wherever there is increase in the equivalent axle load like in the cases of quarry leading roads, the vehicle damage factor considered for pavement design shall be based on realistic measurement of axle loads. Where the axle loads do not warrant conducting axle load survey, the indicative vehicle damage factor as given in the table below shall be adopted.
(Table No.VDF1)
Initial traffic in terms of number of commercial vehicles per day
|
Plain / Rolling terrain
|
Hilly terrain
|
0 – 150
|
1.5
|
0.5
|
150 – 1500
|
3.5
|
1.5
|
More than 1500
|
4.5
|
2.5
|
The above factor is to be applied for single axle system. It is also noted that more the axle load (either Tandem axle or Multi axle) higher will be the vehicle damage factor and as per IRC-37 – 2001 it can be calculated as follows.
Single axle load
Equivalency factor = ((Axle load in Kgs based on survey at site) / (8160))4
Tandem axle load
Equivalency factor = ((Axle load in Kgs based on survey at site) / (14968)) 4
In case of tandem axle loads, actual Vehicle damage factor is to be calculated and to be applied. Accordingly corresponding cumulative number of standard axle in Msa will increase which in turn increases the pavement thickness.
7.Lane distribution factor (D) (As per IRC-37 – 2001)
Lane distribution factor indicates the distribution of commercial traffic over the carriage way. The following distribution values shall be used for the pavement design.
(Table No.LDF1)
S. No
|
Type of Lane
|
Lane distribution factor
|
1
|
Single lane
|
1.00
|
2
|
Intermediate lane
|
1.00
|
3
|
Double lane
|
0.75
|
4
|
Four lane (undivided)
|
0.40
|
5
|
Dual two lane carriageway
|
0.75
|
6
|
Dual three lane carriageway
|
0.60
|
7
|
Dual four lane carriageway
|
0.45
|
Based on all the above data, the traffic intensity in terms of cumulative standard axles is calculated.
A typical example is worked out as below:
A = No of commercial vehicles at the end of construction period in
2011 is 2101
2011 is 2101
F = Vehicle damage factor is 4.5 (As 2101 is more than 1500)
D = Lane distribution factor of 1 corresponding to intermediate lane
r = Rate of growth of 7.5%
The design traffic in terms of cumulative standard axle for a design period of 15 years is,
= 365 x (1+0.075)15 – 1) x 2101 x 1x 4.5
0.075
= 90131668.87 (or) dividing by 106 to get in terms of millions, we get
= 90.13 Msa.
In case of pavement design for a new formation or widening of an existing road, the pavement design is made as per IRC-37 – 2001, ‘The Guidelines for the design of flexible pavements’, considering the Design Traffic volume in terms of MSA as calculated above and the sub grade CBR value. The Guidelines for the design of flexible pavements, gives the pavement design catalogue for a range of CBR values from 2% to 10% corresponding to a design traffic intensity varying from 1 msa to 150 msa.
8.PAVEMENT DESIGN CATALOGUE
The following catalogue of tables give the total pavement thickness required and its distribution into various pavement composition like Sub base, Base and Bituminous layers. The tables include combination of lower range of design traffic ( 1 – 10 msa) with lowest & highest design CBR of 2 % & 10% respectively and also higher range of design traffic (10 – 150 msa) with lowest & highest design CBR of 2 % & 10% respectively.
Recommended Design For Traffic Range
CBR – 2 % (Table No.1)
| |||||
Cumulative Traffic (msa)
|
Total Pavement Thickness (mm)
|
PAVEMENT COMPOSITION in mm
| |||
Bituminous Surfacing
|
Granular Base
|
Granular Sub base
| |||
Wearing Course
|
Binder Course
| ||||
1
|
660
|
20 PC
|
---
|
225
|
435
|
2
|
715
|
20 PC
|
50 BM
|
225
|
440
|
3
|
750
|
20 PC
|
60 BM
|
250
|
440
|
5
|
795
|
25 SDBC
|
70 DBM
|
250
|
450
|
10
|
850
|
40 BC
|
100 DBM
|
250
|
460
|
CBR – 3 %
| |||||
Cumulative Traffic (msa)
|
Total Pavement Thickness (mm)
|
PAVEMENT COMPOSITION in mm
| |||
Bituminous Surfacing
|
Granular Base
|
Granular Sub base
| |||
Wearing Course
|
Binder Course
| ||||
1
|
550
|
20 PC
|
---
|
225
|
325
|
2
|
610
|
20 PC
|
50 BM
|
225
|
335
|
3
|
645
|
20 PC
|
60 BM
|
250
|
335
|
5
|
690
|
25 SDBC
|
60 DBM
|
250
|
440
|
10
|
760
|
40 BC
|
90 DBM
|
250
|
380
|
CBR – 4 %
| |||||
Cumulative Traffic (msa)
|
Total Pavement Thickness (mm)
|
PAVEMENT COMPOSITION in mm
| |||
Bituminous Surfacing
|
Granular Base
|
Granular Sub base
| |||
Wearing Course
|
Binder Course
| ||||
1
|
480
|
20 PC
|
---
|
225
|
255
|
2
|
540
|
20 PC
|
50 BM
|
225
|
265
|
3
|
580
|
20 PC
|
50 BM
|
250
|
280
|
5
|
620
|
25 SDBC
|
60 DBM
|
250
|
285
|
10
|
700
|
40 BC
|
80 DBM
|
250
|
330
|
CBR – 5 %
| |||||
Cumulative Traffic (msa)
|
Total Pavement Thickness (mm)
|
PAVEMENT COMPOSITION in mm
| |||
Bituminous Surfacing
|
Granular Base
|
Granular Sub base
| |||
Wearing Course
|
Binder Course
| ||||
1
|
430
|
20 PC
|
---
|
225
|
205
|
2
|
490
|
20 PC
|
50 BM
|
225
|
215
|
3
|
530
|
20 PC
|
50 BM
|
250
|
230
|
5
|
580
|
25 SDBC
|
55 DBM
|
250
|
250
|
10
|
660
|
40 BC
|
70 DBM
|
250
|
300
|
CBR – 6 %
| |||||
Cumulative Traffic (msa)
|
Total Pavement Thickness (mm)
|
PAVEMENT COMPOSITION in mm
| |||
Bituminous Surfacing
|
Granular Base
|
Granular Sub base
| |||
Wearing Course
|
Binder Course
| ||||
1
|
390
|
20 PC
|
---
|
225
|
165
|
2
|
450
|
20 PC
|
50 BM
|
225
|
175
|
3
|
490
|
20 PC
|
50 BM
|
250
|
190
|
5
|
535
|
25 SDBC
|
50 DBM
|
250
|
210
|
10
|
615
|
40 BC
|
65 DBM
|
250
|
260
|
CBR – 7 %
| |||||
Cumulative Traffic (msa)
|
Total Pavement Thickness (mm)
|
PAVEMENT COMPOSITION in mm
| |||
Bituminous Surfacing
|
Granular Base
|
Granular Sub base
| |||
Wearing Course
|
Binder Course
| ||||
1
|
375
|
20 PC
|
---
|
225
|
150
|
2
|
425
|
20 PC
|
50 BM
|
225
|
150
|
3
|
460
|
20 PC
|
50 BM
|
250
|
160
|
5
|
505
|
25 SDBC
|
50 DBM
|
250
|
180
|
10
|
580
|
40 BC
|
60 DBM
|
250
|
230
|
CBR – 8 %
| |||||
Cumulative Traffic (msa)
|
Total Pavement Thickness (mm)
|
PAVEMENT COMPOSITION in mm
| |||
Bituminous Surfacing
|
Granular Base
|
Granular Sub base
| |||
Wearing Course
|
Binder Course
| ||||
1
|
375
|
20 PC
|
---
|
225
|
150
|
2
|
425
|
20 PC
|
50 BM
|
225
|
150
|
3
|
450
|
20 PC
|
50 BM
|
250
|
150
|
5
|
475
|
25 SDBC
|
50 DBM
|
250
|
150
|
10
|
550
|
40 BC
|
60 DBM
|
250
|
200
|
CBR –9 %&10%
| |||||
Cumulative Traffic (msa)
|
Total Pavement Thickness (mm)
|
PAVEMENT COMPOSITION in mm
| |||
Bituminous Surfacing
|
Granular Base
|
Granular Sub base
| |||
Wearing Course
|
Binder Course
| ||||
1
|
375
|
20 PC
|
---
|
225
|
150
|
2
|
425
|
20 PC
|
50 BM
|
225
|
150
|
3
|
450
|
20 PC
|
50 BM
|
250
|
150
|
5
|
475
|
25 SDBC
|
50 DBM
|
250
|
150
|
10
|
540
|
40 BC
|
50 DBM
|
250
|
200
|
Recommended Design For Traffic Range
CBR – 2 %
| ||||
Cumulative Traffic (msa)
|
Total Pavement Thickness (mm)
|
PAVEMENT COMPOSITION in mm
| ||
Bituminous Surfacing
|
Granular Base
and Sub base
(mm)
| |||
BC
(mm)
|
DBM
(mm)
| |||
10
|
850
|
40
|
100
|
Base = 250
Sub-base = 460
|
20
|
880
|
40
|
130
| |
30
|
900
|
40
|
150
| |
50
|
925
|
40
|
175
| |
100
|
955
|
50
|
195
| |
150
|
975
|
50
|
215
| |
CBR – 3 %
| ||||
Cumulative Traffic (msa)
|
Total Pavement Thickness (mm)
|
PAVEMENT COMPOSITION in mm
| ||
Bituminous Surfacing
|
Granular Base
and Sub base
(mm)
| |||
BC
(mm)
|
DBM
(mm)
| |||
10
|
760
|
40
|
90
|
Base = 250
Sub-base = 380
|
20
|
790
|
40
|
120
| |
30
|
810
|
40
|
140
| |
50
|
830
|
40
|
160
| |
100
|
860
|
50
|
180
| |
150
|
890
|
50
|
210
| |
CBR – 4 %
| ||||
Cumulative Traffic (msa)
|
Total Pavement Thickness (mm)
|
PAVEMENT COMPOSITION in mm
| ||
Bituminous Surfacing
|
Granular Base
and Sub base
(mm)
| |||
BC
(mm)
|
DBM
(mm)
| |||
10
|
700
|
40
|
80
|
Base = 250
Sub-base = 330
|
20
|
730
|
40
|
110
| |
30
|
750
|
40
|
130
| |
50
|
780
|
40
|
160
| |
100
|
800
|
50
|
170
| |
150
|
820
|
50
|
190
| |
CBR – 5 %
| ||||
Cumulative Traffic (msa)
|
Total Pavement Thickness (mm)
|
PAVEMENT COMPOSITION in mm
| ||
Bituminous Surfacing
|
Granular Base
and Sub base
(mm)
| |||
BC
(mm)
|
DBM
(mm)
| |||
10
|
660
|
40
|
70
|
Base = 250
Sub-base = 300
|
20
|
690
|
40
|
100
| |
30
|
710
|
40
|
120
| |
50
|
730
|
40
|
140
| |
100
|
750
|
50
|
150
| |
150
|
770
|
50
|
170
| |
CBR – 6 %
| ||||
Cumulative Traffic (msa)
|
Total Pavement Thickness (mm)
|
PAVEMENT COMPOSITION in mm
| ||
Bituminous Surfacing
|
Granular Base
and Sub base
(mm)
| |||
BC
(mm)
|
DBM
(mm)
| |||
10
|
615
|
40
|
65
|
Base = 250
Sub-base = 260
|
20
|
640
|
40
|
90
| |
30
|
655
|
40
|
105
| |
50
|
675
|
40
|
125
| |
100
|
700
|
50
|
140
| |
150
|
720
|
50
|
160
| |
CBR –7 %
| ||||
Cumulative Traffic (msa)
|
Total Pavement Thickness (mm)
|
PAVEMENT COMPOSITION in mm
| ||
Bituminous Surfacing
|
Granular Base
and Sub base
(mm)
| |||
BC
(mm)
|
DBM
(mm)
| |||
10
|
580
|
40
|
60
|
Base = 250
Sub-base =230
|
20
|
610
|
40
|
90
| |
30
|
630
|
40
|
110
| |
50
|
650
|
40
|
130
| |
100
|
675
|
50
|
145
| |
150
|
695
|
50
|
165
| |
CBR – 8 %
| ||||
Cumulative Traffic (msa)
|
Total Pavement Thickness (mm)
|
PAVEMENT COMPOSITION in mm
| ||
Bituminous Surfacing
|
Granular Base
and Sub base
(mm)
| |||
BC
(mm)
|
DBM
(mm)
| |||
10
|
550
|
40
|
60
|
Base = 250
Sub-base =200
|
20
|
575
|
40
|
85
| |
30
|
590
|
40
|
100
| |
50
|
610
|
40
|
120
| |
100
|
640
|
50
|
140
| |
150
|
660
|
50
|
160
| |
CBR – 9 %
| ||||
Cumulative Traffic (msa)
|
Total Pavement Thickness (mm)
|
PAVEMENT COMPOSITION in mm
| ||
Bituminous Surfacing
|
Granular Base
and Sub base
(mm)
| |||
BC
(mm)
|
DBM
(mm)
| |||
10
|
540
|
40
|
50
|
Base = 250
Sub-base =200
|
20
|
570
|
40
|
80
| |
30
|
585
|
40
|
95
| |
50
|
605
|
40
|
115
| |
100
|
635
|
50
|
135
| |
150
|
655
|
50
|
155
| |
CBR – 10 %
| ||||
Cumulative Traffic (msa)
|
Total Pavement Thickness (mm)
|
PAVEMENT COMPOSITION in mm
| ||
Bituminous Surfacing
|
Granular Base
and Sub base
(mm)
| |||
BC
(mm)
|
DBM
(mm)
| |||
10
|
540
|
40
|
50
|
Base = 250
Sub-base =200
|
20
|
565
|
40
|
75
| |
30
|
580
|
40
|
90
| |
50
|
600
|
40
|
110
| |
100
|
630
|
50
|
130
| |
150
|
650
|
50
|
150
| |
Illustrated Example
Design a pavement for the widening portion of an existing single lane carriage way of a major district road having the following traffic particulars:
Vehicle type (a)
|
Average No of vehicles per day (b)
|
Equivalent multiplication factor (c)
|
Total PCU per day (b x c)
|
No of Commercial vehicles with more than
3 t weight
|
Passenger car
|
276
|
1
|
276
|
-
|
Tempo(LCV)
|
360
|
1
|
360
|
360
|
Auto rickshaw
|
63
|
1
|
63
|
-
|
Agriculture tractor
|
99
|
1
|
99
|
99
|
Cycle
|
124
|
0.5
|
62
|
-
|
Motor cycle and Scooter
|
424
|
0.5
|
212
|
-
|
Truck
|
851
|
3
|
2553
|
851
|
Bus
|
259
|
3
|
777
|
259
|
Agricultural tractor – trailer unit
|
519
|
3
|
1557
|
519
|
Cycle rickshaw
|
12
|
1.5
|
18
|
-
|
Horse drawn vehicle
|
5
|
4
|
20
|
-
|
Bullock cart (Large)
|
28
|
8
|
224
|
-
|
Bullock cart (Small)
|
34
|
6
|
204
|
-
|
Total
|
3054
|
6425
|
1691
|
From the above table, it is seen that the total passenger car unit is 6425, which is more than 6000; the road is eligible for intermediate lane. (Refer Table No.DSV1)
The following table shows the recommended carriage way width for different lanes as per IRC: 86-1983.
Description
|
Lane width with out kerbs in m
|
Lane width with Kerbs
in m
|
Two lane
|
7.00
|
7.50
|
Three Lane
|
10.50
|
11.00
|
Four Lane
|
14
|
14
|
Six Lane
|
21
|
21
|
Hence the road having PCU of 6425 is eligible for intermediate lane as it has a PCU more than 5000. For pavement design only the total No of commercial vehicles having gross weight of 3.00 MT and above is to be considered. In this case 1691 is to be considered for pavement design purpose.
Calculation of Traffic intensity:
Data:
Vehicle Damage factor - 4.5 (For any number of vehicles more than 1500, as per Table No VDF1)
Lane Distribution factor – 1 (For intermediate lane as per Table No LDF1)
Traffic growth rate – 7.5% (Since previous traffic particulars are not available, refer Clause 4)
Design Life – 10 years (Since MDR, as per Table DL1)
Initial traffic - 1691 (if,Year of traffic census and year of construction are same)
Period of construction – 9 Months (Less than a year and road will be opened for traffic in the same year)
Cumulative standard axle = 365 x ((1+0.075)10 -1) x 1691 x1x 4.5
0.075x106
= 39.29 msa
Pavement Design for Widening
Case: 1 CBR – 2% (Refer Table No – 9)
Total Pavement thickness = 912 (or) 915 mm
Granular Sub Base = 460 mm
Granular Base = 250 mm
Binder Course = 165 mm Dense Bituminous Macadam
Wearing Course = 40 mm Bituminous Concrete
Case: 2 CBR – 10% (Refer Table No – 17)
Total Pavement thickness = 589 (or) 590 mm
Granular Sub Base = 200 mm
Granular Base = 250 mm
Binder Course = 100 mm Dense Bituminous Macadam
Wearing Course = 40 mm Bituminous Concrete
Overlay Pavement Design
Pavement design for an Overlay as per IRC -81 – 1997 essentially requires the following factors:
1. Design traffic intensity in terms of cumulative standard axles.
2. Characteristic deflection value in mm obtained by conducting Benkelman deflection test over the existing pavement.
The design traffic intensity is calculated in same way as in case of widening.
CALCULATION OF CHARACTERSTIC DEFLECTION
Overlay design for a given section is based not on individual deflection values but on a statistical analysis of all the measurements in the section corrected for temperature and seasonal variations. For calculation of characteristics Deflection with temperature correction and seasonal variation, the following parameters are required.
a) Pavement Temperature.
b) Field Moisture Content.
c) Plasticity Index of the sub soil.
d) Annual Rainfall of the Region.
Temperature Correction:
When the pavement thickness is more than 40mm,this correction is applied to the observed deflection.
Temperature Correction= Deflection + (Temperature – 35) x 0.01
Correction for seasonal variation :
Correction for seasonal variation is based on the PI Value of the Subgrade and Annual Rainfall of the zone at which the road whose pavement deflection is determined .IRC – 81- 1997 recommends the correction seasonal variation to be applied when the pavement deflection is measured during the dry months.
1) PI -0 and Annual Rainfall less than 1300mm
This involves calculation of mean deflection, standard deviation and characteristic deflection. The characteristic deflection for design purpose shall be taken as given in equations (4) and (5). The formula to be used in the calculation are as follows:
DESIGN OF OVERLAY
The characteristic deflection value obtained and the traffic intensity are interpolated from the following graph to get the required total pavement thickness in terms of bituminous macadam.
The total BM thickness obtained from this curve is distributed in to Binder and Wearing courses corresponding to the traffic intensity as per pavement design catalogue of IRC 37 – 2001. For this, wherever the BM thickness is to be converted into DBM , BC
1 cm of Bituminous Macadam = 0.7 cm of DBM / SDBC / BC
1 cm of Bituminous Macadam = 1.5 cm of Wet Mix macadam
For example, if the traffic intensity is 10 msa and the characteristic deflection obtained is 2 mm, then the pavement thickness from the above curve is 165 mm Bituminous Macadam. As per Pavement design catalogue of IRC – 37 – 2001, the recommended bituminous overlay for 10 msa is Dense Bituminous Macadam with Bituminous Concrete as wearing surface.
As per the equivalency factor, 165 mm BM = 0.7 x 165 = 116 mm of DBM/BC.
This shall be split into 80 mm DBM and 40 mm BC and adopted as overlay. For traffic intensity falling in between two curves, the Bituminous macadam thickness required shall suitably be interpolated.
Embankment Construction
The performance of the pavement is governed by drainage measures and lack of if any leads to accumulation of moisture below pavement layers which leads to softening of sub grade. It is recommended to have bottom of sub grade at 0.6m – 1m above the highest flood level. Material used for the embankment shall have a maximum Liquid limit and Plastic limits of 70 & 45 respectively. Soil with free swelling index exceeding 50 shall not be used for filling. As per IS – 2720 (Part-40), free swell is the increase in volume of a soil, without any external constraints, on submergence in water. The size of coarse material in the fill shall not exceed 75 mm in embankment and 50mm when placed in sub grade. Only the material satisfying the following density requirement as per table 300-1 of MORTH Revision-IV shall be used for the embankment and sub grade.
Type of work
|
Maximum Dry Density/Proctor’s density
|
Embankment height up to 3m which is not subjected to extensive flooding
|
Not less than 1.52 gm/cc
|
Embankment height exceeding 3m
which is subjected to flooding
|
Not less than 1.60 gm/cc
|
Sub grade and Earthen shoulders
|
Not less than 1.75 gm/cc
|
Embankments exceeding the height of 2.5 m shall be designed for Slope Stability and for probable settlement. This shall be based on the geotechnical properties of the foundation soil. Where the adequate land width is available, an embankment slope of 1V: 2H shall be adopted. Wherever acute space for side slopes is encountered, sides slope of 1V: 1.5H with revetments using either Cement concrete blocks or rough stones as the case may be depending on the availability of stone shall be adopted. For easy handling, the CC blocks of M15 having size 0.23 x 0.23 x 0.23 m may be adopted. Retaining walls shall be recommended only where no side slopes can be provided for want of land width.
Sub grade
The top 500 mm of the embankment which is immediately below the pavement is called as the sub grade. The fill material used for sub grade shall be non expansive in nature. The size of coarse material used in sub grade shall not exceed 50 mm. The individual compacted layer thickness shall not exceed 200 mm. Sub grade shall be compacted to 97 % of maximum dry density (Proctor’s Density).
The CBR value of the sub grade material shall be 6% to 10% depending on the local availability. A data bank on sub grade CBR values of various roads shall be maintained by the Divisional Engineer. For this soil test of sub grade CBR, shall be done for all the roads in phased manner and should be available as ready reckoner for preparation of estimates. It is also recommended to record the sub grade CBR values in the register of roads as a permanent record.
Granular Sub Base
Granular Sub base shall be of well graded and compacted material over the properly prepared sub grade. From drainage considerations, the granular sub base shall be extended over the full width of embankment. The thickness of GSB shall be for the full design life of the pavement. The material used for GSB shall have a liquid limit and Plasticity index of not more than 25 and 6 respectively.
This work consists of laying and compacting well-graded material on prepared sub grade in accordance with the requirements of these specifications. The material shall be laid in one or more layers as sub-base or lower sub-base and upper sub-base (termed as sub-base hereinafter) as necessary or as directed by the Engineer.
Grading For Close-Graded Granular Sub-Base Materials
(Adopted where gravel with PI value less than 6 is available)
IS Sieve Designation
|
Percent by weight passing the sieve
| ||
Grading - I
|
Grading – II
|
Grading - III
| |
75.0 mm
|
100
|
--
|
--
|
53.0 mm
|
80-100
|
100
|
--
|
26.50 mm
|
55-90
|
70-100
|
100
|
9.50 mm
|
35-65
|
50-80
|
65-95
|
4.75 mm
|
25-55
|
40-65
|
50-80
|
2.36 mm
|
20-40
|
30-50
|
40-65
|
0.425 mm
|
10-25
|
15-25
|
20-35
|
0.075 mm
|
3-10
|
3-10
|
3-10
|
CBR Value (Minimum)
|
30
|
25
|
20
|
Grading For Coarse Graded Granular Sub-Base Materials
(Adopted where gravel with PI value less than 6 is available)
IS Sieve Designation
|
Percent by weight passing the sieve
| ||
Grading - I
|
Grading – II
|
Grading - III
| |
75.0 mm
|
100
|
--
|
--
|
53.0 mm
|
100
|
--
| |
26.50 mm
|
55-75
|
50-80
|
100
|
9.50 mm
| |||
4.75 mm
|
10-30
|
15-35
|
25-45
|
2.36 mm
| |||
0.425 mm
| |||
0.075 mm
|
<10
|
<10
|
<10
|
CBR Value (Minimum)
|
30
|
25
|
20
|
Close Graded Granular Sub-Base Materials or Coarse Graded Granular Sub-Base Materials are to be used considering cost analysis.
As by and large, plasticity index of Gravel available is more than 6, hence crushed stone with following gradation of Granular sub base as per Table 400-1 of Specification for Road and Bridge works (Revision – IV) shall be adopted.
IS sieve designation, in mm
|
Percent by weight passing the IS sieve
|
75
|
100
|
53
|
80 – 100
|
26.5
|
55 – 90
|
9.50
|
35 – 65
|
4.75
|
25 – 55
|
2.36
|
20 – 40
|
0.425
|
10 – 25
|
0.075
|
3 - 10
|
Static roller of 80 – 100 kN shall be used up to 100 mm compacted thickness. Vibratory smooth wheeled roller shall be used for single layer maximum compacted thickness of 225 mm.
Base Course (Non Bituminous)
I . WATER BOUND MACADAM SUB-BASE/BASE
This work consist of clean, Crushed aggregates mechanically interlocked by rolling and bonding together with screening, binding material where necessary and water laid on a properly prepared subgrade/ sub-base/base or existing pavement, as the case may be and finished in accordance with the requirements of these specifications and in close conformity with the lines, grades, cross-sections and thickness as per approved plans as necessary or as directed by the Engineer .
Grading Requirements Of Course Aggregates
Grading No.
|
IS Sieve Designation
|
% by weight passing
| |
1.
|
90 mm to 40 mm
|
125 mm
|
100
|
90 mm
|
90-100
| ||
63 mm
|
25-60
| ||
45 mm
|
0-15
| ||
22.4 mm
|
0-5
| ||
2.
|
63 mm to 45 mm
|
90 mm
|
100
|
63 mm
|
90-100
| ||
53 mm
|
25-75
| ||
45 mm
|
0-15
| ||
22.40 mm
|
0-5
| ||
3.
|
53 mm to 22.40 mm
|
63 mm
|
100
|
53 mm
|
95-100
| ||
45 mm
|
65-90
| ||
22.40 mm
|
0-10
| ||
11.20 mm
|
0-5
|
II . WET MIX MACADAM SUB-BASE/BASE
This work shall consist of laying and compacting clean, Crushed, graded aggregate and granular material ,premixed with water, to a dense mass on a prepared / sub-base and finished in accordance with the requirements of these specifications. The material shall be laid in one or more layers as necessary to lines, grades and cross-sections shown on the approved drawings or as directed by the Engineer .
Grading Requirements Of Aggregates For Aggregates for Wet Mix Macadam
IS Sieve Designation
| |
53.00 mm
|
100
|
45.00 mm
|
95-100
|
26.50 mm
|
---
|
22.40 mm
|
60-80
|
11.20 mm
|
40-60
|
4.75 mm
|
25-40
|
2.36 mm
|
15-30
|
600.00 micron
|
8-22
|
75.00 micron
|
0-8
|
By and large, as the Water bound macadam blindage material of Gravel available is more than 6, Water bound macadam may be replaced by Wet Mix Macadam, for its superior quality, construction method and for its reasonable cost. It is also recommended to extend the useage of Wet Mix Macadam in ODR also where it is warranted based on the design parameters . The minimum single layer compacted thickness of Wet Mix Macadam is 75 mm and it can be increased to maximum 200 mm when vibratory roller is used.
PRIME COAT OVER GRANULAR BASE
This work shall consist of Application of a single coat of low viscosity liquid bituminous material to a porous granular surface preparatory to the superimposition of bituminous treatment or mix and should be decided according to the surface conditions as per code of practice. For Prime Coat, slow setting primers are recommended.
TACK COAT
This work shall consist of Application of a single coat of low viscosity liquid bituminous material to an existing bituminous road surface preparatory to the superimposition of bituminous mix, when specified in the Contract or instructed by the Engineer The types of Tack coat to be adopted for the bituminous works are as below:
Location of work
|
Type of tack coat
|
Urban
|
Rapid setting
|
Non urban
|
Medium setting
|
. BITUMINOUS MACADAM
This work shall consist of Construction in a single course having 50 mm to 100 mm thickness or in multiple courses of compacted crushed aggregates premixed with a bituminous binder on a previously prepared base to the requirements of these Specifications. Bituminous macadam is more open graded than the dense graded bituminous materials .
COMPOSITION OF BITUMINOUS MACADAM
Mix desiganation Nominal aggregate size Layer thickness
IS Sieve (mm)
|
Grading 1
40 mm
80mm-100mm
|
Grading 2
19 mm
50mm-75mm
|
Cumulative % by weight of total aggregate passing
| ||
45
|
100
| |
37.50
|
90-100
| |
26.50
|
75-100
|
100
|
19.00
|
--
|
90-100
|
13.20
|
35-61
|
56-88
|
4.75
|
13-22
|
16-36
|
2.36
|
4-19
|
4-19
|
0.30
|
2-10
|
2-10
|
0.075
|
0-8
|
0-8
|
Bitumen content, % by weight of total mixture.
|
3.10 - 3.40
|
3.30 - 3.50
|
DENSE GRADED BITUMINOUS MACADAM
This clause specifies the Construction of Dense Graded Bituminous Macadam (DBM), for use mainly, but not exclusively, in base/ binder and profile corrective courses.DBM is also intended for use as road base material. This work shall consist of construction in a single or multiple layers of DBM on a previously prepared base or sub-base. The thickness of a single layer shall be 50 mm to 100mm.
COMPOSITION OF DENSE GRADED BITUMINOUS MACADAM PAVEMENT LAYERS
Grading
|
1
|
2
|
Nominal aggregate size.
|
35-61
|
56-88
|
Layer Thickness
|
80-100 mm
|
50-75 mm
|
IS Sieve (mm)
|
Cumulative % by weight of total aggregate passing
| |
45
|
100
| |
37.50
|
95-100
|
100
|
26.50
|
63-93
|
90-100
|
19.00
|
--
|
71-95
|
13.20
|
55-75
|
56-80
|
9.50
|
--
|
--
|
4.75
|
38-54
|
38-54
|
2.36
|
28-42
|
28-42
|
1.18
|
--
|
--
|
0.60
|
--
|
--
|
0.30
|
7-21
|
7-21
|
0.15
|
---
|
--
|
0.075
|
2-8
|
2-8
|
Bitumen content, % by weight of total mixture.
|
Min 4.0
|
Min 4.50
|
SEMI-DENSE BITUMINOUS CONCRETE
This clause specifies the Construction of Semi Dense Bituminous Concrete (SDBC), for use in wearing and profile corrective courses. This work shall consist of construction in a single or multiple layers of semi dense bituminous concrete on a previously prepared bituminous bound surfaces. A single layer shall be 25 mm.
COMPOSITION OF SEMI-DENSE BITUMINOUS CONCRETE
PAVEMENT LAYERS
Grading
|
1
|
2
|
Nominal aggregate size.
|
13 mm
|
10 mm
|
Layer Thickness
|
35 - 40 mm
|
25 - 30 mm
|
IS Sieve (mm)
|
Cumulative % by weight of total aggregate passing
| |
45
| ||
37.50
| ||
26.50
| ||
19.00
|
100
| |
13.20
|
90-100
|
100
|
9.50
|
70-90
|
90-100
|
4.75
|
35-51
|
35-51
|
2.36
|
24-39
|
24-39
|
1.18
|
15-30
|
15-30
|
0.60
|
---
|
---
|
0.30
|
9-19
|
9-19
|
0.15
|
---
|
--
|
0.075
|
3-8
|
3-8
|
Bitumen content, % by weight of total mixture.
|
Min 4.5
|
Min 5.0
|
Bitumen grade(Pen)
|
65
|
65
|
BITUMINOUS CONCRETE
This clause specifies the Construction of Bituminous Concrete (BC), for use in wearing profile corrective courses. This work shall consist of construction in a single or multiple layers of bituminous concrete on a previously prepared bituminous bound surfaces.
COMPOSITION OF BITUMINOUS CONCRETE
PAVEMENT LAYERS
Grading
|
1
|
2
|
Nominal aggregate size.
|
19 mm
|
13 mm
|
Layer Thickness
|
50 - 65 mm
|
30 - 45 mm
|
IS Sieve (mm)
|
Cumulative % by weight of total aggregate passing
| |
45
| ||
37.50
| ||
26.50
|
100
| |
19.00
|
79-100
|
100
|
13.20
|
59-79
|
79-100
|
9.50
|
52-72
|
70-88
|
4.75
|
35-55
|
53-71
|
2.36
|
28-44
|
42-58
|
1.18
|
20-34
|
34-48
|
0.60
|
15-27
|
26-38
|
0.30
|
10-20
|
18-28
|
0.15
|
5-13
|
12-20
|
0.075
|
2-8
|
4-10
|
Bitumen content, % by weight of total mixture.
|
Min 5.0 – 6.0
|
Min 5.0 – 7.0
|
Bitumen grade(Pen)
|
65
|
65
|
Bituminous Layers
Bituminous layers provided in both widening and strengthening portions of the pavement shall have homogeneity. For this the provision of binder and wearing courses made for strengthening the existing carriageway shall be same as that of proposed widening portion. For all bituminous constructions the stage construction shall be limited to 5 years. Whenever bituminous macadam is proposed as binder course SDBC alone should be proposed as wearing surface and not the BC. Bituminous macadam and Semi dense bituminous concrete alone is recommended for traffic up to 5 msa.
Defect Liability Period
Defect liability Period is the time duration that the contractor has to maintain and up keep the road work free from defects after completion of work from the date of completion. Defect liability period for road and Bridge Structure /works shall be separately mentioned in the agreement. The following liability period are recommended for different types of woks as below.
Type of work
|
Liability period
|
For Plan Works
| |
Widening / Formation of road from sub base
|
36 months
|
Bridges , RCC culverts and other structural works
|
60 months
|
For Non plan works
| |
Only Wearing surface (PR works)
|
12 months
|
Binder course with Wearing surface
|
24 months
|
Widening of Carriage way on Curves (As per IRC:86-1983)
At sharp horizontal curves, it is necessary to widen the carriage way to provide for safe passage of vehicles. The widening required has two components vide,
i. Mechanical widening, to compensate the extra width occupied by a vehicle on the curve due to tracking of the rear wheels.
ii. Psychological widening to permit easy crossing of vehicles since vehicles in a lane tend to wander more on a curve than on a straight reach.
On a two lane road both the above components should be fully catered for so that the lateral clearance between vehicles on curves is maintained as equal to the clearance available on straights. For single lane roads it is sufficient that only the mechanical component of widening is taken into account.
Based on the above considerations, the following table presents the recommended extra width of carriage way to be provided at horizontal curves on single and two lane roads as per IRC: 86-1983.
Radius of curve in m
|
Up to 20
|
21 – 40
|
41 – 60
|
61 – 100
|
101 – 300
|
Above 300
|
Extra width in m for Two lane
|
1.5
|
1.5
|
1.2
|
0.9
|
0.6
|
Nil
|
Extra width in m for Single lane
|
0.9
|
0.6
|
0.6
|
Nil
|
Nil
|
Nil
|
The widening shall be effected by increasing the width at an uniform rate along the transition curve and continued over the full length of the circular curve. The widening should be applied equally on both sides.
Paved Shoulders
The capacity of the two lane roads can be increased by providing paved and surfaced shoulders of atleast 1.5 m width on either side. Provision of paved shoulders results in slow moving traffic being able to travel on the shoulder which reduces the interference to fast traffic on the main carriageway. Under these circumstances, 15% increase in capacity can be expected in the above mentioned value as per IRC: 64-1990. Wherever the carriage way width changes from single lane to intermediate lane or from intermediate lane to double lane, the transition should be effected through a taper of 1 in 15 to 1 in 20.
Criteria for Paved Shoulders:
To get capacity benefit from shoulders, especially under mixed traffic conditions, it has been decided that subject to availability of funds, 1.5 metre wide paved shoulders may be provided on either side of two-lane National Highways in plain/rolling terrain in a selective manner. As regards four-lane sections, it is already in policy of the Ministry to construct paved shoulders in conjunction with the four-laning.
While initiating proposals for paved shoulders on two-lane sections, the following criteria should be kept in view:
(i). The present traffic on NH should be generally around 10,000 PCUs, or more.
(ii).The traffic should consist of sizeable percentage of slow moving vehicles.
Apart from above, provision of paved shoulders could also be considered when:
(a). the concerned section is located in or near an urbanized area with considerable local traffic, or
(b). a stretch is particularly accident prone mainly due to lack of paved with for overtaking and passing maneuvers.
Final selection of lengths would be according to priority given to each section on the basis of traffic intensity and/ or safety considerations and overall availability of funds.
Thickness of Paved Shoulders:
As far as practicable, paved shoulders, when constructed simultaneously with the central pavement, should have the same thickness as pavement of the main carriageway.
.A.) Typical design of a paved shoulder will thus consist of:
(i). A suitable thickness of granular sub-base with the bottom 150mm portion preferably extended over the full formation width to ensure efficient drainage.
(ii). A base course of Water Bound Macadam (WBM) or Wet Mix Macadam (WMM) in three layers of 75mm each, with the top layer being primed and
(iii) A bituminous wearing course consisting of 2 coats of surface dressing, premix carpet, concrete mix seal, or semi-dense bituminous concrete carpet. The texture of the shoulder wearing surface should be different from the main carriageway to ensure clear contrast between them.
In case of construction and specification for 1.50m wide paved shoulders hence forth should be the same as that of main carriage way. This would also help as that main carriage way. (Ministry of Surface Transport (Raods wing) New Delhi
Some Important points from IRC – 37 - 2001
Total required Pavement thickness and their distribution into pavement layers for sub grade CBR values between 2 & 10 shall be obtained from IRC – 37 – 2001.
The sub-base material should have minimum CBR of 20 per cent for cumulative traffic upto 2 msa and 30 per cent for traffic exceeding 2 msa.
Where the granular sub-base material conforming to the above specifications is not available economically, other granular sub-bases, like, Water Bound or Wet Mix Macadam conforming to MORT&H Specifications are recommended. (As given in para 4.2.1.2-in I.R.C.37-2001)
From drainage considerations the granular sub-base should be extended over the entire formation width in case the subgrade soil is of relatively low permeability. (As given in para 4.2.1.3-in I.R.C.37-2001)
The thickness of sub-base should not be less than 150mm for design traffic less than 10 msa and 200 mm for design traffic of 10 msa and above. (As given in para 4.2.1.4-in I.R.C.37-2001)
Where the CBR value of the subgrade is less than 2 per cent, the design should be based on subgrade CBR value of 2 per cent and a capping layer of 150 mm thickness of material with a minimum CBR of 10 Per cent shall be provided in addition to the sub-base. (As given in para 4.2.1.5-in I.R.C.37-2001)
Where stage constructions is adopted for pavements, the thickness of sub-base shall be provided for ultimate pavement section for the full design life. (As given in para 4.2.1.6-in I.R.C.37-2001)
The recommended minimum thickness of granular base is 225 mm for traffic upto 2 msa and 250 mm for traffic exceeding 2 msa. (As given in para 4.2.2.2-in I.R.C.37-2001)
Where WBM construction is adopted in the base course for roads carrying traffic more than 10 msa, the thickness of WBM base shall be increased from 250mm to 300 mm (i.e., thickness) for ease of construction with corresponding reduction in the sub-base thickness keeping the overall pavement thickness unchanged as deduced from the design chart. (As given in para 4.2.2.4-in I.R.C.37-2001)
The use of bituminous macadam binder course to IRC/MORT&H Specifications may desirably be restricted only to roads designed to carry traffic less than 5 msa. Dense Bituminous Macadam binder course is recommended for roads designed to carry more than 5 msa. (As given in para 4.2.3.1-in I.R.C.37-2001)
However, in case the granular base is manually laid or if recommended by the Engineer, the Dense Bituminous Macadam (DBM) binder course may be preceded by a 75mm thick Bituminous Macadam (BM) layer. Where this is done the thickness of the DBM layer will be suitably reduced. For practical purpose 10 mm BM can be taken as equivalent to 7 mm DBM for modifying the thickness of DBM layer. (As given in para 4.2.3.3-in I.R.C.37 -2001)
MAINTENANCE OF ROADS
Basic Maintenance Objectives
The basic objectives of maintenance function are to maintain and operate the highway system in a manner such that:
a) Comfort, convenience and safety are afforded to the public;
b) The investment in roads, bridges and appurtenances is preserved;
c) The aesthetics and compatibility of highway system with the environment is preserved; and
d) The necessary expenditure of resources is accomplished with continuing emphasis on economy.
Classification of Maintenance Activities
The maintenance activities can be broadly classified under the following three sub-heads:
Ordinary repairs / routine maintenance: The ordinary repairs include the following nature of work:
i) Upkeep of road pavements and side shoulders;
ii) Upkeep of roadside drain system;
iii) Upkeep of culverts and bridges, and earth retaining structures and parapets;
iv) Keeping the sign boards, Km stones and other traffic aids and furniture in good shape and condition.
v) Maintenance of roadside arboriculture; and
vi) Upkeep and maintenance of rest houses, inspection bungalows and gang huts.
Periodic maintenance: It covers periodic renewals to the carriageway whether it is graveled road, metalled road or blacktopped road to ensure the adequate level of serviceability is maintained.
Special repairs and flood damage repairs: These include the details of urgent repairs not covered under ordinary repairs/ periodic maintenance.
Works taken up under different types of maintenance activities
1. Special Repairs// Periodic Renewal
State Highways /
Major District Roads :
1. Advance BT Patches 50mm thick
2. Bituminous Macadam 50mm thick in patches (Not Continuously)
3. Semi Dense Bituminous concrete 25mm thick.
Other District Roads :
1. Advance BT Patches 50mm thick
2. WBM Gr.III 0.075m thick
3. Premix Carpet with seal coat Type A.
Special Repairs to be carried out after 3 year of last date of check measurement. Periodical Renewal as per maintenance chart depending on category of road / rainfall data.
2. Ordinary Repair
(a) Urgent Repairs to the road (SH/MDR/ODR)
(i) WBM Patches 0.075m thick .
(ii) Advance BT Patches 50mm thick.
(iii) PC SC Type A.
(b).Urgent Repairs to the Culvert/ Protective Wall
All provisions required for culvert except total quantity required for dismantling as the structure is reported to be damaged partially/ fully.
(b).Urgent Repairs to the Berms
High berm cutting/ making up of berms where gangs could not be utilized effectively and the removal of berms require machinery like JCB.
3. Temporary Restoration
a. Earth filling in the breached portion.
b. Supply of fixing of pipes where the culvert gets collapsed.
c. Rubble boulders packing in the embankment portion.
d. Cradle concrete for the pipes and its headwalls.
4. Permanent Restoration
a. Road work: SH/MDR: Strengthening as per CBR method (or) BBDT test.
b. ODR: Subbase /Base as per CBR requirements (or) WBM Gr.III 75mm thick & PCSC Type A 20mm thick
5. Restoration to the pipe cut portions
As per provisions contemplated in the model estimate circulated by Chief Engineer General.
The provisions explained above are arrived based on field experience However the maintenance treatment is to be arrived considering filed conditions and maintenance treatment is case specific.
Berms
It is generally observed that the importance given to the formation and maintenance of carriageway is not being given to the maintenance of shoulders/berms.
Due to the Poor maintenance of berms, the life of the pavement gets affected, possibilities of occurrence of accidents gets increased etc.
Hence to make aware of the function of berms, construction of berms their maintenance are given below.
I Function of berms
· Berms (shoulders) provide lateral support to the pavement. They are used for parking vehicles in case of single lane roads, provide room for passing vehicles where carriageway width is insufficient and also comes in handy for the parking of disabled vehicles. These are at times serve as a track for slow moving vehicles.
· The properly maintained shoulders also help the drainage of surface water quickly to the side drains. Improper maintenance of side shoulder will cause drainage along the edge of the pavements resulting in caving and there by penetration of moisture to the sub grade.
In order to perform satisfactorily the functions stated above, care should be taken during the formation of embankment itself.
· a) Formation of Embankment on sloping Ground
b) Drain provision for Existing Pavement
· When the traditional granular construction is provided on a relatively low permeability sub grade, the granular sub-base should be extended over the entire formation width in order to drain the pavement structural section.
· It is necessary that the surface of the shoulders is hard enough to resist the abrasive action of vehicles. Hard granular/stabilized soil is preferable to earth shoulders from overall considerations of improved performance
II Formation of berms
· The earthen shoulders shall be constructed of the material like gravel or carted earth available at site,
· To avoid the failure, soils having maximum dry densities of less than 1.44 gm per c.c. are ordinarily considered unsuitable and shall not be used in embankments as far as possible. Soils having maximum dry densities of less than 1.52 gm per c.c. are ordinarily considered unsuitable for use in embankments exceeding 3 m in height or in embankments of any height subject to long periods of inundation. Soils with a maximum dry density of less than 1.65 gm per c.c. are ordinarily considered unsuitable for use in the top 50 cm soil layer immediately below the surface of the sub grade and shall be replaced with suitable soil or granular material.
· To obtain adequate compaction, the embankment shall be constructed in uniform layers. Successive layers of embankment shall not be placed until the layer under construction has been thoroughly compacted to satisfy the requirements. The embankment material shall be deposited in layers not exceeding 25 cm in loose thickness. The soil shall be spread uniformly over the entire width of the embankment.
· The moisture content of each layer of soil at the time of compaction should be from 1 per cent above to 2 per cent below the optimum moisture content. The soil spread in layers shall be thoroughly compacted by means of suitable compacting plant. Each compacted layer shall be tested in the field for density and accepted before the operations for net layer are begun.
· Particular attention shall be paid to drainage for roads built on sloping ground, by the provision of side drains designed to carry the maximum flow ever likely to be required of them. Quick drainage from road shoulders is generally ensured by keeping the surface of the shoulder properly sloped and smoothed. Shoulders should be shaped regularly, specially before and during the monsoons in order to avoid damage to the road pavement and its surface.
· Drainage of existing pavement of ‘Trench Type’ section on low permeability sub grades can be improved by providing a continuous drainage layer of 100-150 mm thickness under the shoulders at the sub grade level or by providing a combination of longitudinal and lateral drains, the latter spaced at 5 to 6 m intervals. The drains are cut through the shoulders up to the sub grade level and backfilled with coarse drainage material.
III Maintenance of berms
· Shoulders should be accorded special attention during subsequent maintenance operation too. They should be dressed periodically so that they always conform to the requisite cross-fall and are not higher than the level of carriageway at any time.
· Shoulders should be made up of impervious material so as not to allow water to permit into the body of the pavement.
· The cross fall for the earth shoulders should be at least 0.5 percent steeper than the slope of the pavement subject to minimum of 3 percent. Earthen shoulders provided will have 4 percent slope.
· The work of maintenance consists of periodically replacing earth or moorum carried away from the shoulders, to remove ruts, and restore the slope to the designed level.
Mode of Execution
· Present practice of carrying out the new formation of berms in the widening of road works through the main contractor need to be relooked for efficiency. The main contractor who is doing pavement work invariably shows lack of sincerity in forming the berms.
· Hence it is suggested that the Construction of berms is entrusted with separate contractors.
· However construction of berms needs to be taken up immediately on completion of pavement work for securing good condition of the pavement edges. The estimate also need to be suitably prepared and sanctioned to facilitate taking up of berms separately.
