Pavement Design for Lalsot-Dausa section of NH-11A Ext. in the state of Rajasthan - A case study Shabana Thabassum*, Rajesh Gavvala** and Apparao G*** ABSTRACT India is one of the fastest growing nations in the world. India’s economy has grown manifolds in the recent past and likely to grow further as per the present trends. The Government of India has launched major initiatives to upgrade and strengthen National Highways (NH) through various phases of National Highways Development Project (NHDP). The project stretch of NH-11A Ext. starts from Dausa at km. 0.000 and ends at Lalsot at km. 41.000 in the state of Rajasthan. The major commodity plying along the project stretch is sand. Bamanwas is one of the very good sand quarries of Rajasthan. This quarried sand is being transported to Bharatpur, Agra and beyond from Bamanwas along this route with approximately 90% overloading giving very high VDF values. The pavement design for this section is very critical due to the high vehicle damage factor (VDF) values. Different flexible pavement design options and rigid pavement design have been tried and it is concluded that flexible pavement design with stage construction as per IRC:37-2012 using new form of construction and materials is economical for this project stretch.
1 INTRODUCTION India is one of the fastest growing nations in the world. India’s economy has grown manifolds in the recent past and likely to grow further as per the present trends registered in the past couple of years. Increase in the economy has lead to increase of loading on the infrastructure corridors available within the country. Surge for better infrastructure corridor facilities for sustained growth of economy have been well realized and recognized by the Govt. of India in line with the rising trends of economy. National Highways Authority of India (NHAI) is an autonomous organization under the Ministry of Road Transport & Highways and was constituted by an act of Parliament, the National Highways Authority of India Act, 1988. NHAI is responsible for the Development, Maintenance, and Management of National Highways and for matters concerned thereto. The Government of India has launched major initiatives to upgrade and strengthen National Highways (NH) through various phases of National Highways Development Project (NHDP). 2 PROJECT LOCATION The section of NH-11A Ext. starts from Dausa at km. 0.000 and ends at Lalsot
at km. 41.000 in the state of Rajasthan. The total length of the project is 41.000 km. the Project road passes through Kareda, Bhurti, Rajdhira Pura and Hodayali. The existing pavement is of totally flexible type. 3 PROJECT CORRIDOR – NETWORK AND IMPORTANCE The project corridor is important for various reasons. The project corridor NH-11A Ext. is connecting NH-11 with NH-12 in shortest path. It further connects Sawai Madhopur and Karauli to Jaipur. Apart from connectivity considerations, the development of this corridor has been perceived to be important from the perspective of enhanced mobility levels of people, and with time more importantly in terms of direct benefits to the community by the way of VOT and VOC savings, towards achieving development in Rajasthan at large and in Lalsot and Dausa regions in particular. 4 SOCIO ECONOMIC PROFILE OF THE PROJECT AREA The project stretch passes through the state of Rajasthan, which is the Western State of Indian Peninsula. Rajasthan is the largest state in the country with a geographical area of 3.42 lakh sq. km. comprising seven administrative divisions and 33 districts. It occupies
about 10% of the total area of India. The west and north-west part of the state comprising of twelve districts having about 61 percent of the total area of the state is either desert or semi-desert and is known as the Great Indian Desert, “Thar”. It is the driest part of the country. The average annual rainfall of the state is 530 mm which is erratic. As a result Rajasthan witnesses frequent droughts. Around 30.9% of the state's area is classified as wastelands. According to the 2011 Census, the State has a total population of 68,621,012. Out of this, 75.1% is rural and 24.9% is urban population. The population density of 201 persons per sq. km. in the state is lower than the national average of 370 person per sq. km. The literacy rate in Rajasthan has seen upward trend and is 67.06% as per 2011 population census. As per Economic Review- 2011 of Rajasthan, 62% of the working population are into agriculture and allied activities. The primary sector in Rajasthan employs 62% of the workforce and contributes to 26% of State GDP. The tertiary sector employs 31% of workforce and similarly the secondary sector employs only 7% of workforce. As per the land utilization statistics of 2008-09, out of the total geographical
* Associate Professor, Department of Civil Engineering, St. Martin’s College of Engineering, Hydrabad, E-mail:
[email protected], ** Assistant Executive Engineering, Irrigation & CAD Department, APPSC., *** Assistant Professor, Department of Civil Engineering, GITAM University, Hydrabad
INDIAN HIGHWAYS, December 2014
11
TECHNICAL PAPERS area, the combined cropped area of the project district was 341406 hectares
with net sown area of 222022 hectares as shown in Table 1.
4% 0%
AADT Vehicle Composition 38%
31%
Table 1 Land Use Pattern S. No.
Unit
Dausa
1)
Total Reporting Area for Land Utilization
Land Utilization Particulars
Hectare
350789
2)
Total Cropped Area
Hectare
341406
3)
Net Area Sown
Hectare
222022
4)
Net Area Irrigated
Hectare
161315
5 TRAFFIC VOLUME COUNT ANALYSIS 5.1 Traffic Surveys and Collection of Data An accurate estimate of the traffic that is likely to use the Project road is very important as it forms the basic input in planning, design, operation and financing. A thorough knowledge of the travel characteristics of the traffic likely to use the Project road as well as other major roads in the influence area of the study corridor is essential for future traffic estimation. In order to capture the entire traffic, Classified Traffic Volume Count surveys are carried out at km. 36.500. To capture the traffic and travel characteristics of predominant category of vehicles, Origin-Destination surveys by Road side Interview (RSI) method are conducted along the project stretch at the same TVC location. Axle Load surveys are conducted at km. 36.500 for 2 normal days. A map showing the Project stretch with all survey locations is enclosed in Fig. 1.
Fig. 1 Traffic Survey Location
12
5.2 Annual Average Daily Traffic The Annual Average Daily Traffic obtained by multiplying the Average Daily Traffic (ADT) with the seasonal correction factor of 1.02 for petrol vehicles and 1.04 for diesel vehicles. The AADT of vehicles for the year 2013 along the Project stretch is presented in Table 2. Table 2 Annual Average Daily Traffic (AADT) Vehicle Type
km. 36.500
Passenger Vehicles
4834
2 Axle
317
3 Axle
680
M Axle
352
HEM
27
LCV/LGV
137
Mini LCV
331
Tractor and tractor with trailer
395
Non Motorized Veh and others
264
Total Traffic
7365
5.3 AADT Modal Split ● Car Traffic is about 21% in the total traffic along the corridor. ● The share of non-motorized vehicles from 1 to 3%. ● The commercial vehicles contribute 28% and buses constitute 4% of the total vehicles using the corridor. ● Two wheelers and three wheelers together constitute 44% of the total traffic along this corridor as shown in Fig. 2.
2W 3W Car/Jeep (White) Car/Jeep (Yellow) Bus Goods Non Moor zed Exempted Vehicles
Fig. 2 AADT Vehicle Composition
6 OR I G I N - D EST I N AT I O N SURVEY AND ANALYSIS O-D surveys are to assess spatial patterns (Origin & Destination) of travel by all types of Passenger and Goods vehicles currently using the project road. Table 3 O - D Sample Size Vehicle Type
km. 36.500
LCV
28%
2 Axle
24%
3 Axle
30%
M Axle
21%
Mini LCV
24%
Dausa, Manoharpur, Baradi, Shah pura, Bairas, Lalsot, Tonk and Dhan darin the state of Rajasthan and Delhi are the major influencing zones in terms of trip generation and attraction. Desire lines are the straight lines connecting origins with destinations, summarised into different area groups. The width of such line is drawn proportional to the number of trips in both directions. Building materials, exclusively Sand from Bamanwas on NH-11 A Ext. travels to reach other parts of Rajasthan and India. The desire line diagrams indicate the importance of project corridor in the economic growth of Dausa and Sawai Madhopur districts of the state of Rajasthan. The spatial pattern of the goods vehicles showing trips from Lalsot to Dausa, Agra, Sainthal and Delhi regions of Rajasthan and India. 7 AXLE LOAD SURVEY AND VEHICLE DAMAGE FACTOR The ever increasing vehicle population and heavy axle loads has caused substantial damage to Indian roads.
INDIAN HIGHWAYS, December 2014
TECHNICAL PAPERS Trucks carry loads much in excess of legal limits and are largely responsible for poor road conditions in addition to the inadequate structural capacity of pavements and diminishing allocation of funds year after year for maintenance and rehabilitation. Very huge capital investments are now needed to upgrade and rehabilitate the existing road network to make it capable to withstand high stresses and tyre pressures caused by heavy wheel loads. There are several input parameters that are required to design a pavement structure. One vital component is an accurate account of the expected magnitude and frequency of traffic loads over the design life of the pavement. Key factors in designing
a pavement structure are the magnitude and number of repeated equivalent single axle loads (ESALs). Traffic can be characterized using ESALs. ESALs convert the effect of mixed axle load applications into the equivalent number of applications of standard axles that would be required to produce the same amount of pavement distress. Axle pads with digital recording meters are being employed to weigh the loads of vehicles. An assemblage of two or more consecutive axles considered together in determining their combined load effect on a pavement structure is called an axle group. The standard and permissible axle loads for Indian conditions are given in Table 4.
Table 4 Axle Types and Loads
number of commercial vehicles of different axle loads to Standard Axle Loads (SAL). Equivalency factor (EF) is normally worked out by using the Fourth Power Rule derived by AASHTO and approved by CRRI. With the help of equivalency factors and frequency distribution of axle loads, Equivalent Axle Loads (EAL) are computed. The VDF calculated for different categories of commercial vehicles based on fourth power rule are as shown in Table 6.
Fig. 3 Load Spectrum Analysis Table 6 Vehicle Damage Factor (VDF)
Axle Type
Permissible Load in Tonnes as per IRC:3-1983
Standard Load in Tonnes as per IRC:37-2012(8)
Single Axle (Single wheel)
6.00
6.50
Single Axle (Duel wheel)
10.20
8.00
2 Axle
9.20
0.58
9.2
Tandem Axle (Duel wheel)
18.00
14.80
3 Axle
53.23
0.47
54
22.40
M Axle
54.64
8.39
55
LCV
8.39
0.04
8.5
Tridem Axle (Duel wheel)
To provide adequate information on axle load distributions, axle loads are required. Such a survey can conveniently be made using portable weigh pads that are widely available. This survey was conducted for 2 normal days in both directions of traffic simultaneously with volume count of commercial vehicles (Trucks and LCV) at km. 36.500 along the project stretch. The random selection of vehicles for axle load measurement was done, ensuring suitable sample for each category of commercial vehicles consisting of overloaded and empty vehicles. The sample size for the survey is presented in Table 5. Table 5 Sample Size Mode
To Dausa
To Lalsot
2 Axle
21%
23%
3 Axle
31%
21%
M Axle
20%
21%
LCV
26%
33%
The load spectrum analysis has been done to check the distribution of wheel loads over the pavement and the results are presented in Fig. 3. It is found from the analysis, that over 90% of the commercial vehicles are overloaded in this stretch. There are legal limits for the axle loads and gross weights of vehicles but they are neither observed by the transporters nor enforced stringently by the authorities. Unchecked overloading has a disastrous effect on the performance of pavements and overriding influence on pavement design. It is believed that the damage caused to a pavement by an axle load twice the standard axle load is 16 times the damage by the standard axle is carried by vehicles with their gross weights with in legal limits. The Vehicle Damage Factor (VDF) is an index characterizing the traffic loading for a highway and is defined as a multiplier for converting the
INDIAN HIGHWAYS, December 2014
Mode
Km 36.500 To Dausa
Adopted
To Lalsot
The major commodity plying along the project stretch is sand. Bamanwas is one of the very good sand quarries of Rajasthan. This quarried sand is being transported to Bharatpur, Agra and beyond from Bamanwas on this route. It is observed from the axle load survey that 90% of the vehicles are overloaded. Generally sand is transported in 3 and Multi axle vehicles, hence the VDF for these vehicles is above 50, which is a very high value and throws a challenge to the pavement designer. 8 PAVEMENT DESIGN The pavement design basically aims at determining the total thickness of the pavement structure as well as thickness of individual structural components. Pavement is the most significant component of a road and therefore its design strengths must be assured to support the projected traffic loading throughout the design period.
13
TECHNICAL PAPERS The pavement design is carried out for both flexible and rigid option by using IRC and AASHTO methods. The overall thickness of both types has been worked out, the results were compared, and the optimized solution based on characteristics of existing materials, best engineering judgment and environmental conditions has been adopted. 8.1 Million Standard Axles (MSA) Design traffic in terms of Million Standard Axles has been determined for the given period using the following relationship. N = 365*[(1 + r) n - 1] *A*D*L*F/r Where, N: The cumulative number of standard axles to be catered for in the design in terms of msa. A: Initial traffic in the year of completion of construction in terms of the number of commercial vehicles per day L: Lane Distribution Factor (0.75) D: Directional Distribution Factor (0.50) n: Design Life in years r: Annual Growth rate of commercial vehicles. F: Vehicle Damage Factor The above said traffic parameters and VDF for individual vehicles have been used for the computations of cumulative million standard axles. The monsoon brings relief to the sultry and sun-baked terrain of Rajasthan during the month of June in the eastern region and mid- July in the western arid regions. The temperature drops from 400 to 350. With the fall in temperature, humidity increases. The state receives maximum rainfall during this period. There is a second phase of monsoon that continues from July to September. In view of the above it is assumed that, the sand quarrying will be off in rainy season. So, 300 days in a year is considered for calculation of msa and the results are given in Table 7.
14
Table 7 Million Standard Axles (MSA) From (km)
To (km)
Length (km)
8 Years msa
15 Years msa
20 Years msa
0.000
41.000
41.000
100
210
320
8.2 Design of Flexible Pavement by IRC:37-2012 The flexible pavement has low flexural strength and hence layers reflect the deformation of the lower layers/ subgrade on to the surface layer after the withdrawal of wheel load. To control the deflections in the subgrade so that no permanent deflections results the pavement thickness is so designed that the stresses on the subgrade soil are kept within its bearing power. Loading of bituminous pavement requires the stiffest layers to be placed at the surface with successive weaker layers down to subgrade. Two options have been considered for pavement design and are as follows Option-A : Stage Construction (8 years from COD) Option-B : Total Construction (15 years from COD) The guidelines present fatigue and rutting model corresponding to 80% and 90% reliability while the old code deals with 80% reliability. Traffic greater than 30 msa should be designed for 90% reliability. Different grades of bitumen can be used depending upon the requirement. For traffic greater than 30 msa, VG 40 has been recommended for both DBM and BC. DBM has air voids 3%
after rolling (Bitumen content being 0.5-0.6% higher than optimum). For lower traffic, VG 30 may be used. Effective CBR concept is also introduced to account for difference in CBR of embankment and sub grade. The guidelines recommend construction with cementitious materials in the interest of saving the environment and using the local and marginal materials after stabilization. Pavement design is carried out for the following base and sub-base options. Case 1: Granular base and sub-base. Case 2: Cementitious bases and subbases with a crack relief layer of aggregate interlayer below bituminous surfacing. Case 3: Cementitious bases and sub-bases with SAMI in between bituminous surfacing and the cementitious base layer for retarding the reflection cracks into the bituminous layer. Case 4: Bituminous surfacing over treated RAP and cemented sub base. Stage construction is not permitted when cemented base and sub-bases are used according to the guidelines of the code as it may lead to cracking of the stabilized layer leading to failure of the pavement. Input parameters for both the options are presented in Table 8.
Table 8 Inputs for the Pavement Design Design Inputs
Option-A (Stage)
Option-B (Total)
Wearing Course (granular base and sub base)
8 Years
8 Years
Wearing Course (cemented base and sub base)
NA
15 Years
Granular Sub-base and Base Course
15 Years
15 Years
Cemented base and sub- base
NA
15 Years
Wearing Course
100
100*
Sub-base and Base Course
210
210
Cemented base and sub- base
NA
390
MSA
Sub-grade CBR
10%
Embankment CBR
7%
* Note: msa of 100 is restricted to make use of the existing road with overlay.
INDIAN HIGHWAYS, December 2014
TECHNICAL PAPERS The designed flexible pavement composition using above input for
both the options in case 1 is given in Table 9.
Table 9 Pavement Composition for Case 1 Option
Eff. CBR
MSA
VG
Option-A
10%
100
Option-B
10%
100
Crust Composition (mm) BC
DBM
WMM
GSB
Total
VG-40
50
110
250
200
610
VG-40
50
110
250
200
610
be carried out at the end of 7th year and the characteristic deflections has to be worked out. Suitable overlay will be designed for the projected traffic and the characteristic deflection at the end of the 7th year. Based on the AASHTO Guide lines the layer coefficients for the Pavement at the time of opening to the traffic and after some design period are given in Table 10.
8.3 Strengthening of New Pavement in 8th Year as per AASTHO Guidelines The flexible pavement has to be designed for a period of 15 years. But in this case, design for full 15 years is uneconomical. To minimize the initial investment, the pavement has been designed for two options as explained above. The Benkelman Beam Deflection (BBD) studies has to
Table 10 Layer Coefficients as per AASHTO Pavement Component
New Pavement
Pavement after Design Period
Layer Coefficient
Drainage Coefficient
Layer Coefficient
Drainage Coefficient
BC
0.36
1.00
-
-
DBM
0.36
1.00
0.24
1.00
WMM
0.14
0.90
0.14
0.90
GSB
0.11
0.90
0.11
0.90
Because of continuous movement of heavy traffic in the design life, it is assumed that at the end of the design period, the total surface layer (BC) will be get deteriorated, the effect on DBM
will be very less or negligible and no effect on sub-base and base layers. Actual pavement thickness for 15 years design period and the Structural Number (SN) is given in Table 11.
Table 11 Pavement Thickness and its SN Description
Base and Sub Base Course Thickness (mm)
Wearing and Binder Course Thickness (mm)
Total Thickness (mm)
SN
GSB
WMM
DBM
Design Life of 15 Years (SN 15)
200
250
165
50
665
5.07
Design period of 8 years (SN 8)
200
250
110
50
630
3.06
The required overlay at the end of design period is estimated from the
BC
SN15 and SN8 and the details are given in Table 12.
Table 12 Required Overlay at the End of the 8th Year Structure Numbers (SN)
Overlay Thickness (mm)
SN15
SN8
SN15 - SN8
BC
DBM
Total
5.07
3.06
2.01
50
80
130
8.4 Strains in the Pavement Structure The designed flexible pavement composition using above input for
both the options from Case 2 to 4 are given in Table 13. The actual tensile strains were calculated using the various pavement
INDIAN HIGHWAYS, December 2014
design parameters as inputs in the IITPAVE program. The actual strains are computed using various trial pavement structural layer combinations. The tyre pressure used in the analysis is 0.56 MPa. Standard axle used is dual type, having a mass of 8160 kg. This resulted in a single tyre load of 20,012 N. The Poisson’s ratio of bituminous layer is taken as 0.5, 0.25 for CTB & CTSB and 0.35 for Aggregate Inter Layer & sub-grade layers. Resilient modulus/ Elastic modulus for Bituminous layers as 3000MPa, 450MPa for Aggregate Interlayer, 5000 Mpa for CTB, 600 MPa for CTSB and 77 MPa for Subgrade. The calculated strains are presented in Table 14. 9 DESIGN OF RIGID PAVEMENT It is a general practice to design rigid pavement for heavy loaded corridors. Rigid pavement will be done in accordance with IRC:58-2011. a) Design Life and Traffic Parameters 30 years design period has been considered for the project stretch. The cumulative number of commercial vehicles in the predominant direction over 30 years design life is estimated and 25% of this traffic is considered as design traffic. The design tyre pressure has been taken as 0.8 MPa. b) Wheel Base Characteristics Axles with spacing of less than 4.5 m (transverse joint spacing) are considered for the estimation of topdown cracking damage analysis. The percentage of axles with less than 4.5 m wheel base are estimated from the axle load survey. c) Temperature Differential According to Table 1 of IRC:58-2011, the temperature differential is a function of geographical location of the project road and the temperature differential to be adopted for the project area i.e., Rajasthan.
15
TECHNICAL PAPERS Table 13 Pavement Composition Case
Eff.
Options Option-A Option-B Option-A Option-B Option-A Option-B
2 3 4
MSA
VG
10%
210
VG-40
10%
210
VG-40
10%
210
VG-40
CBR
Crust Composition (mm) BC DBM AIL CTB CTSB Not Recommended 50 70 100 110 250 Not Recommended 50 50 SAMI 170 250 Not Recommended 50 70 160 (RAP) 250
Total 580 520 530
Table 14 Pavement Structural Analysis Case
MSA
Thickness in mm BC
2 3 4
DBM
AIL
CTB
Total
Ten.
Allowable Strains (Micro)
Ten.
Ver. Ten. Strain on Strain Strain Strain SG Below BT Below CTB below BT
Ten. Strain below CTB
Ver. Strain on SG
150 210 150
50 50 50
50 70 50
100 100 SAMI
110 110 160
250 250 250
560 580 510
136 120 -
51 46 56
204 188 181
153 140 -
65 63 65
292 271 292
210 150 210
50 50 50
50 50 70
SAMI 170 160 (RAP) 160 (RAP)
250 250 250
520 510 530
136 123
53 -
172 265 242
153 140
63 -
271 292 271
d) Modulus of Sub-Grade Reaction Dry Lean Concrete (DLC) sub base is generally recommended for a modern concrete pavement, particularly those with high intensity of traffic.
● Effective CBR of the sub grade soil is considered as 10% ● 150 mm DL Clayer is provided as sub-base. ● Effective k-value, after providing DLC layer is 300 MPa/m e) Concrete Strength The 90 days flexural strength for the pavement quality concrete (PQC) has been taken as 4.95 Mpa for the purpose of design. f) Modulus of Elasticity, Poisson’s Ratio & Coefficient of Thermal Expansion The values of the various para meters adopted are: Modulus of Elasticity = 30000 MPa Poisson’s Ratio = 0.15 Coefficient of thermal expansion = 10 x 10-6/ºC g) Design of slab thickness The flexural stress due to the combined action of traffic loads and temperature differential between the top and bottom fibers of the concrete slab is considered
16
Actual Strains (Micro)
CTSB
for design of pavement thickness. Positive temperature during day time will create bottom-up cracking and negative temperature during night will create top-down cracking in concrete slab. Hence analysis has been done for these two cases. For bottom-up cracking case, the combination of load and positive non-linear temperature differential has been considered where as for top-down cracking analysis, the
combination of load and negative linear temperature differential has been taken. For a trial slab thickness and other design parameters, the pavement will be checked for cumulative bottom-up and top-down fatigue damage. h) Design Thickness Following Rigid Pavement design elements are proposed as shown in Table 15 for the project road under consideration.
Table 15 Pavement Composition for Rigid Pavement S. No.
Item
Rigid Pavement Design with Tied Concrete Shoulders
1
PQC of M40 grade, mm
290
2
DLC of M10 grade, mm
150
3
GSB, mm
150
4
Dia. of Dowel bar, mm
36
5
Length of Dowel bar, mm
450
6
Spacing of Dowel bar, mm
380
7
Dia. of Tie bar, mm (Ribbed bars)
16
8
Length of tie bar, mm
800
9
Spacing of tie bar, mm
1185
10 Conclusions The design life msa for 8 years is 100, 15 years is 210 and for 20 years is 320 for the project stretch. IRC:37–2012 provides flexible pavement design upto 150 msa maximum. So it is concluded that stage construction technique should be followed for the design of
flexible pavement to minimise the initial construction cost and for the full utilisation of pavement layers for the full design life. Reconstruction of the entire project stretch with rigid pavement is not a feasible option by considering difficulties in diversion of existing traffic and construction cost.
INDIAN HIGHWAYS, December 2014
