Power Point presentation on @ Low Volume Flexible Pavement Design .pptx

Low Volume Roads (LVRs) play a crucial role in providing connectivity to rural and remote areas.
Proper design, drainage, and maintenance are essential for ensuring long-term performance and cost-effectiveness.
The use of locally available materials, appropriate design methods (like IRC:SP:72), and adequate drainage provisions enhance durability.
Shoulders and proper lateral support contribute significantly to pavement stability.
Adopting scientific design principles and periodic maintenance ensures sustainability and serviceability of LVRs under limited traffic and budget conditions.
Overall, a well-designed low volume road offers safe, economical, and reliable access for rural development and social integration.

1. 1 A PRESENTATION ON DESIGN OF LOW VOLUME FLEXIBLE PAVEMENT by ADITYA RANJAN PATRA PHD SCHOLAR (Pavement engineering) DEPARTMENT OF CIVIL ENGINEERING

2. 2 Contents : Introduction DESIGN STEPS ESTIMATION OF DESIGN TRAFFIC SUBGRADE STRENGTH EVALUATION PAVEMENT THICKNESS DESIGN & COMPOSITION DESIGN PROCEDURE DRAINAGE AND SHOULDERS MAINTENANCE ADVANTAGES Conclusion References

3. 3 A low volume flexible pavement is a road surface made of asphalt and aggregate that is designed for roads with low traffic, typically found in rural areas, and uses a layered system of materials to spread loads to the subgrade. Low-volume roads are primarily intended for rural traffic loads of less than 2 million standard axles ( msa ) over a 10-year design life. Low Volume Roads (LVR): Carrying < 450 CVPD. Their objective is to improve rural connectivity and support economic development, while emphasizing the use of locally available materials and ensuring the minimum required level of serviceability. IRC:SP:72-2015,(2007 - First Edition) provides design guidelines for flexible pavements for low volume rural roads, focusing on cost-effective, performance-based, and locally adaptable solutions. Introduction:

4. 4 New Design, upgradation and rehabilitation Pavement design for traffic up to 2 msa (Million Standard Axles) Traffic Volume CVPD(Commercial Vehicles Per Day ) → Cumulative ESAL(Equivalent Single Axle Load) and Traffic divided into 9 categories. Subgrade strength in terms of soaked CBR – divided into 5 categories (From S1 to S5) depending upon the strength of soil. Minimum sub-grade CBR - 5%. Thickness design as per AASHTO ( American Association of State Highway and Transportation Officials) guide for low volume roads, 50% reliability and a terminal serviceability index of 2.0 and an initial PSI(Present Serviceability Index) of 4.0. Design life up to 10 years. Material Specifications: Base, Sub-base, Surfacing. Important Points in IRC SP 72, 2015:

5. 5 Design Steps (IRC:SP:72-2015 Reference): For working out, suitable and economical pavement, designs for the low volume, rural roads, design procedures have been set forth; for (a) new roads and for (b) upgradation/rehabilitation of existing roads. New Roads: Estimation of traffic: When no existing road is available, traffic estimation for the design life is based on counts from nearby roads with similar conditions. These counts, along with data on local population and produce, help estimate expected traffic on the proposed road. Assessment of subgrade strength: A detailed soil survey with IS classification, compaction, and CBR tests must be done, considering groundwater, rainfall, and environment.

6. 6 Determination of pavement thickness and composition: A field materials survey and lab tests should be done to utilize local materials or industrial waste for pavement layers. Using design traffic and subgrade strength, pavement thickness is determined from the Design Catalogue. Soil may be improved by stabilization or additives like lime, fly ash, or cement. Design Steps (IRC:SP:72-2015 Reference): Upgradation / rehabilitation of existing roads: Traffic parameter: The amount of traffic expected to ply over the future design life of the existing road, can directly be based on actual traffic counts on the existing road. Subgrade strength: For upgrading or rehabilitating an existing road, subgrade strength is assessed through a CBR test on soil remolded to field density and moisture after the monsoon. If testing at field moisture isn’t possible, a 4-day soaked CBR test is conducted. This simulates the worst moisture condition for accurate strength evaluation.

7. 7 Overlay thickness requirement: The causes of pavement distress should be identified using data from the existing road, as issues often arise from poor drainage or inadequate shoulder support. Such deficiencies should be corrected before strengthening. If design analysis shows the required pavement thickness exceeds the existing one, an overlay must be provided. Cont.. Fig.- (Newly constructed Low volume road some where in India)

8. 8 Design procedure: 1. Traffic Estimation: Only commercial vehicles of gross laden weight ( the total maximum operating weight of a vehicle, including its own empty weight, plus the driver, passengers, fuel, and cargo or payload ) of 3 tons and above ( Heavy Commercial Vehicle and Medium Commercial Vehicle ) to be considered. Rural vehicles with single axle loads different from 80 kN , and tandem axle loads different from 148 kN can be converted into standard axles using the Axle Equivalency Factor. For single-lane and intermediate-lane roads, the design shall be based on the total number of commercial vehicles per day in both directions. For double-lane roads, the design should be based on 75% of the total number of vehicles in both directions. Traffic Growth Rates By local enquiries, by establishing econometric models as per the procedure outlined in IRC: 108 (Guidelines for Traffic Prediction on Rural Highways). In the absence of any specific information, assume average annual growth rate 6%.

9. 9 A. Variation of Traffic: The total number of repetitions (N) of a given vehicle type during the course of a year is given by: Here, N – Number of repetitions of A given vehicle type during A year. T – Lean Season Traffic nt – Peak Season Traffic t – Duration of Harvesting Season AADT – Average Annual Daily Traffic

10. 10 B. Traffic Growth Rate: Trend Analysis – Past trend of growth is analyzed, and the rate is established by fitting a relationship. T n = T (1 + r) n Here, T n = Traffic in the n th year T = Traffic in the zero year n = number of years r = growth rate (Assuming a uniform traffic growth rate r of 6% over the design life (n) of 10 years in the absence of any specific information available) C. Determination of ESAL : Traffic in terms of Equivalent Standard axles using fourth power law; (Page no 12 of IRC-SP-72-2015). Axle Equivalency Factor = ( ) 4 Here, W = Actual Single axle load (in kN ) of the rural vehicle in question. Ws = Standard Axle Load of 80 kN or 148 kN in case of single or tandem axles.  

11. 11 The Vehicle Damage Factor (VDF) is a multiplier for converting the number of commercial vehicles of different axle loads to the number of standard axle load repetitions. It is defined as "equivalent number of standard axles per commercial vehicle". While the VDF value is arrived at from axle load surveys on the existing roads, the project size and traffic volume in the case of rural roads may not warrant conducting an axle load survey. For calculating the VDF, the following categories of vehicles may be considered: Laden Heavy Commercial Vehicles (HCV). Overloaded Heavy Commercial Vehicles. Unladen/Partially Loaded Medium-heavy Commercial Vehicles. Unladen/Partially Loaded Heavy Commercial Vehicles. Laden Medium-heavy Commercial Vehicles (MCV). Overloaded Medium-heavy Commercial Vehicles. D. Vehicle damage factor: as per IRC:SP-72-2015 page no 13,14 Towards the computation of ESAL applications, the indicative VDF values (i.e. Standard Axles per Commercial Vehicle) are given here: Vehicle Type Laden Unladen/Partially Laden HCV 2.86 0.31 MCV 0.34 0.02

12. 12 Assuming a uniform traffic growth rate r of 6% over the design life (n) of 10 years, the cumulative ESAL applications (N) over the design life can be computed using the following formula:- E. Equivalent Single Axle Load Calculation Where, T = ESAL per day = number of commercial vehicles per day in the year of opening × VDF L = lane distribution factor; L = 1 (One) for single lane/intermediate lane L = 0.75 for two-lane roads HCV : laden, unladen and overloaded. MCV : laden, unladen and overloaded must be obtained from actual traffic counts and, using appropriate VDF values.

13. 13 F. Traffic Categories: For pavement design, the traffic has been categorized into nine categories ( T 1 to T 9 ) as under: Traffic Category Cumulative ESAL Applications T 1 10,000-30,000 T 2 > 30,000-60,000 T 3 > 60,000- 100,000 T 4 > 100,000-200,000 T 5 > 200,000-300,000 T 6 > 300,000-600,000 T 7 > 600,000-1,000,000 T 8 > 1,000,000- 1,500,000 T 9 > 1,500,000- 2,000,000 Source; As per IRC:SP-72-2015 clause no 3.5,page no 15. https://law.resource.org/pub/in/bis/irc/irc.gov.in.sp.072.2015.pdf

14. 14 Design procedure: 2. Subgrade Strength Evaluation : The subgrade, whether in cutting or in embankment, should be well compacted to utilize its full strength and to economize on the overall pavement thickness. For determining the CBR value in the laboratory, the standard test procedure laid down in IS 2720 (Part 16) must be adopted. The CBR of the subgrade can be estimated by any of the following methods : By conducting actual CBR tests in the laboratory. Based on soil classification (which gives typical presumptive CBR values) Using the equations for plastic and non-plastic soils. Table; Typical Presumptive Design CBR Values Description of Subgrade Soil IS Soil Classification Typical Soaked CBR Value (% ) Highly Plastic Clays and Silts CH, MH * 2 - 3 Silty Clays and Sandy Clays ML, MI CL, CI 4 - 5 Clayey Sands and Silty Sands SC, SM 6 - 10 * Expansive clays like BC Soil may have a soaked CBR of less than 2%

15. 15 Cont.. The strength of subgrade for design of new roads shall not be less than the values specified below. The minimum recommended CBR values for rural roads is 5%, even when the traffic volumes are low. In case, the subgrade CBR is less than 5%, the subgrade should be stabilized to achieve a minimum design CBR of 5%. When subgrade CBR is less than 2% , the top 300 mm of subgrade shall be replaced with suitable soil. Quality of Class Subgrade Range (CBR%) Very Poor S 1 2 Poor S 2 3 - 4 Fair S 3 5 - 6 Good S 4 7 - 9 Very Good S 5 10 - 15

16. 16 Design procedure: 3. Pavement Thickness Design & Composition : Surface Course: Gravel / Thin Bituminous surfacing Granular Base: WMM / GSB (compacted) Granular Sub-base: Local material with CBR ≥ 15% Total thickness derived from design catalogue. Maximizing Use of Locally Available Materials. - Maximizing the use of locally available materials, suitable and economical designs can be worked out and the most suitable and economical design adopted. Selected granular soil for use in subgrade. Mechanical stabilization, stabilization with lime, cement, lime and fly ash, as appropriate. Naturally occurring softer aggregate like moorum , kankar , gravel etc. Brick and overburnt brick metal. Stone metal and Industrial Wastes.

17. 17

18. 18 Pavement Design of Gravel/Soil-Aggregate Roads Gravel/Soil-Aggregate is a mix of stone, sand and fine-sized particles used as a subbase, base or surfacing on a road. The gradation and plasticity requirements for use in subbase, base and surfacing are given in Clauses 401 and 402 of the MORD Specifications for Rural Roads (Ref 14). For gravel (aggregate-surfaced) roads, when the subgrade CBR is above 2 , the traffic level considered is up to 60,000 repetitions of 80 kN ESAL . However, the subgrade CBR is above 5, a gravel/aggregate-surfaced road can take upto 1,00,000 ESAL applications during the design life (Ref 2).

19. 19 Design of Flexible Pavement For Traffic Over 100,000 Cumulative ESAL Repetitions Granular sub-base materials conforming to the MORD Specifications for Rural Roads (Ref 14) are recommended for use. These specifications suggest three gradings and specify that the materials passing 425 micron sieve should have liquid limit and plasticity index as indicated below; The soaked CBR value should not be less than 20. In case the subbase material of the requisite soaked CBR value is not available within economical leads, the subbase material meeting any of the prescribed gradings and other requirements with a soaked CBR value of not less than 15 can be permitted with the approval of the competent authority.

20. 20

21. 21 Bituminous Surface Treatment: Surfacing : For rural roads designed for cumulative ESAL repetitions, over 100,000, a bituminous surface treatment of two coat surface dressing or 20 mm premix carpet is recommended, as per MORD Specifications for Rural Roads (Ref 14). Bituminous surfacing will be advantageous where subgrade is poor ( CBR < 4%), the design traffic > 60000 ESAL applications and annual rainfall exceeds 1000 mm.

22. 22 Drainage and Shoulders: Pavement design assumes the following drainage provisions: ( i ) Proper cross-slopes on carriageway and shoulders for quick water runoff. (ii) Raised subgrade — at least 300 mm above ground level (GL) and 600 mm above highest groundwater table (GWT) . (iii) Adequately designed roadside ditches/drains . (iv) All necessary cross-drainage structures are provided. Drainage of pavement layers is important, especially over low-permeability (clayey) subgrades . No separate drainage layer is needed for rural roads, but: At least half the sub-base thickness (minimum 100 mm) should extend across the shoulders for drainage. This should be done only when both subgrade and shoulders are clayey with poor drainage. In sub-base material, percent passing 75 µm sieve ≤ 5% . A typical cross-section shows drainage of pavement layers (as per the manual).

23. 23 Adequate lateral support from roadside shoulders is essential for good pavement performance. Shoulders should be of subbase quality , compacted to 100 mm thickness . The outer edge of the shoulder should be grassed to prevent erosion. For non- graveled shoulders with very low traffic , grass the entire shoulder area for protection and stability.

24. 24 Maintenance: Proper compaction at Optimum Moisture Content. Adequate side drains and cross slope. Periodic maintenance: re-gravelling, pothole repairs. Simple and field-oriented. Utilizes locally available materials. Cost-effective and durable. Focus on drainage reduces premature failures. Advantages: Fig. Low volume road construction site somewhere in India.

25. 25 Conclusions: Low Volume Roads (LVRs) play a crucial role in providing connectivity to rural and remote areas. Proper design, drainage, and maintenance are essential for ensuring long-term performance and cost-effectiveness. The use of locally available materials , appropriate design methods (like IRC:SP:72 ), and adequate drainage provisions enhance durability. Shoulders and proper lateral support contribute significantly to pavement stability. Adopting scientific design principles and periodic maintenance ensures sustainability and serviceability of LVRs under limited traffic and budget conditions. Overall, a well-designed low volume road offers safe, economical, and reliable access for rural development and social integration.

26. 26 References: IRC:SP:20-2002 Rural Roads Manual.( IRC SP 020: Rural Roads Manual ) Guidelines For The Design Of Flexible Pavement For Low Volume Rural Roads. IRC:SP-72-2015.( https://law.resource.org/pub/in/bis/irc/irc.gov.in.sp.072.2015.pdf ) AASHTO Guide for Design of Pavement Structures, AASHTO, 1993. MORD Specifications for Rural Roads, Indian Roads Congress, New Delhi, 2014(First Revision). IRC:37-1984 Guidelines for the Design of Flexible Pavements (First Revision), Indian Roads Congress, 1984. IRC:37-2001 Guidelines for the Design of Flexible Pavements (Second Revision), Indian Roads Congress, 2001. Other Internet Sources.