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IRC SP 73 : 2015

Manual of Specifications and Standards for Two-Laning of Highways with Paved Shoulders

AASHTO LRFD Bridge Design Specifications (USA) · Austroads Guide to Pavement Technology (Australia) · Design Manual for Roads and Bridges (DMRB) (UK)
CurrentFrequently UsedCode of PracticeTransportation · Roads and Pavement
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Summary

This IRC manual is a vital resource for engineers undertaking the two-laning of existing highways, with a specific emphasis on the provision of paved shoulders. It details design considerations, material specifications, construction methodologies, and quality assurance procedures. The inclusion of paved shoulders is critical for enhancing road safety by providing emergency stopping space, facilitating safe overtaking maneuvers, and improving the overall structural integrity and longevity of the pavement. The document aims to standardize practices, ensuring a consistent and high-quality outcome for such road improvement projects across India.

This manual provides comprehensive specifications and standards for the two-laning of existing highways, focusing on the incorporation of paved shoulders. It covers all aspects of design, construction, and quality control necessary for upgrading single or intermediate lane carriageways to a two-lane configuration with the added benefit of paved shoulders for improved safety and operational efficiency.

Key Values
minimum lane width3.60 m (Clause 4.1.1.1)
minimum shoulder width paved1.50 m (Clause 4.1.2.1)
minimum shoulder width unpaved2.50 m (Clause 4.1.2.2)
Practical Notes
! The design speed should be chosen conservatively based on the terrain and the ability of the existing road geometry to accommodate it after widening.
! Adequate drainage is paramount to prevent water ingress into the pavement layers, especially under paved shoulders, to maintain their structural integrity and prevent premature failure.
! The selection of appropriate aggregate gradations for GSB and GWB layers is critical for load distribution and preventing pumping action of fines.
! Compaction of all pavement layers must be meticulously controlled to achieve the specified densities, which directly impacts the load-bearing capacity and durability of the road.
! The construction of paved shoulders should be coordinated with the main carriageway construction to ensure seamless integration and consistent quality.
! Provisions for drainage outlets from paved shoulders, such as scuppers or weep holes, are essential to prevent water accumulation.
! The use of quality control tests at regular intervals throughout the construction process is non-negotiable to ensure compliance with specifications.
! Material sourcing for aggregates and bitumen should be from approved quarries and refineries to guarantee the required quality.
! Strict adherence to traffic management plans is necessary to ensure the safety of construction workers and the traveling public.
! Regular maintenance of paved shoulders, including cleaning of drains and repair of any surface distress, will significantly extend their service life.
! The existing subgrade's CBR value should be assessed thoroughly, and if it falls below the minimum requirement, strengthening measures like soil stabilization or a thicker sub-base layer should be implemented.
! Consideration should be given to the longitudinal and cross-sectional drainage during the design phase to effectively manage surface water runoff.
! The choice of bitumen grade should be based on the climatic conditions and the anticipated traffic loading.
! The construction of the paved shoulder should commence after the main carriageway pavement layers are in place to allow for proper compaction and bonding.
highway engineeringroad constructionpavement designtwo-laningpaved shouldersIRC codesroad specificationstraffic safetyIndian roadsinfrastructure developmentIRC
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Similar International Standards
AASHTO LRFD Bridge Design Specifications (USA)
MediumCurrent
Austroads Guide to Pavement Technology (Australia)
MediumCurrent
Design Manual for Roads and Bridges (DMRB) (UK)
MediumCurrent
Key Differences
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Key Similarities
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Parameter Comparison
ParameterIS ValueInternationalSource
Lane Width
Minimum Paved Shoulder Width
Subgrade CBR Requirement
Design Speed (Plain Terrain)
Compaction Density (GSB)
⚠ Verify details from original standards before use
Quick Reference Values
minimum lane width3.60 m (Clause 4.1.1.1)
minimum shoulder width paved1.50 m (Clause 4.1.2.1)
minimum shoulder width unpaved2.50 m (Clause 4.1.2.2)
design speed rural80 kmph (Table 4.1)
design speed plain rolling80 kmph (Table 4.1)
design speed mountainous steep50 kmph (Table 4.1)
cbr requirement subgradeMinimum 4% (Clause 5.2.1)
layer thickness gsbMinimum 150 mm (Clause 5.3.3.1)
layer thickness gwbMinimum 100 mm (Clause 5.3.4.1)
layer thickness dbmMinimum 50 mm (Clause 5.3.5.2)
layer thickness bmMinimum 25 mm (Clause 5.3.6.1)
layer thickness asphalt concreteMinimum 25 mm (Clause 5.3.7.1)
minimum camber rural section2.0% (Table 4.4)
minimum camber hilly section3.0% (Table 4.4)
traffic volume threshold for 2 laningConsidered based on existing conditions and projected growth (Implied in Scope)
compaction density subgrade97% of MDD (Clause 5.2.2)
compaction density gsb98% of MDD (Clause 5.3.3.3)
compaction density gwb98% of MDD (Clause 5.3.4.3)
compaction density dbm93-97% of theoretical density (Clause 5.3.5.5)
compaction density asphalt concrete93-97% of theoretical density (Clause 5.3.7.5)
Key Formulas
SSD = v*t + v^2 / (2*g*(f + sin(theta)))
ISD = 2.5 * SSD
OSD = v*t2 + 2*S*v + v^2 / (2*a) + v^2 / (2*g*(f + sin(theta)))
Theoretical Density = (100 / ((P_agg / rho_agg) + (P_bitumen / rho_bitumen)))
Key Tables
Table 4.1: Design Speed for Different Terrain Types
Table 4.2: Ruling Gradients
Table 4.3: Sight Distance Requirements
Table 4.4: Camber Values for Different Road Sections
Table 5.1: CBR Requirements for Subgrade
Table 5.2: Granular Sub-Base (GSB) Gradation and Properties
Table 5.3: Granular Working Base (GWB) Gradation and Properties
Table 7.1: Requirements for Bituminous Macadam (BM) Mix
Table 7.2: Requirements for Dense Bituminous Macadam (DBM) Mix
Table 7.3: Requirements for Asphalt Concrete (AC) Mix
Table 9.1: Quality Control Tests for Pavement Layers
Key Clauses
Clause 4.1: Geometric Design Standards for Two-Laning
Clause 4.1.1: Lane Width
Clause 4.1.2: Shoulder Width and Type
Clause 5.1: Subgrade Preparation
Clause 5.2: Subgrade Strength and Compaction
Clause 5.3: Pavement Layers Specifications (GSB, GWB, DBM, BM, AC)
Clause 6.1: Drainage Requirements
Clause 7.1: Material Specifications for Bituminous Layers
Clause 8.1: Construction Procedures for Paved Shoulders
Clause 9.1: Quality Control and Assurance
Clause 10.1: Traffic Management during Construction
Clause 11.1: Maintenance Requirements for Paved Shoulders
What is the primary objective of providing paved shoulders in two-laning projects according to this IRC manual?+
The primary objective is to enhance road safety and operational efficiency. Paved shoulders provide a stable area for vehicles to pull over in emergencies, act as a buffer zone, and allow for safe overtaking maneuvers. They also contribute to the structural integrity of the road by reducing stress on the main carriageway and preventing edge deterioration, thus extending the service life of the highway.
What are the minimum requirements for lane width and paved shoulder width specified in this manual?+
The manual specifies a minimum lane width of 3.60 meters (Clause 4.1.1.1) for two-laning. For paved shoulders, the minimum width stipulated is 1.50 meters (Clause 4.1.2.1). These dimensions are crucial for safe vehicular movement and maneuverability, especially in challenging traffic conditions.
How does the manual address the strength requirements of the subgrade for two-laning with paved shoulders?+
The manual mandates a minimum California Bearing Ratio (CBR) of 4% for the subgrade (Clause 5.2.1). If the existing subgrade does not meet this requirement, it necessitates strengthening measures such as soil stabilization, improving the subgrade by excavation and replacement with better material, or providing a thicker sub-base layer to ensure adequate load-bearing capacity and prevent pavement distress.
What are the typical pavement layer thicknesses prescribed for the different strata in this manual?+
The manual outlines minimum layer thicknesses for various pavement components. For instance, the Granular Sub-Base (GSB) requires a minimum thickness of 150 mm (Clause 5.3.3.1), Granular Working Base (GWB) a minimum of 100 mm (Clause 5.3.4.1), Dense Bituminous Macadam (DBM) a minimum of 50 mm (Clause 5.3.5.2), and Asphalt Concrete (AC) a minimum of 25 mm (Clause 5.3.7.1). These thicknesses are designed to distribute traffic loads effectively.
What is the importance of drainage design in the context of two-laning with paved shoulders?+
Drainage is critically important because water ingress into pavement layers can lead to a significant reduction in their strength and stability, causing premature failure such as rutting, cracking, and pumping. The manual emphasizes proper camber and the provision of adequate drainage structures (Clause 6.1) to efficiently remove surface water and prevent its accumulation, especially under the paved shoulders.
Are there specific material requirements for the bituminous layers used in paved shoulders?+
Yes, the manual specifies material requirements for Bituminous Macadam (BM), Dense Bituminous Macadam (DBM), and Asphalt Concrete (AC) in Chapter 7. This includes guidelines on the aggregate gradations, binder types and properties, and the mix design requirements to ensure durability and performance of the paved shoulders under traffic and environmental conditions.
What are the key quality control measures recommended in this manual for pavement construction?+
The manual emphasizes a robust quality control system, outlined in Chapter 9, which includes regular testing of materials and executed works. This involves checking the CBR of the subgrade, compaction density of GSB and GWB layers, aggregate gradations, bitumen content and properties, and the surface regularity and skid resistance of bituminous layers. Table 9.1 lists specific tests and their frequency.
How does the manual address the design speed considerations for two-laning projects?+
The manual provides different design speeds based on terrain types in Table 4.1. For rural and plain/rolling terrain, the design speed is typically 80 kmph, while for mountainous and steep terrain, it is reduced to 50 kmph. These speeds dictate geometric design parameters like sight distances, curve radii, and superelevation, ensuring safe vehicular operation.
What is the purpose of having both paved and unpaved shoulders in some cases?+
While the manual focuses on paved shoulders, it acknowledges the existence of unpaved shoulders in some contexts (Clause 4.1.2.2) for reasons of cost-effectiveness or specific project requirements. Unpaved shoulders primarily serve as run-off-road areas and can accommodate occasional slow-moving vehicles, but paved shoulders offer superior structural support and safety benefits due to their stability and load-carrying capacity.
What are the recommended camber values for different road sections?+
Camber is essential for surface drainage. The manual specifies minimum camber values in Table 4.4. For rural sections, a minimum camber of 2.0% is recommended, while for hilly sections, a higher camber of 3.0% is advised to facilitate rapid runoff of rainwater and prevent pooling on the road surface.