MANMOHAN TECHNICAL UNIVERSITY

SCHOOL OF ENGINEERING
Budhiganga-4 Morang

A PAPER ON RUTTING IN FLEXIBLE PAVEMENT

A CASE STUDY OF ROADS BIRATNAGAR-ITAHARI
Transportation Engineering-II

Submitted by: Submitted to:

Name: Sandeep Sinjali Magar - Department of Civil Engineering
Roll. No: 019 - Date of Submission: 2081-01-19
Year/Part: III/I
 Contents
ABSTRACT...................................................................................................................................................iii
KEYWORDS.................................................................................................................................................iii
1. Introduction.........................................................................................................................................1
2. Causes of Rutting.................................................................................................................................2
3. Consequences of Rutting.....................................................................................................................2
4. Rutting Mechanism..............................................................................................................................3
5. Types of Stress acting on pavement....................................................................................................3
6. Phenomenon of Rutting.......................................................................................................................5
7. Prevention of rutting...........................................................................................................................5
8. Repair..................................................................................................................................................6
9. Case study: Biratnagar to Itahari.........................................................................................................7
10. Conclusion.......................................................................................................................................8
11. References.......................................................................................................................................8
 ABSTRACT
Rutting is a prevalent and serious form of distress in flexible pavements, often compromising
ride quality, safety, and structural performance. This paper explores the mechanisms behind
rutting, categorizing it into types such as mix rutting and subgrade rutting, and examines the
stresses—particularly from repeated traffic loads and environmental conditions—that
contribute to its formation. The role of pavement layer interaction under loading is analyzed to
understand the root causes of permanent surface deformation. Preventive strategies are
discussed, including the use of high-quality materials, proper mix design, effective compaction
practices, and adequate drainage systems. Additionally, various repair techniques such as
milling and overlay, as well as full-depth reconstruction, are evaluated for their effectiveness in
restoring pavement integrity. To contextualize the theoretical discussion, a case study of the
Biratnagar–Itahari road section in Nepal is presented. This segment, a critical transportation
corridor, has exhibited significant rutting issues. The study investigates the underlying factors,
assesses the condition of the pavement, and reviews the measures taken to address the
problem. The findings underscore the importance of timely maintenance, quality assurance
during construction, and the need for site-specific pavement design to effectively manage and
reduce rutting in flexible pavement.

KEYWORDS: Rutting, Asphalt, Stress, Milling, Overlay, Hydroplaning

1. Introduction
Rutting is the longitudinal surface depression or groove formed in the wheel paths of
flexible pavement due to repeated traffic loads. It appears as sunken tracks where vehicle
tires commonly travel, often with ridges along the sides of the ruts. This distress is a
widespread issue across road networks and can manifest in both the upper asphalt layers
and the lower subgrade foundation. Factors such as the asphalt mixture’s material
properties, drainage efficiency, ambient temperature, and traffic intensity influence where
rutting occurs in the pavement structure and how it progresses over time. Therefore, it is
essential to categorize the contributing parameters behind permanent deformation before
initiating any repair or maintenance interventions.
A road rut presents as a depression in the pavement surface, representing a localized area
that sits lower than the surrounding roadway. These surface depressions can be classified
by severity—low, medium, or high—ranging from minor indentations that are only
noticeable when water accumulates after rainfall, to more pronounced depressions that are
visibly apparent and may pose a risk of hydroplaning
"Rutting depth at a given location is defined as the vertical measurement from the crest of
the adjacent heave to the lowest point of the surface depression."
Rutting can be classified in to different types:
1. Surface Rutting (Asphalt Layer Deformation):
This type of rutting originates in the upper asphalt layers due to shear strain or
insufficient compaction during construction. High pavement temperatures combined
with repeated loading cause the asphalt to laterally displace. It's commonly linked to
mix instability and can often be mitigated through resurfacing or corrective overlays.

2. Subsurface Rutting (Base or Subgrade Distress):

Subsurface rutting develops in the granular base or subgrade layers, typically due to
inadequate structural support, poor drainage, or water-sensitive soils. It compromises
the load-bearing capacity of the pavement and requires more invasive treatments like
full-depth reclamation or stabilization to restore structural integrity.

3. Mix-Design Rutting (Material Instability):

This occurs when the asphalt mixture lacks sufficient stiffness or cohesion—often due to
excess binder, poor aggregate interlock, or improper gradation. The pavement deforms
plastically under repeated axle loads. Prevention involves using performance-graded
binders and well-graded, rut-resistant aggregate structures tailored to site conditions.

4. Structural Rutting (Systemic Pavement Failure):

Structural rutting reflects a comprehensive failure in the pavement structure, where
cumulative traffic loading exceeds design tolerances. It typically affects multiple layers
and progresses rapidly. Surface repairs are ineffective; rehabilitation usually demands

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 structural redesign and reconstruction to accommodate current and projected traffic
demands.

2. Causes of Rutting
1. Inadequate Pavement Design
 Insufficient structural thickness of pavement layers.
 Improper material selection, especially for subgrade and base layers.
 Failure to account for traffic loads, particularly heavy vehicle

2. Material Related Issues

 Low-quality asphalt binder: Soft or temperature-sensitive binders deform easily
under loads.
 Poor aggregate gradation or shape, leading to less interlock and stability.
 Insufficient compaction: Leads to low density and higher susceptibility to
deformation.
 Use of moisture-sensitive materials that weaken over time.

3. Traffic Loading
 High traffic volumes, especially with a high percentage of heavy trucks.
 Repeated axle loads cause cumulative deformation, especially in hot weather

4. Construction Deficiencies
 Poor compaction during construction, particularly in the subgrade or base layer.
 Segregation of asphalt mix, leading to weak spots.
 Incorrect layer thicknesses compared to the design.

5. Subgrade Weakness
 Soft or unstable subgrade soils (e.g., clay, silt).
 Presence of excess moisture leading to reduced load-bearing capacity.
 Lack of proper drainage leading to water accumulation.

6. Environmental Conditions
 High temperatures soften asphalt, increasing susceptibility to rutting.
 Freeze-thaw cycles weaken base and subgrade layers over time.
 Water infiltration can reduce support from subgrade or base due to loss of cohesion
or saturation

3. Consequences of Rutting
Definitely, defects in roads does not have positive impacts. It can lead to several real-world
issues that affects the performances of road, safety and maintenances. Major consequences
of rutting can be stated as:
a. Water accumulation and Hydroplaning Risk
b. Steering and Vehicle Control Problem

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 c. Reduced Ride comfort
d. Accelerated pavement deterioration
e. Increased maintenance cost

4. Rutting Mechanism
Rutting is defined in the mechanistic empirical Design Guide as occurring in three distinct
stages: Due to specific material characteristics; Due to excess loading under certain
temperatures; and Due to certain climatic conditions. Figure 1 illustrates the stages of
rutting, with the primary stage representing the initial level of rutting and a decrease in the
rate of plastic deformation, primarily due to volumetric changes. The secondary stage
shows an increase in shear deformation, while the tertiary stage is characterized by a
significant level of permanent deformation, which is mainly associated with shear (plastic)
deformation under conditions with no volume change.

Figure 1: Rutting behavior under repeated load

5. Types of Stress acting on pavement

Rutting in flexible pavement is a form of permanent deformation, primarily in the wheel
path, and is caused by repeated traffic loads. The table below shows the major types of
stress acting on pavement, their sources, acting location and their contribution in rutting of
pavement:

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Types of stress Location in Source of stress or Cause Contribution to Rutting
Pavement
Vertical Subgrade, base and Wheel load acting Causes densification &
compressive stress Asphalt layer vertically downward deformation
Shear stress Upper Asphalt layer Braking, turning and Causes lateral flow and
acceleration forces surface distortion
Tensile Stress Bottom of Asphalt Pavement Bending due to Minor Contributor: More
Layer traffic loads related to fatigue cracking
Repetitive(Cyclic) Entire pavement Repeated Vehicle passes Accumulates deformation
structure (Especially heavy trucks) over time: key to rutting

Figure: Types of Stress acting of Flexible Pavement

Figure: Types of Stress on Flexible Pavement under moving load

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6. Phenomenon of Rutting
The primary driver behind rutting is the repeated application of wheel loads. When vehicles
pass over a pavement, they impose dynamic stresses on the structure. If the materials in the
asphalt surface, base, or subgrade layers are weak, inadequately compacted, or overly
stressed, they may deform irreversibly. Over time, this deformation accumulates, forming
ruts.

Wheel loads affect rutting in two key ways:

1. Vertical Stress Transmission: Heavy wheel loads compress the pavement

structure downward. If the subgrade is not strong enough, it fails to rebound,
leading to rutting from the bottom up (subgrade rutting).
2. Shear Deformation: In the asphalt layers, wheel loads create horizontal shear
forces. If the asphalt is too soft or improperly designed, it can flow sideways
under pressure, leading to rutting within the surface or intermediate layers (mix
rutting).

High temperatures can worsen rutting because asphalt softens, reducing resistance to
shear and compaction. Therefore, wheel load magnitude, frequency, speed, and
environmental conditions all significantly influence rutting development.

7. Prevention of rutting
Rutting, like many failures in life, begins not with a single blow but through the quiet
repetition of pressure. To prevent it is to understand that strength lies not only in what
is seen on the surface, but in the unseen layers beneath. Just as a strong foundation
supports enduring character, so too must a pavement be built with thoughtful design,
resilient materials, and care in its construction. Drainage, often overlooked, is like
wisdom—guiding what flows through and protecting from what seeps in. Maintenance,
meanwhile, reflects mindfulness: a willingness to tend to the small imperfections before
they grow. In pavement as in life, enduring form follows from deliberate structure,
attention, and adaptation. We can prevent rutting of pavement by different measures
such as:

1. Material related Measures

Measure Description

Use Rut-Resistant Use dense-graded, stone matrix asphalt (SMA), or polymer-modified

Asphalt Mixes binders with high rutting resistance.
High-Quality Ensure well-graded, angular, and durable aggregates that resist
Aggregates movement under loads.
Control Binder Excess asphalt binder leads to a soft mix prone to rutting—optimize
Content content through mix design.

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 Maintain 3–5% air voids to prevent densification and excessive
Proper Air Voids
compaction under traffic.
Additives and Use fiber reinforcement, polymer-modified asphalt, or anti-rutting agents
Modifiers to improve resistance.

2. Structural Design Measures

Measure Description
Adequate Layer Design sufficient thickness in the asphalt and base layers to distribute
Thickness loads and reduce stress.
Strong Base and Improve weak subgrades using stabilization, geotextiles, or granular base
Subgrade reinforcement.
Ensure effective surface and sub-surface drainage to prevent moisture-
Drainage Design
induced weakening of base or subgrade.

3. Construction Quality Control

Measure Description
Adequate Layer Design sufficient thickness in the asphalt and base layers to distribute
Thickness loads and reduce stress.
Strong Base and Improve weak subgrades using stabilization, geotextiles, or granular base
Subgrade reinforcement.
Ensure effective surface and sub-surface drainage to prevent moisture-
Drainage Design
induced weakening of base or subgrade.

4. Traffic and Maintenance Measures

Measure Description
Traffic Load Limit heavy axle loads or enforce axle load limits to prevent overstressing
Management pavement.
Seal cracks, patch deformations, and maintain surface to prevent water
Timely Maintenance
ingress and structural weakening.

8. Repair
Repairing rutting in flexible pavement depends on severity, depth, and cause of the rutting.
Here’s a breakdown of rutting repairs methods, categorized by approach and application.
1. Minor Rutting (Shallow,<10)
-Surface level Repairs
 Fog Seal or Slurry Seal
Use: When rutting is minimal and caused by surface wear
Action: Restores surface textures and seals fine cracks
Note: Preventive only; does not correct structural rutting

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  Micro-surfacing
Use: For shallow, non-structural ruts (typically <10mm)
Action: Applies a thin, quick setting mix to restore smoothness
Advantage: Cost-effective, minimal traffic disruption

2. Moderate Rutting (10-20mm)

-Shaping and Overlay
 Milling and Overlay
Use: When rutting is moderate but not deeply structural
Action: Mill affected area and overlay with new asphalt
Result: Restores shape and strength
 Levelling Course (Wedge Paving)
Use: To fill depressions before final overlay
Action: Applies asphalt levelling mix selectively in rutted area

3. Severe Rutting( >20 mm or structural Rutting)

-Full depth or Structural Repairs:
 Full Depth Reclamation or Removal and placement
Use: When rutting results from subgrade/base failure
Action: Remove all affected layers and rebuild pavement structure
Materials: May involve new aggregate base, stabilized subgrade and asphalt
layers.

9. Case study: Biratnagar to Itahari

The 25 km highway connecting Biratnagar to Itahari is a vital transport corridor in Province
1. However, recent site observations and commuter reports confirm noticeable rutting,
particularly along the segments between Bargachhi to Kanchanbari, and Dhaat to Tanki.
These areas see heavy daily traffic, including commercial trucks, passenger buses, and two-
wheelers.
In several sections, rut depths of 20–35 mm have been visually confirmed, with ruts running
parallel to the wheel paths—especially near intersections and stops. These deformations
are primarily due to repetitive heavy axle loads, high summer temperatures, and insufficient
pavement thickness or compaction. Poor drainage also plays a role, as water accumulation
in rutted zones during rainfall accelerates pavement wear and increases skid risk.
Frequent complaints have been registered by locals and transport operators regarding
vehicle instability, hydroplaning incidents, and increased tire and suspension damage.
Despite periodic maintenance, most repairs have been surface-level patchwork, not
addressing the underlying structural weakness.
To ensure safety and extend pavement life, mill-and-overlay resurfacing, axle load control,
and upgraded pavement design are urgently recommended for these segments.

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10. Conclusion
Rutting is a critical form of pavement distress in flexible roads, often resulting from
repeated loading, inadequate materials, poor drainage, and weak subgrade conditions.
Preventing rutting requires a holistic approach that includes the use of high-performance
asphalt mixes such as stone matrix asphalt, high-quality aggregates, optimized binder
content, and effective compaction. Equally important is designing pavement layers with
sufficient thickness and ensuring proper drainage to prevent water-induced weakening.
Routine inspection—whether through manual methods or advanced laser and 3D profiling
—enables timely identification of rutting severity, leading to appropriate repair
interventions ranging from micro-surfacing for shallow ruts to full-depth reconstruction in
structurally compromised areas.

The Biratnagar to Itahari road, a major transport corridor in eastern Nepal, exemplifies the
consequences of prolonged neglect and overloading. The road experiences heavy
commercial traffic and monsoonal moisture, both of which accelerate rut formation. In
many sections, inadequate drainage and substandard construction have worsened surface
deformation, affecting safety and travel efficiency. To restore and preserve this corridor, a
long-term strategy is essential—one that emphasizes structural strengthening, the use of
durable materials, enforcement of axle load regulations, and proactive maintenance. With
such measures, the Biratnagar–Itahari route can evolve into a resilient, high-performing
roadway that supports regional development for years to come.

11. References
1. Impact of overloaded Vehicle on Flexible pavement: Case study of Belhiya-Butwal In Nepal,
IOSR journal of Mechanical and Civil Engineering,(Padma Bahadur Shahi and Bel Bahadur
Nepali)
2. www.researchgate.net
3. State-of-the-Art Review Of Research on the Rutting of Flexible pavement (Zainab Ahmed
Alkaisi and Kammelah Ahmed Al-Kaissi)
4. Wang,H., Zhang, Q, and Tan,J., “Investigation of layer contributions to asphalt pavement
rutting,” Journal of materials in Civil Engineering
5. Qi-sen Zhang, Yu liang chen, Xue-Lian Li Rutting in Asphalt under Heavy Load and High
Temperature, ASCE Library