This document provides an overview of the Sigma Six model used to analyze cracking in the Arbaminch-Wolaita-Sodo Federal Road project in Ethiopia. It describes the project and outlines the DMAIC improvement cycle phases: Define, Measure, Analyze, Improve, Control. In the Define phase, tools like a project charter and value stream mapping were used. Road cracking is defined, with specific focus on factors that cause pothole cracking like rainfall, temperature, soil drainage, materials used, traffic load, and plants/trees. Models are presented to simulate the effects of these factors on flexible pavement cracking.

1. 1
SIGMA SIX MODEL FOR CIVIL
ENGINEERING PROJECTS
DMAIC SIGMA SIX REPORT ON
ROAD/FLEXIBLE PAVEMENT CRACKING
The Case of Arbaminch-Wolaita-Sodo Federal
Road Project, Ethiopia
ASQ-QC-CiEP-GP6
OCTOBER 07, 2022

2. 2
OUTLINE
1. SIGMA SIX MODEL
2.1. Overview
2.2. DMAIC Improvement Cycle
2.2.1. DEFINE
2.2.2. MEASURE
2.2.3. ANALYSES
2.2.4. IMPROVE
2.2.5. CONTROL
3. Conclusion
3. Reference

3. 2.1. Project Overview
Sigma Six Model
Fig: GoogleMap of the AM – WS Asphalt Road FH
• The study road is located in the SNNP
region of Ethiopia which is about 500
km south of Addis Ababa at an average
elevation of 1285m asl and between the
Geographic Coordinate of Latitude &
Longitude range of 362’N2193’E and
420’N2340’E respectively.
• Specifically, the AM-WS Federal
Highway extends from Humbo Woreda
at the Wolaita zone to Arbaminch at the
Gamo Gofa zone.
• The DMAIC problem-solving Sigma
Six model is focused on answering why
and how cracks are formed in this active
operational road project and will answer
the root cause with corrective and
preventive actions.
2. SIGMA SIX MODEL

4. 2.2. DMAIC Improvement Cycle
➢ DMAIC is an acronym for five interconnected phases: Define,
Measure, Analyze, Improve, and Control. It is used in Lean
when Lean is combined with Six Sigma.
➢ It is a data-driven structured, disciplined, and rigorous
approach used for improving, optimizing, and stabilizing
business processes and designs while consisting of the
five phases mentioned, and each phase is linked logically
to the previous phase as well as the next phase.
➢ When applied as a problem-solving sigma six models, more
emphasis is given to the Define, Measure & Analyze phases
while at the end of Analyze phase, the DMAIC model yields
three to five solutions. In the Improve phase, a solution is
chosen and piloted
Sigma Six Model

5. 5
Sigma Six Model
Fig: DMAIC improvement cycle taken from Google image document

6. 6
Evaluation of the AM-WS Asphalt road project was carried out in
2019. The functional classification of the road is the main access
road (FH); hence, the road was designed to serve 15 years (DP)
providing continuous and periodic maintenance. Unfortunately, a lot
of cracks (Potholes) formed along the road segment which highly
affected the functionality and serviceability of the road shortly after 5
years of opening for traffic. Meanwhile, residents and motor vehicle
operators at the AM-WS FH have been complaining and urging for
service improvement through design, construction & maintenance
intervention. Thus, the Ethiopian Road Authority (ERA) has decided
to implement the DAMIC problem-solving Sigma Six model in order
to improve, optimize and stabilize the functionality and design
process of the FH project. Therefore, the ASQ-QC-CEGPT,
consultancy firm has been selected to implement the DMAIC
improvement cycle. As a result, a detailed project chartering
document was generated and included with this document.
DEFINE
2.2.1. DEFINE

7. 2.2.1.
DEFINE
➢ Tools utilized in the define phase
of DMAIC used to investigate
Asphalt Road Cracking of the
AM-WS Federal Highway in
Ethiopia
✓ Project Charter
✓ Background on Road
Cracking
✓ Value Stream Mappin
7

8. Project
Charter
8
DEFINE

9. 9
The Problem
Asphalt Road Cracking (distress) has occurred on the Arbaminch (AM)-
Wolaita Sodo (WS) Federal highway (FH), Ethiopia
Purpose
The Evaluation of the AM-WS Federal Highway was carried out in 2019.
Despite the project design period (15 years), POTHOLE cracks were found
the major problem affecting the functionality and serviceability of the road
shortly after 5 years of operation. Therefore, implementing DMAIC Problem-
Solving Six Sigma Model to improve the functionality, design, construction,
and maintenance process of the AM-WS, FH helps implement corrective
action, sustain the improvement progress and accomplish objectives
Project Scope
The project scope ranges from defining the process map of Asphalt Road
design and construction to identifying workflow components from an input
supply (data collection, sample site test analyses, preparing design
specification document), construction, and the final product (sample site
testing for material quality, drainage cross-section peak discharge,
compaction, design manual, DFMEA, PFMEA simulation models, standard
specifications). Although the AM-WS Federal highway is the primary focus,
similar interventions are planned for Tigray Rehabilitation.
Project Benefit
DEFINE

10. 10
Road Cracking
➢ Asphalt road cracking is a structural problem that limits the
functionality and serviceability of the road project due to the
combined effect of Geological, Geotechnical, Design,
Construction, and Maintenance problems
➢ Climatic/weather/environmental factors, poor maintenance and
site preparation, aging, and the stress from heavy traffic load led
to Asphalt road cracking. This may continue to worsen resulting
in pothole formation when moisture is absorbed into the
asphalt's base
DEFINE

11. 11
Asphalt Road Cracking includes
✓ Alligator Cracking
✓ Block Cracking
✓ Longitudinal Cracking
✓ Transverse Cracking
✓ Edge Cracks
✓ Joint Reflection Cracks
✓ Slippage Cracks
✓ Potholes
✓ Depressions
✓ Rutting
✓ Shoving
✓ Upheaval
✓ Raveling
✓ Patch Failures
✓ Bleeding
DEFINE

12. 12
Fig: Road/Flexible Pavement cracking Analysis
Climatic/Weather/Environmental input
factors:
Rainfall/precipitation
Temperature
Humidity
Forest
Landscape & Topography
Soil drainage
Water Table Level
Plants & trees
Oil & Chemicals
DEFINE

13. 13
Fig: Asphalt Pavement cracking/distress
DEFINE

14. 14
Pothole Cracks
➢ A pothole crack is a depression in a road surface, usually asphalt
pavement, where traffic has removed broken pieces of the pavement
structure
➢ When water penetrates an asphalt pavement first weakens the materials,
including loose gravel, forming the roadbed; traffic loads then fatigue and
break the poorly supported asphalt surface
➢ Potholes further allow water to enter the pavement layers causing
softening and weakening of the pavement and lower layers. This causes
early failure of the asphalt pavement.
➢ Cooling and heating up of water trigger the pavement surface to expand
and contract, leading to pavement distress with the added pressure from
traffic load.
DEFINE

15. 15
DEFINE

16. 16
Fig: Pothole cracking/distress formation
DEFINE

17. 17
Main Factors for Pothole Cracking
Rainfall (Precipitation)
➢ Water penetrates the asphalt pavement and washes out the base course
underneath it, causing it to crack, break down, and collapse.
✓ Precipitation, humidity, and depth of water table are
climatic/weather/environmental factors that have significant influences
on asphalt pavement functionality.
✓Rainfall on asphalt has the potential to cause cracking, large potholes,
depressions, and other damage, specifically with a high amount of
rainfall (depth), intensity, and aspect (angle) of rainfall.
✓The interaction of pavement surface with rainfall causes loss of
pavement binding (bitumen).
✓The effect of rainfall and its interaction with the pavement surface is
analyzed using Intensity-Duration Frequency (IDF) curves.
✓Water enters under the pavement; as the groundwater expands and
contracts, it causes potholes to form on the pavement
DEFINE

18. 18
➢ When water enters and tends to freeze, it occupies more space
beneath the pavement, leading to expansion, bending, and
cracking of the pavement, making the pavement material weak.
➢ when the frozen water melts, the pavement will contract, leaving
voids or gaps in the surface beneath the asphalt pavement, where
water can enter and get trapped.
➢ As the water freezes and thaws repeatedly, the pavement will
wear out and begin cracking.
➢ When traffic load moves over the driveway's weak area, it
weakens pieces of the driveway material, causing the pavement
material to be displaced or deteriorate from the weight, and
creating the pothole.
✓ This is associated with the soil material used particularly with
the Permeability and Porosity of the selected soil used in the sub
and base grade of the pavement
Cont’d…
DEFINE

19. 19
Temperature
➢ Oxidation reaction breaks down and dries out the once
flexible liquid asphalt that holds the aggregate together.
This causes raveling and shrinking cracks, allowing water
to penetrate beneath the surface. If asphalt is paved outside
of the design temperatures, undesirable outcomes to the
quality of the driveway begin to take play, and in the long
run; the driveway will deteriorate much quicker than a
driveway that was paved and constructed during proper
temperatures
DEFINE

20. 20
Fig: Simulation as temperature changes on pavement layers
DEFINE

21. ➢ Temperature effect on pavement layers and the impact of
temperature change during the day are simulated using
COMSOL Multiphysics software as shown:
➢ Temperature has a high effect on pavement layers, especially on
the bitumen surface layer; during the expansion and contraction
of bitumen, the temperature effect can cause pavement cracking.
21
Cont’d…
DEFINE

22. The figure below depicts the variation of temperature over a 24-hour
period at various distances from the surface layer; the figure indicates
that there is a peak temperature from 13:00 to 16:00, so the
temperature has a high effect on the pavement layer during this time
period, leading to surface layer expansion; if the temperature drops
suddenly, this leads to cracking on the pavement layer.
22
Fig: Variation of temperature in 24hrs
DEFINE

23. Soil Drainage
➢ As water causes both heat and cold-related pothole cracks, if
asphalt road doesn't have an adequate drainage system, then it’s
susceptible to pothole cracking
➢ Beyond the structural strength, how well the soil beneath drains
matters most in asphalt road construction. When soil holds onto
water, it swells, affecting the asphalt pavement
➢ Additionally, over-flooding on the road causes road cracking
associated with the dimensions of the drainage.
➢ Overflooding may also be caused due to a lack of routine
maintenance such as cleaning of debris & silt, and removal of
grass & trees from the drainage channel & edge of the road.
➢ The effect of the drainage system is analyzed and simulated
using the rational formula and SCS formula.
23
DEFINE

24. Materials
➢ Asphalt roads comprise aggregates, gravel, sand, and stone.
These ingredients make up 95% of average asphalt road
construction. The rest 5% is asphalt or cement used as
binding material. Those materials sound durable and long-
lasting, but cause pavement cracking when poor quality
➢ Thus, not all soils are suitable to build a pavement structure
at the top of soils that are considered weaker including loose
saturated sand, peat, silt, and clay. silt, Peat, and clay are all
soil deposits.
➢ Soils deposits with high quantities of organic matter content
and building asphalt pavement on them makes the road prone
to drainage and flooding which causes pavement cracking
➢ The surface of the formation shall be substantially uniform in
density throughout its entire width and shall conform to the
density requirements for compaction and the trial compaction
should confirm that during the construction process.
24
DEFINE

25. Traffic Load
➢ Most asphalt roads are designed for cars to drive over a traffic
peak period. keeping this in mind, the asphalt road that receives
heavier traffic load would be susceptible to pothole cracking
and distress and needs maintenance frequently
➢ The thickness of a driveway asphalt pavement depends on the
amount of traffic flow. Proper thickness is needed to avoid a
sudden and unexpected degradation of asphalt pavement.
➢ If the sub-base is not solid, and the asphalt thickness is not
sufficient, the pavement can degenerate rapidly and require
repairs and maintenance frequently.
25
DEFINE

26. Load Vs Flexible Pavement
➢ Composed of several layers of material with better quality
materials usually placed on top where the intensity of traffic
loads is high and lower quality materials at the bottom where
the stress intensity is low.
➢ Constructed from bituminous or unbound material, the stress is
transmitted to the subgrade through the lateral distribution of
the applied load with depth.
➢ The bituminous material is often asphalt, whose viscous nature
allows significant plastic deformation.
References:
https://www.aboutcivil.org/flexible-pavement-road.html
https://pavementinteractive.org/asphalt-pavements-that-last/
https://rosap.ntl.bts.gov/view/dot/36064
26
DEFINE

27. 27
Fig: FP layers (From Soil Subgrade to surface course)
DEFINE

28. 28
Fig: Truncated cone-shape load distribution in flexible pavement
DEFINE

29. 29
Fig: EverstressFE for Load Effect Simulation on FP
DEFINE

30. 30
Fig: Vertical displacement illustration due to dual Wheel Single Axle Load
DEFINE

31. 31
Fig: Pavement Strain in FP
DEFINE

32. 32
Fig: Dual Wheel Tandem Axle in FP
DEFINE

33. 33
Fig: EverstressFE-Vertical displacement in FP
DEFINE

34. 34
Figure: EverstressFE strain in FP
DEFINE

35. 35
Fig: Vertical displacement & strains FP with high-grade Bitumen & Materials
DEFINE

36. 36
Figure: Vertical displacement in FP
DEFINE

37. 37
Fig: EverstresFE-Strain in FP
DEFINE

38. Plants & Trees
➢ Vegetation can lead to damage of any pavement type from
wandering roots and weeds underneath the surface.
➢ If plants and trees have close vicinity to the asphalt surface, their
root can stretch out across the road foundation, and this leads to
road cracking.
➢ It is vital to have removed and cleaned dirt, dust, and other debris
that can get inside and beneath the asphalt pavement.
38
DEFINE

39. Oil & Chemicals
➢ The introduction of chemicals such as oils to asphalt pavement,
including gas and oil, can often cause it to break down more
rapidly than expected.
➢ Additionally, oil and other chemicals on a pavement surface
facilitate the expansion and shrinking process altering the heating
and cooling temperature of the asphalt pavement.
➢ After 3 to 5 years, asphalt pavements begin to turn gray, become
brittle, and start cracking. Then water enters the cracks, freezes,
and thaws during the yearly cycle and causes larger cracks and
potholes. Rain enters the trials and causes base damage.
39
DEFINE

40. Pavement deflection/ Ground movement (BDE)
➢ The gravel layer of the ground comprises the pavement base.
Thus, Asphalt pavements might end up developing cracks if the
ground shifts. Natural events such as floods and earthquakes and
seasonal factors like frost, rain, and soil erosion are known to
shift the ground beneath the pavement and ultimately lead to
cracks.
40
DEFINE

41. 41
Physical model for PS Meshing of B-SEM 1
➢ To understand the overall effect of BRD on the asphalt pavement stiffness
and deflection resistance, semi-rigid base, rigid base, and flexible base AP are
simulated by the B-SEM1 with different bedrock depths [9].
➢ 1 B-SEM: Fixed Value boundary conditions are structural analysis
approaches that set a fixed displacement on the assigned face or volume.
DEFINE

42. 42
➢ At the same measurement point, with increasing BRD, the
deflection peak magnitude increases & then gradually stabilizes.
➢ The peak deflection at different measurement points for the three
kinds of pavement with different BRD is shown in the next
picture.
✓ AP sections manifest varying peak deflection in mm.
✓ When BRD exceeds 300 cm, the deflection peak will fluctuate
with a small amplitude.
✓ The BRD ranges that correspond to the fluctuations in the
deflections of different asphalt pavements differ.
✓ The Curve represents the time of peak deflection at a different
measurement point
Cont’d…
DEFINE

43. 43
AP with a semi-rigid base AP with a rigid base
Cont’d…
AP with a Flexible Pavement
DEFINE

44. 44
Fig. Effects of bedrock on FP deflections for (a) D0 time; (b) D900 time history
➢ Pavement Stiffness Sensitivity with respect to
bedrock existence: Li et al., 2017 [10], simulate &
articulated the PSS with respect to bedrock
availability
✓ Stiffness of bedrock is based on typical rock properties with an EM
of 7000 MPa and a Poisson’s ratio of 0.2.
✓ D0: Deflection under central load, D900: Deflection 900 mm away
from the central load, and BRD = 3000 mm from the PS
DEFINE

45. Lack of O&M
➢ Potholes are a very serious problem on asphalt roads. On asphalt
roads, pothole cracks will inevitably get bigger, and sometimes it
doesn't take long before it endures severe consequences for the
traffic. Thus, as soon as spotted even a small crack in the road,
must be repaired right away. It's wise to use more asphalt to seal
the cracks before it gets deeper or spread wider. The following
maintenance tips are recommended to increase the asphalt
lifespan.
✓ Limit traffic load/
✓ Install proper drainage
✓ Crack filling/Seal coating
45
DEFINE

46. Conclusion
➢ Pothole crack is a defect on the surfaces of paved asphalt
roads. Pothole cracks are reproduced when traffic abrades
small pieces of the asphalt pavement surface. The
pavement then continues to distress and disintegrate
because of poor surface quality. Weak spots on the base or
subgrade or because of severe alligator cracking. The
following factors contribute to pothole cracking:
✓ Asphalt content is too low
✓ Excessive heating of Asphalt
✓ Poor quality mixture
✓ Lack of compaction allowing ingress of water
✓ Excessive axle load
✓ Mechanical damage due to poor reinstatement of roads
after services installations
✓ Injury to the pavement
✓ Spills or leakage 46
DEFINE

47. 2.2.2.
MEASURE
➢ Tools utilized in the measurement phase
of DMAIC used to investigate Asphalt
Road Cracking
✓ 5W2H
✓ Process Map
✓ Measuring sample studies and
analyzing failure modes
✓ Interim Containment action
47
MEASURE

48. 5WH2H-QUESTIONS
What happened? Crack in a flexible pavement.
Who reported? Arbaminch (AM) – Wolita Sodo (WS) residents
Where happened? AM - WS FH
When did it happen? 2019, after five years of traffic opening.
Why did it happen? Due to different failure modes.
How much is it? 32.5% (based on PCI analysis)
How did it determine? By visualization inspection and PCI analysis.
MEASURE

49. Process Map for
Road Design &
Construction
49
MEASURE

50. Quality Control in Road
Design & Construction
Process
50
MEASURE

51. Quality control & Testing
➢ The road is classified into four sections of different lengths and
checked the pavement condition index, the one-way ANOVA
results are shown below:
51
MEASURE

52. 52
MEASURE

53. Table: PCI classification according to ASTM
PCI range Class Weighted Average (PCI) in percent
85-100 Good -
70-85 Satisfactory -
55-70 Fair -
40-55 Poor
25-40 Very poor
30.71%(section-4)
30.01%(Section-1)
10-25 Serious 21.15%(Section-2)
17.98%(section-3)
0-10 Failed
MEASURE

54. 54
Potholes at the Arbaminch-Wolaita-Sodo Asphalt road, (source AU, 2019)
Block crack at the Arbaminch-Wolaita-Sodo Asphalt road, (source AU, 2019)
MEASURE

55. Pareto analysis of different road crack
MEASURE

56. Pareto Analysis Based on Defected Area
MEASURE

57. 57
Containment Action Owner Target Status
Temporary diversion of traffic
flow to gravel road on the
side
Design Engineering
team
Feb 02, 2022 Completed
Provide Road surface
marking
Transport
Engineering team
Feb 03, 2022,
G.C.
Completed
Culvert and pipe
maintenance
Maintenance team Feb 07, 2022 Completed
Providing effective and
efficient drainage system.
Hydrology/Geology
team
June 02, 2022 Completed
Repairing potholes Maintenance team June 24, 2022 Completed
Interim Containment action
MEASURE

58. Action Owner Target Status
D3-6: Repairing edges Maintenance team June 20, 2022 Completed
D3-7: Sealing cracks Maintenance team Section 1 2 3 4 Completed
D3-8:Surface dressing Maintenance team June 05, 2022 Completed
D3-9: Slurry sealing Maintenance team June 08, 2022 Completed
MEASURE

59. 2.2.3.
ANALYZE
➢ Tools utilized in the Analyze phase of
DMAIC used to investigate potential
failure modes of Road Cracking.
✓ Fishbone Diagram
✓ 5WHY
✓ Simulation Models
✓ Root Cause Analysis
59
ANALYZE

60. Pot hole crack on
flexible pavement
Unskilled operator
Personal
Material
Environment
Method
Machine/
Equipment
Measurement
Soil and
geographical
landscape
Metrology and
metrological data
Traffic load and volume
Selection of wrong material
Unskilled Designer
Grading process
Strength and texture of the
aggregate
Reactivity of the material
Utilization of standards
Grade of the bitumen
Temperature
Mix design process
Rain falling angle
Compaction process
Flood
Rainfall intensity
Accuracyand precision
of data
Operator error
Availability of sufficient
data
Violationofworkinstructions
Poor construction
management
Design error
Violation of procedures and
methods
Set up of the machinery
Productivity of the
machinery
Calibration of the
testers
Gage R&R of testers
Lack of appropriate
construction manual
Paving process
Dynamicsofearth
Utilization of inappropriate analysis
Inspection cycle
Selection of bad material suppliers
Lack of work instruction
Poor quality control
Lack of appropriate DOE
Porosityofthe soil
Density of the soil
Strength of the soil
Soil to material
interaction
Variationofsoil propertyover
the seasons
Validationtoolforcalibration
Validation of
machinery
Lack DFMEA
Lack PFMEA
Fishbone Diagram…
ANALYZE

61. Table: Test Possible Causes Researching
61
Possible Cause Does not
Explain
Explains Only if… Status
Environment
✓ Temperature
✓ Rainfall/Precipitation
✓ Traffic load
✓ Temperature change affects asphalt stability
during the wet and dry seasons
✓ Rainfall penetration via asphalt surface affects
load capacity of base course
✓ High volume of traffic load affects the
pavement performance
Most likely
Process
✓ Compaction and
grading
✓ Paving
✓ The construction process doesn’t satisfy design
specifications due to a lack of proper grading
and compaction
✓ In proper paving of asphalt mix affects the
pavement strength
Most likely
Materials
✓ Aggregate strength
✓ Bitumen grade
✓ Clay & silt dust
✓ Gradation of combined aggregates and binder
content doesn’t satisfy mix formula and the
design specification
Most likely
ANALYZE

62. 62
Possible
Cause
Does not
Explain
Explains Only if… Status
Soil property ✓Low soil density affects the
subgrade strength
Most likely
Machinery ✓Lack of appropriate Set up and
validation
✓Low productivity of Machinery
Likely
Measurement ✓Lack calibration
✓Lack of validation
Most likely
ANALYZE

63. Table: Action Plans to Verify Root Causes
63
TASK/ ASSIGNED ACTIVITIES OWNER STATUS
Check if the bitumen grade is appropriate
For the extreme temperature .
Bitumen Inspector Completed
Check if the cross-section of side ditch is
appropriate for the peak runoff.
Hydrology Completed
Investigate if the selected material have
adequate strength.
Material Engineer Completed
Investigate if the compaction process is
with in the specification limit.
Construction Team Completed
Check the availability of adequate
metrological data.
Hydrology/Geology Completed
Check the customization of design manuals. Design Engineering Completed
ANALYZE

64. 64
Task/ Assigned Activities Owner Status
Check the adequate traffic volume
estimation.
Transportation
Engineering
Completed
Check the availability of DFMEA and
PFMEA
Quality Engineering Completed
Check the consideration of interaction
among different factors affecting the
Performance of pavement surface.
Quality Engineering Completed
ANALYZE

65. 65
Problem statement Pavement/road crack
1st Why Pothole crack happens in the pavement.
2nd Why Poor stability exists in asphalt mixture.
3rd Why Temperature change effect.
4th Why Inappropriate bitumen grade .
5th Why Material selection/Design error.
5 Why RCA: Temperature
ANALYZE

66. 66
Problem
Statement
Pothole road cracking
1st Why Accumulation of water on the pavement surface
2nd Why Rainfall/Precipitation
3rd Why Removal of Asphalt binding material (Bitumen)
4th Why Due to high rainfall/precipitation amount,
intensity, and aspect/angle.
5th Why Poor estimation of rainfall characteristics, poor
bitumen quality /design Error.
5 Why RCA: Rainfall (PCP)
ANALYZE

67. 67
Problem
Statement
Pavement/Road crack
1st Why Pothole crack happens in the pavement.
2nd Why Over-flooding effect.
3rd Why Inadequate drainage system.
4th Why Inadequate side ditch drainage.
5th Why Poor design .
5 Why RCA: Drainage
ANALYZE

68. 68
Problem Statement Pavement/road crack
1st Why Pothole crack happens in the pavement.
2nd Why Excessive moisture in the sub-base grade
3rd Why High amount of clay and silt content.
4th Why Poor sieve size analysis (gradation)
5th Why Inappropriate material selection.
5 Why RCA: Soil Aggregate and Grading
ANALYZE

69. 69
Problem Statement Road crack
1st Why Pothole crack happens in the pavement.
2nd Why Low subgrade strength .
3rd Why Low dry density of the soil .
4th Why In conformance of MDD with the OMC.
5th Why Due to poor control of compaction process.
5 Why RCA: Compaction
ANALYZE

70. 70
Problem Statement Road crack
1st Why Pothole crack happens in the pavement.
2nd Why Low load bearing capacity of the layers.
3rd Why Inappropriate bedrock depth estimation.
4th Why Lack of actual & site-specific design
consideration
5th Why Inappropriate design manual
5 Why RCA: Design Manual
ANALYZE

71. 71
MnPAVE Software Analysis
✓ Applicable for rutting and fatigue cracking
✓ Design thickness and strength of pavement structure
Table: Traffic class & subgrade strength classes of road design (ERA)
ANALYZE

72. 72
Figure: Selected pavement layer (ERA Manual)
We used simulation software to check whether the structural design is
performing well under the application of traffic load
The subgrade strength is 8.6 (CBR), and the equivalent static axle traffic
load in the road's design term of 15 years is 35.56 million, so the thickness
of the pavement layers from the ERA manual will be (S4 and T9)
Selected pavement layer (wearing asphalt, Base course and subbase, and
subgrade ) from ERA manual is [90: 190: 175]
ANALYZE

73. 73
Fig: Total damage on the road due to fatigue and rutting in all seasons
The performance of the pavement design and the reliability of the structural
design was computed using MnPAVE software as below
ANALYZE

74. 74
Fig: The calculated reliability value of the road design from the software
Reliability and probability of failure analysis…
ANALYZE

75. 75
➢ The reliability value for fatigue and rutting is 38% and 35%, respectively,
while the minimum recommended reliability value is 95%.
➢ This result indicates that the pavement design has an error in the
structural layers’ strength; to achieve the reliability value during the
design life of the road, it is advised that the road's subgrade strength be
increased.
𝑅𝑒𝑙𝑖𝑎𝑏𝑖𝑙𝑖𝑡𝑦 = 1 − 𝑝𝑟𝑜𝑏𝑎𝑏𝑖𝑙𝑖𝑡𝑦 𝑜𝑓 𝑓𝑎𝑖𝑙𝑢𝑟𝑒
𝑃𝑟𝑜𝑏𝑎𝑏𝑖𝑙𝑖𝑡𝑦 𝑜𝑓 𝑓𝑎𝑖𝑙𝑢𝑟𝑒 = 1 − 𝑟𝑒𝑙𝑖𝑎𝑏𝑖𝑙𝑖𝑡𝑦
𝑃𝑟𝑜𝑏𝑎𝑏𝑖𝑙𝑖𝑡𝑦 𝑜𝑓 𝑓𝑎𝑖𝑙𝑢𝑟𝑒 𝑑𝑢𝑒 𝑡𝑜 𝑓𝑎𝑡𝑖𝑔𝑢𝑒 = 1 − 0.38 = 62%
𝑃𝑟𝑜𝑏𝑎𝑏𝑖𝑙𝑖𝑡𝑦 𝑜𝑓 𝑓𝑎𝑖𝑙𝑢𝑟𝑒 𝑑𝑢𝑒 𝑡𝑜 𝑟𝑢𝑡𝑡𝑖𝑛𝑔 = 1 − 0.35 = 65%
➢ Therefore, the road cannot provide its attended use within its design life;
it is highly likely to fail due to high value of probability of failure.
ANALYZE

76. A. Comparison of the
plastic index of the
subgrade with
specification
 According to the ERA
the plastic index of
the subgrade must
be less than 30.
Hence, an
Independent t-test
was carried out to
see the difference
between the
specification and
the actual test from
the sample
collected, and the
result presented
below
76
Material failure testing
ANALYZE

77. 77
From the graph below, the PI is not less than the specification and almost
all are above the specification.
Fig: Sample t Test for the Mean of PI
ANALYZE

78. 78
B.
Comparison of the
subgrade’s optimum
moisture content with
stipulated specification
The expected optimum moisture
content to achieve the required dry
density was below 18%. Hence, an
Independent t-test was carried out to
see if it was within the limit and
presented in the below graphs
Analyzed results showed as
the mean of the samples is
greater than the
specification required, and
all the result of the samples
is above 18%
ANALYZE

79. 79
Fig: Sample t Test for the mean of OMC
ANALYZE

80. 2.2.4.
IMPROVE
➢ Tools utilized in the Improve phase of
DMAIC used to investigate Corrective
Action measures of Road Cracking.
✓ Corrective Action (CA)
80
IMPROVE

81. Corrective Actions
81
Action Owner Status
Perform design of Experiment (DoE)
based on different branches of fishbone
Quality Engineering Completed
Use improved construction technology Construction Team Completed
Use accurate and precise data Hydrology/Survey Completed
Customize the design manual based on
the working environment
Design Engineering Completed
Apply advanced material science
programming.
Material Engineering Completed
Select proper material suppliers. Logistics Completed
Perform design of Experiment (DoE)
based on different branches of fishbone
Quality Engineering Completed
IMPROVE

82. Validation of the Corrective Actions
82
Action Owner Status
Evaluating the pavement performance
with the key parameters from DoE
Quality Engineering Completed
Assessing the gage capability of
aggregate, soil, and bitumen tests
Material Engineering Completed
Evaluating the precision and accuracy
of data collection equipment
Transportation and
Hydrology
Completed
Evaluating the setup and performance
of machinery
Construction team Completed
Assessing the supplier’s quality
material production
Quality Engineering Completed
Investigate the design manual
applicability for the working
environment using simulation analysis.
Design Engineering Completed
Performing DOE to check if the
applied advanced materials improve
the performance of the pavement.
Design Engineering Completed
IMPROVE

83. 2.2.4.
CONTROL
➢ Tools utilized in the control phase of DMAIC
used to investigate the sustainability measures
of Road Cracking.
✓ Quality Control plan
✓ Preparing new design manual
✓ Mistake Proofing (Poka-yoke)
83
CONTROL

84. Action Owner Status
Formulate DFMEA and PFMEA documents Tigray Construction
Management Institute
On Plan
Formulate design manual according to the
performed DOE for similar site
Tigray Construction
Management Institute
On plan
Develop standard specification for aggregate
property and Bitumen grade
Tigray Construction
Management Institute
On plan
Develop a simulation model or template which
shows the correlation of selection soils,
aggregate, and bitumen with road cracking.
Tigray Construction
Management Institute
On plan
Perform DOE to correlate different interaction
effects among factors that affect the
performance and reliability of the pavement
Tigray Construction
Management Institute
On plan
Preventive Actions
CONTROL

85. THANK YOU.

86. [1]“8D | Eight Disciplines of Problem Solving | Quality-One,” Jul. 15, 2016. https://quality-
one.com/8d/ (accessed Jul. 07, 2022).
[2] “8D Problem Solving Report.” https://www.whatissixsigma.net/8d-report/ (accessed Jul. 07,
2022).
[3] Tantu, Temesgen Yonas, “Investigating the Causes of Different Pavement Distress and its
Remedial Measures: A Case Study along Wolaita-Arbaminch Road Section,” Arbaminch
University, 2020.
[4]E. R. Authority and E. R. AUTHORIT, “Pavement Design Manual,” Addis Ababa, 2002.
[5] A. Leighton, “8D Problem Solving Process,” Sofeast. https://www.sofeast.com/glossary/8d-
problem-solving-process/ (accessed Jul. 12, 2022).
[6] “ERA-Ethiopia-2013-Rigid+Pavement+Design+Manual-ERA-v130322.pdf.” Accessed: Jul. 12,
2022. [Online]. Available: https://www.research4cap.org/ral/ERA-Ethiopia-2013-
Rigid+Pavement+Design+Manual-ERA-v130322.pdf
[7]D. Okes, Root cause analysis: The core of problem-solving and corrective action. Quality Press,
2019.
[8] “The 8D (Disciplines) Problem Solving Process | Operational Excellence Consulting LLC.”
https://www.operational-excellence-consulting.com/opex-articles/8d-problem-solving-process
(accessed Jul. 13, 2022).
REFERENCES
3. References

87. [9] Wang Y.; Zhao Y.; Zhang M.; Fu G.; Influence of bedrock on the dynamic deflection response
and dynamic back-calculation results of asphalt pavement: Insights from the numerical simulation
of falling weight deflectometer tests, Construction and Building Materials, Volume 330, 2022,
127252, ISSN 0950-0618, https://doi.org/10.1016/j.conbuildmat.2022.127252.
[10] Li M.; Wang H.; Xu G.; Xie P.; Finite element modeling and parametric analysis of viscoelastic
and nonlinear pavement responses under dynamic FWD loading, Construction, and Building
Materials, Volume 141, 2017, Pages 23-35, ISSN 0950-0618,
https://doi.org/10.1016/j.conbuildmat.2017.02.096.
REFERENCES