STRUCTURAL EVALUATION OF FLEXIBLE PAVEMENTS.ppt

Evaluation

1. STRUCTURAL REQUIREMENTS
& EVALUATION OF FLEXIBLE
PAVEMENTS

2. Structural Requirements of flexible
pavements
•The total thickness of pavement and the thickness
of individual layers should be such that they are
not subjected to stresses / strains exceeding the
permissible limits
•The pavement layers should be able to withstand
repeated applications of wheel loads of different
magnitudes under the actual conditions of
subgrade, climate, drainage and other
environmental conditions without causing
excessive permanent in the form of rutting and
cracking of bituminous surface.

3. NEED FOR STRUCTURAL
CONDITION EVALUATION
•PAVEMENT COMPONENT LAYERS NEED
ADEQUATE STABILITY TO WITH STAND
DESIGN TRAFFIC UNDER ADVERSE
CONDITIONS
•DISTRESS DUE TO TRAFFIC AND CLIMATIC
VARIATIONS
•NECESSITY OF STRUCTURAL OVERLAYS –
RIGHT PAVEMENT, RIGHT MATERIAL AND
THICKNESS AT RIGHT TIME
•FAILURE – REHABILITATION AND COSTLY
REPAIRS

4. Factors affecting structural
condition of flexible pavements
•Subgrade support
•Pavement structure
•Loading
•Variation in Moisture content
•Variation in temperature
•Pavement deterioration/distress

5. NON-DESTRUCTIVE STRUCTURAL
EVALUATION
EVALUATION OF THE
STRUCTURAL ADEQUACY AND
LOAD CARRYING CAPACITY
WITHOUT DISTURBING OR
DESTROYING THE COMPONENTS

6. Advantages of Nondestructive
evaluations over destructive
evaluation
•Low cost
•Least disturbance to traffic
•No damage to pavements
•Sufficient number of measurements can be
made to quantify variability

7. Analytical approaches to structural
evaluation
•Comparison of measured behaviour i.e deflection to allowable
deflection based on past performance.
•Comparison of measured behaviour against calculated
allowable criteria using elastic layer theory, in terms of
deflection
•Using an existing method to estimate the remaining life or load
carrying capacity with measured behaviour as an input
•Use of measured deflections and layer thickness data to
quantify the material preoperties of each layer using back
calculation technique.
•Combining laboratory material test results with back
calculation procedure to provide material properties required
for a theoretical analysis of fatigue and measured behaviour to
provide limiting criteria

8. •First three approaches have been successful
under limited conditions and hard to adapt to
changes in materials, environment and load limits
•Last two approaches offer a general solution to
structural evaluation problem, however not easy
to implement due to inherent limitations of the
currently available mechanistic pavement
analysis models

9. NON-DESTRUCTIVE TESTING
METHODS
•MEASUREMENT OF RESPONSE TO A
STATIC LOAD OR A SINGLE APPLICATION
OF A SLOW MOVING LOAD (static devices)
•RESPONSE TO A REPEATED OR DYNAMIC
LOAD (Impulse devices)
•RESPONSE TO A VIBRATORY OR CYCLIC
LOAD (VIBRATORY DEVICES)
•WAVE PROPAGATION TECHNIQUE

10. NON-DESTRUCTIVE TESTING
EQUIPMENT
Static Devices
•BENKELMAN BEAM – TRUCK WHEEL LOADS
•PLATE BEARING TESTS – STATIC DEFLECTION
PROCEDURE
•CURVATURE METER – STATIC TRUCK LOAD
•AUTOMATED DEFLECTION BEAMS – SLOW
MOVING WHEEL LOADS – LA CROIX
DEFLETOGRAPH
•CURVIAMETER – SLOW MOVING WHEEL
LOADS

11. Curvature Meter
•Estimate radius of curvature
•Calculate maximum deflection on a pavement
surface due to stationary wheel load
•Long thin aluminium bar with supporting feet at
ends and dial guage fixed at the centre
•Placed betn the dual wheels of a stationary truck
and deflection basin measured at middle ordinate
of a curve with a chord length of 12 inches

12. Benkelman Beam
•Automated Benkelman Beam –
To increase speed of deflection measurements, the beam
mounted on the loaded truck and maximum deflection
recorded automatically from one point to other while the
truck moves along the pavement
•Modified Benkelman Beam –
4 additional levers with probes in addition to probe of
benkelman beam for measuring rebound deflection

13. Automated Deflection Beams
•Automated Benkelman Beam
•La Croix Deflectograph – Europe
–Vehicle
–Vehicle moves at a constant speed of 3 km
per hour
–Vertical deflections measured betn twin rear
wheels of the loaded axle by means of a sensor
rod connected to a reference beam

14. CURVIAMETER
•Pavement deflection measured under moving
loads upto a speed of 18km/hr
•Rapid and continuous measurement of
deformation of the pavement along a wheel track,
starting one metre in front of moving twin wheels
load and ending 4m behind the wheels
•Geometry of curviameter designed to prevent
influence of front axle on measurement
•Temperature of air and pavement surface stored
for each measurement.

15. •Transducers used for measuring is
geophone fixed in a chain of 15 mts long
closed loop. The chain passes between
twin wheels which load the pavement
•Each geophone successively deposited at
the pavement surface while the truck is
running

16. NON-DESTRUCTIVE TESTING
EQUIPMENT
•Vibratory Devices
-DYNAFLECT
-ROAD RATER
IMPULSE DEVICE
- FWD
•WAVE PROPOGATION EQUIPMENT

17. Dynaflect
•Light load fixed frequency device
•Force generator and five geophones housed in a small
two wheel trailer
•Remote control and read out panel carried in the towing
vehicle , allows operation from drivers seat
•Load generated by two counter eccentric masses rotating
at 8 hz
•Dynamic load genrated is 453kg distributed between two
wheels
•Five geophones mounted on trailer tow bar at 12 inch
interval measure the deflection basin

18. Road Rater
•Capable of varying both load magnitude and
frequency
•Magnitude of static load varied by transferring
the weight of the trailer from the travel wheels to
the deflection load plate
•To generate dynamic load a mass is hydraulically
raised and lowered
•Four velocity transducers to measure deflection,
one at the centre of the load plate and three
placed at one foot interval

19. FWD
•Fwd – Impulse device
•Employ a mass falling on to a bufferred load plate
•Variations in the applied peak force achieved by varying
magnitude of the dropping mass and the height of drop
•Vertical peak deflections measured in the centre of the
loading plate and at varying distances away from the plate
plotted as deflection basins
•The transient force impulse created by the FWD in the
pavement more closely relates to pulse created by moving
load than either static or steady state vibratory load device
•FWD adopted for Long term pavement performance
(LTPP) study in the strategic Highway Research program
(SHRP)

20. FALLING WEIGHT
DEFLECTOMETER

21. FWD - Types
•Dynatest FWD – Model 8000
–Calibrated geophones used to register peak deflections
–The operating sequence completely automated
–Pulse loads between 1500 to 27,000 pounds are
produced
Dynatest FWD – Model 800
- pulse loads between 6500 to 19,000 pb produced
Optional features in various dynatest FWD models –
- automated pavement temperature sensing, air
temperature sensing, geophone extension bar

22. •KUAB FWD
- Trailer mounted and completely enclosed by a metal
housing
- Doors in the bottom of the unit automatically open to
allow the test equipment to be lowered to the pavement
surface, thus protecting the components from water, oil &
dust
- popular models – model 50 – impulse force range 2700
to 11250 lp, model 150 – impulse range 2700 to 33700 lb
- completely automated operation
- housed transducers used to measure deflection
- transducers can be calibrated in the field with a
micrometer incorporated in the housing
- impact load applied to the plate using two mass system,
creates wider pulse duration, which better represents the
stress duration created by trucks

23. •Phoenix FWD
• - Model ML 10000 FWD produces dynamic
impulse load range of 2300 to 23000 lb. It
includes 3 or 6 deflection transducers in
adjustable mounts along a 2.4m bar.
•The electronic control system consists of
microcomputer, control software and sensors
•Include features like air & surface temperature
measuring devices
•Has a protective metal housing and covering for
the FW assembly (300 kgs)
•Impact transmitted via rubber pads over load
plate

24. •FHWA Thumper
–Federal Highway Administration device
known as Thumper
–Limited application since not commercially
available
–Only research oriented deflection measuring
device

25. Structural Capacity Index
•Many attempts have been made to define a
structural capacity or structural adequacy
index (SAI) in terms of same scale as PSI
(0-5) or RCI (0-10)
•Determination of SAI utilises maximum
tolerable deflection (MTD) versus load
repetitions relationship.

26. Steps involved in determination of
SAI
•Truck factor (TF) & Design Traffic Number (DTN)
calculated in order to estimate total equivalent single axle
loads (ESAL)
•TF = 0.0353 + 0.0003 (AADT / 2) X (LDF) X [{(1+g)
n
+ 1}/2]
- AADT – annual average daily traffic (2 directions)
- LDF – lane distribution factor (1.0 for 2 lane; 0.8 for 4 lane)
g – compound annual traffic growth rate
n – no. of years in the analysis period
Min value of TF is 0.75 and max is 2.0. The DTN is calcualted as
DTN = (AADT/2) X LDF X T X TF X [{(1+g)
n
+ 1}/2]X LEF

T – fraction of commercial traffic
LEF – the load equivalency factor

27. The number of repititions of an 8 tonne ESAL over the
analysis period n is determined as follows
•ESAL = DTN X 300 X n
•300 represents the effective number of design days in a year
•MTD is calculated in terms of BBD using
•MTD
B
= 10.0
[0.40824 – 0.30103 X log
10
(ESAL)]
•MTD
B
= 0.1 for ESAL <= 47651
•MTD
B = 0.02 for ESAL> 10
7
•Pavement is structurally inadequate if measured / design deflection (mean +
2) > MTD
•SAI – 10 perfect pavement
•SAI – 0 structurally inadequate
•SAI – 5 barely adequate structure
•SAI calculated using deduct values as follows
•Calculate difference between design deflection & MTD
•Determine the percentage of deflection measurements which exceed the calculated
MTD, for a positive difference calculated in 1 or % deflection measurements which is
less than the calculated MTD for negative difference calculated in 1.
•Determine the traffic range (low, medium high)
•Read the value of density corresponding to the parametersevaluated in 1,2,and 3 from
table
•Subtract density determined in step 4 from the adequate score of 5 to give SAI

28. •In the negative difference case – density is
determined by reversing the order of the
traffic columns so that high traffic column
applies to ranges of low traffic volumes,
low traffic column applies to ranges of
high traffic volumes and medium traffic
column applies to medium range of traffic
volumes. Instead of subtracting the
corresponding density from 5, it is added
to 5 to giveSAI.

29. FUNCTION OF STRUCTURAL
OVERLAYS
•STRENGTHEN THE EXISTING
PAVEMENT
•IMPROVES RIDING QUALITY
•REDUCES THE STRESSES ON THE
PAVEMENT COMPONENT LAYERS AND
SUBGRADE
•SERVES AS A PART OF STAGE
CONSTRUCTION PROCESS TO CATER
TO INCREASED MAGNITUDE OF WHEEL
LOADS

30. OVERLAY DESIGN CONCEPT
•MATERIALS WITH HIGHER STABILITY AND
DURABILITY IN UPPER LAYERS TO SUSTAIN
HIGHER MAGNITUDE OF STRESSES
•SURFACE COURSE SUBJECTED TO SEVERE
WEATHERING ACTION AND WEAR AND TEAR
DUE TO TRAFFIC
•OVERLAY MATERIAL SHOULD BE STRONGER
AND SUPERIOR THAN SURFACE COURSE
MATERIAL OF THE EXISTING PAVEMENT / OR
OF THE SAME QUALITY

31. PRINCIPLE OF REBOUND DEFLECTION
METHOD OF STRUCTURAL CONDITION
EVALUATION
•NON-DESTRUCIVE EVALUATION
•DEFLECTION IS AN INDICATOR OF
STRUCTURAL CONDITION
•HIGHER THE VALUE OF DEFLECTION,
WEAKER IS THE PAVEMENT
•LOWER THE VALUE OF DEFLECTION,
STRONGER IS THE PAVEMENT

32. FACTORS AFFECTING THE
DEFLECTION VALUES
•SUBGRADE SOIL TYPE
•MOISTURE CONTENT OF THE SUBGRADE SOIL
•TYPE AND THICKNESS OF THE PAVEMENT
COMPONENT LAYERS
•TEMPERATURE OF THE BITUMINOUS
SURFACE LAYER
•PREVIOUS LOADING HISTORY
•MAGNITUDE OF WHEEL LOAD,
CONFIGURATION AND CONTACT PRESSURE

33. REBOUND DEFLECTION PRINCIPLE
AND ITS IMPORTANCE
•INSERVICE PAVEMENTS BEHAVE
ELASTICALLY
•SURFACE DEFLECTION IS THE SUM
TOTAL OF THE VERTICAL COMPRESSION
OF ALL PAVEMENT COMPONENT LAYERS
•DEFLECTION IS RELATED TO THE
SERVICE LIFE
– 0.5 mm DEFLECTION – 60 lakh REPETITIONS
– 1.5 mm DEFLECTION – 2 lakh REPETITIONS

34. PROCEDURE FOR
DEFLECTION SURVEY
•CONDITION SURVEY – COLLECT
INFORMATION OF ROAD
STRUCTURE BASED ON
PERFORMANCE
•ACTUAL DEFLECTION
MEASUREMENTS

35. PAVEMENT CONDITION
SURVEY
•VISUAL OBSERVATION ON:
SOIL TYPE
CRACKS
RUT DEPTH
SURFACE DISTRESS
•GROUPING OF HOMOGENEOUS
SECTIONS

36. PAVEMENT CONDIION
CLASSIFICATION
• GOOD – NO CRACKS, RUTS < 10
mm
• FAIR - NO CRACKS OR
CRACKING CONFINED TO SINGLE
CRACK, 10 mm < RUT < 20 mm
•POOR – EXTENSIVE CRACKING,
RUT > 20 mm

37. ADDITIONAL INFORMATION
•DRAINAGE CHARACTERISTICS
•DEPTH OF WATER TABLE
•ROAD IN CUT OR EMBANKMENT
•CHANGES IN SOIL PROFILE
•TOPOGRAPHY
•RAINFALL DETAILS
•CLIMATIC CONDITIONS
•THICKNESS AND COMPOSITION OF
PAVEMENT COMPONENT LAYERS

38. EQUIPMENT FOR DEFLECTION
MEASUREMENT
•LOADED TRUCK – WT. 8170 kg FITTED
WITH DUAL WHEELS, 10 X 12 PLY
TYRES, TYRE PRESSURE – 5.6 kg/sq.cm
•BENKELMAN BEAM WITH DIAL GAUGE
•THERMOMETER
•CUTTING TOOLS
•GLYCEROL, CHALK AND TAPE ETC.,

39. PRELIMINARY PREPARATIONS
•IDENTIFICATION AND CLASSIFICATION OF
SUBGRADE SOIL AND DIVISION OF SUB-
STRETCHES BASED ON SOIL TYPE
•VISUAL INSPECTION TO ASSESS THE
PAVEMENT CONDITION AND GROUPING INTO
SUB-SECTIONS
•MARKING AT 90 cm FROM PAVEMENT EDGE
FOR TWO LANE, 60 cm FOR SINGLE LANE
ROADS
•20 POINTS PER STRETCH
•CHECK LOAD OF TRUCK AND TYRE PRESSURE

40. PAVEMENT MARKINGS
X X X X
X X X

41. PROCEDURE
•PARK THE LOADED TRUCK AT THE
FIRST DEFLECTION OBSERVATION
POINT – RECORD INITIAL DIAL GAUGE
READING, D
o
•MOVE THE TRUCK BY 2.70 m – RECORD
THE INTERMEDIATE DIAL GAUGE
READING, D
i
•MOVE THE TRUCK BY A FURTHER 9 m –
RECORD THE FINAL READING D
f

43. SCHEMATIC DIAGRAM OF
DEFLECTION MEASUREMENT

45. COMPUTATION OF DEFLECTION
• IF (Di~Df) < = 2.5 divisions,
D = 2 (Do – Df) x LC of dial gauge
•IF (Di~Df) > = 2.5 divisions,
D = 2 (Do – Df) x LC of dial gauge + 2 K (Di – Df) x LC of dial gauge
•K IS A FACTOR DEPENDENT ON THE BENKELMAN BEAM
DIMENSUINS
FOR CONVENTIONAL BENKELMAN BEAM K = 2.91

46. PAVEMENT TEMPERATURE
•REBOUND DEFLECTION VARIES DURING THE
DAY BECAUSE OF CHANGES IN PAVEMENT
TEMPERATURE
•MAKE A SMALL HOLE, 40 mm DEPTH, FILL IT
WITH GLYCEROL AND MEASURE THE
TEMPERATURE OF THE PAVEMENT
•TEMPERATURE OF THE PAVEMENT IS
MEASURED AT TWO TO THREE SPOTS,
BEFORE AND AFTER THE DEFLECTION
STUDIES

47. SUBGRADE MOISTURE CONTENT
•DEFLECTIONS ARE AFFCTED BY
SEASONAL VARIATIONS IN CLIMATE
•COMPUTATION OF DEFLECTION
CORRESPODING TO THE WEAKEST
SUBGRADE CONDITION – POST
MONSOON PERIOD
•IF NOT FEASIBLE, APPLY SEASONAL
CORRECTION FACTORS

48. CORRECTION FOR
TEMPERATURE VARIATIONS
•STIFFNESS OF THE BITUMINOUS LAYER VARIES WITH
PAVEMENT TEMPERATURE
•NEED TO CORRECT THE DEFLECTIONS TO A STANDARD
TEMPERATURE
•RECOMMENDED STANDARD TEMPERATURE = 35
o
C
•CORRECTION FOR VARIATION IN TEMPERATURE OTHER
THAN 35
o
C IS 0.01 mm FOR EACH DEGREE VAIATION FROM
STD. TEMPERATURE
•EXAMPLE, DEFLECTION AT 37
o
C = 0.80 mm, DEFLECTION
CORRESPONDING TO 35
o
C = (0.80 – 2 X 0.01) = 0.78 mm
•DEFLECTION AT 32
o
C = 0.80 mm, DEFLECTION
3ORRESPONDING TO 35
o
C = (0.80 + 2 X 0.01) = 0.88 mm

49. CORRECTION FOR
SEASONAL VARIATIONS
CORRECTION FACTOR DEPENDS ON:
TYPE OF SUBGRADE SOIL
FIELD MOISTURE CONTENT
AVERAGE ANNUAL RAINFALL
CLASSIFICATION OF SOIL
SANDY/GRAVELLY
CLAYEY WITH LOW PLASTICITY (PI < 15)
CLAYEY SOIL WITH HIGH PI (PI > 15)
RAINFALL
LOW – ANNUAL RAINFALL <1300 mm
HIGH – ANNUAL RAINFALL > 1300 mm

52. TRAFFIC
•CONSIDER ONLY COMMERCIAL
VEHICLES (LADEN WT. MORE THAN
3t)
•TRAFFIC GROWTH RATE
PAST TREND

ELASTICITY OF TRANSPORT
DEMAND
ADOPT AV. VALUE OF 7.5 %

53. DESIGN LIFE
•MAJOR ROADS - ATLEAST 10
YEARS
•LESSER IMPORTANT ROADS – NOT
LESS THAN 5 YEARS

54. DESIGN TRAFFIC
•COMPUTE CUMULATIVE
STANDARD AXLE LOAD
REPETITIONS CONSIDERING:
COM. VEHICLE VOLUME
VDF
TRANSVERSE DISTRIBUTION FACTOR

55. CHARACTERISTIC
DEFLECTION
•Dc = (MEAN DEFLECTION + N *
STD. DEVIATION)
•N= 2 FOR MAJOR ARTERIALS LIKE
NH AND SH
•N=1 FOR ALL OTHER ROADS

56. DESIGN OF OVERLAY
THICKNESS
•ADOPT THICKNESS VALUES AS PER
DESIGN CURVE
•OVERLAY THICKNESS IN TERMS OF BM
CONSTRUCTION
•ADOPT EQUIVALENCIES FOR OTHER
MATERIALS
1 cm OF BM = 1.5 cm OF WBM/WMM/BUSG
1 cm OF BM = 0.8 cm OF DBM/BC/SDC

57. OVERLAY THICKNESS DESIGN CURVES

58. OTHER
RECOMMENDATIONS
•MIN. THICKNESS OF BM OVERLAY
= 50 mm WITH ADDITIONAL
THICKNESS OF 50 mm DBM OR 40
mm BC
•IF NO STRUCTURAL DEFICIENCY,
PROVIDE THIN SURFACING

59. OTHER
RECOMMENDATIONS
•TYPE AND THICKNESS OF
OVERLAY DEPENDS ON:
IMPORTANCE OF ROAD
DESIGN TRAFFIC
THICKNESS AND CONDITION OF
EXISTING BITUMINOUS SURFACING
CONSTRUCTION CONVENIENCE
RELATIVE ECONOMICS

60. OTHER
RECOMMENDATIONS
•THICKNESS OF WEARING COURSE AS
PER IRC:37:2001
•BEFORE OVERLAY CONSTRUCTION.
CARRY OUT PROFILE CORRECTION,
FILL THE CRACKS, POT HOLES, RUTS
AND UNDULATIONS
•NO PART OF THE OVERLAY SHALL BE
USED TO CORRECT SURFACE
IRREGULARITIES

61. EXAMPLE
•TWO LANE SINGLE CARRIAGEWAY
•INITIAL TRAFFIC = 400 cv/day
•TRAFFIC GROWTH = 7.5 %
•DESIGN LIFE = 15 YEARS
•VEHICLE DAMAGE FACTOR = 2.5
•DESIGN CSA = 7. 2 msa

62. EXAMPLE
D
o
D
i
D
f
D,mm
100 38 36 1.28
100 36 34 1.32
100 24 21 1.75

63. COMPUTATION OF DEFLECTION
•
IF (Di~Df) < = 2.5 divisions,
D = 0.02 (Do – Df), mm
•IF (Di~Df) > = 2.5 divisions,
D = 2 (Do – Df) + 2 K (Di – Df)
= 2(Do – Df) + 2 * 2.91 (Di – Df)
= 0.02(Do – Df) + 0.0592 (Di – Df) mm
•K IS A FACTOR DEPENDENT ON THE
BENKELMAN BEAM DIMENSUINS
FOR CONVENTIONAL BENKELMAN BEAM K =
2.91

64. COMPUTATION OF OVERLAY
THICKNESS
•
MEAN DEFLECTION = 1.50 mm
•STANDARD DEVIATION = 0.18 mm
•CHARACTERISTIC DEFLECTION = (1.50 + 2 *
0.18) = 1.86 mm
•MEAN PAVEMENT TEMPERATURE = 40 o C
•TEMPERATURE CORRECTED DEFLECTION =
{ (1.86 – (40-35) * 0.01)} = 1.81 mm
•SUBGRADE MOISTURE CONTENT = 5%
•SOIL TYPE = GRAVELLY/SANDY SOIL
•RAINFALL = LOW
•MOISTURE CORRECTION FACTOR = 1.17

65. COMPUTATION OF OVERLAY
THICKNESS
•DEFLECTION VALUE CORRECTED FOR
SEASONAL VARIATIONS = (1.81 * 1.17) =
2.12 mm
•THICKNESS OF BM OVERLAY = 150 mm
•EQUIVALENT OVERLAY THICKNESS :
1 cm

OF BM = 0.7 cm OF DBM/BC



EQUIVALENT OVERLAY THICKNESS
REQUIRED = 105 mm of DBM/BC
PROVIDE (65 mm DBM + 40 mm BC)
OVERLAY