forensic investigations of pavement pre-mature failure of a national highway pavement due to poor...

8/11/2019 Forensic Investigations of Pavement Pre-Mature Failure of a National Highway Pavement Due to Poor Sub-Surface Drainage

1/14

FORENSICINVESTIGATIONSOFPAVEMENTPRE-MATUREFAILUREOFANATIONAL HIGHWAY 153

PAVEMENTDUETOPOORSUB-SURFACEDRAINAGE

Journal of the Indian Roads Congress, July-September 2010

Paper No. 562

FORENSIC INVESTIGATIONS OF PAVEMENT PRE-MATURE

FAILURE OF A NATIONAL HIGHWAY PAVEMENT DUE TO

POOR SUB-SURFACE DRAINAGEA. VEERARAGAVAN* & LT. COL. SHAILENDRAGROVER**

ABSTRACT

This Paper presents investigations of premature failure of a section of a national highway pavement due to poor sub-surface drainage.

Forensic investigation to ascertain the cause for the failure was carried out by testing the different pavement layers in the field and through

laboratory tests on core samples of various pavement component layer materials. The contributing factors for the pre-mature failure were

identified as inadequate compaction of subgrade/ embankment, excess fines and high plasticity index in the Granular Sub-Base (GSB) layers,

low binder content in the bituminous layers, etc. The laboratory tests on GSB layer materials and permeability tests indicate that the

dramatic pavement failures may be attributable to poor sub-surface drainage and also due to the heavy commercial traffic allowed on the

dense bituminous macadam layers.

Benkelman Beam Deflection (BBD) survey was carried out for structural evaluation of the pavement. Dynamic Cone Penetration (DCP)

test data was used in the analysis. Empirical relations from published literature were used to compute the resilient moduli of various

pavement layers. The moduli values were used as input in MICHPAVE (Michigan Flexible Pavement Design System) computer program to

compute the stresses and strains in the pavement layers. The tensile strain values in the bituminous layers and vertical compressive strain

values on top of the subgrade were calculated. The computed strain values were used to predict the performance of the pavement section in

terms of cracking and rutting. These predicted pavement distresses were then compared with the field performance data to validate the test

results. The analysis shows that the theoretically computed stresses and strains can be advantageously used to predict the field performance.

Remedial measures to repair the pavement section and to improve the sub-surface drainage are presented.

1 INTRODUCTION

Indian road network at over 3.3 million km falls under

one of the world's longest road networks. Most of the

highways and airfield pavements built in our country in

the past 30 years or so, have very slow draining systems,

largely because standard design practices emphasizes on

density and stability but place little importance on sub-

surface drainage. The poor sub-surface drainage on these

roads leads to large amount of costly repairs or

replacements long before reaching their design life. Not

much importance has been given to this aspect in India.The current practices of pavement construction in India

consider the Granular Sub-Base (GSB) as a drainage

layer. However, the gradation and properties of layermaterials seldom permit the layer to be an effective

drainage layer, leading to entrapment of water within the

pavement causing a "bathtub" condition, resulting in

premature failures and chronic pavement distresses.

The present study is an investigation of the pre-mature

failure of a National Highway pavement section

constructed as part of the National Highway Development

Programme (NHDP). The construction of pavement

layers upto the second layer of Dense Bituminous

Macadam (DBM) was completed on this road stretchduring the last week of December 2003 and the road

was opened to traffic movement by January 2004. The

* Professor of Civil Engineering,

** Former M.Tech Student.Indian Institute of Technology Madras, Chennai - 600 036.}


2/14


154 VEERARAGAVAN& GROVERON

annual average rainfall in the region varied between 384

and 949 mm per year during the ten years period 1996-

2005. The traffic was allowed on the Dense Bituminous

Macadam layer before the Bituminous Concrete (BC)

surface course was laid. Premature failures wereobserved on this stretch within one year after opening to

traffic with pavement showing signs of distress in the

form of deformation, cracks, potholes, ravelling and

rutting. The forensic investigation was carried out to

study the effect of sub-surface drainage on the pre-mature

failures and suggest possible remedial measures to prevent

subsequent failures.

OBJECTIVES

The purposes of this investigation are as follows:

(i) To identify the causes of the premature problems

of the national highway pavement section.

(ii) Compare the computed pavement performance

based on laboratory studies with the field

performance values and validation of results.

(iii) To make suggestions for rectification of the

failure and for the improvement of the pavement

section.

1.1 Failure Investigation

To reduce the probability of recurring premature pavement

failures, the causes of problems need to be identified and

the lessons learnt incorporated into future project designs.

Investigations of pavement failures are hence critical, as

the information gained can be used to identify the

underlying cause of the problem and develop an optimal

rehabilitation strategy. In conducting investigation, a

thorough review and analysis of existing construction

records and tests was required. Field tests, such as, BBD,

Dynamic Cone Penetration (DCP), coring, and laboratory

testing were also conducted, to validate/confirm the initial

hypothesis.

1.1.1 Pavement Composition

A typical pavement cross section of the failed pavement

section is as shown in Fig. 1. The composition of the

pavement is as follows:

a) Subgrade-500 mm (Min CBR value 10 %)

b) GSB-300 mm in two layers (0-10% passing 75

micron sieve; LL < 25 %; PI < 6 %)

c) Wet Mix Macadam- 250 mm in two layers

d) Bituminous Macadam-75 mm

e) Dense Bituminous Macadam-110 mm in two layers

f) Bituminous Concrete-50 mm

1.1.2 Observations of the Failures

Extensive deformation and cracking of the pavement

surface was observed near pavement edge along median

portion. Potholes and ravelling, interconnected cracks and

rutting were observed along wheel path. It was observed

that water had entered the pavement layers through the

wide cracks and resulted in further rapid deterioration of

the dense bituminous macadam surface. Fig. 2 to 7 show

different types of pre-mature failures observed on the

pavement section.

Fig. 1. Typical Pavement Cross- Section of National Highway Failed

Section


3/14




Fig. 3(a). Ravelling at Few Locations

Fig. 2(b). Longitudinal Cracks Along Median

Fig. 2(a). Wide Cracks Towards Median

Fig. 3(b). Ravelling on DBM Layer

Fig. 4(a). Hair Line Cracks on DBM Layer

Fig. 4(b). Extensive Cracks and Ravelling


4/14



Fig. 5(a). Fill Soil in the Median Slopes Towards the Depressed

Carriageway

Fig. 5(b). Fill Soil in the Median Slopes Towards the Depressed

Carriageway

Fig. 6(a). Segregation in DBM Mixes

Fig. 6(b). Cracks in DBM Layers

Fig. 7(a). Test Pit Showing Pavement Component Layers

Fig. 7(b). Rutting on DBM Layer


5/14




The ravelling in the bituminous layer may be due to the

weathered rock aggregates that were used in the

construction. It may also be due to the reason that the

binder content was low or due to the fast traffic over the

newly laid DBM layer. This needs further detailedinvestigation.

1.1.3Embankment and Subgrade Soil Test Results

Field investigation and laboratory tests are carried out on

the gradation and other properties of the materials used

in the embankment and subgrade soil used in the

construction. The results are given in Table 1 and

Table 2.

Table 1 Test Results of Fill/Embankment

(Average of Three Samples)

Properties Pavement Edge

Field m/c % 9.2

LL 41

PI 10

Dry Density kg/m3 1700

% Compaction 87.6

Gradation

Size mm % finer

> 4.75 17.34

> 0.075 < 4.75 41.54

< 0.075 41.12

Table 2 Test Results of Subgrade (Average of three samples)

Properties Pavement Pavement Edge

Failed Location Sound Location

Field M/c % 9.2 5.5

LL 35 33

CBR, % 9.0 11

PI 10 7

Dry density kg/m3 1590 1900

% Compaction 81.96 97.9

Gradation

Size mm % Finer % Finer % Finer

> 10 36.5 53.1

> 4.75 16.0 14.7 17.3

> 0.075 < 4.75 22.9 20.3 25.3

< 0.075 24.7 11.9 57.3

It is found that the dry density values and the degree of

compaction achieved on the embankment just below the

subgrade layer were much lower than the desirable limits.

The density of the fill soil at the failed location was as

low as 1.7 g/cc and the degree of compaction achieved

was only about 88 per cent near the edge of the pavement,

whereas, this should be more than 95 per cent (MORTH

Specifications, 2001). The density of compaction of the

subgrade soil at the failed locations was around

82 per cent which was much lower than the desirable

value of 97 per cent (MORTH Specifications, 2001).

However, at sound locations, the degree of compaction

of the subgrade was over 97 per cent. This indicates the

erratic compaction controls exercised in the fill and

subgrade layers during the construction.


6/14



1.1.4 Granular Subbase Layer Test Results

The results of the tests carried out on Granular sub-base

layer material as part of failure investigation of the

pavement is as given in Table 3.

It is observed that the material used in GSB layercontained excessive fines. The percentage of material

passing through 75 micron sieve varied from 14 per cent

Table 3 Tests Results of GSB layers (Average of three locations)

Properties Pavement Pavement Edge

Failed Location Sound Location

Field M/c % 8.5 6.2 15.3

LL 31 35 40

PI 10 10 8Gradation of GSB

Sieve Size mm Specified % Finer at % Finer at sound % Finer at pavement

Limits failed locations locations edge and shoulder

> 10 100 100 100 100

> 4.75 55-75 97.3 64.06 100

> 0.075 < 4.75 10-30 56.4 36.04 92.61

< 0.075 0-10 25.3 14.24 75.10

Table 4 Variation of Permeability with Percentageof Fines

Type of fines Permeability, m/day

Percent passing 75 micron sieve

0 5 10 15

Silica or 3 0.021 0.024 0.009

limestone

Silt 3 0.024 0.0003 0.000 06

Clay 3 0.003 0.000 15 0.000 027

Re f: AASHTO Guide for Design of Pavement

Structures, 1986

NOTE- The coefficient of permeability for impervious soils such

as stiff clay, semi-pervious soil such as silty clay

and pervious soil such as sand and gravel are

1 x 10-5 m/ sec respectively as per IRC:SP:42-1994

to as high as 25 per cent. The GSB layer has to serve as

a drainage layer. The permeability and drainage

characteristics of the GSB layer depends on the

percentage passing through 75 micron sieve. The

permeability characteristics of dense graded aggregatesdrastically reduces with the increase in the percentage

of fines as can be seen in the table given in Table 4.

The permeability test results are shown in Table 5:

Table 5 Permeability Test Results

Test Test Results

WMM GSB

material Material

Modified Proctor Compaction

Test Results:

Optimum Moisture Content, % 5.9% 6.25%

Maximum Dry Density, kg/m3 2400 2360

Permeability by falling weight 2.47 2.35

method, m/day

It can be inferred that the gradation of the material to be

used in the granular subbase layer as per Ministry's

specification Table 400-1 (per cent passing 75 micron


7/14




sieve upto 10 per cent) has a permeability of 0.03 x 10-3

cm/sec whereas the minimum permeability requirements

of a drainage layer is 0.023 cm/sec. (20 m/day)

(AASHTO, 1986)

The very high percentages of fines in the GSB layers

have prevented efficient drainage. The high value of

plasticity index added to the problem. Soils with higher

plasticity have higher clay content. Higher the percentage

of clay content, lower will be the permeability. If the

percent passing 75 micron sieve is restricted to 3 to 5 per

cent, the permeability increases to 7.6 x 10-3 cm/sec (250

times permeability when compared to MoRTH

Specifications of Table 400-1). When the percent of fines

lesser than 2.0 mm sieve are zero, the permeability

increases to 12 x 10-3 cm/sec (400 times permeability

when compared to MoRTH specifications of

Table 400-1)

During the investigation the percent of fines in the drainage

layer was found to vary from 14 per cent to as high as 75

per cent towards the pavement edge and shoulders,

indicating poor drainage characteristics of the granular

sub-base layer, particularly towards the shoulders This

has prevented effective drainage of water to the drains.

This has also resulted in the rising of water level entering

the pavement layers to rise through the WBM and BM

layers. The field moisture content of the layer used at

the pavement edge is as high as 15.3 per cent. It is seen

that the gradation of material used at sound location is

better than at failed location.

1.1.5Bituminous Macadam Layer Test Results

The samples of the Bituminous Macadam mix taken from

test pits at failed and sound locations during the field

investigations were tested. The results of bitumen content

and aggregate gradation and mix properties of BM layer

are as given in Table 6.

Table 6 Test Results of Bituminous Macadam

Layer (Average of three samples)

Properties of Test pits from Standard

BM layer Failed Sound values as per

Location Location MoRTH

Specifications

Bitumen

Content % 2.83 4.14 3.3-3.5

AIV % 17.67 Max 30%

Bulk Density,

kg/m3 2380 2440

VMA, % 13 11

Gradation

Sieve Size mm % Finer % Finer26.5 97.47 100 100

19 89.47 79.43 90-100

13.2 74.27 73.86 26-88

4.75 41.33 48.29 16-36

2.36 35.07 38.71 4-19

0.3 16.4 17.14 2-10

0.075 7.47 6.31 0-8

However, some core samples could not be taken as the

BM specimen samples crumbled while extraction, due to

stripping and consequent loss in strength of BM layers,

as can be seen in Fig. 8. Substantial stripping of the

Fig. 8. Core Samples of BM


8/14



bitumen was observed in the BM layer. The percentage

of bitumen in the BM layer is higher than the specified

limits of 3.3 and 3.5 per cent. Higher bitumen was used

as the mix was harsh with more percentage of fine

material passing 2.36 mm sieve viz., about 35 to 38 percent when compared to the desirable percentage in the

range of 4-19 per cent. This indicates inconsistent values

of bitumen content and poor gradation in the BM layer

and poor implementation of quality control during

construction.

1.1.6Dense Bi tuminous Macadam Layer Test

Results

The average bitumen content extracted from the core

samples of DBM first layer was 3.62 per cent, whereas

the bitumen content required as per the mix design was4.5 per cent. The binder content in the second layer of

DBM was 3.08 per cent at the failed location.

Table 7 shows the gradation of the dense bituminous

macadam layer at the failed location as well as sound

location.

Table 7 Test Results of Dense Bituminous Macadam Layer

Properties Pavement Standard Values as per

Failed Location Sound Location MoRTH

Bitumen Content % 3.62 Min 4.5%

Bulk Density, kg/m3 2390 2470

Effective bitumen content, % 4.18 4.5

Bulk sp. Gravity of aggregates 2.695 2.745

Air voids, % 3.98 4.5

Gradation

Sieve Size mm Limits % Finer % Finer

45 100 100 100 100

37.5 100 100 100 100

26.5 90-100 100 100 90-100

19 71-95 100 94.67 71-95

13.2 56-80 86.27 74.4 56-80

9.5 - 71.07 61.6 -

4.75 38-54 56.53 44 38-54

2.36 28-42 50.4 34.8 28-42

1.18 - 37.6 25.47 -

0.6 - 31.33 19.47 -

0.3 7-21 26.13 14.4 7-210.15 - 20.93 9.47 -

0.075 2-8 18.8 4.53 2-8

Lower values of bitumen content and higher proportion

of fines in the aggregate mix of DBM layer was noticed

at the failure locations. This also indicates inconsistent

quality control measures in the DBM layer during

construction.


9/14




Table 8 Classified Daily Traffic Volume

Day Cars, Buses Trucks, LCV, Two Animal Drawn Cycles Tractor

jeeps, vans Multi-axle wheelers vehicles

1 1369 646 2785 1190 38 758 523

2 1610 605 3034 1447 51 1025 556

3 1439 618 3131 1359 106 1150 569

4 1398 618 3182 1316 100 1175 484

5 1401 582 3082 1312 95 1216 580

6 1354 638 3165 1233 101 1391 560

7 1438 607 3058 1484 165 1321 534

Total 10009 4314 21437 9341 656 8036 3806

AADT 1430 616 3062 1334 94 1148 544

Table 9 Test Results of Benkelman Beam Deflection Study

Sl No. Chainage MSA Characteristic Benkelman beam Required equivalent of BM

Rebound Deflection, mm overlay, mm

Outer lane Inner lane Outer lane Inner lane

LWP RWP LWP RWP LWP RWP LWP RWP

1 370.4-371.3 52 0.993 2.109 0.853 0.915 100 205 80 90

2 371.42 - 372.3 52 1.520 0.949 1.212 0.742 160 90 130 60

3 372.4 - 373.3 52 1.185 1.090 0.921 0.762 125 110 90 60

4 373.4 - 374.4 52 0.990 1.121 1.080 0.714 100 110 110 80

2 TRAFFIC DETAILS

The details of the daily traffic along the section are given

in Table 8.

2.1 Benkelman Beam Deflection Studies

Benkelman beam deflection studies were carried out as

per IRC:81-1997. The results of the Benkelman beam

deflection studies are given in Table 9.

The thickness of overlay required varies from 50 to 140

mm. Therefore, an additional overlay thickness

requirement of 75 to 80 mm dense bituminous macadam/

bituminous concrete overlay is indicated over the existing

DBM layer depending on the location. But, if the overlay

or next layer is directly laid over failed stretches, even

this overlay will fail pre-maturely.

2.2 Observations during Test Pit Studies

a) The subgrade CBR of the soil was found to be

more than 10 per cent and varied in the range

12.4 per cent to 21 per cent.

b) The CBR value of the GSB layer was found to be

in the range 36 to 44.5 per cent.


10/14



c) Substantial stripping of the bituminous macadam

layer was observed.

d) No clear indication of the crack width with varying

depth was observed in the dense bituminous

macadam layer.

e) The field moisture content in the wet mix macadam

layer was found to be high. The percentage of fines

(finer than 75 micron) was high even in the wet

mix macadam layer and this has resulted in poor

drainage.

f) The granular sub-base layer consisted of only

moorum soil. The soil used in the GSB layer had

high percent of fines passing 75 micron sieve and

also high plasticity index. This is the primary cause

for poor drainage.

g) The field moisture content of the GSB layer was

above 10 per cent, which was due to poor drainage

characteristics of the GSB layer.

h) The soil used in the sub-base layer and the subgrade

layer appeared to have similar properties.

i) The field moisture content of the subgrade is above

the optimum moisture content.

2.3 Summary of the Observations on Various

Tests Results

a) The field density value in the fill/embankment

portion of the road stretch was 1.7 g/cc, which is

low. This corresponds to 88 per cent of the

maximum dry density, resulting in settlement of till

during heavy rains and consequent damages to

pavement layers

b) The field density values on the subgrade layer at

the locations where cracks were observed was

found to be 1.59 g/cc. This corresponds to 82 per

cent of maximum dry density. This also results in

settlement of subgrade and failure of pavement

layers. However, the field density values were

higher at locations which are not cracked/failed.

c) The granular sub-base layer has excessive fines,

ranging from 14 to 25 per cent. The proportion of

fines in the GSB layer at shoulder portion was much

higher. The plasticity index value was also found

to be high, ranging from 8 to 10 per cent. This has

resulted in poor drainage characteristics of the GSB

layer.

d) The binder content in the bituminous macadam layerwas found to be inconsistent. Due to ingress of

water, stripping of the aggregates was found in the

layer materials. The core samples could not be taken

out and the samples crumbled.

e) The binder content in the dense bituminous

macadam layer was found to be 3 to 3.62 per cent

which was lower than the specified values.

Segregation of aggregates during construction was

observed.

f) The median along the embankment portion was

found to be sloping filled with uncompacted soil.

Due to lack of lateral confinement, wide cracks

were observed all along the central median.

g) The results of the Benkelman beam deflection

studies indicate the structural inadequacy and the

need for a strengthening layer, after removal and

reconstruction of failed portions in large patches.

2.4 Primary Causes of Premature Pavement

Failure

a) Grossly inadequate compaction of soil in the filland subgrade at the failed locations, resulting in

settlement and yielding of pavement layers on failed

locations

b) High proportion of fines and PI value in GSB layer,

particularly very high proportion of fines and PI

values in the portion of GSB layer towards the

pavement edge and shoulders. This has resulted in

GSB layer to be totally ineffective as a drainage

layer, particularly at locations where premature

failure of the DBM layer occurred. There was no

possibility for the water to drain out of the pavement

layers.

c) Porous/open textured locations on the top of the

DBM layer at several locations due to segregation

of mix that has occurred during various stages of

construction. This has resulted entry of rain water

from the surface also.


11/14




d) The water which entered into the pavement layers

during rains from (a) loose soil fill in the median (b)

shoulders and (c) pervious surface at some

locations of the DBM layer, could not drain out

through the impervious GSB layer and thus theentrapped water level increased within the

pavement, saturating the WMM and BM layers.

Consequently, the BM layer and part of DBM

layers got deteriorated and failed as a result of

stripping and weakening of the bituminous mix.

2.5 Other Contributing Factors for Pavement

Failure

a) Inconsistent quantity of binder in the bituminous

macadam layer and poor gradation of materials

b) Low quantity of binder in the dense bituminous

macadam layer and gradation of aggregates not

fulfilling the specifications

c) Inadequate compaction and poor quality of materials

used in the median

d) Permitting heavy commercial vehicles to use the

partly completed carriageway over the DBM layer.

The DBM layer is a binder course and traffic should

not have been allowed on this layer before theconstruction of the wearing course.

3 COMPUTED PAVEMENT PERFORMANCE

BASED ON DCP FIELD DATA

The effect of inadequate sub-surface drainage on

pavement performance has been quantified by using the

Dynamic Cone Penetrometer data of failure section to

calculate the resilient modulus of the different layers and

then using these material layer properties as input in

MICHPAVE program the maximum tensile strain in

asphalt layer and compressive vertical strain at top of

subgrade are calculated and these values are compared

with the laid down limits, hence predicting the performance

of pavement in terms of cracking and rutting. These

predicted pavement distresses are then compared with

the field performance values for validation of results

3.1 Calculation of Resilient Modulus from DCP

data

On the failed pavement stretch a total of 28 test pits were

dug at known chainages where DCP test has been

carried. This DCP data is analysed and resilient modulus(MR) is calculated using PR-MR Relationship (Chen et

al., 2005): MR = 537.8 X PR0.664where, PR (Penetration

Rate) is in mm/blow and MR is in MPa. The value of

CBR is calculated by TRL relationship (1993):

CBR = 302 X PR1.057 .The results of calculated resilient

modulus of various layers of pavement are as shown in

Fig. 9. It is to be mentioned that the above empirical

relation is valid only for the range of values that were

considered in the model development and are not the

actual values of resilient moduli values. Repeated load

triaxial tests are to be conducted to get the resilient modulivalues in the laboratory. However, the laboratory moduli

values are dependent on the specimen size, aggregate

size, confining pressure, load, frequency, rest period, etc.

The traffic was allowed to ply for a period of four months

before the failure was observed.

3.2 Calculation of Stresses and Strains in

Pavement Layers Using MICHPAVE

The calculated resilient moduli from the DCP data areused as an input in MICHPAVE (Michigan State

University 2000) (Michigan Flexible Pavement Design

System) computer program, which uses nonlinear finite

element program for analysis of flexible pavements. After

giving the various inputs data the program is run for all

the 28 test locations and stresses and strains in various

pavement component layers were determined.

Fig. 9. Resilient Modulus Variations at Different Pit Locations


12/14



Cracking occurs when the tensile (radial) strain in the

asphalt layer exceeds the allowable limit of 538 micro-

strains under 106 load applications (Shell, 1978). A graph

showing the calculated radial tensile strains along with

the laid down permissible limit, and cracking observed at

various pit locations is shown in Fig. 10

Rutting occurs when the compressive (vertical) strain at

the top of subgrade exceeds the permissible limit of 885

micro-strains under 106 load applications (Shell, 1978).

A graph showing the calculated vertical compressive

strains along with the laid down permissible limit, and

rutting observed at various pit locations is shown in

Fig. 11

locations and it is seen in the field that cracking has

occurred in field at these locations of the failed stretch

(Fig. 10) in the intensity that is proportional to the

calculated tensile strains using MICHPAVE. When the

observed cracking in field is plotted against calculated

radial tensile strain, we get an R2of 0.83 as shown in

Fig. 12.

The values of compressive strains at top of subgrade

exceed the permissible compressive strain limit at 16 of

the 28 pit locations and it is seen in the field that rutting

has occurred in field at these locations of the failed stretch

(Fig. 13.) in the intensity that is proportional to the

calculated compressive strains using MICHPAVE.

3.3 Validation of MICHPAVE Results

The material properties considered in the analysis are as

follows:

a) Bituminous layer - 1377 MPa

b) Wet Mix Macadam -864 MPa

c) Granular sub-base- 195 MPa

d) Subgrade soil - 93 MPa

The values of calculated tensile strains in asphalt layer

exceed the permissible tensile strain limit at all the 28 pit

Hence, from the plot of observed field cracking vs

calculated radial tensile strain as shown in Fig. 12., and

observed field rutting vs calculated vertical compressive

strain in Fig. 13, it is inferred that the results of

MICHPAVE are validated.

4 RECOMMENDATIONS FOR IMPROVE-

MENT OF PAVEMENT PERFORMANCE

It is recommended that the following measures be taken

to improve the sub-surface drainage of the pavement

section at the edge in order to improve the performance

of the pavement:

Fig. 10. Radial Tensile Strain Calculated and Cracking Observed at

Different Pit Locations on Failed StretchFig. 12. Cracking Observed vs Radial Tensile Strain

Fig. 13. Rutting Observed vs Vertical Compressive StrainFig. 11. Vertical Compressive Strain Calculated and Rutting

Observed at Different Pit Locations on Failed Stretch


13/14




a) Construction of longitudinal aggregate drains by

digging trenches at the pavement edge on the

shoulder portion with a minimum width of 500 mm

at the bottom as shown in Fig. 14. The aggregate

drain should fulfill the requirements of drainage asgiven in Table 10 (Type A grading of Table 300-4

of MORTH Specifications for Road and Bridge

Works).

b) Transverse aggregate drains (shoulder drains)

of width 500 mm and depth 500 mm connecting

the longitudinal aggregate drains as shown in

Fig.14, to be provided at 10 m intervals on the

straight portion and at 5 m intervals at the curve

portion.

Table 10 Grading Requirements for Aggregate

Drains (MORTH Specifications, 2001)

Sieve Size, mm Percent Passing by Weight

63 -37.5 100

19 -

9.5 45-100

3.35 25-80

600 micron 8-45

150 micron 5-10

75 micron < 5

c) In the straight portion, where, both the carriageways

are at the same level, longitudinal aggregate drainsof width 500 mm and required depth upto the top

of the subgrade level to be installed by excavating

trenches in the median (Fig. 15, along the kerb and

filled with the aggregates as per the above table

specifications upto the top of the median fill to

prevent water from the fill to enter into the

Fig. 14. Construction of Longitudinal and Transverse Aggregate

Drains at Pavement Edge

Fig. 15. Construction of Longitudinal Aggregate Drain in the

Median


14/14



pavement layers. Alternatively, a cut-off may be

constructed along the kerb upto the GSB layer

which could also serve as a retaining wall of the

median fill. Retaining walls with provision for drains

are to be constructed to prevent shear failure. The

drains should have weep holes at the bottom levelof the sub-base layer to facilitate internal drainage.

d) The cracked areas of the DBM surface (having

wide, medium and fine cracks) should be marked

into large rectangular areas. The cracked DBM

layer/or both layers of DBM should be milled and

removed and patched up and compacted well using

DBM mix, before the overlay is constructed.

e) The entire road stretch may be divided into two

sets of sub-stretches (A) the stretch, where, the

failures and cracking has been extensive and (B)

stretches where only longitudinal cracks and some

fine cracks have developed in less than 10 per cent

of paved area. The damaged portion is to be marked

and cut to the depth to which the cracks have

propagated, loose material to be removed and

cleaned using compressed air and later, tack coat

to be applied both to the sides and bottom of the

cut portion and patched with pre-mixed material

with DBM gradation and compacted to the required

density and profile using suitable rollers. After

patching, it is suggested that:

1. Sub-stretches of category A may be overlaid

with (i) 50 mm thick DBM layer and (ii) 50

mm thick BC layer using 2 per cent by weight

of lime as a filler and SBS polymer modified

bituminous binder using good quality SBS

polymer modified binder from the refinery.

2. Sub-stretches of category 'B' may be overlaid

with 50 mm thick BC layer as above.

5 CONCLUSIONS

a) The forensic investigations of the pre-mature failureof the highway pavement helped the researchers

to identify the root cause of the problem, which

was poor sub-surface drainage. There is a need to

revise the specifications for the granular sub-base

layers. The specification should consider the

permeability of the layer as an essential

requirement.

b) The comparison of the computed stressed and

strains in the pavement layers based on the field

data with the observed performance validated the

findings of the investigation.

c) There is a need to study the effect of construction

quality on the performance of all the highway

pavements constructed so far and incorporate the

lessons learnt in the revised guidelines/

specifications for pavement construction.

d) The suggested remedial measures are likely to

retard the rate of deterioration due to good sub-

surface drainage.

e) The lessons learned from this study may be

incorporated in future road project designs.

REFERENCES

1 AASHTO (1986). "Pavement Design Guide."

American Association of State Highway and

Transportation Officials.

2 Chen D.H., Lin D.F., Liau P.H., and Bilyen J.

(2005). "A Correlation Between Dynamic Cone

Penetrometer Values and Pavement Layer Moduli."

Geotech. Test. Journal, 28(1), pp 42-49.

3 IRC:81-1997, Guidelines for Strengthening of

Flexible Road Pavements Using Benkelman Beam

Deflection Technique, First Revision, Indian RoadsCongress, New Delhi.

4 Michigan State University (2000), MICHPAVE

User Manual, Department of Civil and

Environmental Engineering, Michigan State

University, East Lansing, USA.

5 MORTH Specifications for Road and Bridge Works

(2001). Ministry of Road Transport and Highways,

Government of India, New Delhi.

6 Shell (1978). "Shell Pavement Design Manual -

Asphalt Pavements and Overlays for Road

Traffic." Shell International Petroleum Company

Limited, London, UK.

7 Transport Research Laboratory (TRL) (1993).

"Overseas Road Note 31: A Guide to the Structural

Design of Bitumen-Surfaced Roads in Tropical and

Subtropical Countries." Transport Research

Laboratory, Crowthorne, U.K.

166 VEERARAGAVAN& GROVERONFORENSICINVESTIGATIONSOFPAVEMENTPRE-MATURE

FAILUREOFANATIONAL HIGHWAYPAVEMENTDUETOPOORSUB-SURFACEDRAINAGE

forensic investigations of pavement pre-mature failure of a national highway pavement due to poor...

Documents