evaluation and strengthening of reconstructed roads excavated for utilities using benkelman beam...

International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),

ISSN 0976 – 6316(Online), Volume 6, Issue 1, January (2015), pp. 27-38 © IAEME

27

EVALUATION AND STRENGTHENING OF

RECONSTRUCTED ROADS EXCAVATED FOR

UTILITIES USING BENKELMAN BEAM DEFLECTION

(BBD) TECHNIQUE (A CASE STUDY)

Umersalam1, Alsana Bashir

2, Dr.Mohammad Shafi Mir

3, Tanzeel Rashid

4

1Research Scholar, National Institute of Technology, Srinagar

2Junior Engineer Public Works Department-J&K,(M-Tech-Structural Engineering)

3Professor, National Institute of Technology, Srinagar

4 Junior Engineer Public Works Department-J&K

ABSTRACT

The study highlights the need of pavement evaluation and pavement evaluation measures

for the road pavements of urban areas in Kashmir which are often being cut and refilled after laying

of utilities like optical fiber cables,municipal water supply pipes, construction of severs etc. This

paper includes the collection of required field data like soil subgrade data, existing pavement

structure, traffic data, pavement surface condition and rebound deflection by using BBD technique,

laboratory investigations and finally the design of the overall thickness of the road pavement and

overlay whatsoever required to strengthen the road stretches. This paper also includes the

comparison between newly proposed thicknesses and existing ones. Conclusions are drawn from the

overall study conducted on the two road stretches followed by some useful recommendations. On the

basis of our study and results that we obtained we found both the road stretches falling short in both

design and performance fronts discussed in detail later in this paper.

Keywords: Strengthening of roads, BBD technique, Overlay design, Design of roads, Rebound

deflection of road pavements, CBR method.

INTRODUCTION

Strengthening of pavement is defined as the process of providing the required overlays on the

existing pavements so that it performs more effectively over a given design period of time under

given dynamic and static loads, once the pavement is evaluated for these loads prior to design.

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ISSN 0976 – 6308 (Print)

ISSN 0976 – 6316(Online)

Volume 6, Issue 1, January (2015), pp. 27-38

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As is rightly believed that “the prosperity of a nation is depicted by the roads it has”, thus

roads become a prime concern for every nation big or small. Pavements once constructed need to be

maintained well. And strengthening is the most adopted method as a pavement maintenance

measure. One of the easiest and convenient ways of designing an overlay for strengthening is by

using Benkelman Beam Deflection (BBD) Technique which measures the rebound deflection of the

pavements. Even though there are many methods for designing of overlays such as, Lacroix Deflect-

graph, Dynaflect, Falling weight Deflectometre (FWD) and Benkelman Beam Deflection Technique

among all these BBD technique is the easy and convenient method as mentioned earlier as well.

Road stretches used for this study were selected from the eastern side of Srinagar city, Stretch

1 is From Dargah (Hazratbal-Srinagar) to Lal-chowk (Srinagar) road about 7.5kms long and

Segment 2 is from Dergah (Hazratbal-Srinagar) to Lal-bazar (Srinagar) road about 6kms long)

designated here as SITE-01 and Site-02 respectively. Both these roads were excavated partially

(about 1km from each) for laying of optical fiber cables and construction of new sewers and both

these segments were reconstructed so these stretches were the perfect examples to study the effects

and present a pilot study in Srinagar-Kashmir.

BACKGROUND OF BBD TECHNIQUE

Alvin CarltonBenkelman (1895-1987) devised the simple deflection beam in 1953 for

measurements of pavement surface deflection on the AASHO test road. It is widely used all over the

world for evaluation of the requirements of strengthening of flexible pavements. Deflection beam

has been in use in India for more than two decades by different organizations. IRC (Indian Roads

Congress) has laid down a uniform procedure for the design of flexible pavement overlays using the

Benkelman Beam Deflection technique through its publication titled, “TentativeGuidelines of

Flexible Road Pavements Using Benkelman Beam Deflection Technique”, IRC:81-1997.

The BBD technique is popular all over the world for estimating the required overlay

thickness. The popularity is possibly because of its simplicity and low cost. The permissible

maximum allowable Benkelman Beam deflection for satisfactory performance of a road stretch

depends upon the traffic, material of construction, and the environmental factors, Benkelman Beam

Deflection more than the allowable deflection suggests that the pavement may require an overlay.

In India the earlier guidelines in strengthening by overlay using BBD method have been revised, and

the present guidelines IRC:81-1997 have evolved from a broader perspective of experience gained

through research and practice in India and other countries.

NEED OF STUDY

Whenever certain roads (sections or stretches) are excavated for utilities like laying of water

supply pipe lines, electrical cables, sewage pipelines, telephone, internet cables and optical fiber

cables etc, then after completion of the installation works over these road sections or stretches these

are usually refilled without following proper guidelines for their reconstruction. The basic and the

most important thing in road construction works that is not paid attention is the proper compaction of

the refilled subgrade material. As per Indian Roads Congress (IRC) it is recommended that the top

50 cm of subgrade should be compacted at least upto 95% to 100% of the proctor density, which

usually lacks in reconstruction works. So the result is that the road section thus constructed fails and

is not as strong as that of the unexcavated segment. This road section then gradually deteriorates and

develops distresses like rutting, cracking, raveling, pothole formation etc.

The need of our study is to evaluate the strength and resilience to distresses that get

developed with time and increase in traffic volume and propose remedial measures to check their

degradation by designing the required overlay thickness using IRC 81-1997 recommended

International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976

ISSN 0976 – 6316(Online), Volume 6, Issue 1, January (2015), pp.

Benkelman Beam Deflection (BBD) technique, so as to make them handle the design traffic loads

efficiently and economically.

Overall Methodology followed.

The methodology of the project work is classified into two major steps. The first one is the

survey/traffic data collection and the other one is the data analysis and design. The overall

methodology involves:

I. The survey for the classification of pavement as good, fair, or poor depending upon the rut depth

measurements.

II. Evaluation of soil subgrade and existing pavement

III. Traffic survey.

IV. Actual measurement of deflections using Benkelman Beam.

V. The calculation and the application of correction factors for temperature variation and other

seasonal variations.

VI. Design of required overlay thickness.

VII. Evaluation of pavement and conclusion.

As the design of overlay depends upon the traffic volume on the pavement the traffic data

collection is therefore an important step for this method. The cumulative number of standard axles to

be catered for in the design is determined w

initial traffic (in terms of number of commercial vehicles per day); annual growth rate of commercial

vehicles and vehicle damage factor (in terms of number of standard axles per commercial vehicle

Figure-01: Flowchart depicting overall methodology followed in the work.

International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976

6316(Online), Volume 6, Issue 1, January (2015), pp. 27-38 © IAEME

29

n (BBD) technique, so as to make them handle the design traffic loads


ion and the other one is the data analysis and design. The overall

The survey for the classification of pavement as good, fair, or poor depending upon the rut depth

Evaluation of soil subgrade and existing pavement thickness.

Actual measurement of deflections using Benkelman Beam.

The calculation and the application of correction factors for temperature variation and other

Design of required overlay thickness.

nt and conclusion.



be catered for in the design is determined which further requires the data for design life (in years);


vehicles and vehicle damage factor (in terms of number of standard axles per commercial vehicle

Flowchart depicting overall methodology followed in the work.


© IAEME

n (BBD) technique, so as to make them handle the design traffic loads


ion and the other one is the data analysis and design. The overall

The survey for the classification of pavement as good, fair, or poor depending upon the rut depth

The calculation and the application of correction factors for temperature variation and other



hich further requires the data for design life (in years);


vehicles and vehicle damage factor (in terms of number of standard axles per commercial vehicles).

Flowchart depicting overall methodology followed in the work.



30

The various deflections obtained from the Benkelman beam are to be reduced to a

characteristic deflection (in mm). The design of overlay is then obtained from the design curves

relating the characteristic pavement deflection to the cumulative number of standard axles to be

carried over the design life.

The overall methodology is illustrated in Flow Chart (Figure-01)

RESULTS

The results obtained from all the laboratory tests and field surveys conducted and their

necessary analysis can be summed up as under:

1. Pavement Condition Survey (PCS)

(a) SITE 1:from RD 0.00m to 210m the road stretch is classified as “fair” and beyond RD 210.6m

upto RD 1000m it is classified as “poor” thus this site is dealt and classified as a poor pavement from

PCS point of view.

(b) SITE 2:From RD 0.00m to RD 450m there are no visible ruts, cracking or any other road

distresses, this part is good from PCS criteria but beyond RD 450m to RD 1000m there are few

meters of length where condition is poor but overall the pavement can be treated as fair from PCS

point of view.

2. Pavement Structure Survey (PSS)

The total existing pavement thicknesses recorded were 51 mm and 46 mm for Site 1 and Site

2 respectively. On site 1 the layer wise thicknesses were Bitumen 12 mm, Water Bound Macadam

(WBM) 17 mm and Granular Sub Base (GSB) 22mm. And that for Site 2 they were Bitumen 12 mm,

Water Bound Macadam (WBM) 15 mm and Granular Sub Base (GSB) 19 mm.

3. Laboratory Investigation

(a) Field Moisture Content

The field moisture content for the sub-grade soil sample taken from site 1 is 9% and that for

Site 2 its value was 7%.

These field moisture content values are needed for applying the moisture correction to the

deflection values that we get from pavement deflection survey.

(b) Consistency Tests

Consistency tests are performed to classify the sub-grade soils which later help in calculating

the moisture correction factors.

The values of Plasticity Index (PI) and Liquidity Index (LI) for sub-grade soil sample from

site 1 are 4.875% and 37.4% respectively. With the help of Figure 2.9 the sub-grade soil of site 1 is

classified as clayey soil with certain percentage of inorganic silts (silty clay). The values of Plasticity

index and liquidity index for subgrade soil sample from site 2 are 5.9935% and 34% respectively;

this soil again falls in the same soil class i.e. (silty clay).

(c) Compaction Test

This test is performed so as to get the pre-requisites like Optimum Moisture Content (OMC)

and Maximum Dry Density (MDD) for conducting the CBR test.



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• Site 1: The Optimum Moisture Content (OMC) value =19.55% and Maximum Dry Density

(MDD)=1.676g/cm3

• Site 2: The Optimum Moisture Content (OMC)value for this sample =19.65% and Maximum

Dry Density(MDD)=1.668g/cm3

(d) California Bearing Ratio (CBR) Test

This test is performed for getting the strength of the road materials and it is a pre-requisite for

the design of both pavement thickness and overlay thickness in the CBR method of pavement design

as is followed here. The results of these tests conducted on the samples are as:

• CBR value for sub-grade soil sample from Site 1=2% and

• For Site 2 CBR value =3%

3. Traffic Survey

From the 7-day 24 hour traffic study for each sites the average daily traffic for site 1 is 700

vehicles/day (≥3 tons) and that for the site 2 its value is 500 vehicles/day (≥ 3tonns).

For design traffic average daily traffic(ADT) values are used in the formula and the final traffic

results are taken in terms of Million Standard axles (msa). The values of design traffic come out to

be:

• For Site 1 = 25msa.

• For site 2 = 19msa.

These values of traffic obtained are then used in the recommended graphs (IRC : 37 and IRC:

81) to deduce the value of the thickness of overlay and overall pavement required.

4. Pavement Deflection Measurement

On performing the pavement deflection measurements using BBD technique as per the

recommendations of IRC: 81-1997, the characteristic deflection of 0.86 mm and 0.87 mm on Site 1

and Site 2 respectively were recorded. Using these values to design the overlay for strengthening the

two selected sites the thicknesses came out to be 95 mm and 60 mm (Table 3.2) for Site 1 and Site 2

respectively.

On comparing with the unexcavated (Intact) section it was found that only a minimum

thickness (50 mm) is to be provided on both the selected stretches.

Below given figures from Figure-02 to Figure-05 we can see the distresses that are present

and caused in these road segments reconstructed after the cutting and filling.

Figure-06 and figure-07 are the soil samples collected from the site-01 and site-02

respectively. Then laboratory analysis results and plots are shown along with the preparations that

were made for taking the deflections and pavement temperatures from both the sites along with

traffic data and after applying the corrections (if any) the design parameters are computed and road

thicknesses required from the strength point of view.



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33



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Figure-17: Measurement of Pavement

temperature.

Figure-18: Marking of points for taking Deflections Figure-19: BBD beam under dual wheel

For taking deflections

Table-01: Summery of the field deflections for Site-01



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Table-02: Summery of the field deflections for Site-02

Table-03: Characteristic Deflection Data for Site-01

Table-04: Characteristic Deflection Data for Site-02



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Table-05: Design overlay thickness

SUGGESTED OVERLAY CONSTRUCTION

The recommended WBM thickness (as per IRC : 37) are 75 mm, 100 mm, 150 mm, 200 mm,

250 mm.

Following are the suggestions from the IRC: 81-1997:

Table-06: Suggested Overlay

Thickness of

Overly

Required in

terms of B.M

(mm)

DBM/SDBE

(mm)

DBM/SDBC

(in term of

equivalent

BM) (mm)

BM (mm) WBM

Calculated

(mm)

Suggested (mm)

100 40 57 50 - Not Needed

150 40 57 50 43 75

200 40 57 50 93 100

250 40 57 50 143 150

300 40 57 50 193 200

350 40 57 50 243 250

400 40 57 50 293 300

1 cm BM = 0.7 cm DBM/SDBC/BC

The recommended WBM thickness (as per IRC : 37) are 75 mm, 100 mm, 150 mm, 200 mm,

250 mm.

CONCLUSIONS

After evaluating the two selected sites as per the guidelines laid by IRC, we came to following

conclusions:

1. On the basis of PCS, it was found that the periodic maintenance procedures on the two roads

were lacking despite the fact that both roads are of great importance to the nation, which led to

the fast deterioration of the road surface characteristics.

2. On evaluating the total existing pavements thicknesses for Site1 and Site 2 were 510 mm and

460 mm respectively. While comparing them with the new designed overall pavement



37

thicknesses (870 mm for Site 1 and 780 mm for Site 2) it is evident that Site 1 falls short by

360 mm and Site 2 falls short by 320 mm.

3. On performing the pavement deflection survey it was concluded that site 1 and Site 2 require

overlay thicknesses of 95 mm and 60 mm respectively to strengthen them. It was also found

that the unexcavated portion requires nominal minimum overlay thickness (50 mm) for the

Sites.

4. The pavement was not designed properly taking all the considerations and recommendations of

IRC as the results obtained during our work were not matching with the existing ones. After

excavation and installation of the utilities, the infill was not compacted properly due to which

with due course of time the soil compacted under the wheel loads and affected the entire

pavement.

5. Water affects the entire serviceability of a road. Too much water in the base materials weakens

the road. Water allowed remaining on top of gravel or blacktopped road weakens the surface,

and when combined with traffic causes potholes, cracking, and rutting. If improperly

channeled, water causes soil erosion and breakdown of pavement edges. No proper drainage

system was present to remove the water from the road surface during the rains even the water

from the areas around the road comes on the road surface.

6. No proper camber is present to divert the water from the road surface to the surrounding areas.

RECOMMENDATIONS

1. Periodic maintenance procedures should be implemented so as to maintain the design

serviceability and increase the life span of the road.

2. While designing the new pavements or excavated roads proper investigation (Field and

Laboratory) and IRC guidelines should be followed.

3. If existing roads are excavated for utilities before laying of overlay proper compaction should

be done. If the cut section is small where rollers cannot be used vibrators should be used to get

the desired compaction.

4. The infill used must be of desired characteristics which can be fully compacted with ease to

attain the required strength.

5. Proper drainage system is must for every road. This will increase the life span of the road.

6. Proper camber and shoulders should be present

7. There should be coordination between the various agencies responsible for laying of utilities

and the construction of roads.

8. It is also recommended that the characteristic deflections obtained in different sections of

roadway from BBD testing should be appropriately used for strengthening the roadway by

providing suitable thickness as per the code of design, or practice followed.

REFERENCES

1. AASHTO interim guide for design of pavement structures, 1972.

2. Allen H.S ,Bullock D.L, Evaluation of deflection data as criteria for the posting and removal

of spring load limits, Transportation Research Record 1106, National Research Council,1987.

3. Chakerborati, Dass; Principles of Transportation Engineering; Prentice Hall of India Pvt. Ltd,

Connaught Circus, New Delhi (India)

4. Canadian Good Roads Association, the C.G.R.A, Benkelman Beam Procedure, 1959.

5. Dr. Shah. N.C, Strength Evaluation of Flexible Pavement of Runway Using BBD Technique

for Surat Airport Project; Civil Engg. Department NIT Surat.



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6. Gupta B. L, Gupta Amit; Roads, Railways, Bridges, Tunnels & Harbor Dock Engineering;

Standard Publishers Distributors, Delhi (India).

7. IRC: 81-1997; “Guidelines For Strengthening Of Flexible Road Pavements Using Benkelman

Beam Deflection Technique”

8. IRC: SP: 72-2007; “Guidelines For The Design Of Flexible Pavements For Low Volume

Rural Roads.

9. IRC: 37-2001; “Guidelines For The Design Of Flexible Pavements”

10. S. K. Khanna, C. E. G. Justo; Highway Engineering; Nem Chand &Bos, Roorkee (U.A).

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