EVALUATION AND STRENGTHENING OF RECONSTRUCTED ROADS EXCAVATED FOR UTILITIES USING BENKELMAN BEAM DEFLECTION (BBD) TECHNIQUE (A CASE STUDY)

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 Bashir2
, Dr.Mohammad Shafi Mir3
, Tanzeel Rashid4
1
Research Scholar, National Institute of Technology, Srinagar
2
Junior Engineer Public Works Department-J&K,(M-Tech-Structural Engineering)
3
Professor, 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)
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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.

31
• 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.

32

33

34
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

35
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

36
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.

38
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).
11. Setra; Technical Road Guide.
12. Kuldip Singh, R K Pandey, C S Mishra, Dr Y K Bind and A K Rai, “Analysis on Utilization
of Cement Kiln Dust Stabilized Red Mud for Road Construction” International Journal of
Civil Engineering & Technology (IJCIET), Volume 5, Issue 8, 2014, pp. 56 - 61, ISSN Print:
0976 – 6308, ISSN Online: 0976 – 6316.
13. Bhasker Vijaykumar Bhatt and Kamlesh Chinabhai Chandpa, “Road Crashes and Losses in
Surat City and Umra” International Journal of Civil Engineering & Technology (IJCIET),
Volume 5, Issue 5, 2014, pp. 105 - 113, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.
14. Rumman Mowla Chowdhury, Sardar Yafee Muntasir, Md. Niamul Naser, Sardar Rafee
Musabbir, “Water Quality Analysis of Surface Water Bodies Along The Dhaka-Mawa-
Bhanga Road Based on Pre-Monsoon water Quality Parameters For Aquaculture”
International Journal of Civil Engineering & Technology (IJCIET), Volume 3, Issue 2, 2012,
pp. 154 - 168, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.

EVALUATION AND STRENGTHENING OF RECONSTRUCTED ROADS EXCAVATED FOR UTILITIES USING BENKELMAN BEAM DEFLECTION (BBD) TECHNIQUE (A CASE STUDY)

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