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

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1 International INTERNATIONAL Journal of Civil Engineering JOURNAL and Technology OF CIVIL (IJCIET), ENGINEERING ISSN AND (Print), TECHNOLOGY (IJCIET) ISSN (Print) ISSN (Online) Volume 6, Issue 1, January (2015), pp IAEME: Journal Impact Factor (2014): (Calculated by GISI) IJCIET IAEME EVALUATION AND STRENGTHENING OF RECONSTRUCTED ROADS EXCAVATED FOR UTILITIES USING BENKELMAN BEAM DEFLECTION (BBD) TECHNIQUE (A CASE STUDY) Umersalam 1, Alsana Bashir 2, Dr.Mohammad Shafi Mir 3, Tanzeel Rashid 4 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. 27

2 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 Deflectgraph, 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 ( ) 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: 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: 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 recommended 28

3 International Journal of Civil Engineering and Technology (IJCIET), ISSN (Print), 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 thickness. 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 which further requires the data for design life (in years); 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 vehicles). Figure-01: Flowchart depicting overall methodology followed in the work. 29

4 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 % 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. 30

5 Site 1: The Optimum Moisture Content (OMC) value =19.55% and Maximum Dry Density (MDD)=1.676g/cm 3 Site 2: The Optimum Moisture Content (OMC)value for this sample =19.65% and Maximum Dry Density(MDD)=1.668g/cm 3 (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: , 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. 31

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8 Figure-17: Measurement of Pavement temperature. Figure-18: Marking of points for taking Deflections For taking deflections Figure-19: BBD beam under dual wheel Table-01: Summery of the field deflections for Site-01 34

9 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 35

10 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: : Thickness of Overly Required in terms of B.M (mm) DBM/SDBE (mm) Table-06: Suggested Overlay DBM/SDBC BM (mm) (in term of equivalent BM) (mm) 36 Calculated (mm) WBM Suggested (mm) Not Needed 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

11 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, 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, 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, Dr. Shah. N.C, Strength Evaluation of Flexible Pavement of Runway Using BBD Technique for Surat Airport Project; Civil Engg. Department NIT Surat. 37

12 6. Gupta B. L, Gupta Amit; Roads, Railways, Bridges, Tunnels & Harbor Dock Engineering; Standard Publishers Distributors, Delhi (India). 7. IRC: ; Guidelines For Strengthening Of Flexible Road Pavements Using Benkelman Beam Deflection Technique 8. IRC: SP: ; Guidelines For The Design Of Flexible Pavements For Low Volume Rural Roads. 9. IRC: ; 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 , ISSN Print: , ISSN Online: 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 , ISSN Print: , ISSN Online: 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 , ISSN Print: , ISSN Online: