Grameen Sampark Final April 0... - pmgsy

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20 A maximum of 50mm rut depth was recommended for the unpaved roads. The reliability adopted is 50%. Asphalt Institute [5] adopted the following subgrade strain criteria Where, Grameen Sampark -2 0.223 = 1.05*10 *[1/N] (5) N = No of 80 kN equivalent single axle loads; Z Z = Vertical subgrade strain ( micro strain) at top of the subgrade layer TRRL [6] considers the following relationship to complete allowable subgrade strains for 85 percent probability of survival to a design life of N repetitions of o 80kN axle and a pavement temperature of 20 C. Log (N) = -7.21-3.95* log ( ) (6) Z The failure condition considered for the above criteria is rutting of 20 mm The Shell [7] design method uses the following subgrade strain for different confidence levels: -2 -0.25 50% confidence = 2.8*10 *N (7) Z -2 -0.25 85% confidence = 2.1*10 *N (8) Z -2 -0.25 95% confidence = 1.8*10 *N (9) Z A terminal value of percent serviceability (PSI) of 2.5 was taken as failure condition. Indian Road Congress (IRC 37:2001) [8] adopted the following performance criteria for high volume roads. N R = -8 4.5337 4.1656*10 [1/ Z ] (10) N R = Number of cumulative standard axels to produce rutting of 20 mm. Z = Vertical subgrade strain (micro strain). Development of an average rut depth of about 20 mm is considered to be failure in rutting mode. IRC:SP:20:2002 [9] is for design of low-volume rural roads in India. The criterion for determining the thickness of a flexible pavement with a thin bituminous surfacing is the vertical compressive strain on top of the subgrade imposed by a standard axle load (80kN). The maximum rutting allowed is 50mm before any rehabilitation work is taken up. The design charts have reportedly been prepared as per Road Note 29 of TRL, IRC: 37 and other related experiences in India. No mechanistic rutting criterion has been proposed correlating the design life with subgrade strain or any other parameter. Mohanty et al [10] studied the performance of 59 village road sections in Orissa and proposed some design charts for construction of new low-volume rural roads. The pavement condition data collected on these sections were correlated with mechanistic response of the pavement to develop a performance criteria based on limiting rutting value.
Where, -11 5.44 N = 3.42 x 10 (1/ ) (11) N = Number of standard axle repetitions to cause 50 mm rutting; V = Vertical sub grade strain Performance criterion is the most important aspect considered in the design of pavements and all rational design methods must have properly developed performance criteria. It is seen that most of the design methods in vogue have design criteria mostly in terms of subgrade strain and aim to control rutting. The main concerns with the design practices followed in India are that either they do not have performance critferia or even if there is mention of performance criteria there is not much evidence of the criteria having been developed on the basis of sufficient data. This emphasizes the need for collection of data on the performance of different types of low-volume roads on a long term basis. The recent initiative taken by NRRDA for collection of performance data on the recently constructed PMGSY will go a long way in filling this major void in the low-volume road design in India. References 1. American Association of State Highway and Transportation Officials, “AASHTO Guide for Design of Pavement Structures 1993, AASHTO, Washington, D.C. 2. Austroads Pavement Research Group 1998, A guide to the design of new pavements for light traffic: a supplement to Astroads pavement design, APRG Report No. 21, ARRB Transport Research, Vermont South, Victoria. 3. Austroads, Pavement design a guide to the structural design of road pavements, AP-17/92, Austroads, Sydney, 1992. 4. Vermont Agency of Transportation, “Low Volume Pavement Design Procedure”, Vermont Agency of Transportation, Montpelier, VT, March 2002 V Pradhan Mantri Gram Sadak Yojana 5. Ibid. Shook J.F., Finn F. N.., Witczak M. W. and Monismith C. L., “Thickness Design of Asphalt Pavements The Asphalt Institute Method, pp. 17- 44. 6. Lister N. W. and Powell W. D., “ Design Practice for Bituminous Pavements in United Kingdom” Proc. 6th International Conference on Structural Design of Asphalt Pavements”, Vol-1, 1987, pp. 220-231. 7. Gerristen A. H. and Koole R. C. “Seven Years' experience with the structural aspects of the Shell Pavement Design Manual”, Proc. 6th International Conference on Structural Design Asphalt Pavements”, Vol-1 1987, pp. 94-106. 8. Indian Road Congress, IRC:37:2001 Guidelines for Design of Flexible Pavements, New Delhi, 2001. 9. Indian Road Congress, IRC:SP:20-2002 Rural Roads Manual, 2002, New Delhi. 10. Mohanty S. K., Reddy K. S. and Pandey B. B.., “Performance and Design of Village Roads”, Highway Research Bulletin No. 55, IRC, 1996, pp. 66-84. Grameen Sampark 21
Page 2 and 3: In this Issue Editorial 3 Potential
Page 4 and 5: 4 Potential Applications of Interlo
Page 6 and 7: 6 Interlocking Concrete Block Pavem
Page 8 and 9: 8 materials used for production of
Page 10 and 11: 10 Construction of Sub grade This i
Page 12 and 13: 12 Typical Pavement Compositions Ty
Page 14 and 15: 14 Guidelines for the use of In
Page 16 and 17: 16 layers due to repeated applicati
Page 18 and 19: 18 Subgrade Failure Criterion The b
Page 22 and 23: 22 Stabilization of Soil Subgrade w
Page 24 and 25: 24 Changes in Cohesion and Direct
Page 26 and 27: 26 Increase in the C.B.R. value is
Page 28 and 29: 28 Laboratory Test (Under Vertical
Page 30 and 31: 30 Apart from the above, both faces
Page 32: News in Brief General Body Meeting

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