Grameen Sampark Final April 0... - pmgsy

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16 layers due to repeated application of traffic wheel loads. Most of the existing analytical design procedures have performance criteria that give limiting strain (identified critical strain parameter) values to ensure that the extent of structural distress during the service life of pavement will not exceed acceptable levels. Any rational pavement design method should have the following main components: a) Identification of critical distress parameters for defining the performance of the pavement. These can be in terms of surface profile parameters such as roughness (Fifth Wheel Bump Integrator, International Roughness Index etc.) mostly reflecting the functional performance of the pavement. The performance parameters can also be in terms of structural distresses such as cracking of bound layers and rutting in different layers or even a combined index such as the Present Serviceability (PSI) used by AASTHO. Grameen Sampark b) Selection of proper performance criteria developed by correlating the observed performance of pavements with carefully chosen performance parameters. While performance has to be defined in terms of the traffic that can be handled by the pavement before excess failures or distresses occur, the parameters selected for explaining the performance (distress or failure) can be a combination of various pavement parameters (thicknesses, material properties etc.) or a combination of critical mechanistic parameters (deflection, stresses and strains). c) A framework or a list of steps specifying as to how the parameters can be selected and/or computed. The rationality of the design procedure can be judged from the way corresponding performance criteria have been developed. The criterion is generally developed considering a failure condition, which may be any structural or functional failure or both. The rural roads in
India mostly consist of granular pavements with thin bituminous surfacing, in which rutting is considered as the only mode of failure. This is attributed to the vertical compressive strain at the top of subgrade layer. Several highway organizations have developed their own failure condition and performance criterion for design of low-volume roads. In this study, the criteria developed by AASTHO, AustRoads, Asphalt Institute TRRL, etc. have been discussed. Performance and Failure Criteria for Pavement Design In mechanistic design methods, the limiting values of stresses and/or strains at which a given degree of distress will occur are commonly known as the performance criteria. The rationality of the design procedure can be judged from the way the corresponding performance criteria have been developed. Performance criterion is generally developed considering a failure condition, which may be any structural or functional failure or both. Fatigue cracking of bituminous surfacing and permanent deformation (rutting) along wheel paths, mainly due to repeated application of traffic loads, have been identified as the two major modes of structural failures that need to be addressed in the structural design of pavements. Some performance criteria also use roughness as the mode of failure in terms of present serviceability index (PSI) [1]. The low-volume rural Pradhan Mantri Gram Sadak Yojana roads in India mostly consist of granular pavements with thin bituminous surfacing, in which rutting is considered as the only mode of failure, which occurs due to vertical compressive strain at the top of subgrade. In this paper, the rutting criteria adopted by different highway organizations for design of low-volume road pavements have been presented with the objective of comparing these criteria with that adopted for design of Indian roads. Selection of Critical Performance Parameters Horizontal tensile strain at the bottom fibre of bituminous bound layer and vertical compressive strain on top of subgrade have traditionally been taken to be causative for the two major modes of failures considered, i.e., fatigue cracking and rutting. Excessive strains applied repeatedly have been considered to be the major factors for the development of the two modes of failures. Figure 1 shows a typical layered flexibile pavement system subjected to a dual wheel loading applied at the surface. Deformation or rutting provides the principal indication of deterioration in granular pavements with thin bituminous surfacing. It develops chiefly in the wheel tracks,and increases with time or more precisely with the cumulative application of commercial traffic. Bituminous Surfacing Granular Base Granular Sub-base Subgrade Figure 1: Critical mechanistic parameters ε z ε E t 1,µ 1 E, 2 µ 2 E, 3 µ 3 E, 4 µ 4 Grameen Sampark 17
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 18 and 19: 18 Subgrade Failure Criterion The b
Page 20 and 21: 20 A maximum of 50mm rut depth was
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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