The total thickness obtained from the chart is distributed into surface course of thickness x, base of thickness y, and sub-base of thickness z, as shown in Table 7.3. The pavement design chart extrapolated up to 200 million standard axles is shown in Fig. The method of computing the cumulative standard axles the number of standard axles per commercial vehicle is designated as ‘vehicle damage factor (VDF)’. Recommendations on the types of pavement materials suitable for various courses. New set of design curves relating the cumulative standard axles and the CBR value to the total pavement thickness.Ģ. The salient features of IRC guidelines revised in 1984 are:ġ. ‘Traffic’ denotes the total number of vehicles in both directions (irrespective of whether the design is for a two-lane or a dual carriageway.) For estimation of future traffic, the growth rate is assumed as 7.5 per cent.įor single-lane roads, the traffic intensity is taken to be twice that for two-lane roads (because of the concentration of traffic on one lane only). The thickness of construction is given by a set of 7 curves, as shown in Fig. IRC Guidelines for Design of Flexible Pavements :
(iii) The curves are applicable only under the conditions for which they were method is not reliable for high values of CBR. The advantage of the CBR method is that it can be used to find the total thickness of the pavement and that of the individual courses in addition to the thickness of the subgrade soil (provided the CBR-values of the materials of the courses are also known). The California bearing ratio (CBR) value of the subgrade soil was the basis for the method of design of flexible pavements, developed originally by the California State Highway Department, and adopted by The Road Research Laboratory, London, for developing their own design procedure and design charts. (This method is obsolete and is of historical importance.) The higher the group index, the weaker is the subgrade soil. The group-index of a soil, an arbitrary index assigned to different soil types based on the percent fines, liquid limit and plasticity index, is defined by the following equation – Highway Engineers (Highway Research Board) in 1945. The group-index method was devised by the U.S. IRC Guidelines for Low Traffic Volume Roads: (IRC: SP: 72-2007 and IRC: SP: 77-2008) 5. Traffic Loading 5.Hence, only the following methods will be presented here: 1. Allows use of current procedures and provides for inclusion of improved procedures in the future.NCHRP 1-37ADesign GuideDesign GuideHierarchical Input (Not Design) Hierarchical Input (Not Design) ProcessProcess Level 1 (High Reliability)Analysis of special problemsUsually will incorporate TestingHigh Visibility/Risk/Cost Projects Level2 (Medium Reliability)Standard Design - Most Cases(Rigorous but practical) Level 3 (Lower Reliability)Lower impact/risk projectsNCHRP 1-37ADesign GuideDesign GuideHIERARCHIAL APPROACH ( AC MODULUS)HIERARCHIAL APPROACH ( AC MODULUS)xx,II2f()f()f()xxx,I2LEVEL MIX BINDER RELIABILITY1 E* Lab Test G*, Lab Test2E*Predictive equationG*, Lab Test3E*Predictive equationAC Grade topropertiesx,III2NCHRP 1-37ADesign GuideDesign GuideMechanistic Mechanistic -Empirical DesignEmpirical Design Calculate stress, strain, or deflection due to traffic or environmental loadings Relate the number of repetitions to a physical distress such as cracking, rutting, or faulting Calibrate with observed performanceNCHRP 1-37ADesign GuideDesign Guide 1. Level of effort consistent with the importance of the project.
FLEXIBLE PAVEMENT DESIGN AASHTO PROFILE SOFTWARE
NCHRP 1-37ADesign GuideDesign GuideNear the End of the Long RoadNear the End of the Long RoadNCHRP 1-37ADesign GuideDesign GuideSome General Overview Some General Overview Concepts of the 2002 Design Concepts of the 2002 Design Guide For Asphalt PavementsGuide For Asphalt PavementsNCHRP 1-37ADesign GuideDesign GuideObjectiveObjectiveDevelop and deliver the 2002 guide for design of new and rehabilitated pavement structures Based on mechanistic-empirical principals Accompanied by the necessary computational software For adoption and distribution by AASHTONCHRP 1-37ADesign GuideDesign GuideStudy Project StatementStudy Project Statement Development based on (to the greatest possible extent): Existing models Existing data bases No additional laboratory or field testingNCHRP 1-37ADesign GuideDesign GuideHierarchical InputsHierarchical Inputs The 2002 guide will use a hierarchical approach for determining design inputs.