[MUSIC] Hello I am Pierre Hornych from IFSTTAR. I'm head of the laboratory In charged of research activities on pavement testing, design and modeling. The objective of this video is to present the principles of the design of bituminous pavement. The video will first present the characteristics of bituminous pavements structures and mechanical behavior and failure modes. Then it will explain the principles of the French pavement layout. The pavement structure consists of three main layers. The sub grade, the road base and the surface course. The sub grade is the natural soil It is often covered with a copping layer, consisting of granular material, or cement treated soil. The role of the copping layer, is to protect the natural soil and improve its the bearing capacity. The tension of the road base, is to support the traffic loads, and to spread the loads in the sub-grade. The world base can be divided in two layers, the base layer and the sub base. The surface course has two functions. To protect the road base and to ensure good surface characteristics, evenness, skid resistance, evacuation of water. On heavy traffic pavements it can consist of two layers. The wearing course and the binder course. Bituminous pavements can be divided into two groups. Low traffic pavements which consist of a single bituminous wearing course generally less than 12 cm thick and a granual base. These pavements are limited in France to traffic slower than 150 heavy vehicles per day. Thick bituminous pavements which have a bituminous wearing course and a bituminous road base with a thickness varying generally between 15 and 40 cm. Each type of pavement layer presents different failure mechanisms. Surface courses can present different modes of deterioration, rutting, wear, stripping, cracking, due in particular to aging or thermal fatigue. The deterioration of surface course is considered as a maintenance problem and it is generally not taken in to account in design. Bituminous base layers present mainly fatigue cracking due to repeated tensile stresses in use by the traffic loads at the bottom of bituminous layers and also layer the bonding. Unbound layers and soils present mainly permanent deformations rutting due to the vertical stresses applied by the traffic. The objective of pavement design is to define the pavement structure materials, layer thicknesses, satisfying the constraints of the project. Type of road, traffic level, design life, and budget. At first I will present some general principles of pavement design, then I will focus on the example of the French pavement design method. Most recent pavement design methods can be defined as mechanistic empirical methods. Because they are based on the mechanical pavement model adjusted by the introduction of empirical calibration coefficients Determined by comparison with performance of real pavements. Mechanistic-empirical pavements design methods are generally based on the following principles. A multi-layer linear elastic model is used to calculate the critical strengths in the pavement structure. And given standard equivalent single axle load or easel. The material properties used in the model, the modulus, and the fatigue strength of each material are determined from laboratory tests. Each calculated critical strain is compared with the limit value or design criterium. The figure on the right presents the results of the review of 17 different design methods, used for bituminous pavements. Two design criteria are almost universally used. Fatigue criteria for bituminous layers. And permanent deformation criterium for the sub-grade, and for unbound granular layers. However, some methods also introduce additional design criteria based on other failure mechanisms. Rutting of bituminous layers, top down cracking or thermal cracking. The French pavement design method considers only the two most common design criteria, fatigue and permanent deformations. The pavement model is used to calculate two critical strains. The maximum tensile strain at the bottom of the bituminous layers. This tensile strain is compared with limit value to avoid fatigue failure. The maximum vertical strain at the top of the sub-grade. This vertical strain is compared again With a limit value to avoid excessive permanent deformations. This slide presents the fatigue design criteria used in the French pavement design method. This criterion is based on the fatigue load determined from laboratory fatigue tests which defines the number of load cycles leading to fatigue failure. This fatigue law is then adjusted by several coefficients. This slide presents the permanent deformation criterion for the sub-grade. This criterion is empirical and defines the limit vertical strain, epsilon lim. In function of the number of load cycles, this criterion can also be applied to unbound granual layers. The french pavement design method is described in the french standard NF-P-98086 Road Pavement Structural Design. This method is also implemented in the design software ALIZE- LCPC. Reminder of the key points. Pavements structures consist of 3 main layers, the subgrade, the road base which is the main structure of element and the surface course which determines the surface characteristics. Bituminous pavements present two main structural failure modes. The fatigue of bituminous layers and the permanent deformation of the sub grade and unbound general layers. The French pavement design method is based on linear elastic pavement model and defines the fatigue criterion to calculate the design life of the bituminous layers, and permanent deformation criterion to calculate the design life of the sub-grade. Thanks for your attention. [MUSIC]