Considerations about highways shoulders design. / Considerações sobre o projeto de acostamentos para rodovias.
Eilaine de Lourdes Martini de Oliveira
DATA DE PUBLICAÇÃO
Shoulders has important functions in a highway, so much in relation to the improvement of the operational conditions, such as the capacity and the road safety, as for the pavements performance, protecting the structure of the mainline, improving the drainage and load transfer conditions. However, the shoulders have been suppressed or implanted in incorrect way for economy reasons. The present work gathered criteria and existent recommendations on the implantation of shoulders related to its influence in the capacity and road safety, to their geometric characteristics, to the methods for the definition of the type, design method and failures in the pavements, in the shoulders and in the tracks. It also made analyses to measure the importance of the shoulders in the good performance of a highway, so much in relation to the operational conditions, as of the pavement performance. Starting from these analyses it was verified that the suppression of shoulders in a highway can reduce its capacity in 7% and to increase the predicted accidents index in up to 28%. Regarding the pavements performance, starting from the functional and structural conditions of the existent pavements in the road mesh belonging to the Regional Division DR-2 of the Department of Highways of the State of São Paulo (DER/SP) in 2005, it was verified that the value of Final Quality Index of the mesh composed by highways with shoulders is superior to the mesh composed by highways without shoulders. Then, analyses were made to verify the influence of the shoulders (i) in the flexible and rigid pavements life cycle through the use of the AASHTO design method; (ii) in the concrete thickness of the rigid pavements through the AASHTO and PCA design methods; (iii) in the stresses in the concrete plate of the rigid pavements through the analysis mechanic with the use of the software EVERFE 2.24. All of the analyses showed that the shoulders improve significantly the pavement performance of the mainline, increasing its life cycle from 100 to 400% or reducing the necessary thickness of the covering of the mainline in about 25%. It also took place a cost analysis to guide the definition of the traffic to be considered in the shoulders pavement design, where it was verified that the value of 5% of the total traffic considered for the mainline increases only 2 to 3% in the total costs of the paving, being advisable its use. Finally, it was proposed a Flowchart for Project based on the accomplished analyses and with the objective of guiding the decision of implanting or not the shoulders, as well as supplying recommendations to be following in both cases.