FACTORS OF DESIGN IN PAVEMENTS

The factors that intervene in the design of pavements are the following:


Transit
The heaviest loads per axle (simple, tandem), expected in the most requested design lane, that determine the pavement structure of the road during the adopted design period are of interest for sizing the pavements. The repetition of traffic loads and the consequent accumulation of deformations on the pavement (fatigue) are fundamental for the calculation. In addition, the maximum contact pressures, the tangential stresses in special sections (curves, braking and acceleration zones, etc.), the operating speeds of vehicles (especially the slow ones in vehicle parking areas) must be taken into account. heavy), the channeling of traffic, etc.

Sub grade
The thickness of a pavement, whether flexible or rigid, depends to a large extent on the quality of this layer. As an evaluation parameter of this layer, the bearing capacity or resistance to deformation due to shear stress under the transit loads is used. It is necessary to take into account the sensitivity of the soil to humidity, both in terms of resistance and possible changes in volume (swelling-retraction). The volume changes of an expansive subgrade type soil can cause great damage to the structures that rest on it, for this reason when a pavement is built on this type of soil should be taken to prevent variations in soil moisture for which it will be necessary to think about the waterproofing of the structure. Another way to deal with this problem is through the stabilization of this type of soil with some additive, in our country the best results have been achieved by stabilizing soils with lime.

Weather
The factors that in our environment most affect a pavement are rainfall and changes in temperature.
The rains by their direct action in the elevation of the phreatic level influence in the resistance, the compressibility and the volumetric changes of the ground of subgrade especially. This parameter also influences some construction activities such as earthmoving and the placement and compaction of granular and asphalt layers.
The changes of temperature in the slabs of rigid pavements cause in these very high efforts, that in some cases can be superior to those generated by the loads of the vehicles that circulate on them.

In the flexible pavements and since the asphalt has a high thermal susceptibility, the increase or decrease of temperature can cause a substantial modification in the modulus of elasticity of the asphalt layers, causing in them and under special conditions, deformations or cracks that would influence at the service level of the road.

Materials
The available materials are decisive for the selection of the most suitable pavement structure technically and economically. On the one hand, aggregates available in quarries and alluvial deposits in the area are considered. In addition to the required quality, in which the desired homogeneity is included, it is necessary to pay attention to the available available volume, to the exploitation facilities and to the price, conditioned to a large extent by the haulage distance. On the other hand, the most expensive basic materials should be considered: binders and binders especially.
The analysis of construction costs must be complemented with a prevention of pavement behavior during the design period, the necessary conservation and its updated cost and, finally, an estimate of future structural reinforcements, surface renovations or reconstructions.
In addition, the user's costs related to their safety and the delays that originate in relatively congested roads due to conservation and resurfacing work should be taken into account.