Design procedures for flexible pavement
For flexible pavements, structural design is
mainly concerned with determining appropriate layer thickness and composition.
The main design factors are stresses due to traffic load and temperature
variations. Two methods of flexible pavement structural design are common
today: Empirical design and mechanistic empirical design.
Empirical design
An empirical approach is one which is based on the results of
experimentation or experience.
Some of them are
either based on
physical properties or
strength parameters of
soil subgrade. An empirical approach is one which is based on the
results of experimentation or experience. An empirical analysis of flexible
pavement design can be done with or with out a soil strength test. An example
of design without soil strength test is by using HRB soil classification
system, in which soils are grouped from A-1 to A-7 and a group index is added
to differentiate soils within each group. Example with soil strength test uses
McLeod, Stabilometer, California Bearing Ratio (CBR) test. CBR test is widely
known and will be discussed.
Mechanistic-Empirical Design
Empirical-Mechanistic
method of design is based on the mechanics of materials that relates input,
such as wheel load, to an output or pavement response. In pavement design, the
responses are the stresses, strains, and deflections within a pavement
structure and the physical causes are the loads and material properties of the
pavement structure. The relationship between these phenomena and their physical
causes are typically described using some mathematical models. Along with this
mechanistic approach, empirical elements are used when defining what value of
the calculated stresses, strains, and deflections result in pavement failure.
The relationship between physical phenomena and pavement failure is described
by empirically derived equations that compute the number of loading cycles to
failure.
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