Módulo de Elasticidad de acuerdo a la deflexión (LFWD)

La siguiente es la fórmula para el cálculo del módulo elástico de la estructura sobre el suelo (E-module). Este cálculo es de acuerdo a la deflexión del equipo utilizado (en este caso, utilizado para el LWD).

Keros Prima 100

The E-module in Keros Prima 100 is calculated according to the theory of elasticity, developed by Boussinesq.

The E-module for the center of the load is calculated from:

where:

E = Surface E-Module (MPa)

ν = Poissons ratio

σ₀ = Applied stress at surface(kPa)

a = Radius of loading plate (mm)

d₀ = Deflection (μm)

f = Factor that depends on the stress distribution:

Uniform: f = 2

Rigid plate: f = π/2

Parabolic, granular: f = 8/3

Parabolic, cohesive: f = 4/3

In the old version of the Prima data collection software (version 2) the stress distribution factor is 2 and the Poissons ratio is 0.35. It is possible for the user to set the values in the newest version of our data collection software (version 3 and higher).

According to the theory of elasticity the E-module at a distances of more than two radii from the center of the load can be found from:

where:

r = Distance from center

d₀(r)= Deflection at the distance r from center(μm)

There are several descriptions of the theory of elasticity in the literature, f.x "Modelling Flexible Pavement Response and Performance" Written by "Per Ullidtz" ISBN 87-502-0805-5

As one will see, the velocity is not present at all. The signal from the geophone is however proportional to the velocity and has to be integrated to get the wanted deflection.

One of the most important things to do when measuring with a portable FWD is to assure a good contact between the loading plate and the surface, especially when the surface is rough. The easiest way to ensure that, is to use a thin layer of quartz sand with a grain size of approximately 2 mm beneath the plate.

Note: Always ensure that the deflection sensor is loose and that it doesn't rest on the plate!

Fuente: Keros Prima 100 Portable FWD, instrucyion for use. (Dynatest).
La norma es la ASTM_E2835-11 y se puede consultar haciendo click en el link.