stressTraffic {soilphysics}

Predicting Soil Stress Due to Agricultural Trafficability

Description

Contact area, stress distribuition and stress propagation based on the SoilFlex model (Keller 2005; Keller et al. 2007) are calculated.

Usage

stressTraffic(inflation.pressure, recommended.pressure, tyre.diameter, 
    tyre.width, wheel.load, conc.factor, layers, plot.contact.area = FALSE, ...) 

Arguments

inflation.pressure

tyre inflation pressure, kPa

recommended.pressure

recommended tyre inflation pressure at given load, kPa

tyre.diameter

overall diameter of the unloaded tyre, m

tyre.width

tyre width, m

wheel.load

wheel load, kg

conc.factor

concentration factor; a numeric vector ranging from 3 (wet soil) to 6 (dry soil), depending on water content.

layers

a numeric vector containing values of depth (in meters) for the soil layers. Note that layers can also be a unique value

plot.contact.area

logical; shall soilTraffic plot the distribution of stress over the contact area?

...

further graphical arguments. See par.

Value

A list of

Area

Contact area parameters.

Loads

Estimated wheel loads.

Stress

Stress propagation into soil; sigma_vertical: vertical stress; sigma_mean: mean normal stress

stress.matrix

The matrix of applied stress at a specific depth and radial distance from the tyre centre.

fZStress

The function of stress propagation in z direction (vertical stress).

fmeanStress

The function of mean normal stress propagation.

fStress

The function of stress propagation.

fXStress

The function of stress propagation in x (footprint length or driving) direction.

fYStress

The function of stress propagation in y (tire width) direction.

Author(s)

Renato Paiva de Lima <[e-mail]>

Anderson Rodrigo da Silva <[e-mail]>

Alvaro Pires da Silva <[e-mail]>

References

Keller, T. 2005. A model to predict the contact area and the distribution of vertical stress below agricultural tyres from readily-available tyre parameters. Biosyst. Eng. 92, 85-96.

Keller, T.; Defossez, P.; Weisskopf, P.; Arvidsson, J.; Richard, G. 2007. SoilFlex: a model for prediction of soil stresses and soil compaction due to agricultural field traffic including a synthesis of analytical approaches. Soil and Tillage Research 93, 391-411.

Examples

stress <- stressTraffic(inflation.pressure=200, 
	   recommended.pressure=200, 
	   tyre.diameter=1.8, 
	   tyre.width=0.4, 
	   wheel.load=4000, 
	   conc.factor=c(4,5,5,5,5,5),
           layers=c(0.05,0.1,0.3,0.5,0.7,1), 
	   plot.contact.area = TRUE)

stress

# Building a fancier plot for the contact area
# library(fields)
# image.plot(x = as.numeric(rownames(stress$stress.matrix)), 
#	       y = as.numeric(colnames(stress$stress.matrix)), 
#	       z = stress$stress.matrix,  
#	       xlab="Tyre footprint length (m)", ylab="Tyre width (m)") 
# End (not run)

# Stress Propagation 
# Vertical Stress
stress.v <- stress$Stress$sigma_vertical
layers <- stress$Stress$Layers
plot(x = 1, y = 1, xlim=c(0,300),ylim=c(1,0),xaxt = "n",
     ylab = "Soil Depth",xlab ="", type="l", main="")
axis(3)
mtext("Stress (kPa)",side=3,line=2.5)
lines(x=stress.v, y=layers)

# Mean normal stress
stress.p <- stress$Stress$sigma_mean
lines(x=stress.p, y=layers, lty=2)
legend("bottomright", c("Vertical stress", "Normal mean stress"), lty = 1:2)

# End (not run)