soilphysics (version 5.1)

sigmaP: Preconsolidation Stress

Description

A function to determine the preconsolidation stress (\(\sigma_P\)). It is a parameter obtained from the soil compression curve and has been used as an indicator of soil load-bearing capacity as well as to characterize the impacts suffered by the use of machines. The function sigmaP() contains implementations of the main methods for determining the pre-consolidation stress, such as the Casagrande method, the method of Pacheco Silva, the regression methods and the method of the virgin compression line intercept.

Usage

sigmaP(voidratio, stress, n4VCL = 3,
    method = c("casagrande", "VCLzero", "reg1", "reg2", "reg3", "reg4", "pacheco"),
    mcp = NULL, graph = TRUE, ...)

Value

A list of

sigmaP

the preconsolidation stress.

method

the method used as argument.

mcp

the maximum curvature point in log10 scale of stress; stored only if the method casagrande is used.

CI

the compression index.

SI

the swelling index.

Arguments

voidratio

a numeric vector containing void ratio (or bulk density) values.

stress

a numeric vector containing the applied stress sequence.

n4VCL

the number of points for calculating the slope of the soil Virgin Compression Line (VCL), which is obtained by linear regression.

method

a character indicating which method is to be computed; one of the following: casagrande (default), VCLzero, reg1, reg2, reg3, reg4 or pacheco; see Details.

mcp

the maximum curvature point in log10 scale of stress; required only if the method casagrande is used.

graph

logical; if TRUE (default) the compression curve is plotted.

...

further graphical arguments.

Author

Anderson Rodrigo da Silva <[e-mail]>

Details

casagrande is the method proposed by Casagrande (1936). The preconsolidation stress obtained via VCLzero corresponds to the intersection of the soil Virgin Compression Line (VCL) with the x-axis at zero applied stress, as described by Arvidsson & Keller (2004). reg1, reg2, reg3 and reg4 are regression methods that obtain the preconsolidation stress value as the intercept of the VCL and a regression line fitted with the first two, three, four and five points of the curve, respectively, as described by Dias Junior & Pierce (1995). pacheco is the method of Pacheco Silva (ABNT, 1990).

You may follow the flowchart below to understand the determination of the preconsolidation stress through sigmaP().

References

ABNT - Associacao Brasileira de Normas Tecnicas. (1990). Ensaio de adensamento unidimensional: NBR 12007. Rio de Janeiro. 13p.

Arvidsson, J.; Keller, T. (2004). Soil precompression stress I. A survey of Swedish arable soils. Soil & Tillage Research, 77:85-95.

Bowles, J. A. (1986). Engineering Properties of Soils and their Measurements, 3rd edition. McGraw-Hill Book Company, Inc. NY, 218pp.

Casagrande, A. (1936). The determination of the pre-consolidation load and its practical significance. In: Proceedings of the International Conference on Soil Mech. and Found. Eng. (ICSMFE), Cambridge, MA, 22-26 June 1936, vol. 3. Harvard University, Cambridge, MA, USA, pp. 60-64.

Dias Junior, M. S.; Pierce, F. J. (1995). A simple procedure for estimating preconsolidation pressure from soil compression curves. Soil Technology, 8:139-151.

See Also

voidratio, maxcurv, fitlbc

Examples

pres <- c(1, 12.5, 25, 50, 100, 200, 400, 800, 1600)
VR <- c(0.846, 0.829, 0.820, 0.802, 0.767, 0.717, 0.660, 0.595, 0.532)

plot(VR ~ log10(pres), type = "b") # find the 'mcp'
sigmaP(VR, pres, method = "casagrande", mcp = 1.6, n4VCL = 2)

# fitting the VCL
sigmaP(VR, pres, method = "casagrande", mcp = 1.6, n4VCL = 3)

# self-calculation of "mcp" argument for Casagrande method
sigmaP(VR, pres, method = "casagrande", n4VCL = 3)

# Pacheco method
sigmaP(VR, pres, method = "pacheco")

# Regression method
sigmaP(VR, pres, method = "reg3")

# End (not run)