soilphysics (version 1.1)

sigmaP: Preconsolidation Stress

Description

A function to determine the preconsolidation stress ($\sigma_P$).

Usage

sigmaP(voidratio, stress, n4VCL = 2,
    method = c("casagrande", "VCLzero",
    "reg1", "reg2", "reg3", "reg4", "pacheco"),
    mcp = NULL, graph = TRUE, ...)

Arguments

voidratio

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

stress

a numeric vector containing the applied stress sequence; see Note.

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 p

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.

Value

• sigmaP returns the preconsolidation stress value.

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).

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(0.99, 0.97, 0.95, 0.89, 0.78, 0.61, 0.43, 0.23, 0.01)

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

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

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

# End (not run)