soilphysics (version 2.1)

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, ...)

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 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

• 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.

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().

sigmaPfluxo.jpg

{options: scale = 1}

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(1.43, 1.41, 1.40, 1.39, 1.35, 1.31, 1.25, 1.18, 1.12)

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)