ASTM D5924-96(2010)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: D5924 − 96 (Reapproved 2010)
Standard Guide for
Selection of Simulation Approaches in Geostatistical Site
Investigations
This standard is issued under the fixed designation D5924; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
Geostatistics is a framework for data analysis, estimation, and simulation in media whose
measurable attributes show erratic spatial variability yet also possess a degree of spatial continuity
imparted by the natural and anthropogenic processes operating therein. The soil, rock, and contained
fluids encountered in environmental or geotechnical site investigations present such features, and their
sampled attributes are therefore amenable to geostatistical treatment. Geostatistical simulation
approaches are used to produce maps of an attribute that honor the spatial variability of sampled
values. This guide reviews criteria for selecting a simulation approach, offering direction based on a
consensus of views without recommending a standard practice to follow in all cases.
1. Scope a given professional service must be judged, nor should this
document be applied without consideration of a project’s many
1.1 This guide covers the conditions that determine the
unique aspects. The word “Standard” in the title of this
selection of a suitable simulation approach for a site investi-
document means only that the document has been approved
gation problem. Alternative simulation approaches considered
through the ASTM consensus process.
here are conditional and nonconditional, indicator and
Gaussian, single and multiple realization, point, and block.
2. Referenced Documents
1.2 This guide describes the conditions for which the use of
2.1 ASTM Standards:
simulation is an appropriate alternative to the use of estimation
D653 Terminology Relating to Soil, Rock, and Contained
in geostatistical site investigations.
Fluids
1.3 This guide does not discuss the basic principles of
D5549 Guide for The Contents of Geostatistical Site Inves-
geostatistics. Introductions to geostatistics may be found in
tigation Report (Withdrawn 2002)
numerous texts including Refs (1-3).
D5922 Guide for Analysis of Spatial Variation in Geostatis-
tical Site Investigations
1.4 This guide is concerned with general simulation ap-
D5923 Guide for Selection of Kriging Methods in Geostatis-
proaches only and does not discuss particular simulation
tical Site Investigations
algorithms currently in use. These are described in Refs (4-6).
1.5 This guide offers an organized collection of information
3. Terminology
or a series of options and does not recommend a specific
3.1 Definitions of Terms Specific to This Standard:
course of action. This document cannot replace education or
3.1.1 conditional simulation, n—a simulation approach
experienceandshouldbeusedinconjunctionwithprofessional
where realizations of the random function model are con-
judgment. Not all aspects of this guide may be applicable in all
strained by values at sampled locations.
circumstances. This ASTM standard is not intended to repre-
3.1.2 drift, n—in geostatistics, a systematic spatial variation
sent or replace the standard of care by which the adequacy of
of the local mean of a variable, usually expressed as a
polynomial function of location coordinates.
This guide is under the jurisdiction ofASTM Committee D18 on Soil and Rock
and is the direct responsibility of Subcommittee D18.01 on Surface and Subsurface
Characterization. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved May 1, 2010. Published September 2010. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1996. Last previous edition approved in 2004 as D5924–96(2004). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/D5924-96R10. the ASTM website.
2 4
The boldface numbers in parentheses refer to a list of references at the end of The last approved version of this historical standard is referenced on
the text. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D5924 − 96 (2010)
3.1.3 field, n—in geostatistics, the region of one-, two- or 5. Selection of Simulation Approaches
three-dimensional space within which a regionalized variable
5.1 Simulation Versus Estimation—A common objective of
is defined.
geostatistical site investigations is to produce a two- or
3.1.4 indicator variable, n—a regionalized variable that can
three-dimensional spatial representation of a regionalized vari-
have only two possible values, zero or one.
able field from a set of measured values at different locations.
Such spatial representations are referred to here as maps.
3.1.5 kriging, n—an estimation method where sample
Estimation approaches, including all forms of kriging, yield
weights are obtained using a linear least-squares optimization
maps that exhibit a smoothing effect, whereas simulation
procedure based on a mathematical model of spatial variability
approaches yield maps that preserve the spatial variability of
and where the unknown variable and the available sample
the regionalized variable.
values may have a point or block support.
5.1.1 If mapped values of the regionalized variable are
3.1.6 nonconditional simulation, n—a simulation approach
required to provide an estimate of actual values at unsampled
where realizations of the random function model are uncon-
points, then an estimation approach such as kriging is appro-
strained by sample data.
priate.
3.1.7 nugget effect, n—the component of spatial variance
5.1.2 If mapped values of the regionalized variable are to
unresolved by the sample spacing and the additional variance
preserve the spatial variability of values at unsampled points,
due to measurement error.
then simulation rather than estimation should be used.
3.1.8 point, n—in geostatistics, the location in the field at
NOTE 1—Preservation of in-situ spatial variability is important if
which a regionalized variable is defined. It also commonly
mapped values of the regionalized variable are to be entered in a
refers to the support of sample-scale variables.
numerical model of a dynamic process, and therefore, simulation should
generally be used. For example, mapped values of transmissivity to be
3.1.9 realization, n—an outcome of a spatial random func-
entered in a numerical model of groundwater flow should be generated by
tion or a random variable.
simulation (8). However, if the numerical process model is insensitive to
3.1.10 regionalized variable, n—a measured quantity or a
spatialvariationsoftheregionalizedvariable,thenanestimationapproach
numerical attribute characterizing a spatially variable phenom- may also be used.
enon at a location in the field.
5.2 Conditional Versus Nonconditional Simulation
3.1.11 simulation, n—in geostatistics, a numerical proce- —Geostatistical simulation methods are able to produce maps
dure for generating realizations of fields based on the random of a regionalized variable that honor values observed at
function model chosen to represent a regionalized variable. sampled points, a selected univariate distribution model, and a
selected model of spatial variation. The univariate distribution
3.1.12 smoothing effect, n—in geostatistics, the reduction in
model may be that of the observed sample values or a model
spatial variance of estimated values compared to true values.
thatisdeemedmoreappropriate.Themodelofspatialvariation
3.1.13 spatial average, n—a quantity obtai
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