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Western Dam Engineering
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<br />8
<br />Table 1 – Summary of Characterization, Test Methods, and Sample Types for Key Soil Properties
<br />Soil Property / Design
<br />Aspect Characterization and Design Considerations Key Testing Methods Sample Type for
<br />Laboratory Testing
<br />Shear Strength
<br /> (ϕ – friction angle)
<br /> (c- cohesion)
<br /> Influenced by soil type, in-situ dry unit weight,
<br />degree of saturation, pore water pressure,
<br />degree of compaction, plasticity, cementation,
<br />seismic loading, weathering.
<br /> Consists of frictional and cohesion components
<br /> Estimated from in situ field tests, gradation data,
<br />density, Atterberg limits, and drained and
<br />undrained strengths from lab tests.
<br /> Strength considerations for slope stability
<br />analyses are discussed in Vol. 1, Issue 3 (Nov
<br />2013) newsletter.
<br />In Situ (Field): standard
<br />penetration test, vane
<br />shear test, cone
<br />penetration test, pocket
<br />penetrometer
<br />Laboratory: direct shear
<br />(DS), triaxial shear (TS),
<br />unconfined compression
<br />(UC) tests
<br />Undisturbed1 sample
<br />needed for DS, TS, or
<br />UC tests. Remolded2
<br />sample used for
<br />testing proposed new
<br />embankment fill.
<br />Permeability (k)
<br /> Influenced by soil type, fines content, degree of
<br />compaction, cracking; and joints, fractures and
<br />weathering in rock.
<br /> For analyses & design often need embankment,
<br />foundation, and filter material “k” values.
<br /> Anisotropy: horizontal “k” can be up to 1000
<br />times greater than vertical “k”.
<br />In Situ: pressure (packer)
<br />test, constant/falling/rising
<br />head tests, pump tests
<br />Laboratory: Falling head,
<br />constant head, and back
<br />pressure permeability
<br />tests performed in triaxial
<br />cell.
<br />Undisturbed1 or
<br />remolded2 sample
<br />used for back pressure
<br />permeability test,
<br />falling / constant head
<br />tests.
<br />Protective Filters
<br /> Gradation data and permeability estimates
<br />needed for base and filter materials.
<br /> Filter design discussed in Vol. 1, Issue 1 (March
<br />2013) newsletter.
<br />Laboratory: sieve
<br />analysis, hydrometer (to
<br />estimate fines fraction);
<br />see above for lab
<br />permeability test methods
<br />Disturbed or
<br />undisturbed sample:
<br />Sieve analysis. See
<br />above for permeability
<br />test.
<br />Compressibility
<br /> -settlement
<br /> -consolidation
<br /> -shrink/swell
<br /> -collapse
<br /> Influenced by soil type, plasticity, loading,
<br />consolidation history, degree of compaction, in-
<br />situ unit weight, cementation.
<br /> Embankment fill typically experiences immediate
<br />settlement, consolidation (squeezing out of pore
<br />water), and secondary compression
<br /> Shrink/swell – largely dependent on soil plasticity
<br />and clay content; fat clays are of concern.
<br /> Collapse susceptibility w/wetting – foundation
<br />deposits with dry unit weight approximately < 95
<br />pcf, low moisture content, above water table.
<br />In Situ: settlement plates;
<br />test fill measurement for
<br />proposed fill
<br />Laboratory: consolidation,
<br />sieve analysis, Atterberg
<br />limits, dry unit weight,
<br />permeability, collapse
<br />potential
<br />Undisturbed sample:
<br />dry unit weight,
<br />consolidation, collapse
<br />potential, permeability.
<br />Disturbed or
<br />undisturbed sample:
<br />sieve analysis,
<br />Atterberg Limits.
<br />Erosion
<br />-Internal erosion (IE)
<br />-Surface erosion (SE)
<br />
<br /> IE and SE influenced by soil type, in-situ dry unit
<br />weight, gradation, degree of compaction,
<br />plasticity, cementation, weathering.
<br /> IE also influenced by embankment defects such
<br />as internal cracking, under-compacted soil
<br />adjacent to penetrations or lifts, dispersive soils,
<br />gap grading, and inadequate/no filter.
<br /> Potential for IE also relates to the soil’s
<br />dispersibility (see below)
<br />
<br />In Situ: VJT (SE)
<br />Laboratory, direct erosion
<br />tests: EFA, SERF, HET,
<br />RETA.
<br />Laboratory, indirect tests
<br />for evaluating IE likelihood
<br />and erosion resistance:
<br />sieve analysis, Atterberg
<br />limits, dry unit weight
<br />Undisturbed sample:
<br />EFA, SERF, HET,
<br />RETA, dry unit weight
<br />Disturbed or
<br />undisturbed sample:
<br />sieve analysis,
<br />Atterberg Limits.
<br />Dispersibility
<br /> Typically montmorillonitic or illitic clays, high in
<br />sodium, low to medium in dissolved salts, and
<br />are easily erodible.
<br /> Avoid using, selectively place, treat with lime,
<br />protect from drying/cracking, and/or provide a
<br />robust filter for dispersive soils.
<br />Laboratory: Double
<br />hydrometer, pinhole,
<br />crumb test. Note that all
<br />three tests are usually
<br />required
<br />Remolded sample:
<br />crumb test, pinhole
<br />test. Disturbed or
<br />Undisturbed sample:
<br />double hydrometer
<br />Compaction
<br />Characteristics
<br /> Compaction increases strength and reduces
<br />permeability, compressibility, and erodibility.
<br />Field: test fill
<br />Laboratory: Standard
<br />Proctor Compaction
<br />Disturbed sample.
<br />1 Relatively undisturbed samples commonly obtained from thin-wall (e.g. Shelby) tube or modified California samplers.
<br />2 Remolded (or reconstituted) samples can be created using soil from either undisturbed or disturbed3 samples.
<br />3 Disturbed bag or bucket samples commonly obtained from split spoon sample, test pit spoil, or auger cuttings
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