ASTM D4823-95(2003)e1
(Guide)Standard Guide for Core Sampling Submerged, Unconsolidated Sediments
Standard Guide for Core Sampling Submerged, Unconsolidated Sediments
ABSTRACT
This guide covers core-sampling submerged, unconsolidated sediments. It also covers terminology, advantages and disadvantages of different types of core samplers, core-distortions that may occur during sampling, techniques for detecting and minimizing core distortions, and methods for dissecting and preserving sediment cores. Sampling procedures and equipment are divided into categories based on water depth. Critical dimensions and properties of open-barrel and piston samplers like the cutting-bit angle, core-liner diameter, inside friction factor, outside friction factor, area factor, core-barrel length, barrel surfaces, and chemical composition of sampler parts shall conform to this standard guide. The following factors shall be considered for decisions in choosing between an open-barrel sampler and a piston sampler: depth of penetration, core compaction, flow-in distortion, surface disturbance, and repenetration. Driving techniques included in this guide are free core samplers, implosive and explosive samplers, punch-corer samplers, vibratory-driven samplers and impact-driven samplers. Guides are also included for collecting short cores in shallow water, collecting long cores in shallow water, and collecting short and long cores for a range of water depth. Field record shall be provided for every sampling operation. Guides are also provided for core extrusion for samplers with no liners, slitting core and core liners, sectioning cores, sampling through liner walls, preserving cores, and displaying cores.
SCOPE
1.1 This guide covers core-sampling terminology, advantages and disadvantages of different types of core samplers, core-distortions that may occur during sampling, techniques for detecting and minimizing core distortions, and methods for dissecting and preserving sediment cores.
1.2 In this guide, sampling procedures and equipment are divided into the following categories based on water depth: sampling in depths shallower than 0.5 m, sampling in depths between 0.5 m and 10 m, and sampling in depths exceeding 10 m. Each category is divided into two sections: equipment for collecting short cores and equipment for collecting long cores.
1.3 This guide emphasizes general principles. Only in a few instances are step-by-step instructions given. Because core sampling is a field-based operation, methods and equipment must usually be modified to suit local conditions. This modification process requires two essential ingredients:operator skill and judgment. Neither can be replaced by written rules.
1.4 Drawings of samplers are included to show sizes and proportions. These samplers are offered primarily as examples (or generic representations) of equipment that can be purchased commercially or built from plans in technical journals.
1.5 This guide is a brief summary of published scientific articles and engineering reports. These references are listed in this guide. These documents provide operational details that are not given in this guide but are nevertheless essential to the successful planning and completion of core sampling projects.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. For specific hazard statements, see Notes 1 and 2.
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Designation: D 4823 – 95 (Reapproved 2003)
Standard Guide for
Core Sampling Submerged, Unconsolidated Sediments
This standard is issued under the fixed designation D4823; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Warning notes were editorially moved into the standard text in August 2003.
1. Scope sign, and Construction Purposes
D1129 Terminology Relating to Water
1.1 This guide covers core-sampling terminology, advan-
D1452 Practice for Soil Investigation and Sampling by
tages and disadvantages of different types of core samplers,
Auger Borings
core-distortions that may occur during sampling, techniques
D1586 Test Method for Penetration Test and Split-Barrel
for detecting and minimizing core distortions, and methods for
Sampling of Soils
dissecting and preserving sediment cores.
D1587 Practice for Thin-Walled Tube Sampling for Geo-
1.2 In this guide, sampling procedures and equipment are
technical Purposes
divided into the following categories based on water depth:
D4220 Practices for Preserving and Transporting Soil
sampling in depths shallower than 0.5 m, sampling in depths
Samples
between0.5mand10m,andsamplingindepthsexceeding10
D4410 Terminology for Fluvial Sediment
m. Each category is divided into two sections: equipment for
collecting short cores and equipment for collecting long cores.
3. Terminology
1.3 Thisguideemphasizesgeneralprinciples.Onlyinafew
3.1 Definitions—For definitions of terms used in this guide,
instances are step-by-step instructions given. Because core
refer to Terminology D1129 and Terminology D4410.
sampling is a field-based operation, methods and equipment
3.2 Definitions of Terms Specific to This Standard:
must usually be modified to suit local conditions. This modi-
3.2.1 check valve—a device (see Fig. 1) mounted atop an
fication process requires two essential ingredients: operator
open-barrel core sampler.As the sampler moves down through
skill and judgment. Neither can be replaced by written rules.
water and sediment, the valve remains open to allow water to
1.4 Drawings of samplers are included to show sizes and
flow up through the barrel. When downward motion stops, the
proportions. These samplers are offered primarily as examples
valve closes. During retrieval, the valve remains closed and
(orgenericrepresentations)ofequipmentthatcanbepurchased
creates suction that holds the core inside the barrel.
commercially or built from plans in technical journals.
3.2.2 core—averticalcolumnofsedimentcutfromaparent
1.5 This guide is a brief summary of published scientific
deposit.
articles and engineering reports. These references are listed in
3.2.3 core catcher—a device (see Fig. 2) that grips and
this guide. These documents provide operational details that
supports the core while the sampler is being pulled from the
are not given in this guide but are nevertheless essential to the
sediment and hoisted to the water surface.
successful planning and completion of core sampling projects.
3.2.4 core conveyor—a device (see Fig. 3) for reducing
1.6 This standard does not purport to address all of the
friction between a core and the inside surface of a core barrel.
safety concerns, if any, associated with its use. It is the
3.2.5 core-barrel liner—a rigid, thin-wall tube mounted
responsibility of the user of this standard to establish appro-
inside the barrel of a core sampler. During the core-cutting
priate safety and health practices and determine the applica-
process, sediment moves up inside the liner.
bility of regulatory limitations prior to use. For specific
3.2.6 core sampler—an instrument for collecting cores.
warning statements, see 6.3 and 11.5.
3.2.7 extrude—Theactofpushingacorefromacorebarrel
2. Referenced Documents or a core-barrel liner.
3.2.8 open-barrel sampler—in simplest form, a straight
2.1 ASTM Standards:
tube open at both ends. More elaborate open-barrel samplers
D420 Guide to Site Characterization for Engineering, De-
have core catchers and check valves.
This guide is under the jurisdiction ofASTM Committee D19 on Water and is
the direct responsibility of Subcommittee D19.07 on Sediments, Geomorphology, Annual Book of ASTM Standards, Vol 04.08.
and Open-Channel Flow. Annual Book of ASTM Standards, Vol 11.01.
Current edition approved June 10, 2003. Published August 2003. Originally Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
approved in 1988. Last previous edition approved in 1999 as D4823–95(1999). this guide.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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D 4823 – 95 (2003)
NOTE—(a) Strips of metal foil slide up through the core barrel as the
cutting edge advances downward. (5) (b) The plastic sleeve unfolds from
pleats stored near the cutting edge. This sleeve surrounds the core as the
NOTE—Dark bands represent stiff sediments; light bands represent
barrel moves down. (4)
plastic sediments. As coring proceeds, sediment below the barrel moves
FIG. 3 Core Conveyors
laterallyawayfromthecuttingedgeandplasticsedimentsinsidethebarrel
are compressed. “A” is the core’s length and “B” is the barrel’s
penetration depth.
FIG. 1 Deformations Caused by Open-Barrel Core Samplers (1)
NOTE—During penetration the shear pins break but the flow-restricting
orifice holds the clevis and piston together. During retrieval, water in the
top chamber flows through the orifice and allows the piston and clevis to
separate. Cable tension pulls the clevis up against the stop but friction
NOTE—(a)Theleavesseparateduringpenetrationandthencloseduring
locks the piston and core barrel together.
retrieval. Strips of gauze can be woven around the leaves to provide
FIG. 4 Piston Immobilizer (9)
additional support. (3) (b) The lever trips down during retrieval to release
the spring and twist the fabric sleeve shut. (4) (c) The cupped plate drops
during retrieval to block the entrance and support the core. (4) (d) The
ofthecuttingbitand“B”isthedistancefromthesurfaceofthe
lever releases the spring-loaded blade which pivots downward to hold the
parent deposit to the bottom of the cutting bit.
core. (4)
3.2.12 repenetration—a mishap that occurs when a core
FIG. 2 Core Catchers
sampler collects two or more cores during one pass.
3.2.13 surface sampler—a device for collecting sediment
3.2.9 piston immobilizer—a special coupling (see Fig. 4) from the surface of a submerged deposit. Surface samplers are
that protects a core from disruptive forces that arise during sometimes referred to as grab samplers.
sampler pull-out. Piston immobilizers are also called split 3.2.14 trip release—amechanism(seeFig.5andFig.6(b))
pistons or break-away pistons. that releases a core sampler from its suspension cable and
3.2.10 piston sampler—a core sampler (see Fig. 5) with a allows the sampler to freely fall a predetermined distance
solid cylinder (piston) that seals against the inside walls of the before striking the bed.
core barrel. The piston remains fixed at the bed-surface 3.2.15 undisturbed sample—sediment particles that have
elevationwhilethecorebarrelcutsdownthroughthesediment. notbeenrearrangedrelativetooneanotherbytheprocessused
3.2.11 recovery ratio—the ratioA/B where “A” (see Fig. 1) to cut and isolate the particles from their parent deposit. All
is the distance from the top of the sediment core to the bottom core samples are disturbed to some degree because raising the
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D 4823 – 95 (2003)
FIG. 7 Critical Dimensions for Cutting Bits and Core Barrels (11)
NOTE—(a) The sampler is lowered slowly through the water. (b) The
sampler falls free when the trip weight contacts the bed. (c) The core
barrel cuts downward but the piston remains stationary.
4.2 Cutting-BitAngle—Theangle“b”onthecuttingbit(see
FIG. 5 Operation of a Piston-Type Core Sampler (2)
Fig. 7) should be less than about 10°; the optimum angle is
about 5°. If the angle is smaller than about 2°, the bit cuts
efficiently but its edge chips and dulls easily.
4.3 Core-Liner Diameter, D (see Fig. 7)—D should be
s s
larger than about 5 cm; however, the upper limit for D is
s
difficult to establish. As D increases, the amount of core
s
compaction decreases but the sampler becomes heavier and
larger. A survey of existing samplers shows that 10 cm is a
practical upper limit. A few samplers have barrels larger than
10 cm but these are used only for special applications (12).
4.4 Inside Friction Factor—The dimensions D and D (see
s e
Fig. 7) set the inside friction factor defined as C =(D −
i s
D )100/D . For a barrel without a core conveyor, the optimum
e e
C value depends mainly on the barrel’s length. C should be
i i
smaller than 0.5 if the barrel is shorter than about 2 m. If the
barrelislongerthanabout2m, C shouldfallbetween0.75and
i
1.5. For a barrel with a core conveyor, C should be smaller
i
than 0.5 regardless of the barrel’s length. Notice that in all
instances D is lightly greater than D . The small expansion
s e
above the cutting bit minimizes friction where the outside of
NOTE—(a) The messenger weight strikes the hook and releases the
the core contacts the inside of the barrel or liner. Friction
stringholdingthecheckvalve. (6)(b)Thetripweightstrikesthesediment
distorts the core’s strata by bending horizontal layers into
and unhooks the sampler. (7) (c) The cable slackens and allows the
spring-loaded hook to open. (8) curved, bowl-shaped surfaces shown on the upper part of Fig.
FIG. 6 Release Mechanism
8. Friction also causes overall end-to-end compaction of the
core and thereby reduces recovery ratios. If friction becomes
cores to the water surface causes pore water and trapped gases very large, sediment fails to enter the cutting bit. Instead,
sediment moves aside as the bit penetrates downward. This
to expand (10). In common usage, the term “undisturbed
sample” describes particles that have been rearranged but only lateral motion, commonly referred to as “staking,” prevents
deep-lying strata from being sampled. It is important to
to a slight degree.
observe upper limits on C because too large an expansion
i
4. Critical Dimensions of Open-Barrel and Piston
causes another form of distortion, the core slumps against the
Samplers
walls as the sediment slides up into the barrel.
4.1 Dimensions of a sampler’s cutting bit, core tube, and 4.5 Outside Friction Factor—The dimensions D and D
w t
core-tubeliner(seeFig.7)arecriticalinapplicationsrequiring (see Fig. 7) set the outside friction factor defined as C =(D
o w
undisturbed samples. These dimensions control the amount of − D)100/D. C shouldbezeroforbarrelsusedincohesionless
t t o
distortion in recovered cores. The recommendations in this sediments; but C should be between 1.0 and about 3.0 for
o
section were developed from tests on open-barrel core sam- barrels used in cohesive sediments. Notice that in all instances
plers (11);however,therecommendationsareusuallyextended D is larger than D. The small contraction above the bit
w t
to cover piston-type core samplers. reduces friction at the outside surface of the barrel and makes
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D 4823 – 95 (2003)
decision frequently depends not only upon characteristics of
the two samplers but also upon other factors such as hoisting-
equipment capabilities, working platform stability, water
depth, operator experience, and the purpose for collecting the
cores.Thissectioncoversfactorstoconsiderbeforemakingthe
final choice.
5.2 Depth of Penetration—Most open-barrel samplers and
most piston samplers rely on momentum to drive their barrels
into sediment deposits. Momentum-driven samplers are re-
leased at a predetermined point so as to acquire momentum
while falling toward the bed. A momentum-driven piston
sampler generally penetrates deeper than a momentum-driven
open-barrel sampler provided the two samplers have equal
weights, equal barrel-diameters, and equal fall-distances (2).
5.3 Core Compaction—When compared under equal test
FIG. 8 Flow in and Strata-Bending Distortions Inside a Core
Barrel (13) conditions (see 5.2), a piston sampler causes less core com-
paction than an open-barrel sampler. However, the piston must
beheldmotionlessatthebed-surfaceelevationwhilethebarrel
it easier to push the core barrel into the bed. On a long barrel,
penetrates downward. If the piston is allowed to shift down
friction can be reduced by installing one or more sleeves (see
with the barrel, the core undergoes serious compaction.
Fig. 7). The sleeves not only plough a path for the barrel but
5.4 Flow-in Distortion—Flow-in distortion is caused by
they also serve as clamps to hold barrel sections together.
suction at the entrance of a sampler. Sediment is sucked into
4.6 Area Factor—The dimensions D and D set the area
w e
2 2
the barrel instead of being severed and encircles by the cutting
factor defined as C =(D ) 100/D . C should be less than
a w e a
edge. Flow-in rarely occurs with open-barrel samplers; how-
10 or possibly 15. Notice that C is proportional to the area of
a
ever, it can be a problem with piston samplers (14). Flow-in
sediment displaced by the bit divided by the area of the bit’s
usuallyoccursduringpull-outfollowingashallowpenetration.
entrance; therefore, C is an index of disturbance at the cutting
a
Conditionsleadingtoflow-inareshowninFig.5(c).Thebarrel
edge. A sampler with too large an area factor tends to
isattheendofitsdownwardtravelbutthepistonliesbelowthe
oversample during early stages of penetration when friction
piston stop. During pull-out, the upward force on the cable
along the inner wall of the barrel is low. Oversampling occurs
slides the piston up through the barrel before the cutting edge
because sediment laying below and outside the bit shift inward
clears the bed.As the piston slides, it pulls the core up through
as the bit cuts downward.
the barrel.As the core moves, sediment flows in to fill the void
4.7 Core-Barrel Length—Asampler’s core barrel should be
at the lower end of the barrel. Strata lines at the bottom of the
slightly longer than L, the longest core that can be collected
recovered core are distorted and resemble those in Fig. 8.A
without causing significant compaction. L and D (see Fig. 7)
s
pistonimmobilizerhelpspreventflow-indistortionbybreaking
setthecore-lengthfactordefinedas L = L/D . L shouldbeless
f s f
the connection between the cable and the piston during the
than 5.0 (or possibly 10) for a sampler used in cohesive
pull-out process.
sedi
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