ASTM D4823-95(1999)
(Guide)Standard Guide for Core Sampling Submerged, Unconsolidated Sediments
Standard Guide for Core Sampling Submerged, Unconsolidated Sediments
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.
General Information
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Standards Content (Sample)
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Designation: D 4823 – 95 (Reapproved 1999)
Standard Guide for
Core Sampling Submerged, Unconsolidated Sediments
This standard is issued under the fixed designation D 4823; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope D 1129 Terminology Relating to Water
D 1452 Practice for Soil Investigation and Sampling by
1.1 This guide covers core-sampling terminology, advan-
Auger Borings
tages and disadvantages of different types of core samplers,
D 1586 Test Method for Penetration Test and Split-Barrel
core-distortions that may occur during sampling, techniques
Sampling of Soils
for detecting and minimizing core distortions, and methods for
D 1587 Practice for Thin-Walled Tube Geotechnical Sam-
dissecting and preserving sediment cores.
pling of Soils
1.2 In this guide, sampling procedures and equipment are
D 4220 Practice for Preserving and Transporting Soil
divided into the following categories based on water depth:
Samples
sampling in depths shallower than 0.5 m, sampling in depths
D 4410 Terminology for Fluvial Sediment
between 0.5 m and 10 m, and sampling in depths exceeding 10
m. Each category is divided into two sections: equipment for
3. Terminology
collecting short cores and equipment for collecting long cores.
3.1 Definitions—For definitions of terms used in this guide,
1.3 This guide emphasizes general principles. Only in a few
refer to Terminology D 1129 and Terminology D 4410.
instances are step-by-step instructions given. Because core
3.2 Definitions of Terms Specific to This Standard:
sampling is a field-based operation, methods and equipment
3.2.1 check valve—a device (see Fig. 1) mounted atop an
must usually be modified to suit local conditions. This modi-
open-barrel core sampler. As the sampler moves down through
fication process requires two essential ingredients: operator
water and sediment, the valve remains open to allow water to
skill and judgment. Neither can be replaced by written rules.
flow up through the barrel. When downward motion stops, the
1.4 Drawings of samplers are included to show sizes and
valve closes. During retrieval, the valve remains closed and
proportions. These samplers are offered primarily as examples
creates suction that holds the core inside the barrel.
(or generic representations) of equipment that can be purchased
3.2.2 piston sampler—a core sampler (see Fig. 2) with a
commercially or built from plans in technical journals.
solid cylinder (piston) that seals against the inside walls of the
1.5 This guide is a brief summary of published scientific
core barrel. The piston remains fixed at the bed-surface
articles and engineering reports. These references are listed in
elevation while the core barrel cuts down through the sediment.
this guide. These documents provide operational details that
3.2.3 core—a vertical column of sediment cut from a parent
are not given in this guide but are nevertheless essential to the
deposit.
successful planning and completion of core sampling projects.
3.2.4 core catcher—a device (see Fig. 3) that grips and
1.6 This standard does not purport to address all of the
supports the core while the sampler is being pulled from the
safety concerns, if any, associated with its use. It is the
sediment and hoisted to the water surface.
responsibility of the user of this standard to establish appro-
3.2.5 core conveyor—a device (see Fig. 4) for reducing
priate safety and health practices and determine the applica-
friction between a core and the inside surface of a core barrel.
bility of regulatory limitations prior to use. For specific hazard
3.2.6 core-barrel liner—a rigid, thin-wall tube mounted
statements, see Note 1 and Note 2.
inside the barrel of a core sampler. During the core-cutting
2. Referenced Documents process, sediment moves up inside the liner.
3.2.7 core sampler—an instrument for collecting cores.
2.1 ASTM Standards:
3.2.8 extrude—The act of pushing a core from a core barrel
D 420 Guide to Site Characterization for Engineering, De-
2 or a core-barrel liner.
sign, and Construction Purposes
3.2.9 open-barrel sampler—in simplest form, a straight
tube open at both ends. More elaborate open-barrel samplers
have core catchers and check valves.
This guide is under the jurisdiction of ASTM Committee D-19 on Water and is 3.2.10 trip release—a mechanism (see Fig. 2 and Fig. 5(b))
the direct responsibility of Subcommittee D19.07 on Sediments, Geomorphology,
and Open-Channel Flow.
Current edition approved Sept. 10, 1995. Published November 1995. Originally Annual Book of ASTM Standards, Vol 11.01.
published as D 4823 – 88. Last previous edition D 4823 – 88. The boldface numbers in parentheses refer to the list of references at the end of
Annual Book of ASTM Standards, Vol 04.08. this guide.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 4823
NOTE 1—(a) The leaves separate during penetration and then close
NOTE 1—Dark bands represent stiff sediments; light bands represent
during retrieval. Strips of gauze can be woven around the leaves to
plastic sediments. As coring proceeds, sediment below the barrel moves
provide additional support. (3) ( b) The lever trips down during retrieval
laterally away from the cutting edge and plastic sediments inside the barrel
to release the spring and twist the fabric sleeve shut. (4) ( c) The cupped
are compressed.“ A’’ is the core’s length and “B’’ is the barrel’s
plate drops during retrieval to block the entrance and support the core. (4)
penetration depth.
4 (d) The lever releases the spring-loaded blade which pivots downward to
FIG. 1 Deformations Caused by Open-Barrel Core Samplers (1)
hold the core. (4)
FIG. 3 Core Catchers
NOTE 1—(a) Strips of metal foil slide up through the core barrel as the
NOTE 1—(a) The sampler is lowered slowly through the water. (b) The
cutting edge advances downward. (5) (b) The plastic sleeve unfolds from
sampler falls free when the trip weight contacts the bed. (c) The core
pleats stored near the cutting edge. This sleeve surrounds the core as the
barrel cuts downward but the piston remains stationary.
barrel moves down. (4)
FIG. 2 Operation of a Piston-Type Core Sampler (2)
FIG. 4 Core Conveyors
that releases a core sampler from its suspension cable and
from the surface of a submerged deposit. Surface samplers are
allows the sampler to freely fall a predetermined distance
sometimes referred to as grab samplers.
before striking the bed.
3.2.15 undisturbed sample—sediment particles that have
3.2.11 piston immobilizer—a special coupling (see Fig. 6)
not been rearranged relative to one another by the process used
that protects a core from disruptive forces that arise during
to cut and isolate the particles from their parent deposit. All
sampler pull-out. Piston immobilizers are also called split
core samples are disturbed to some degree because raising the
pistons or break-away pistons.
cores to the water surface causes pore water and trapped gases
3.2.12 recovery ratio—the ratio A/B where 88A’’ (see Fig.
to expand (10). In common usage, the term 88undisturbed
1) is the distance from the top of the sediment core to the
sample’’ describes particles that have been rearranged but only
bottom of the cutting bit and 88B’’ is the distance from the
to a slight degree.
surface of the parent deposit to the bottom of the cutting bit.
4. Critical Dimensions of Open-Barrel and Piston
3.2.13 repenetration—a mishap that occurs when a core
Samplers
sampler collects two or more cores during one pass.
3.2.14 surface sampler—a device for collecting sediment 4.1 Dimensions of a sampler’s cutting bit, core tube, and
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 4823
FIG. 7 Critical Dimensions for Cutting Bits and Core Barrels (11)
NOTE 1—(a) The messenger weight strikes the hook and releases the
difficult to establish. As D increases, the amount of core
s
string holding the check valve. (6) (b) The trip weight strikes the sediment
compaction decreases but the sampler becomes heavier and
and unhooks the sampler. (7) (c) The cable slackens and allows the
larger. A survey of existing samplers shows that 10 cm is a
spring-loaded hook to open. (8)
practical upper limit. A few samplers have barrels larger than
FIG. 5 Release Mechanism
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 5 (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
barrel is longer than about 2 m, C should fall between 0.75 and
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
the core contacts the inside of the barrel or liner. Friction
distorts the core’s strata by bending horizontal layers into
curved, bowl-shaped surfaces shown on the upper part of Fig.
8. Friction also causes overall end-to-end compaction of the
core and thereby reduces recovery ratios. If friction becomes
very large, sediment fails to enter the cutting bit. Instead,
sediment moves aside as the bit penetrates downward. This
lateral motion, commonly referred to as “staking,’’ prevents
NOTE 1—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 locks the piston and core barrel together.
FIG. 6 Piston Immobilizer (9)
core-tube liner (see Fig. 7) are critical in applications requiring
undisturbed samples. These dimensions control the amount of
distortion in recovered cores. The recommendations in this
section were developed from tests on open-barrel core sam-
plers (11); however, the recommendations are usually extended
to cover piston-type core samplers.
4.2 Cutting-Bit Angle—The angle “b’’ on the cutting bit
(see 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 FIG. 8 Flow in and Strata-Bending Distortions Inside a Core
larger than about 5 cm; however, the upper limit for D is Barrel (13)
s
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 4823
deep-lying strata from being sampled. It is important to most piston samplers rely on momentum to drive their barrels
observe upper limits on C because too large an expansion into sediment deposits. Momentum-driven samplers are re-
i
causes another form of distortion, the core slumps against the
leased at a predetermined point so as to acquire momentum
walls as the sediment slides up into the barrel. while falling toward the bed. A momentum-driven piston
4.5 Outside Friction Factor—The dimensions D and D
sampler generally penetrates deeper than a momentum-driven
w t
(see Fig. 7) set the outside friction factor defined as C 5 (D open-barrel sampler provided the two samplers have equal
o w
− D )100/D . C should be zero for barrels used in cohesionless
weights, equal barrel-diameters, and equal fall-distances (2).
t t o
sediments; but C should be between 1.0 and about 3.0 for
o 5.3 Core Compaction— When compared under equal test
barrels used in cohesive sediments. Notice that in all instances
conditions (see 5.2), a piston sampler causes less core com-
D is larger than D . The small contraction above the bit
w t
paction than an open-barrel sampler. However, the piston must
reduces friction at the outside surface of the barrel and makes
be held motionless at the bed-surface elevation while the barrel
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
the barrel instead of being severed and encircles by the cutting
2 2
factor defined as C 5 (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
usually occurs during pull-out following a shallow penetration.
entrance; therefore, C is an index of disturbance at the cutting
a
Conditions leading to flow-in are shown in Fig. 2( c). The
edge. A sampler with too large an area factor tends to
barrel is at the end of its downward travel but the piston lies
oversample during early stages of penetration when friction
below the piston stop. During pull-out, the upward force on the
along the inner wall of the barrel is low. Oversampling occurs
cable slides the piston up through the barrel before the cutting
because sediment laying below and outside the bit shift inward
edge clears the bed. As the piston slides, it pulls the core up
as the bit cuts downward.
through the barrel. As the core moves, sediment flows in to fill
4.7 Core-Barrel Length—A sampler’s core barrel should be
the void at the lower end of the barrel. Strata lines at the bottom
slightly longer than L, the longest core that can be collected
of the recovered core are distorted and resemble those in Fig.
without causing significant compaction. L and D (see Fig. 7)
s
8. A piston immobilizer helps pr
...
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