ASTM D4823-95(2008)
(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 warning statements, see 6.3 and 11.5.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D4823 − 95(Reapproved 2008)
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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
1.1 This guide covers core-sampling terminology, advan- 2.1 ASTM Standards:
tages and disadvantages of different types of core samplers, D420GuidetoSiteCharacterizationforEngineeringDesign
core-distortions that may occur during sampling, techniques and Construction Purposes (Withdrawn 2011)
for detecting and minimizing core distortions, and methods for D1129Terminology Relating to Water
dissecting and preserving sediment cores. D1452Practice for Soil Exploration and Sampling byAuger
Borings
1.2 In this guide, sampling procedures and equipment are
D1586Test Method for Penetration Test (SPT) and Split-
divided into the following categories based on water depth:
Barrel Sampling of Soils
sampling in depths shallower than 0.5 m, sampling in depths
D1587Practice for Thin-Walled Tube Sampling of Soils for
between0.5mand10m,andsamplingindepthsexceeding10
Geotechnical Purposes
m. Each category is divided into two sections: equipment for
D4220 Practices for Preserving and Transporting Soil
collecting short cores and equipment for collecting long cores.
Samples
1.3 Thisguideemphasizesgeneralprinciples.Onlyinafew
D4410Terminology for Fluvial Sediment
instances are step-by-step instructions given. Because core
3. Terminology
sampling is a field-based operation, methods and equipment
must usually be modified to suit local conditions. This modi-
3.1 Definitions—For definitions of terms used in this guide,
fication process requires two essential ingredients: operator
refer to Terminology D1129 and Terminology D4410.
skill and judgment. Neither can be replaced by written rules.
3.2 Definitions of Terms Specific to This Standard:
1.4 Drawings of samplers are included to show sizes and
3.2.1 check valve—a device (see Fig. 1) mounted atop an
proportions. These samplers are offered primarily as examples
open-barrel core sampler.As the sampler moves down through
(orgenericrepresentations)ofequipmentthatcanbepurchased
water and sediment, the valve remains open to allow water to
commercially or built from plans in technical journals.
flow up through the barrel. When downward motion stops, the
valve closes. During retrieval, the valve remains closed and
1.5 This guide is a brief summary of published scientific
creates suction that holds the core inside the barrel.
articles and engineering reports. These references are listed in
this guide. These documents provide operational details that
3.2.2 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.
3.2.3 core catcher—a device (see Fig. 2) that grips and
1.6 The values stated in SI units are to be regarded as
supports the core while the sampler is being pulled from the
standard. No other units of measurement are included in this
sediment and hoisted to the water surface.
standard.
3.2.4 core conveyor—a device (see Fig. 3) for reducing
1.7 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
warning statements, see 6.3 and 11.5.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
This guide is under the jurisdiction ofASTM Committee D19 on Water and is Standards volume information, refer to the standard’s Document Summary page on
the direct responsibility of Subcommittee D19.07 on Sediments, Geomorphology, the ASTM website.
and Open-Channel Flow. The last approved version of this historical standard is referenced on
Current edition approved Oct. 1, 2008. Published November 2008. Originally www.astm.org.
´1
approved in 1988. Last previous edition approved in 2003 as D4823–95 (2003) . Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
DOI: 10.1520/D4823-95R08. this guide.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4823 − 95 (2008)
NOTE 1—(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 1—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 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
NOTE 1—(a) The leaves separate during penetration and then close
but friction locks the piston and core barrel together.
during retrieval. Strips of gauze can be woven around the leaves to
FIG. 4 Piston Immobilizer (9)
provideadditionalsupport. (3)(b)Thelevertripsdownduringretrievalto
releasethespringandtwistthefabricsleeveshut. (4)(c)Thecuppedplate
drops during retrieval to block the entrance and support the core. (4) (d)
3.2.10 piston sampler—a core sampler (see Fig. 5) with a
Theleverreleasesthespring-loadedbladewhichpivotsdownwardtohold
solid cylinder (piston) that seals against the inside walls of the
the core. (4)
FIG. 2 Core Catchers core barrel. The piston remains fixed at the bed-surface
elevationwhilethecorebarrelcutsdownthroughthesediment.
3.2.11 recovery ratio—the ratioA/B where “A” (see Fig. 1)
3.2.6 core sampler—an instrument for collecting cores. is the distance from the top of the sediment core to the bottom
ofthecuttingbitand“B”isthedistancefromthesurfaceofthe
3.2.7 extrude—The act of pushing a core from a core barrel
parent deposit to the bottom of the cutting bit.
or a core-barrel liner.
3.2.12 repenetration—a mishap that occurs when a core
3.2.8 open-barrel sampler—insimplestform,astraighttube
sampler collects two or more cores during one pass.
open at both ends. More elaborate open-barrel samplers have
core catchers and check valves. 3.2.13 surface sampler—a device for collecting sediment
from the surface of a submerged deposit. Surface samplers are
3.2.9 piston immobilizer—a special coupling (see Fig. 4)
sometimes referred to as grab samplers.
that protects a core from disruptive forces that arise during
sampler pull-out. Piston immobilizers are also called split 3.2.14 trip release—a mechanism (see Fig. 5 and Fig. 6(b))
pistons or break-away pistons. that releases a core sampler from its suspension cable and
D4823 − 95 (2008)
NOTE 1—(a) The sampler is lowered slowly through the water. (b) The FIG. 7 Critical Dimensions for Cutting Bits and Core Barrels (11)
sampler falls free when the trip weight contacts the bed. (c) The core
barrel cuts downward but the piston remains stationary.
FIG. 5 Operation of a Piston-Type Core Sampler (2)
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,therecommendationsareusuallyextended
to cover piston-type core samplers.
4.2 Cutting-Bit Angle—Theangle“b”onthecuttingbit(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
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 −
NOTE 1—(a) The messenger weight strikes the hook and releases the i s
stringholdingthecheckvalve. (6)(b)Thetripweightstrikesthesediment D )100/D . For a barrel without a core conveyor, the optimum
e e
and unhooks the sampler. (7) (c) The cable slackens and allows the
C value depends mainly on the barrel’s length. C should be
i i
spring-loaded hook to open. (8)
smaller than 0.5 if the barrel is shorter than about 2 m. If the
FIG. 6 Release Mechanism
barrelislongerthanabout2m, C shouldfallbetween0.75and
i
1.5. For a barrel with a core conveyor, C should be smaller
i
allows the sampler to freely fall a predetermined distance
than 0.5 regardless of the barrel’s length. Notice that in all
before striking the bed.
instances D is lightly greater than D . The small expansion
s e
3.2.15 undisturbed sample—sediment particles that have above the cutting bit minimizes friction where the outside of
notbeenrearrangedrelativetooneanotherbytheprocessused
the core contacts the inside of the barrel or liner. Friction
to cut and isolate the particles from their parent deposit. All distorts the core’s strata by bending horizontal layers into
core samples are disturbed to some degree because raising the
curved, bowl-shaped surfaces shown on the upper part of Fig.
cores to the water surface causes pore water and trapped gases 8. Friction also causes overall end-to-end compaction of the
to expand (10). In common usage, the term “undisturbed
core and thereby reduces recovery ratios. If friction becomes
sample” describes particles that have been rearranged but only very large, sediment fails to enter the cutting bit. Instead,
to a slight degree.
sediment moves aside as the bit penetrates downward. This
lateral motion, commonly referred to as “staking,” prevents
4. Critical Dimensions of Open-Barrel and Piston
deep-lying strata from being sampled. It is important to
Samplers
observe upper limits on C because too large an expansion
i
4.1 Dimensions of a sampler’s cutting bit, core tube, and causes another form of distortion, the core slumps against the
core-tubeliner(seeFig.7)arecriticalinapplicationsrequiring walls as the sediment slides up into the barrel.
D4823 − 95 (2008)
analysis of the cores. For example, barrels, pistons, and core
catchers made of plastic should not be used if tests include
phthalate concentrations. Misleading data will result from
plasticizer contamination of the sediments.
5. Open-Barrel Samplers Versus Piston Samplers
5.1 Users sometimes face difficult decisions in choosing
between an open-barrel sampler and a piston sampler. The
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.
FIG. 8 Flow in and Strata-Bending Distortions Inside a Core Bar-
5.2 Depth of Penetration—Most open-barrel samplers and
rel (13)
most piston samplers rely on momentum to drive their barrels
into sediment deposits. Momentum-driven samplers are re-
4.5 Outside Friction Factor—The dimensions D and D
w t
leased at a predetermined point so as to acquire momentum
(see Fig. 7) set the outside friction factor defined as C =(D
o w
while falling toward the bed. A momentum-driven piston
− D)100/D. C shouldbezeroforbarrelsusedincohesionless
t t o
sampler generally penetrates deeper than a momentum-driven
sediments; but C should be between 1.0 and about 3.0 for
o
open-barrel sampler provided the two samplers have equal
barrels used in cohesive sediments. Notice that in all instances
weights, equal barrel-diameters, and equal fall-distances (2).
D is larger than D. The small contraction above the bit
w t
5.3 Core Compaction—When compared under equal test
reduces friction at the outside surface of the barrel and makes
conditions (see 5.2), a piston sampler causes less core com-
it easier to push the core barrel into the bed. On a long barrel,
paction than an open-barrel sampler. However, the piston must
friction can be reduced by installing one or more sleeves (see
beheldmotionlessatthebed-surfaceelevationwhilethebarrel
Fig. 7). The sleeves not only plough a path for the barrel but
penetrates downward. If the piston is allowed to shift down
they also serve as clamps to hold barrel sections together.
with the barrel, the core undergoes serious compaction.
4.6 Area Factor—The dimensions D and D set the area
w e
2 2
5.4 Flow-in Distortion—Flow-in distortion is caused by
factor defined as C =(D ) 100/D . C should be less than
a w e a
suction at the entrance of a sampler. Sediment is sucked into
10 or possibly 15. Notice that C is proportional to the area of
a
the barrel instead of being severed and encircles by the cutting
sediment displaced by the bit divided by the area of the bit’s
edge. Flow-in rarely occurs with open-barrel samplers; how-
entrance; therefore, C is an index of disturbance at the cutting
a
ever, it can be a problem with piston samplers (14). Flow-in
edge. A sampler with too large an area factor tends to
usuallyoccursduringpull-outfollowingashallowpenetration.
oversample during early stages of penetration when friction
Conditionsleadingtoflow-inareshowninFig.5(c).Thebarrel
along the inner wall of the barrel is low. Oversampling occurs
isattheendofitsdownwardtravelbutthepistonliesbelowthe
becausesedimentlayingbelowandoutsidethebitshiftinward
piston stop. During pull-out, the upward force on the cable
as the bit cuts downward.
slides the piston up through the barrel before the cutting edge
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.