1、Designation: D 4823 95 (Reapproved 2003)e1Standard Guide forCore Sampling Submerged, Unconsolidated Sediments1This standard is issued under the fixed designation D 4823; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of l
2、ast revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.e1NOTEWarning notes were editorially moved into the standard text in August 2003.1. Scope1.1 This guide covers core-sampling termi
3、nology, advan-tages and disadvantages of different types of core samplers,core-distortions that may occur during sampling, techniquesfor detecting and minimizing core distortions, and methods fordissecting and preserving sediment cores.1.2 In this guide, sampling procedures and equipment aredivided
4、into the following categories based on water depth:sampling in depths shallower than 0.5 m, sampling in depthsbetween 0.5 m and 10 m, and sampling in depths exceeding 10m. Each category is divided into two sections: equipment forcollecting short cores and equipment for collecting long cores.1.3 This
5、 guide emphasizes general principles. Only in a fewinstances are step-by-step instructions given. Because coresampling is a field-based operation, methods and equipmentmust usually be modified to suit local conditions. This modi-fication process requires two essential ingredients: operatorskill and
6、judgment. Neither can be replaced by written rules.1.4 Drawings of samplers are included to show sizes andproportions. These samplers are offered primarily as examples(or generic representations) of equipment that can be purchasedcommercially or built from plans in technical journals.1.5 This guide
7、is a brief summary of published scientificarticles and engineering reports. These references are listed inthis guide. These documents provide operational details thatare not given in this guide but are nevertheless essential to thesuccessful planning and completion of core sampling projects.1.6 This
8、 standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. For specificwarning st
9、atements, see 6.3 and 11.5.2. Referenced Documents2.1 ASTM Standards:D 420 Guide to Site Characterization for Engineering, De-sign, and Construction Purposes2D 1129 Terminology Relating to Water3D 1452 Practice for Soil Investigation and Sampling byAuger Borings2D 1586 Test Method for Penetration Te
10、st and Split-BarrelSampling of Soils2D 1587 Practice for Thin-Walled Tube Sampling for Geo-technical Purposes2D 4220 Practices for Preserving and Transporting SoilSamples2D 4410 Terminology for Fluvial Sediment33. Terminology3.1 DefinitionsFor definitions of terms used in this guide,refer to Termino
11、logy D 1129 and Terminology D 4410.3.2 Definitions of Terms Specific to This Standard:3.2.1 check valvea device (see Fig. 1)4mounted atop anopen-barrel core sampler. As the sampler moves down throughwater and sediment, the valve remains open to allow water toflow up through the barrel. When downward
12、 motion stops, thevalve closes. During retrieval, the valve remains closed andcreates suction that holds the core inside the barrel.3.2.2 corea vertical column of sediment cut from a parentdeposit.3.2.3 core catchera device (see Fig. 2) that grips andsupports the core while the sampler is being pull
13、ed from thesediment and hoisted to the water surface.3.2.4 core conveyora device (see Fig. 3) for reducingfriction between a core and the inside surface of a core barrel.3.2.5 core-barrel linera rigid, thin-wall tube mountedinside the barrel of a core sampler. During the core-cuttingprocess, sedimen
14、t moves up inside the liner.3.2.6 core sampleran instrument for collecting cores.3.2.7 extrudeThe act of pushing a core from a core barrelor a core-barrel liner.3.2.8 open-barrel samplerin simplest form, a straighttube open at both ends. More elaborate open-barrel samplershave core catchers and chec
15、k valves.1This guide is under the jurisdiction of ASTM Committee D19 on Water and isthe direct responsibility of Subcommittee D19.07 on Sediments, Geomorphology,and Open-Channel Flow.Current edition approved June 10, 2003. Published August 2003. Originallyapproved in 1988. Last previous edition appr
16、oved in 1999 as D 4823 95 (1999).2Annual Book of ASTM Standards, Vol 04.08.3Annual Book of ASTM Standards, Vol 11.01.4The boldface numbers in parentheses refer to the list of references at the end ofthis guide.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 1
17、9428-2959, United States.3.2.9 piston immobilizera special coupling (see Fig. 4)that protects a core from disruptive forces that arise duringsampler pull-out. Piston immobilizers are also called splitpistons or break-away pistons.3.2.10 piston samplera core sampler (see Fig. 5) with asolid cylinder
18、(piston) that seals against the inside walls of thecore barrel. The piston remains fixed at the bed-surfaceelevation while the core barrel cuts down through the sediment.3.2.11 recovery ratiothe ratio A/B where “A” (see Fig. 1)is the distance from the top of the sediment core to the bottomof the cut
19、ting bit and “B” is the distance from the surface of theparent deposit to the bottom of the cutting bit.3.2.12 repenetrationa mishap that occurs when a coresampler collects two or more cores during one pass.3.2.13 surface samplera device for collecting sedimentfrom the surface of a submerged deposit
20、. Surface samplers aresometimes referred to as grab samplers.3.2.14 trip releasea mechanism (see Fig. 5 and Fig. 6(b)that releases a core sampler from its suspension cable andallows the sampler to freely fall a predetermined distancebefore striking the bed.3.2.15 undisturbed samplesediment particles
21、 that havenot been rearranged relative to one another by the process usedto cut and isolate the particles from their parent deposit. Allcore samples are disturbed to some degree because raising theNOTEDark bands represent stiff sediments; light bands representplastic sediments. As coring proceeds, s
22、ediment below the barrel moveslaterally away from the cutting edge and plastic sediments inside the barrelare compressed. “A” is the cores length and “B” is the barrelspenetration depth.FIG. 1 Deformations Caused by Open-Barrel Core Samplers (1)1NOTE(a) The leaves separate during penetration and the
23、n close duringretrieval. Strips of gauze can be woven around the leaves to provideadditional support. (3) (b) The lever trips down during retrieval to releasethe spring and twist the fabric sleeve shut. (4) (c) The cupped plate dropsduring retrieval to block the entrance and support the core. (4) (d
24、) Thelever releases the spring-loaded blade which pivots downward to hold thecore. (4)FIG. 2 Core CatchersNOTE(a) Strips of metal foil slide up through the core barrel as thecutting edge advances downward. (5) (b) The plastic sleeve unfolds frompleats stored near the cutting edge. This sleeve surrou
25、nds the core as thebarrel moves down. (4)FIG. 3 Core ConveyorsNOTEDuring penetration the shear pins break but the flow-restrictingorifice holds the clevis and piston together. During retrieval, water in thetop chamber flows through the orifice and allows the piston and clevis toseparate. Cable tensi
26、on pulls the clevis up against the stop but frictionlocks the piston and core barrel together.FIG. 4 Piston Immobilizer (9)D 4823 95 (2003)e12cores to the water surface causes pore water and trapped gasesto expand (10). In common usage, the term “undisturbedsample” describes particles that have been
27、 rearranged but onlyto a slight degree.4. Critical Dimensions of Open-Barrel and PistonSamplers4.1 Dimensions of a samplers cutting bit, core tube, andcore-tube liner (see Fig. 7) are critical in applications requiringundisturbed samples. These dimensions control the amount ofdistortion in recovered
28、 cores. The recommendations in thissection were developed from tests on open-barrel core sam-plers (11); however, the recommendations are usually extendedto cover piston-type core samplers.4.2 Cutting-Bit AngleThe angle “b” on the cutting bit (seeFig. 7) should be less than about 10; the optimum ang
29、le isabout 5. If the angle is smaller than about 2, the bit cutsefficiently but its edge chips and dulls easily.4.3 Core-Liner Diameter, Ds(see Fig. 7)Dsshould belarger than about 5 cm; however, the upper limit for Dsisdifficult to establish. As Dsincreases, the amount of corecompaction decreases bu
30、t the sampler becomes heavier andlarger. A survey of existing samplers shows that 10 cm is apractical upper limit. A few samplers have barrels larger than10 cm but these are used only for special applications (12).4.4 Inside Friction FactorThe dimensions Dsand De(seeFig. 7) set the inside friction f
31、actor defined as Ci=(DsDe)100/De. For a barrel without a core conveyor, the optimumCivalue depends mainly on the barrels length. Cishould besmaller than 0.5 if the barrel is shorter than about 2 m. If thebarrel is longer than about 2 m, Cishould fall between 0.75 and1.5. For a barrel with a core con
32、veyor, Cishould be smallerthan 0.5 regardless of the barrels length. Notice that in allinstances Dsis lightly greater than De. The small expansionabove the cutting bit minimizes friction where the outside ofthe core contacts the inside of the barrel or liner. Frictiondistorts the cores strata by ben
33、ding horizontal layers intocurved, bowl-shaped surfaces shown on the upper part of Fig.8. Friction also causes overall end-to-end compaction of thecore and thereby reduces recovery ratios. If friction becomesvery large, sediment fails to enter the cutting bit. Instead,sediment moves aside as the bit
34、 penetrates downward. Thislateral motion, commonly referred to as “staking,” preventsdeep-lying strata from being sampled. It is important toobserve upper limits on Cibecause too large an expansioncauses another form of distortion, the core slumps against thewalls as the sediment slides up into the
35、barrel.4.5 Outside Friction FactorThe dimensions Dwand Dt(see Fig. 7) set the outside friction factor defined as Co=(Dw Dt)100/Dt. Coshould be zero for barrels used in cohesionlesssediments; but Coshould be between 1.0 and about 3.0 forbarrels used in cohesive sediments. Notice that in all instances
36、Dwis larger than Dt. The small contraction above the bitreduces friction at the outside surface of the barrel and makesNOTE(a) The sampler is lowered slowly through the water. (b) Thesampler falls free when the trip weight contacts the bed. (c) The corebarrel cuts downward but the piston remains sta
37、tionary.FIG. 5 Operation of a Piston-Type Core Sampler (2)NOTE(a) The messenger weight strikes the hook and releases thestring holding the check valve. (6) (b) The trip weight strikes the sedimentand unhooks the sampler. (7) (c) The cable slackens and allows thespring-loaded hook to open. (8)FIG. 6
38、Release MechanismFIG. 7 Critical Dimensions for Cutting Bits and Core Barrels (11)D 4823 95 (2003)e13it easier to push the core barrel into the bed. On a long barrel,friction can be reduced by installing one or more sleeves (seeFig. 7). The sleeves not only plough a path for the barrel butthey also
39、serve as clamps to hold barrel sections together.4.6 Area FactorThe dimensions Dwand Deset the areafactor defined as Ca=(Dw2) 100/De2. Cashould be less than10 or possibly 15. Notice that Cais proportional to the area ofsediment displaced by the bit divided by the area of the bitsentrance; therefore,
40、 Cais an index of disturbance at the cuttingedge. A sampler with too large an area factor tends tooversample during early stages of penetration when frictionalong the inner wall of the barrel is low. Oversampling occursbecause sediment laying below and outside the bit shift inwardas the bit cuts dow
41、nward.4.7 Core-Barrel LengthA samplers core barrel should beslightly longer than L, the longest core that can be collectedwithout causing significant compaction. L and Ds(see Fig. 7)set the core-length factor defined as Lf= L/Ds. Lfshould be lessthan 5.0 (or possibly 10) for a sampler used in cohesi
42、vesediments, but Lfshould be less than 10 (or possibly 20) for asampler used in cohesionless sediments.The constant factors 5,10, and 20 apply to slow-penetrating, open-barrel samplers.Studies suggest that all of these factors can be increased byraising the samplers penetration speed or using a pist
43、onsampler instead of an open-barrel sampler.4.8 Barrel SurfacesAll surfaces contacting the coreshould be smooth and free of protruding edges to reduceinternal friction and minimize core distortion. The surfacesshould also be clean and chemically inert if the core is to beanalyzed for contaminants or
44、 if the core is to be stored in itsliner for long periods of time.4.9 Chemical Composition of Sampler PartsSamplerparts must not contain substances that interfere with chemicalanalysis of the cores. For example, barrels, pistons, and corecatchers made of plastic should not be used if tests includeph
45、thalate concentrations. Misleading data will result fromplasticizer contamination of the sediments.5. Open-Barrel Samplers Versus Piston Samplers5.1 Users sometimes face difficult decisions in choosingbetween an open-barrel sampler and a piston sampler. Thedecision frequently depends not only upon c
46、haracteristics ofthe two samplers but also upon other factors such as hoisting-equipment capabilities, working platform stability, waterdepth, operator experience, and the purpose for collecting thecores.This section covers factors to consider before making thefinal choice.5.2 Depth of PenetrationMo
47、st open-barrel samplers andmost piston samplers rely on momentum to drive their barrelsinto sediment deposits. Momentum-driven samplers are re-leased at a predetermined point so as to acquire momentumwhile falling toward the bed. A momentum-driven pistonsampler generally penetrates deeper than a mom
48、entum-drivenopen-barrel sampler provided the two samplers have equalweights, equal barrel-diameters, and equal fall-distances (2).5.3 Core CompactionWhen compared under equal testconditions (see 5.2), a piston sampler causes less core com-paction than an open-barrel sampler. However, the piston must
49、be held motionless at the bed-surface elevation while the barrelpenetrates downward. If the piston is allowed to shift downwith the barrel, the core undergoes serious compaction.5.4 Flow-in DistortionFlow-in distortion is caused bysuction at the entrance of a sampler. Sediment is sucked intothe barrel instead of being severed and encircles by the cuttingedge. Flow-in rarely occurs with open-barrel samplers; how-ever, it can be a problem with piston samplers (14). Flow-inusually occurs during pull-out following a shallow penetration.Con
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