US3872935A

US3872935A - Apparatus and method for obtaining undisturbed soil core samples

Info

Publication number: US3872935A
Application number: US465650A
Authority: US
Inventors: Lloyd N Mielke
Original assignee: US Department of Agriculture USDA
Current assignee: US Department of Agriculture USDA
Priority date: 1974-04-30
Filing date: 1974-04-30
Publication date: 1975-03-25
Anticipated expiration: 1992-03-25

Abstract

Large-diameter, undisturbed soil core samples were obtained from a variety of soils. Handling and fracturing of the undisturbed soil cores were minimized by encasing the cores in heatshrinkable plastic tubes during sampling operations.

Description

ilnited States Patent Mielke 1 APPARATUS AND METHOD FOR OBTAINING UNDISTURBED SOIL CORE SAMPLES [75] Inventor: Lloyd N. Mielke, Lincoln, Nebr.

[73] Assignee: The United States of America as represented by the Secretary of Agriculture, Washington, DC.

22 Filed: Apr. 30, 1974 21 Appl. No.: 465,650

[52] US. Cl. 175/58, 175/20 [51] Int. Cl. E2lb 49/02 [58] Field of Search 175/58, 20, 19,253, 239

[56] References Cited 7 UNITED STATES PATENTS 3,092,192 6/1963 Deely 175/253 Primaryfixaminer-David H. Brown Attorney, Agent, or Firms-M. Howard Silverstein; Max D. Hensley; David G. McConnell [s71 ABSTRACT Large-diameter, undisturbed soil] core samples were obtained from a variety of soils. Handling and featuring of the undisturbed soil cores were minimized by encasing the cores in heat-shrinkable plastic tubes during sampling operations.

1 Claim, 5 Drawing Figures BACKGROUND OF THE INVENTION This invention relates to an apparatus and a method for obtaining undisturbed soil cores. Soil cores with undisturbed structure are desirable to measure physical and chemical properties, particularly water content and nutrient movement.

Undisturbed soil sampling techniques using handdriven equipment were reported by Lutz, Soil Sci. 64: 399-401, 1947; and Veihmeyer, Soil Sci. 27: 147-152, 1929. The machine built by Kelly et al., Soil Sci. Soc. Amer. Proc. 12: 85-87, 1947, could take undisturbed soil cores of and lO-cm. (2- and 4-in.) diameters and up to 1.8 m. (6 ft.) long. An earlier machine reported by Kelley and Haise, J. Amer. Soc. Agron. 39: 828-830, 1947, had similar sampling capabilities but required a considerable amount of manual labor. Hydraulic and electric units developed to increase sampling speed have been developed by Jensen et al., Trans. Amer. Soc. Agr. Eng. 3(1): 22-24, 1960; and Buchele, Trans. Amer. Soc. Agr. Eng. 4(2): 185-187, 1961.

Kelley et al. (supra) reported using a split-sheet metal container to protect the soil sample from fracture during transport to the laboratory. Care in sample handling and processing is required for all undisturbed samples. Split-tube-type samplers require that the sample be removed, trimmed, and coated with a casing material. Adsorption of paint-on, or dip-type coating materials, may affect the effective cross-section of the core and provide little mechanical support. Rigid wall sample containers may permit undetected water flow paths which would affect results and conclusions.

Bondurant et a1., Soil Sci. 107: 70-71, 1969, used 2 tip) is up to 4 ft. long and up to about 4 in. in inside diameter. It can be a single piece or it can have a removable cutting head. FIG. 1 is a perspective view of a twopiece sampler tube with sampler body 1 connected to cutting tip 2 which is beveled to give it the desired sharpness. FIG 2 is a section view of the soil sampler ready for use, taken along section-line 2-2 of FIG. 1

showing a heat-shrinkable plastic lining 3 and a comheat-shrinkable tubing (polyolefin) to encase undisturbed soil cores. The space between the soil core and the outer barrier was effectively sealed on soil cores 240 mm. long and 82 mm. diameter.

In accordance with the invention, I have discovered, in an apparatus for collecting undisturbed soil core samples of the type comprising a cylindrical tube or sample body, open at both ends, and having at one end thereof a cutting tip which is sharpened to facilitate entry into the ground, an improvement comprising a tubular lining or flexible heat-shrinkable plastic open'at both ends, contained within said sampler body, and having flI'IOUISldB diameter which is essentially equal to the inside diameter of said sampler body; and a means for securely holding said tubular lining in place.

This heat-shrinkable, plastic-lined soil core sampler is then pressed into the ground, removed from the ground, and the plastic lining heated to a temperature sufficient to cause shrinkage of the plastic to the soil.

The drawings consist of a perspective view and two section views of the sampler body, and two perspective views of retaining rings.

DETAILED DESCRIPTION OF THE INVENTION Many commercially available soil core samplers could be easily modified for use in accordance with the invention. Preferably, the sampler is a thin-walled metal tube with a sharpened cutting tip at one end. Its size is dependent on the type of soil being sampled. Preferably, the entire soil core sampler (i.e., body plus pressible, resiliant retaining ring 4 in place. Retaining ring 4 is positioned in an annular groove 5 in the inner wall of sampler body 1. FIG. 3 shows the same section view as FIG. 2 with the exception that annular groove 5 is internal of threaded section 6 on sampler body 2 Having threads in the annular groove 5 in the embodiment of FIG. 2 provides a gripping surface for the heatshrinkable plastic lining. It is preferred that this or some other type of gripping surface be provided.

The heat-shrinkable plastic lining can be securely held in place by any suitable means, but it is preferably held in place by a compressible,

resiliant retaining ring

4,4 such as that shown in section in FIGS. 2 and 3 and in perspective in FIGS. 4 and 5.. The preferred compressible, resiliant retaining ring is beveled on the leading inside edge 7 as shown in FIG. 3. This bevel prevents undercutting the soil core as it passes through the retaining ring. It is also preferred that the compressible, resiliant retaining ring be split to facilitate compression of the ring in order to fit it into

annular groove

5,5 in the inner wall of the sampler body, and that the retaining ring ends 8,8 in FIGS. 2, 3, 4., and 5 be notched in such a manner that when the ring is in place in

annular groove

5,5 the ends will maintain alignment with respect to each other. The compressible,

resiliant retaining ring

4,4 and

annular groove

5,5 must have dimensions such that, when the heat-shrinkable plastic lining 3,3 and the compressible,

resiliant retaining ring

4,4 are in place, the lining will be held with sufficient security to withstand the forces of friction of the soil core when pushing the soil core sampler into the ground. This was accomplished in one embodiment of the invention, as shown in the figures, by using a retaining ring 4 'such that, when the retaining ring is compressed, its outside diameter is essentially the same as the diameter of the annular groove 5. When the outside diameter of the compressed retaining ring and the diameter of the annular groove are said to be essentially the same, it is herein understood that the diameter of the annular groove is sufficiently larger than the outside diameter of the compressed retaining ring to allow the retaining ring to be put in place with the heatshrinkable plastic lining in between the retaining ring and the surface of the annular groove (cf. FIGS. 2 and 3). The edges of the retaining ring may be of different dimensions so that the outer surface of the ring is beveled as shown in FIG. 5. In this instance annular groove 5 should be beveled in the same manner as the ring as shown in FIG. 2.

Compressible, resiliant retaining rings suitable for use in the invention may be of any material that is rigid, and has sufficient spring to hold itself and the heatshrinkable plastic lining in place. In the embodiment shown in FIGS. 2 and 3

removable cutting tip

2,2 is screwed into sampler body 1,1 forcing the tip against retaining

ring

4,4 in such a way that the ring is held tightly in place. However, a retainingring could be used that has enough force to its *spring" that the he atshrinkable plastic lining would be held securely in an annular groove that was positioned by itselfin the inner wall of the sampler body. In thisembodiment a onepiece sampler body and cutting tip could be used. Methods of securing a removable cutting tip to the sampler body other than threads could be used, such as a bayonet-type mounting.

Commercially available heat-shrinkable plastic tubing have various compositions including tetrafluoroethylene resins (TFE or FTE), polyolefins, and irradiated polyvinyl chloride (PVC). These products are available in continuous rolls and 4-ft. lengths with diameters of up to 8 in. and in various colors or clear plastic. The tubing remains flexible after being heatshrunk and does not soften, when heated, to the point where soil particles might become embedded. Clear, heat-shrinkable plastic tubing is preferred to permit observation of wetting fronts and other conditions such as growth of microorganisms during the measurement of physical and chemical properties of the soil. Shrinking of the plastic is accomplished by subjecting it to temperatures of about 135 C. For optimum results the heat should be applied as evenly as possible over the surface of the encased core.'Suffic ient heat can be applied to the encased core while in the soil core sampler, or the encased core can be removed from the sampler before heating.

In use, the soil core sampler with the heat-shrinkable plastic lining securely in place is pushed into the ground to the desired depth by hydraulic pressure or similar means. Preferably, the sampler is forced into the soil at a constant rate without stopping until the desired depth is reached. The sampler is then pulled out of the ground, and the heat-shrinkable plastic is heated, encasing the soil sample. Means for forcing the sampler into the ground and removing it from the ground are well known in the prior art.

The following example is to further describe the invention and should not be construed as limiting the scope of the invention as defined by the claims.

EXAMPLE 1 White heat-shrinkable FTE tubing 4 in. in diameter and 4 ft. long was shaped to the inside contours of a 4-in. inside diameter, 4-ft. overall length soil core sampler having a threadmounted, removable cutting tip as shown in FIG. 3. A l6-gauge, compressible, resiliant retaining ring of the type shown in FIG. 4 was compressed to its smallest diameter and slipped into place on one end of the heat-shrinkable plastic lining at the edge of the sampler body threads which hold the cutting tip. The cutting tip was then screwed on, forcing the retaining ring against the inner surface of the sampler body (see FIG. 3).

The heat-shrinkable, plastic-lined soil core sampler described above was forced into the ground of a beef cattle feedlot with a Gidding, truck-mounted hydraulic probe, model GSRP-ST equipped with a Kelly bar 5 (driven bar). The sampler was forced into the soil at a constant rate without stopping until a depth of about 4 ft. was reached. The soil core sampler was retracted from the soil, the cutting tip unscrewed, and the. retaining ring removed. The soil core encased in heatshrinkable plastic was removed from the sampler and supported on a flat surface. End plugs about the same size as the sample core were placed in each end of the plastic tube to help shape and protect the soil core when the heat-shrinkable plastic is heated and shrunk. Heat was uniformly applied to the plastic from a portable blower having a 400 to 538C. heat output and a 0.25 m. per minute air output until the shrinkage was uniform.

Six undisturbed cores from to 35 in. long were successfully removed from feedlots underlain with sandy and silty-loam soil, and one undisturbed core 37 in. long was successfully removed from a cropped cornfield.

The undisturbed soil cores were used with gamma ray attenuation techniques as a nondestructive method of investigating water movement under beef cattle feedlots. Initial observations indicated that water movement into feedlot surfaces is very slow. Water applied to the surface of one undisturbed core showed no further infiltration over a 2l-da. period following initial adsorption by the relatively dry organic matter. While this represents an extreme soil and water condition, it shows that an effective seal exists between the soil column and the heat-shrinkable tube.

I claim:

1. In a method of obtaining undisturbed soil core samples of the type which utilizes a soil core sampler comprising a cylindrical tube or sampler body, open at both ends, and having at one end thereof a cutting tip which is sharpened for facilitating entry into the soil, an improvement comprising the steps of:

a. lining the inside surface of a soil core sampler with a flexible heat-shrinkable plastic tube; b. securing said heat-shrinkable plastic tube to the inner wall near the cutting tip end of said soil core sampler;

c. pressing the lined soil core sampler into the ground;

d. removing the soil sampler from the ground; and

e. heating said heat-shrinkable plastic tube evenly on all sides at a temperature sufficient to cause shrinkage.

Claims

1. In a method of obtaining undisturbed soil core samples of the type which utilizes a soil core sampler comprising a cylindrical tube or sampler body, open at both ends, and having at one end thereof a cutting tip which is sharpened for facilitating entry into the soil, an improvement comprising the steps of: a. lining the inside surface of a soil core sampler with a flexible heat-shrinkable plastic tube; b. securing said heat-shrinkable plastic tube to the inner wall near the cutting tip end of said soil core sampler; c. pressing the lined soil core sampler into the ground; d. removing the soil sampler from the ground; and e. heating said heat-shrinkable plastic tube evenly on all sides at a temperature sufficient to cause shrinkage.