Soil Boring Test

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soil boring test

Soil Boring Test Denifition

Tests performed by a geotechnical engineer by drilling holes into the soil in order to determine some or all of the following:
(1) ability of the soil to support structures on the surface with or without additional assistance from footings, piers, and other aids;
(2) permeability of the soil to determine whether it will percolate sufficiently for an on-site septic system;
(3) discover and monitor leakage from underground storage tanks or the presence of other contaminants.

Soil Boring and Sampling

Borings come in two main varieties, large-diameter and small-diameter. Large-diameter borings are rarely used due to safety concerns and expense, but are sometimes used to allow a geologist or engineer to visually and manually examine the soil and rock stratigraphy in-situ. Small-diameter borings are frequently used to allow a geologist or engineer to examine soil or rock cuttings or to retrieve samples at depth using soil samplers, and to perform in-place soil tests.

Soil samples are often categorized as being either “disturbed” or “undisturbed;” however, “undisturbed” samples are not truly undisturbed. A disturbed sample is one in which the structure of the soil has been changed sufficiently that tests of structural properties of the soil will not be representative of in-situ conditions, and only properties of the soil grains (e.g., grain size distribution, Atterberg limits, and possibly the water content) can be accurately determined. An undisturbed sample is one where the condition of the soil in the sample is close enough to the conditions of the soil in-situ to allow tests of structural properties of the soil to be used to approximate the properties of the soil in-situ.

Offshore soil collection introduces many difficult variables. In shallow water, work can be done off a barge. In deeper water a ship will be required. Deepwater soil samplers are normally variants of Kullenberg-type samplers, a modification on a basic gravity corer using a piston (Lunne and Long, 2006). Seabed samplers are also available, which push the collection tube slowly into the soil.

Soil Samplers

Soil samples are taken using a variety of samplers; some provide only disturbed samples, while others can provide relatively undisturbed samples.

Shovel. Samples can be obtained by digging out soil from the site. Samples taken this way are disturbed samples.

Trial Pits are relatively small hand or machine excavated tranches used to determine groundwater levels and take disturbed samples from.

Hand/Machine Driven Auger. This sampler typically consists of a short cylinder with a cutting edge attached to a rod and handle. The sampler is advanced by a combination of rotation and downward force. Samples taken this way are disturbed samples.

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Continuous Flight Auger. A method of sampling using an auger as a corkscrew. The auger is screwed into the ground then lifted out. Soil is retained on the blades of the auger and kept for testing. The soil sampled this way is considered disturbed.

Split-spoon / SPT Sampler. Utilized in the ‘Standard Test Method for Standard Penetration Test (SPT) and Split-Barrel Sampling of Soils’ (ASTM D 1586[1]). This sampler is typically an 18″-30″ long, 2.0″ outside diameter (OD) hollow tube split in half lengthwise. A hardened metal drive shoe with a 1.375″ opening is attached to the bottom end, and a one-way valve and drill rod adapter at the sampler head. It is driven into the ground with a 140-pound (64 kg) hammer falling 30″. The blow counts (hammer strikes) required to advance the sampler a total of 18″ are counted and reported. Generally used for non-cohesive soils, samples taken this way are considered disturbed.

Modified California Sampler. in the ‘Standard Practice for Thick Wall, Ring-Lined, Split Barrel, Drive Sampling ofSoils1’ (ASTM D 3550). Similar in concept to the SPT sampler, the sampler barrel has a larger diameter and is usually lined with metal tubes to contain samples. Samples from the Modified California Sampler are considered disturbed due to the large area ratio of the sampler (sampler wall area/sample cross sectional area).

Shelby Tube Sampler. Utilized in the ‘Standard Practice for Thin-Walled Tube Sampling of Soils for Geotechnical Purposes’ (ASTM D 1587). This sampler consists of a thin-walled tube with a cutting edge at the toe. A sampler head attaches the tube to the drill rod, and contains a check valve and pressure vents. Generally used in cohesive soils, this sampler is advanced into the soil layer, generally 6″ less than the length of the tube. The vacuum created by the check valve and cohesion of the sample in the tube cause the sample to be retained when the tube is withdrawn. Standard ASTM dimensions are; 2″ OD, 36″ long, 18 gauge thickness; 3″ OD, 36″ long, 16 gauge thickness; and 5″ OD, 54″ long, 11 gauge thickness. It should be noted that ASTM allows other diameters as long as they are proportional to the standardized tube designs, and tube length is to be suited for field conditions. Soil sampled in this manner is considered undisturbed.

Piston samplers. These samplers are thin-walled metal tubes which contain a piston at the tip. The samplers are pushed into the bottom of a borehole, with the piston remaining at the surface of the soil while the tube slides past it. These samplers will return undisturbed samples in soft soils, but are difficult to advance in sands and stiff clays, and can be damaged (compromising the sample) if gravel is encountered.

The Livingstone corer, developed by D. A. Livingstone, is a commonly used piston sampler. A modification of the Livingstone corer with a serrated coring head allows it to be rotated to cut through subsurface vegetable matter such as small roots or buried twigs.

Pitcher Barrel sampler. This sampler is similar to piston samplers, except that there is no piston. There are pressure-relief holes near the top of the sampler to prevent pressure buildup of water or air above the soil sample.

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