Investigation Methods and Procedures - Geotechnical Engineering Investigation - page 104

Hardened shoe Ball check

Split tube

(a)

Hardened shoe Outer split tube Ball check

FIGURE 2.61
The split-barrel sampler or split spoon : (a)
without liner; (b) with liner. (Courtesy of
Sprague and Henwood, Inc.)

Thin wall liner

(b)

clays and fine cohesionless soils. Upon retrieval, the barrel between the head and the shoe
is split open (Figure 2.62) , the sample is examined and described, removed, and stored.
In some sampler types, brass liners are used for procuring drive samples of strong cohe-
sive soils for laboratory direct-shear testing.

Sampling Procedure
The sampler is installed on the hole bottom, then driven into the soil with a hammer (nor-
mally 140 lb) falling on the drill rods. The number of blows required for a given weight
and drop height, and a given penetration, are recorded to provide a measure of soil com-
pactness or consistency as described in Section 3.4.5 (Standard Penetration Test).

Thin-Wall Tube Samplers
Purpose
Thin-wall tube samplers are used to obtain UD of soft to stiff cohesive soils for laboratory
testing of strength, compressibility, and permeability.

Tube Materials
Cold-drawn, seamless steel tubing (trade name “Shelby tube”) is used for most soil mate-
rials; brass tubes are used for organic soils where corrosion resistance is required. Wall
thickness is usually 18 gage; heavier gages are available. Lacquer coating can provide cor-
rosion protection and reduce internal frictional resistance and sample disturbance.
Tube diameters and lengths range from 2 to 6 in. in diameter, 24 to 30 in. in length. Tubes
2 in. in diameter are used in 2½ in. exploratory borings, but 2 in. diameter samples have a
large ratio of perimeter disturbance to area and are considered too small for reliable labo-
ratory engineering-property testing.
Tubes 3 in. (2.87 ) in diameter are generally considered the standard type for laboratory

test samples. The tube should be provided with a cutting edge drawn in to provide about
0.04 in. inside clearance (or 0.5 to 1.5% less than the tube I.D.), which permits the sample
to expand slightly upon entering the tube, thereby relieving sample friction along the
walls and reducing disturbance.
Tubes 4 to 6 in. in diameter reduce disturbance but require more costly borings. A 5 in.
tube yields four samples of 1 in. diameter from the same depth for triaxial testing.

Operations
Thin-wall tubes are normally pressed into the soil by hydraulically applied force. After
pressing, the sample is left to rest in the ground for 2 to 3 min to permit slight expansion