Soil Exploration - Soil Properties: Testing, Measurement, and Evaluation - page 12

A more common method of obtaining an undisturbed sample is to
push a thin tube into the soil, thereby trapping the (undisturbed) sam-
ple inside the tube, and then to remove the tube and sample intact. The
ends of the tube should be sealed with paraffin wax immediately after
the tube containing the sample is brought to the ground surface. The
sealed tube should then be sent to the laboratory, where subsequent tests
can be made on the sample, with the assumption that such test results
are indicative of the properties of the soil as it existed in place within the
ground. The thin-tube sampler is called a Shelby tube . It is a 2- to 3-in.
(51- to 76-mm)-diameter 16-gauge seamless steel tube (see Figure 2-6).
When using a thin-tube sampler, the engineer should minimize the
disturbance of the soil. Pushing the sampler into the soil quickly and
with constant speed causes the least disturbance; driving the sampler
into the soil by blows of a hammer produces the most.
Normally, samples (both disturbed and undisturbed) are collected
at least every 5 ft (1.5 m) in depth of the boring hole. When, however, any
change in soil characteristics is noted within 5-ft intervals, additional
samples should be taken.
The importance of properly and accurately identifying and labeling
each sample cannot be overemphasized.
After a boring has been made and samples taken, an estimate of the
groundwater table can be made. It is common practice to cover the hole
(e.g., with a small piece of plywood) for safety reasons, mark it for iden-
tification, leave it overnight, and return the next day to record the
groundwater level. The hole should then be filled in to avoid subsequent
injury to people or animals.
Testing
A large number of tests can be performed to evaluate various soil prop-
erties. These include both laboratory and field tests. Some of the most
common tests are listed in Table 2-1. Three field tests—the standard
penetration test, cone penetration test, and vane test—are described
Figure 2-6
Shelby Tube