Volume 6 – Geotechnical Manual, Site Investigation and Engineering ...

Chapter 2 SAMPLING AND SAMPLING DISTURBANCE
and Poulin 1979). In-situ freezing methods for saturated granular soils and resin impregnation
methods have been implemented to “lock” the soil in the in-situ condition prior to sampling. When
implemented, these methods have been shown to produce high quality undisturbed samples.
However, the methods are rather involved and time consuming and therefore have not seen
widespread use in practice.
Once samples are obtained and transported to the laboratory in suitable containers, they are
trimmed to appropriate size and shape for testing. Block samples should be wrapped with a
household plastic membrane and heavy duty foil and stored in block form and only trimmed shortly
before testing. Every sample must be identified with the following information: project number,
boring or exploration pit number, sample number, sample depth, and orientation.
2.2.2 Disturbed Sampling
Disturbed samples are those obtained using equipment that destroy the macrostructure of the soil
but do not alter its mineralogical composition. Specimens from these samples can be used for
determining the general lithology of soil deposits, for identification of soil components and general
classification purposes, for determining grain size, Atterberg limits, and compaction characteristics of
soils. Disturbed samples can be obtained with a number of different methods as summarized in Table
2.1. Some of the sampling methods given in Table 2.1 are described below.
Split-Barrel (Split Spoon)
The split spoon sampler is a solid steel tube barrel split into two halves longitudinally. The device has
a check valve and a hard steel shoe. When the head and shoe are unscrewed the barrel opens in the
centre exposing the sample. Improvement in design provides liner and the sampler retainer. The ball
valve in the head and the sample retainer valve spring prevent the sample particularly cohesionless
soil from being washed out and lost. The borehole is cleaned before lowering the sampler into the
borehole. The sampler is then driven into the borehole base by hammering to extract the sample.
The sample is then logged on a borelog.
Continuous Auger
Continuous auger or continuous flight augers are augers with continuous spiral on the shaft. As the
hole advances, additional sections of spiral flight are added. In this type of auger, the soils rise to
the top of the hole on the spiral flight and is sampled as it emerges. Moreover the disadvantage of
raising and lowering the auger to remove the soil is eliminated. Condinuous augers can be with solid
or hollow stems also. The limitation of the augers is that these are not effective below water table
as there are constant caving problems and samples are washed off unless cased. Hollow stem auger
can cope with the situation to some extent with special adaptors. The limitations are maximum depth
30m for continuous augers.
Bulk Samples
Bulk samples are suitable for soil classification, index testing, R-value, compaction, California Bearing
Ratio (CBR), and tests used to quantify the properties of compacted geomaterials. The bulk samples
may be obtained using hand tools without any precautions to minimize sample disturbance. The
sample may be taken from the base or walls of a test pit or a trench, from drill cuttings, from a hole
dug with a shovel and other hand tools, by backhoe, or from a stockpile. The sample should be put
into a container that will retain all of the particle sizes. For large samples, plastic or metal buckets or
metal barrels are used; for smaller samples, heavy plastic bags that can be sealed to maintain the
water content of the samples are used.
2-4 March 2009