15 AUGUST 2005
programs usually follow a general pattern and to some extent can be standardized, but they
should be adapted to particular problems and soil conditions. Special tests and research
should be utilized when necessary to develop needed information. The testing program should
be well planned with the engineering features of the structure and backfill in mind; testing
should be concentrated on samples from areas where significant features will be located but
should still present a complete picture of the soil and rock properties. The laboratory test
procedures and equipment are described in ASTM D 2487 and its references.
8-188.8.131.52.1 Identification and Classification of Soils. The Unified Soil Classification
System used for classifying soils for military projects (ASTM D 2487) is a means of identifying
a soil and placing it in a category of distinctive engineering properties. Table 8-3.1 shows the
properties of soil groups pertinent to backfill and foundations. Using these characteristics, the
engineer can prepare preliminary designs based on classification and plan the laboratory
testing program intelligently and economically.
The Unified Soil Classification System classifies soils according to their grain-
size distribution and plasticity characteristics and groups them with respect to their engineering
simple, expedient tests (See ASTM D 2487) and these estimates can be confirmed using
simple laboratory tests. The principal laboratory tests performed for classification are
grain-size analyses and Atterberg limits.
The engineering properties in table 8-3.1 are based on "Standard Proctor"
(ASTM D 2487) maximum density except that the California Bearing Ratio (ASTM D 1883) and
the subgrade modulus are based on ASTM D 1557 maximum density. This information can be
used for initial design studies. However, for final design of important structures, laboratory
tests are required to determine actual performance characteristics, such as ASTM D 1557
compaction properties, shear strength, permeability, compressibility, swelling characteristics,
and frost susceptibility where applicable, under expected construction conditions.
The Unified Soil Classification System is particularly useful in evaluating, by
visual examination, the suitability of potential borrow materials for use as compacted backfill.
Proficiency in visual classification can be developed through practice by comparing estimated
soil properties with results of laboratory classification tests.
8-184.108.40.206.2 Compaction Testing. Compaction test procedures are described in detail in
ASTM D 1557 (app. A.) It is important that the designer and field inspection personnel
understand the basic principles and fundamentals of soil compaction. The principles of soil
compaction are discussed in appendix B of this manual.
The purpose of the laboratory compaction tests is to determine the compaction
characteristics of available backfill materials. Also, anticipated field density and water content
can be approximated in laboratory compacted samples in order that other engineering
properties, such as shear strength, compressibility, consolidation, and swelling, can be
studied. For most soils there is an optimum water content at which a maximum density is