TM 5-818-4/AFM 88-5, Chap. 5
operations can be properly conducted. Data on ground-
density except that the California Bearing Ratio (CBR)
water conditions are also essential for forecasting con-
and the subgrade modulus are based on CE 55 maxi-
struction dewatering requirements and stability prob-
mum density. This information can be used for initial
lems. Groundwater studies must consist of investiga-
design studies. However, for final design of important
tions to determine: groundwater levels to include any
structures, laboratory tests are required to determine
seasonal variations and artesian conditions; the loca-
actual performance characteristics, such as CE 55
tion of any water-bearing strata; and the permeability
compaction properties, shear strength, permeability,
and flow characteristics of water-bearing strata. Meth-
compressibility, swelling characteristics, and frost sus-
ods for investigating groundwater conditions are de-
ceptibility where applicable, under expected construc-
scribed in TM 5-818-1/AFM 88-3, Chapter 7, and TM
tion conditions.
5-818-5/NAVFACP-418/AFM 88-5, Chapter 6.
(c) The Unified Soil Classification System is
particularly useful in evaluating, by visual examina-
b. Laboratory testing. The design of any foundation
tion, the suitability of potential borrow materials for
is dependent on the engineering characteristics of the
use as compacted backfill. Proficiency in visual clas-
supporting media, which may be soil or rock in either
sification can be developed through practice by com-
its natural state or as compacted backfill. The labora-
paring estimated soil properties with results of labora-
tory testing program will furnish the engineer infor-
tory classification tests.
mation for planning, designing, and constructing sub
(2) Compaction testing. Compaction test proce-
surface structures. Laboratory testing programs usual-
dures are described in detail in MIL-STD-621 and
ly follow a general pattern and to some extent can be
ASTM D 1557 (app. A). It is important that the de-
standardized, but they should be adapted to particular
signer and field inspection personnel understand the
problems and soil conditions. Special tests and re-
basic principles and fundamentals of soil compaction.
search should be utilized when necessary to develop
The principles of soil compaction are discussed in ap-
needed information. The testing program should be
pendix B of this manual.
well planned with the engineering features of the
(a) The purpose of the laboratory compaction
structure and backfill in mind; testing should be con-
tests are to determine the compaction characteristics
centrated on samples from areas where significant fea-
of available backfill materials. Also, anticipated field
tures will be located but should still present a complete
density and water content can be approximated in lab
picture of the soil and rock properties. The laboratory
oratory-compacted samples in order that other engi-
test procedures and equipment are described in TM
neering properties, such as shear strength, compressi-
5-818-1/AFM 88-3, Chapter 7, EM 1110-2-1906,
bility, consolidation, and swelling, can be studied. For
and MIL-STD-621.
most soils there is an optimum water content at which
(1) Identification and classification of soils. The
a maximum density is obtained with a particular com-
Unified Soil Classification System used for classifying
paction effort. A standard five-point compaction curve
soils for military projects (MIL-STD-619 and TM
relating density and water content (fig. B-1, app. B)
5-818-1/AFM 88-3, Chap. 7) is a means of identifying
can be developed by the procedures outlined in MIL-
a soil and placing it in a category of distinctive engi-
STD-621.
neering properties. Table 3-1 shows the properties of
(b) The impact compaction test results normally
soil groups pertinent to backfill and foundations.
constitute the basis on which field compaction control
Using these characteristics, the engineer can prepare
criteria are developed for inclusion in the specifica-
preliminary designs based on classification and plan
tions. However, for some cohesionless soils, higher
the laboratory testing program intelligently and eco-
densities can be obtained by the vibratory compaction
nomically.
method (commonly referred to as maximum relative
(a) The Unified Soil Classification System clas-
density), described in appendix XII of EM 1110-2-
sifies soils according to their grain-size distribution
1906. The required field compaction is generally speci-
and plasticity characteristics and groups them with re-
fied as a percentage of laboratory maximum dry densi-
spect to their engineering behavior. With experience,
ty and referred to as percent CE 55 maximum density.
the plasticity and gradation properties can be esti-
Water content is an important controlling factor in ob-
mated using simple, expedient tests (see table 2-2 and
taining proper compaction. The required percentage of
2-3 of TM 5-818-1/AFM 88-3, Chap. 7 or AFM 89-3,
maximum dry density and the compaction water con-
Chap. 2) and these estimates can be confirmed using
tent should be selected on the basis of the engineering
simple laboratory tests. The principal laboratory tests
characteristics, such as compression moduli, settle-
performed for classification are grain-size analyses
ment, and shear strength, desired in the compacted
and Atterberg limits.
backfill. It should be noted that these characteristics
(b) The engineering properties in table 3-1 are
could be adversely effected by subsequent increases in
based on "Standard Proctor" (CE 25) maximum
3-2
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