TM 5-818-4/AFM 88-5, Chap. 5
CHAPTER 3
EVALUATION, DESIGN, AND PROCESSING
OF BACKFILL MATERIALS
3-1. General. The evaluation, design, and proper
plans the detailed field exploration program must
have knowledge of the structure, i.e., its configuration
processing of backfill materials are extremely impor-
and foundation requirements for design loads and set-
tant phases of the preconstruction operations. The
tlement tolerances. The planning engineer should also
purpose of the evaluation phase is to determine the en-
know the type and quantity of backfill required. The
gineering characteristics of potential backfill materi-
importance of employing qualified field exploration
als. The design phase must take into account the engi-
personnel cannot be overemphasized. The exploration
neering characteristics required of the backfill and
crews should be supervised in the field by a soils engi-
specify materials that, when compacted properly, will
neer or geologist familiar with the foundation and
have these characteristics. Proper processing of the
backfill requirements so that changes can be made in
backfill material will ensure that desirable engineering.
the exploration program where necessary to provide
characteristics will be obtained as the material is
adequate information on subsurface conditions.
placed.
(2) The field engineer should also know the loca-
3-2. Evaluation of backfill materlals.
tion of significant features of the structure so that
Evaluation of backfill materials consists of explora-
sampling can be concentrated at these locations. In ad-
tion, sampling, and laboratory testing to determine
dition, he should have an understanding of the engi-
the engineering characteristics of potential backfill
neering characteristics of subsurface soil and rock de-
materials. Detailed instructions for exploration, sam-
posits that are important to the design of the structure
pling, laboratory testing, and foundation design are
and a general knowledge of the testing program so
presented in TM 5-818-1/AFM 88-3, Chapter 7. How-
that the proper type and quantity of samples will be
ever, to emphasize the need for an adequate investiga-
obtained for testing.
tion, some aspects of planning and investigation that
(3) From the samples, the subsurface deposits can
should be considered are discussed in the following
be classified and boring logs prepared. The more con-
paragraphs.
tinuous the sampling operation, the more accurate will
be the boring logs. All borings should be logged with
a. Field exploration and sampling. Field exploration
the description of the various strata encountered as
and sampling are extremely important to the design of
discussed in TM 5-818-1/AFM 88-3, Chapter 7. Accu-
foundations, selection of backfill, and planning for
rate logging and correct evaluation of all pertinent in-
construction. A great amount of material will be avail-
formation are essential for a true concept of subsur-
able from required excavations, and the investigation
face conditions.
for foundation conditions should include the sampling
(4) When the exploratory borings at the construc-
and evaluation of these materials for possible use as
backfill. Where an adequate volume of suitable back-
tion site have been completed, the samples and logs of
borings should be examined to determine if the materi-
fill cannot be obtained from the construction excava-
tion, the exploration and sampling program must be
al to be excavated will be satisfactory and in sufficient
quantity to meet backfill requirements. Every effort
expanded to find other sources of suitable material
should be made to use the excavated materials; how-
whether from nearby borrow areas or commercial
ever, if the excavated materials are not satisfactory or
sources.
are of insufficient quantity, additional exploration
(1) The purpose of the investigation is to delineate
should be initiated to locate suitable borrow areas. If
critical conditions and provide detailed information on
borrow areas are not available, convenient commercial
the subsurface deposits so that proper design and con-
sources of suitable material should be found. Backfill
struction, including backfilling operations, can be ac-
sources, whether excavation, borrow, or commercial,
complished with minimum difficulty. Thus careful
should contain several times the required volume of
planning is required prior to the field exploration and
sampling phase of the investigation. Available geo-
compacted backfill.
logic and soil data should be studied, and if possible,
(5) Groundwater studies prior to construction of
preliminary borings should be made. Once a site has
subsurface structures are of the utmost importance,
been tentatively selected, orientation of the structure
since groundwater control is necessary to provide a
to the site should be established. The engineer who
dry excavation in which construction and backfilling
3-1
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