TM 5-818-4/AFM 88-5, Chap. 5
tion. The procedure using the Proctor penetrometer
gypsum or highly metallic soils such as iron ore, alu-
for determining the relation between wet density,
minum rich soils, and bauxite. Details of the micro-
penetration resistance, and water content is described
wave-oven method used for rapid determination of soil
in ASTM D 1558 and in section B-3, appendix B. The
water content is given in section B-3, appendix B.
hand cone penetrometer procedure also is discussed in
f. Frequency and location of quality acceptance
section B-3.
density tests. Acceptance control testing should be
(c) Many inspectors in the past have had good
more frequent at the start of backfill placement. After
success in estimating density by simply observing the
compaction effort requirements have been firmly es-
resistance of the compacted soil to penetration by a
tablished and inspection personnel have become famil-
spade. This method requires considerable experience
iar with materials behavior and acceptable compaction
and is useful only in detecting areas that might require
procedures, the amount of testing can be reduced.
further density tests.
Many factors influence the frequency and location of
(3) Direct methods. Direct field density deter-
tests. The frequency will be dependent on the type of
mination consists of volume and weight measurements
material, adequacy of the compaction procedures, and
to determine the wet density of in-place backfill and
how critical the backfill being compacted is in relation
water content measurements to determine in-place wa-
to the performance of the structure.
ter contents and dry densities. The three methods used
(1) A systematic testing program should be estab-
for the Corps quality acceptance density determina-
lished at the beginning of the job. Acceptance control
tion are: (a) the sand-cone method according to
tests laid out in a predetermined manner are usually
MIL-STD-621 (Method 106) and ASTM D 1556;
designated as routine control tests and are performed
(b) the rubber-balloon method according to ASTM D
either at designated locations or at random representa-
2167; and for soft, fine-grained cohesive soils, the
tive locations, no matter how smoothly the compaction
drive-cylinder method according to MIL-STD-621
operations are being carried out. A routine acceptance
(Method 102) and ASTM D 2937. In addition to the ap-
control test should be conducted for at least every 200
proved methods, a method sometimes employed to
cubic yards of compacted backfill material in critical
measure densities of coarse-grained cohesionless mate-
areas where settlement of backfill may lead to struc-
rial consists of the large-scale, water-displacement
tural distress and for at least every 500 cubic yards in
method. The large-scale, water-displacement method
open areas not adjacent to structures.
is discussed in EM 1110-2-1911. The sand cone
(2) In addition to routine acceptance control tests,
method is considered to be the most reliable method
tests should be made in the following areas: where the
and is recommended as the proof or calibration test for
inspector has reason to doubt the adequacy of the com-
calibrating other methods such as the nuclear density
paction; where the contractor is concentrating fill
method. The direct field density methods are discussed
operations over relatively small areas; where small
in section B-3, appendix B.
compaction equipment is being used such as in con-
e. Water content by microwave oven. The biggest
fined areas; and where field instrumentation is in-
problem associated with both field compaction tests
stalled, mainly around riser pipes.
and in-place density and water content control tests is
the length of time required to determine water con-
g. Errors in field density measurements. Density
tent. Conventional ovendrying methods require from
and water content measurements determined by any
15 to 16 hours for most fine-grained cohesive soils. In
of the methods discussed above are subject to three
some cases, such as confined zones, the contractor may
possible sources of errors. The three categories of
have placed and compacted several layers of backfill
possible error sources are human errors, errors asso-
over the layer for which density tests were made be-
ciated with equipment and method, and errors attrib-
fore quality acceptance test data are available. Even
uted to material property behavior.
though the contractor places successive layers at his
(1) Human error includes such factors as improper
own risk, a rapid turn around between testing and test
equipment readings and following improper test pro-
results could prevent costly-tear out and recompact
cedures. Human errors are not quantitative. However,
procedures. Drying specimens in microwave ovens of-
errors of this type may be minimized by utilizing com-
fers a practical means for rapid determination of wa-
petent testing personnel familiar with testing proce-
ter content for most backfill materials if properly con-
dures.
ducted. Times required for drying in a microwave oven
(2) There are two types of possible errors related
are primarily governed by the mass of water present in
to test equipment. One type of error relates to the
the specimen and the power-load output of the oven.
sensitivity of the equipment with respect to its capa-
Therefore, drying time must be calibrated with respect
bility to accurately measure the true density or water
to water content and oven output. Also, it may not be
content. Sensitivity errors are quantitative only in the
possible to successfully dry certain soils containing
sense that limiting ranges of possible error can be es-
7-6
Previous Page
