a. Standard Proctor Test. Use standard Proctor tests for ordinary
embankment compaction control. In preparing for control, obtain a family of
compaction curves representing principal borrow materials.
b. Modified Proctor Test. Specially applicable to either a heavily
compacted base course or a subgrade for airfield pavement and may also be
used for mass earthwork.
c. Relative Density of Cohesionless Soils. Proctor tests are often
difficult to control for free-draining cohesionless soils and may give
erratic compaction curves or density substantially less than those provided
by ordinary compaction in the field (see Reference 28, Soil Mechanics, by
Lambe and Whitman). Thus, relative density methods may be preferred. Tests
for maximum and minimum densities should be done in accordance with ASTM
Standard D2049, Relative Density of Cohesionless Soils (Table 3).
3. STRUCTURAL PROPERTIES. Structural properties of compacted-fill
materials classified in the Unified System are listed in DM-7.2, Chapter 2,
4. CALIFORNIA BEARING RATIO (CBR). This test procedure covers the
design for highways and airfields. The resistance of a compacted soil to
the gradual penetration of a cylindrical piston with 3 square inches in area
is measured. The load required to cause either 0.1 inch or 0.2 inch
penetration of the piston is compared to that established for a standard
compacted crushed stone to obtain the bearing ratio. (See DM-21.03 for
approximate relationships between soil type and CBR.) For guidance for
design of subbase and bases, see DM-5.04 and DM-21.03.
TESTS ON ROCK
1. STRUCTURAL TESTS. Standard methods of testing rock in the laboratory
for structural characteristics are only for intact rock. See Table 8 for
testing procedures. Behavior of in situ rock, which typically has bedding
planes, joints, etc., and may contain discontinuities filled with weaker
material, is found to be very different from that of intact rock. In situ
tests of joint strengths and compressibility are, therefore, more
appropriate. See Chapters 1 and 2 for rock and rock joint classifications
and in situ measurements of their properties. The use of data from
laboratory tests for bearing and settlement calculations of shallow and deep
foundations is shown in DM-7.02 Chapters 4 and 5. Factors which correlate
intact rock sample parameters to realistic field parameters are RQD (Rock
Quality Designation) or the ratios of field values to laboratory values of
compression or shear wave velocities (see Chapters 1 and 2).
Change 1, September 1986