UFC 4-150-07
19 June 2001
particularly important where soil grids are used for the express purpose of
reinforcing or strengthening the soil mass.
10-3.2.3 Compaction Control. The performance of soil embankments
improves with density, so fill materials should generally be placed at as high a
density as is economically feasible, particularly with the finer-grained soils at a
density of at least 90% Proctor (ASTM D 698, see below). Where the soil will be
subjected to heavy loads, or where settlement of the fill would be undesirable,
soil density should be increased, even up to 100% modified Proctor (ASTM D
1557, see below). There is a specific moisture content for each soil type at which
the maximum density is obtained under a specific compaction effort. Therefore,
moisture control is an important factor in efficient compaction techniques,
particularly with silts, clays, and mixed soils.
10-3.2.3.1 Compaction Control Standards. The two most common standards
for compaction control are the standard Proctor (ASTM D 698, Laboratory
Compacting Characteristics of Soil Using Standard Effort) and the modified
Proctor (ASTM D 1557, Laboratory Compaction Characteristics of Soil Using
Modified Effort) tests. The latter method represents a larger compactive effort
than the former and has been adopted to account for the higher compactive
capability of modern construction equipment. However, the standard considered
most pertinent for waterfront structures is still the standard Proctor. This is
because the lower compactive effort results in a slightly higher optimum moisture
content for maximum density, and the higher moisture content is more
compatible with the expected in-service conditions of waterfront structures.
10-3.2.3.2 Compaction Selection. The type of compaction selected should be
based on the soil type. Vibratory compaction is more efficient with granular soils,
whereas kneading types of equipment, such as sheepsfoot rollers, are more
applicable to cohesive soils. Vibratory rubber-tired compactors in the 11- to 14-
metric ton range are reasonably effective for all types of soil. Soil lifts should
generally be limited to layers having a compacted thickness of no more than 15
cm, except where it has been demonstrated that the compactors are capable of
achieving the required densities throughout the full depth of thicker lifts. Such a
situation might exist with a vibratory compactor on relatively clean, non-cohesive
material. For backfilling sheet pile cofferdams or other structures with limited
space, it may be necessary to use small hand-operated tampers or compactors.
The difficulty of compaction generally increases with the decrease in grain size of
the soil.
10-3.2.3.3 Compaction Requirements. A typical requirement for many
waterfront structures is to specify a compacted density of 95 percent of standard
Proctor, but this may vary with the type of structure and its present condition. It is
desirable to place a soil material in a structure in as close to its long-term stable
condition as possible. Although clean, granular materials should be placed in as
saturated a condition as is practicable, fine-grained or mix-grained soils may
require moisture contents to be maintained within a particular optimum range.
10-3
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