UFC 3-220-01N
15 AUGUST 2005
o Where excavations are subjected to vibrations from railroad or
highway traffic, operation of machinery, or any other source.
Employees entering bell-bottom pier holes shall be protected by the
installation of a removable-type casing of sufficient strength to resist
shifting of the surrounding earth. Such temporary protection shall be
provided for the full depth of that part of each pier hole that is above the
bell. A lifeline, suitable for instant rescue and securely fastened to the
shafts, shall be provided. This lifeline shall be individually manned and
separate from any line used to remove materials excavated from the bell
footing.
Minimum requirements for trench timbering shall be in accordance with
Table 8-1.3.
Where employees are required to be in trenches 3 ft deep or more,
ladders shall be provided which extend from the floor of the trench
excavation to at least 3 feet above the top of the excavation. They shall
be located to provide means of exit without more than 25 ft of lateral
travel.
Bracing or shoring of trenches shall be carried along with the excavation.
Cross braces or trench jacks shall be placed in true horizontal position,
spaced vertically, and secured to prevent sliding, falling, or kickouts.
Portable trench boxes or sliding trench shields may be used for the
protection of employees only. Trench boxes or shields shall be designed,
constructed, and maintained to meet acceptable engineering standards.
Backfilling and removal of trench supports shall progress together from the
bottom of the trench. Jacks or braces shall be released slowly, and in
unstable soil, ropes shall be used to pull out the jacks or braces from
above after employees have cleared the trench.
8-1.6
Embankment Cross-Section Design
8-1.6.1
Influence of Material Type. Table 8-1.4 lists some typical properties of
compacted soils that may be used for preliminary analysis. For final analysis
engineering property tests are necessary. See Table 8-1.5 for relative desirability of
various soil types in earth fill dams, canals, roadways and foundations. Although
practically any non-organic insoluble soil may be incorporated in an embankment when
modern compaction equipment and control standards are employed, the following soils
may be difficult to use economically:
Fine-grained soils may have insufficient shear strength or excessive
compressibility.
Clays of medium to high plasticity may expand if placed under low
confining pressures and/or at low moisture contents. See UFC3-220-10N,
for identification of soils susceptible to volume expansion.
8-18
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