15 AUGUST 2005
structures. The specified degree of compaction should be commensurate with the tolerable
amount of settlement, and the compaction equipment used should be commensurate with the
allowable lateral pressure on the structure. Drainage blankets and filters having special
gradation requirements should be compacted to within 95 to 100 percent of ASTM D 1557
maximum dry density. Table 8-5.1 gives a summary of type of compaction equipment,
coverage, and lift thickness for the specified degree of compaction of various soil types.
Cold Weather. In areas where freezing temperatures either hamper or halt
construction during the winter, certain precautions can, and should, be taken to prevent
damage from frost penetration and subsequent thaw. Some of these precautions are
Placement of permanent backfill should be deferred until favorable weather
conditions prevail. However, if placement is an absolute necessity during
freezing temperatures, either dry, cohesionless, non frost-susceptible materials
or material containing additives, such as calcium chloride, to lower the freezing
temperature of the soil water should be used. Each lift should be checked for
frozen material after compaction and before construction of the next lift is begun.
If frozen material is found, it should be removed; it should not be disked in place.
Additives should not be used indiscriminately since they will ordinarily change
compaction and water content requirements. Prior laboratory investigation
should be conducted to determine additive requirements and the effect on the
compaction characteristics of the backfill material.
Under no circumstances should frozen material, from stockpile or borrow pit, be
placed in backfill that is to be compacted to a specified density.
Prior to halting construction during the winter, the peripheral surface drainage
system should be checked and reworked where necessary to provide positive
drainage of surface water away from the excavation.
Foundations beneath structures and backfill around structures should not be
allowed to freeze, because structural damage will invariably develop. Structures
should be enclosed as much as possible and heated if necessary. Construction
should be scheduled so as to minimize the amount of reinforcing steel protruding
from a partially completed structure since steel will conduct freezing
temperatures into the foundation.
Permanent backfill should be protected from freezing. Records should be made
of all temporary coverings that must be removed before backfilling operations are
resumed. A checklist should be maintained to ensure that all temporary
coverings are removed at the beginning of the next construction season.
During freezing weather, records should be kept of the elevation of all critical
structures to which there is the remotest possibility of damage or movement due
to frost heave and subsequent thaw. It is important that frost-free benchmarks
be established to which movement of any structure can be referenced.
Benchmarks also should be established on the structures at strategic locations