TABLE 6
Methods of Reducing or Accelerating Settlement or Coping with Settlement
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*
*
*
Method
Comment
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*Procedures for linear fills on *
*
*
*
* swamps or compressible
* surface stratum:
*
*
*
*
*
*Excavation of soft material....* When compressible foundation soils extend to *
*
*
*
depth of about 10 to 15 ft, it may be
*
*
practicable to remove entirely. Partial *
*
*
removal is combined with various methods *
*
*
*
of displacing remaining soft material.
*
*
*
*Displacement by weight of fill.* Complete displacement is obtained only when *
*
*
compressible foundation is thin and very *
*
*
*
soft. Weight displacement is combined
*
*
*
with excavation of shallow material.
*
*
*
*Jetting to facilitate
*
*
*
displacement................* For a sand or gravel fill, jetting within
*
*
*
*
the fill reduces its rigidity and
*
*
*
promotes shear failure to displace soft
*
*
*
foundation. Jetting within soft
*
*
*
foundation weakens it to assist in
*
*
*
displacement.
*
*
*
*Blasting by trench or shooting *
*
*
methods.....................* Charge is placed directly in front of
*
*
*
advancing fill to blast out a trench into *
*
*
which the fill is forced by the weight of *
*
*
surcharge built up at its point. Limited *
*
*
*
to depths not exceeding about 20 ft.
*
*
*
*Blasting by relief method......* Used for building up fill on an old roadway *
*
*
*
or for fills of plastic soil. Trenches
*
*
*
are blasted at both toes of the fill
*
*
slopes, relieving confining pressure and *
*
*
*
allowing fill to settle and displace
*
*
*
underlying soft materials.
*
*
*
*Blasting by underfill method...* Charge is placed in soft soil underlying
*
*
*
*
fill by jetting through the fill at a
*
*
*
preliminary stage of its buildup.
*
*
*
Blasting loosens compressible material,
*
*
accelerating settlement and facilitating *
*
*
displacement to the sides. In some cases *
*
*
relief ditches are cut or blasted at toe *
*
*
of the fill slopes. Procedure is used in *
*
*
*
swamp deposits up to 30 ft thick.
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7.1-242
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