TABLE 6 (continued)
Methods of Reducing or Accelerating Settlement or Coping with Settlement
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*
*
*
Method
Comment
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*Procedures for preconsolidation*
*
*
*
*of soft foundations:
* Surcharge fill.............. *Used where compressible stratum is
*
*
*
*
relatively thin and sufficient time is
*
*
*
available for consolidation under
*
*
*
surcharge load. Surcharge material may
*
*
*
be placed as a stockpile for use later
*
*
*
in permanent construction. Soft
*
*
*
foundation must be stable against shear
*
*
*
failure under surcharge load.
*
*
*
*
*vertical drains............... *Used where tolerable settlement of the
*
*
*
*
completed structure is small, where time
*
*
*
available for preconsolidation is
*
*
limited, and surcharge fill is reasonably *
*
*
*
economical. Soft foundation must be
*
*
*
stable against shear failure under
*
*
*
surcharge load.
*
*
*
*Vertical sand drains with or
*
*
*without surcharge fill........ *Used to accelerate the time for
*
*
*
*
consolidation by providing shorter
*
*
*
drainage paths.
*
*
*
*Wellpoints placed in vertical *
*
*
*
*
the water head, thereby permitting
*
*
*
increased flow into the sand drains.
*
*
*
Particularly useful where potential
*
*
*
instability of soft foundation restricts
*
*
*
placing of surcharge or where surcharge
*
*
*
is not economical.
*
*
*
*Vacuum method................. *Variation of wellpoint in vertical sand drain *
*
*
but with a positive seal at the top of the *
*
*
sand drain surrounding the wellpoint pipe. *
*
*
Atmospheric pressure replaces surcharge in *
*
*
*
consolidating soft foundations.
*
*
*
*Balancing load of structure
*
*
*by excavation................. *Utilized in connection with mat or raft
*
*
*
*
foundations on compressible material or
*
*
where separate spread footings are founded *
*
*
*
in suitable bearing material overlying
*
*
compressible stratum. Use of this method *
*
*
*
may eliminate deep foundations, but it
*
*
*
requires very thorough analysis of soil
*
*
*
compressibility and heave.
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7.1-243
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