Practical Foundation Engineering Handbook_下.pdf

文档介绍：NONGROUTING TECHNIQUES
NONGROUTING TECHNIQUES
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3. v2i should be replaced in Eq. with vi(t), with vi(t) calculated as follows:
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vi(t) = v1i + Uzi · vi ()
where Uzi is the consolidation ratio at the midheight of the ith sublayer, which can be calculated as
m=ϱ 2 Mz
i 2
ᎏᎏ–M Tv
Uz = 1 –Α 2 · sin · e ()
m=0 M Hdp
where zi is the depth from the top of the clay layer to the midheight of the ith sublayer.
It is sometimes difficult to determine Hdp reliably, especially in highly stratified soils containing
alternating layers of cohesive and cohesionless soils, such as varved clays. In these types of soils, it
must be determined whether or not the cohesionless layers are continuous across the site. This deter-
mination requires that extensive boring and sampling be conducted. If the cohesionless layers are
continuous, they will act as drainage layers and Hdp will be considerably reduced. Otherwise their
effect on Hdp will be minimal unless vertical drains are installed.
pression with Additional Surcharge
The pression process can be achieved much quicker in saturated clays if additional sur-
charge is used above that required for simple pression. This method is especially attractive
when the structure to be built on the site is a permanent embankment, such as for highway and
railroad applications. Three possible ways to construct the additional surcharge are illustrated in
Fig. .
The critical factor in essful application of this technique is determining the appropriate time
when the surcharge should be removed (tsr). Proper determination of tsr depends on a thorough un-
derstanding how the pore pressures and effective stresses change in the clay layer as the permanent
and surcharge embankments are constructed, while the additional surcharge is in place, and after the
surcharge is removed.
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Total vertical stress ( v ), pore water pressure (u), and effective ve