Immediate settlement [delta]+v, is estimated as:
+
,
* 1-[gamma]+2, *
[delta]+v, = q B * )))))))))))))* I
* E+u,
*
.
-
q is applied uniform pressure; B is width of loaded area; I is combined
shape and rigidity factor; [gamma] is Poisson's ratio - ranges between 0.3
and 0.5, the higher value being for saturated soil with no volume change
during loading; and E+u, is undrained modulus obtained from laboratory or
field (pressuremeter) tests. Table 1 (Reference 1, Stresses and Deflections
in Foundations and Pavements, by Department of Civil Engineering, University
of California, Berkeley) provides values of I. Empirical relationship
derived from field measurement may be used to determine E+u, when actual
test values are not available; see Table 2 (adapted from Reference 2, An
Engineering Manual For Settlement Studies, by Duncan and Buchignani).
Empirical correlations for estimation of OCR (Over Consolidation Ratio) are
presented in Chapter 3.
If the factor of safety against bearing failure (see DM-7.2, Chapter 4)
is less than about 3, then the immediate settlement [delta]+v, is modified
as follows:
[delta]+c, = [delta]+v/SR,
[delta]+c, = immediate settlement corrected to allow
for partial yield condition
SR
= Settlement Ratio
Determine SR from Figure 4 (Reference 3, Initial Settlement of Structures
on Clay, by D'Appolonia, et al.). See Figure 5 for an example.
2. SETTLEMENT OF COARSE-GRAINED SOILS. This immediate settlement is a
function of the width and depth of footing, elevation of the water table,
and the modulus of vertical subgrade reaction (K+VI,) within the depth
affected by the footing. Figure 6 may be used to estimate K+VI, from the
soil boring log, and to compute anticipated settlement.
For large footings where soil deformation properties vary significantly
with depth or where the thickness of granular soil is only a fraction of the
width of the loaded area, the method in Figure 6 may underestimate
settlement.
3. TOTAL SETTLEMENT IN GRANULAR SOILS. Total settlement is the combined
effect of immediate and long-term settlements. A usually conservative
estimate of settlement can be made utilizing the method in Figure 7
(Reference 4, Static Cone to Compute Static Settlement Over Sand, by
Schmertmann). A review of methods dealing with settlement of sands
utilizing the standard penetration test results can be found in Reference 5,
Equivalent Linear Model for Predicting Settlements of Sand Bases, by Oweis.
7.1-211
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