Environmental Engineering Reference
In-Depth Information
FIGURE 3.55
Pocket penetrometer applied to a Shelby
tube specimen.
Geotechnical Institute (Aas, 1965) to evaluate anisotropy approximately. Relating s u as
measured by the field vane to s u as measured in triaxial tests, Bjerrum et al. (1972) found
that:
s u (compression)
1.5 s u (vane).
s u (extension)
0.5 s u (vane) in low- to medium-PI clays.
s u (extension)
1.0 s u (vane) in highly plastic clays.
Field vane loading time rate is very rapid compared with actual field loadings, and dur-
ing construction values are generally lower (Section 3.4.2) . Rate correction factor
is pro-
posed as a function of plasticity ( Figure 3.57) by Bjerrum et al. (1972) as found by the
analyses of a number of embankment failures constructed over soft clays.
µ
Borehole Shear Test (BST)
The borehole shear test (See Section 3.4.3) in soils is similar to the rock test, except that it
is a staged test and the soil reconsolidates after it is sheared, moving the shear surface out-
ward into fresh soil. In addition, the shear plate teeth are continuous rather than two car-
bide teeth, and regulated pressure from refillable CO 2 cylinders is used to expand the
plates tightly to the hole sides (Wineland, 1975). For greater portability, a hand pump may
also be used. Drainage is rapid, and the test is designed to be a drained test that yields
effective stress shear strength parameters. BST applications for bridge foundation design
is described by Handy et al. (1985) and for slope stability by Handy (1986). Because the
strength is measured vertically along a borehole it is particularly useful in obtaining val-
ues applicable to shaft friction along a pile. Very hard soils are tested using a two-teeth
adaption of the rock tester shear plates.
 
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