Volume 6 – Geotechnical Manual, Site Investigation and Engineering ...

Chapter 3 IN-SITU GEOTECHNICAL TESTING
selection of vanes is available in terms of size, shape, and configuration, depending upon the
consistency and strength characteristics of the soil. The standard vane has a rectangular geometry
with a blade diameter D = 65 mm, height H = 130 mm (H/D =2), and blade thickness e = 2 mm.
Fig. 3.12 illustrates the general VST procedures
Figure 3.12 General Test Procedures for the Field Vane in Fine-Grained Soils. (Note: Interpretation of
Undrained Strength Shown Is Specifically For Standard Rectangular Vane with H/D = 2)
The general advantages and disadvantages of VST is summarised in Table 3.4 as follows.
Table 3.4 General Advantages and Disadvantages of VST
Advantages
Assessment of undrained strength, s uv
Simple test and equipment
Measure in-situ clay sensitivity (S t )
Long history of use in practice
Disadvantage
Limited application to soft to stiff clays
Slow and time-consuming
Raw s uv needs (empirical) correction
Can be affected by sand lenses and seams
By implication, BS 1377 considers that the field vane will not be suitable for testing soils with
undrained strengths greater than about 75 kPa. The vane must be designed to achieve an area ratio
of 12% or less. The test is not suitable for fibrous peats, sands or gravels, or in clays containing
laminations of silt or sand, or stones.
3-16 March 2009