Vane Shear Test (VST):
The undrained shear strength from a vane shear test is calculated from
where T is the maximum torque, h is the height, and d is the diameter of the vane.
The Standard Penetration Test (SPT):
Results from SPT (Chapter 3) have been correlated to several soil parameters. Most of these correlations are weak. Typical correlation among N values, relative density, and f9 are given in Tables . You should be cautious in using the correlation in Table. SPTs are not recommended for fi ne-grained soils, so the correlation should be used only to provide an assessment of the relative shear strength of fi ne-grained soils.
Cone Penetrometer Test (CPT):
The cone resistance qc is normally correlated with the undrained shear strength. Several adjustments are made to qc. One correlation equation is
where Nk is a cone factor that depends on the geometry of the cone and the rate of penetration. Average values of Nk as a function of plasticity index can be estimated from
Results of cone penetrometer tests have been correlated with the peak friction angle. A number of correlations exist. Based on published data for sand (Robertson and Campanella, 1983), you can estimate f9p using
THE ESSENTIAL POINTS ARE:
1. Various fi eld tests are used to determine soil strength parameters.
2. You should be cautious in using these correlations of fi eld test results, especially SPT, with soil strength parameters in design.