The Delft Sand, Clay & Rock Cutting Model, 2019a

2.6.5.1. Consolidated Drained (CD).
Basic Soil Mechanics.
In a consolidated drained test the sample is consolidated and sheared in compression with drainage. The rate of
axial deformation is kept constant, i.e. is strain controlled. The idea is that the test allows the sample and the pore
pressures to fully consolidate (i.e. adjust) to the surrounding stresses. The test may take a long time to allow the
sample to adjust, in particular low permeability samples need a long time to drain and adjust stain to stress levels.
2.6.5.2. Consolidated Undrained (CU).
In a consolidated undrained test the sample is not allowed to drain. The shear characteristics are measured under
undrained conditions and the sample is assumed to be fully consolidated under the stresses applied that should be
similar to the field conditions. Test in particular used if a change in stress is to happen without time for further
consolidation.
2.6.5.3. Unconsolidated Undrained (UU).
In an unconsolidated undrained test the sample is not allowed to drain. The sample is compressed at a constant
rate (strain-controlled).
2.6.6. Shear Test.
Figure 2-36: The Triaxial apparatus cross-section (civilblog.org).
A direct shear test also known as shear box test is a laboratory or field test used by geotechnical engineers to
measure the shear strength properties of soil or rock material, or of discontinuities in soil or rock masses. For soil
the U.S. and U.K. standards defining how the test should be performed are ASTM D 3080 and BS 1377-7:1990
respectively to establish the shear strength properties of soil. It is also possible to estimate typical values of the
shear strength parameters based on the type and classification of the soils. For rock the test is generally restricted
to rock with (very) low (shear) strength. The test is, however, standard practice to establish the shear strength
properties of discontinuities in rock.
Copyright © Dr.ir. S.A. Miedema TOC Page 49 of 454