Do we have any laboratory tests to determine the undrained residual strength parameters ? We use reversal direct shear test or ring shear test to determine residual strength, but in general both of these tests give drained strength parameters. Can we use a ring shear test to determine undrained residual strength parameters?
You can determine untrained residual strength parameters by triaxial test. And also, there is a standard by ASTM which states the standard test method for consolidated undrained direct simple shear testing of fine grain soils ( ASTM D 6528-17) , known as constant volume direct simple shear test, with that you may measure the undrained residual strength. But, as the direct shear test has a limitation of drainage control/pore pressure measurement , I think undrained strength by this test is less reliable than triaxial test.
The undrained residual strength parameter, as well as pore water pressure generation in undrained conditions, can be measured by using the undrained ring shear apparatus. This type of apparatus was developed by Prof Kyoji Sassa (he was my Ph.D. supervisor) from Kyoto University with his colleagues and now replicate also in some other countries. You can check their publications in several journals e.g. Landslides, Canadian Geotech Journal, Engineering Geology, etc. The distinctive feature of this apparatus is that the measurement of residual strength parameters can be done after failure with large shear displacement (up to meters). You can set the sample in normally consolidated or over-consolidated. That feature somehow cannot be deal with if we use direct shear or triaxial (even though triaxial is powerful for undrained condition). If you wish to conduct, you can contact the Research Centre on Landslides in Disaster Prevention Research Institute (DPRI) of Kyoto University.
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