Evaluation of the Clay Cutting Test - Assessment of a new method for measuring undrained shear strength in soils through comparative testing

Abstract

The Clay Cutting Test (CC-Test) is a newly developed laboratory method to assess the undrained shear strength of soil samples. Unlike other tests that provide a single value of strength, the CC-Test presents a continuous strength profile by measuring the resistance as a thin wire cuts through the soil sample. This thesis evaluates the CC-Test through a combination of archive data comparison and in-depth study of strength profiles from clay samples of varying depths. In the archive compilation, representative values of shear strength from the CC-Test were compared to those obtained with direct simple shear (DSS) and fall cone test. For strengths below 25 kPa a good agreement between the methods was observed. At higher strengths, the fall cone becomes less reliable and the DSS data are limited. A parameter study indicated that density, water content and thread diameter have an impact on the measured resistance. However, in the range of typical soils, the deviation of the parameters is within ± 10% of the measured strength. The in-depth analysis focused on 12 stiffer clay samples from 7-35 m depth. For each sample, uniaxial compression test (UCT), CC-Test and fall cone test were conducted on the same specimen, to minimize deviation due to natural variation of the soil. The CC-Test yielded higher values than the fall cone and generally lower than the UCT. For samples below 20 m, even the upper quartile of the CC-Test strength profile could be considered conservative compared to UCT. The correlation between the CC-Test measurements and the UCT was strongest near the locations corresponding to the ends of the shear plane. In some tests, oscillating patterns appeared in the measured strength curves, implying an effect of minor material changes within the soil. These patterns were also present in reference tests, indicating they are not caused by prior loading or sample disturbance. The CC-Test shows potential as a complement to established methods for deter mining undrained shear strength due to its simple setup, fast execution, and ability to present strength variation within the soil specimen. This makes it particularly useful in quality control of soil samples. For it to be accepted in the industry, clear guidelines on how to interpret the data is crucial. Further development, such as measuring the remoulded shear strength with the CC-Test would further strengthen its applicability.