Effect of Testing Temperature on Stiffness, Strength and Apparent Sample Disturbance in Quick Clay Samples from NGTS Quick Clay Site Flotten

Abstract

The effect of temperature on laboratory measurements of soil strength and stiffness has occasionally been revisited as a research topic since the 1960 s. Previous studies indicate that both preconsolidation pressure and undrained shear strength might increase by more than 1 % for every 1 °C decrease in testing temperature.

As part of the NGTS project, CAUC triaxial tests and CRS oedometer have been performed on sensitive soil from the Flotten test site. Tests were carried out both at room temperature and at in-situ temperature. The clay samples used were retrieved with a mini-block sampler, four to six months prior to testing. The temperature during sampling, transportation and storage was approximately constant and close to in-situ temperature (6°C).

Results show a consistent strength and stiffness increase for tests run at in-situ temperature. On average: 7 % increase in undrained shear strength and 13 % increase in preconsolidation pressure. Also, CRS pore pressure data and CAUC water expulsion curves indicate that permeability and creep decreases at low temperature, whilst apparent sample quality improves. These results are generally in accordance with literature.

Some comparison is made with tests run at NGI Oslo on mini-block samples that originated from the same borehole. In addition, some laboratory results are compared with previous Flotten test results on 54 mm samples. The latter further indicates that deep samples in silty, sensitive clays can only be retrieved undisturbed with block-size sampling equipment.