Effect of various storage times for a block sample. Experiences with sample tubes coated with a low friction polymer and a new piston sampler, all on Onsøy clay

This report contains the results of four CAUC triaxial tests, two being performed on block samples and two on 72 mm tube samples. The tests were all performed on plastic clay from Onsøy. The purpose with the block samples was to see if there is any significant improvement in sample quality whether the sample is mounted into the triaxial in the field compared to when it is transported to the laboratory and mounted into the triaxial cell several days later. However, no improvement was observed in sample quality for the test on the sample being mounted in the field. One of the two tube samples was sampled with the ordinary NGI 72 mm piston sampler, but the sample tube was smeared on the inside and the outside with a low friction polymer. However, again, no improvement in sample quality. The other tube (72 mm) sample was sampled with a new piston sampler for a remote operated drilling system (Santos et al, 2015). However, during removal of the sample tube from the sampler a suction was created that spoiled the sample so no conclusion can be drawn regarding this sampler in this cas

Test fill to failure on soft plastic marine clay at Onsøy, Norway

The test fill at Onsøy, close to the town of Fredrikstad in Norway, was built on a very soft marine clay with in situ vane strength as low as 11 kPa and a plasticity index varying from 34 to 50. The dimensions at the bottom of the long test fill were 20 m*60 m and the height 2.3 m. The fill, as placed in the first stage, had a computed factor of safety against foundation failure of 1.35 based on in situ vane strength. The fill was allowed to sit for about 3 years (from 1972 to 1975) before it, in a second stage, was brought to failure in about 4.3 days by raising the height. This second stage is the subject of this paper. Back calculation of the failure by undrained stability analysis based on in situ vane tests performed shortly before the start of the second stage, and based on undrained triaxial and constant volume direct simple shear tests on specimens from tube samples taken shortly before the start of the second stage and reconsolidated to the in situ effective stresses, gave factors of safety varying from 0.88 to 1.45. Settlement values computed at the centreline of the fill for the second stage based on the results from undrained compression triaxial tests, agreed reasonably well with the field measurements.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Normalized Undrained Shear Strength of Clay Shales

This paper examines the possibility of normalizing the undrained shear strength behavior of clay shales. Shales are formed in sedimentary basins by diagenetic processes, which turn young clay sediments into compacted and lithified shales. Cementation at grain contacts affects many properties of shales including the apparent preconsolidation and shear strength. Based on a study of 25 different types of materials, the normalized undrained shear strength of clay shales was found to correlate satisfactorily with overconsolidation ratio following the SHANSEP (Stress History and Normalized Soil Engineering Properties) normalization procedure for clays. The normalized undrained shear strength correlation appears valid regardless of the cause of the apparent preconsolidation. Correlations of the apparent preconsolidation stress with unconfined compressive strength and compressional wave velocity are proposed to predict the normalized undrained shear strength of clay shales