Cyclic tests on high-quality undisturbed block samples of soft marine Norwegian clay (original) (raw)
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Potential improvements of design parameters by taking block samples of soft marine Norwegian clays
Canadian Geotechnical Journal, 2007
Undrained triaxial and direct simple shear tests on samples reconsolidated to the in situ effective stresses and oedometer tests have been carried out on standard piston tube and on high quality block samples from 12 deposits of soft Norwegian marine clays. Based on the results of a selected number of these tests, empirical procedures for estimating the effect of sample disturbance have been developed. These procedures can be used to show the potential increase that may be achieved in undrained shear strength and apparent preconsolidation stress by taking high quality block samples. Suggestions are also given regarding corrections for rate of loading and temperature effects; as well, examples are given regarding possible consequences for design if higher strengths are utilized.Key words: soft clays, sample disturbance, consolidation procedures, stress–strain–strength behaviour.
Simple shear testing of sensitive, very soft offshore clay for wide strain range
Canadian Geotechnical Journal, 2009
Stiffness and damping properties of sensitive very soft clay sediments of the Italian Adriatic continental shelf are determined by means of two staged (a 12stages and a 2-stages test respectively) cyclic simple shear tests. The apparatus used in this research is capable of investigating the stress-strain behaviour of the soil in a wide range of shear strains, from about 0.0004% to 1%. Test results were expressed in terms of small-strain shear modulus G 0 and of normalized equivalent shear modulus (G eq /G 0 ) and damping ratio (D) versus cyclic shear strain amplitude ( c ). These parameters were analyzed in the framework of existing literature by comparison with empirical correlations developed for onshore materials of different plasticity and, limited to G 0 , also for soft soils. The dependence of G 0 , G eq /G 0 - c and D- c on factors such as void ratio, stress history and loading cycles is analyzed and discussed.
Shear bands in undrained plane strain compression of Norwegian quick clays
Canadian Geotechnical Journal, 2017
This work presents the results of plane strain tests carried out at the Laboratoire 3SR Grenoble (France) on undisturbed samples of very sensitive Norwegian soft clay. Discussion of the results focuses on the observed failure mechanisms and zones of localized deformation. The tested clay is defined as quick clay because it liquefies completely upon remolding. Thus, careful handling was necessary, and original procedures were developed to place samples in the plane strain testing device with minimum disturbance. Results show that excess pore-water pressure had developed during shear loading and shear strength was lost after the peak, which is a typical phenomenon in sensitive soils. The sample was held between two glass plates to enable visual tracking of the deformations. A digital image correlation analysis revealed a complex pattern of emerging shear bands, with one or two bands dominating and providing a final failure mechanism. Two local pore-water pressure transducers were atta...
Correlation between the maximum shear modulus and the undrained strength of a remolded marine clay
This paper presents the results of a laboratory investigation conducted to evaluate the relationship between the maximum shear modulus (G0) and the undrained strength (Su) of a remolded marine clay. The soil used in the research was a typical marine clay from Jubarte field, in the Espírito Santo basin, Brazil. From the soil a mud was prepared with a water content of 1.5 times the liquid limit. The specimens for the tests were cut from pre-samples, obtained from the consolidation of the mud under a confining pressure of 100 kPa. Resonant column tests and CIU triaxial compression tests were carried out for the determination of G0 and Su respectively. The tests were performed with different values of confining pressure (35 to 560 kPa) and overconsolidation ratio OCR (1 to 16), amounting to 20 different conditions. The effects of confining pressure e OCR on the maximum shear modulus and on the undrained shear strength are discussed. A correlation between Su and G0 was obtained and a comparison between this correlation and those reported in the literature is presented.
Geofluids, 2021
Small-strain shear modulus, G max , is a key evaluation index to study the dynamic characteristics of soil in geotechnical engineering. It is widely adopted to evaluate the stiffness of soft soil in soil dynamic engineering. In this paper, the cyclic triaxial tests and resonance column tests were carried out to explore the variation of G max of soft clay with respect to various confining stresses, cyclic shear stress ratios, pore pressures, and effective stress paths. Test results indicated that the effective stress decreased gradually with the increase of the cycle shear stress ratio. The failure points were mainly concentrated in a rectangular area, defined by the normalized effective stress from 0.56 to 0.64 and the normalized shear modulus from 0.72 to 0.78. Additionally, a short pause caused a small increase of 1-2% in G max as well as pore pressure. This study demonstrates that G max can be effectively used to characterize the failure of saturated soft clay in a more intuitive...
2016
To develop an estimation method of multi-directional cyclic shear-induced pore water pressure on clays with a wide range of plasticity indices, normally consolidated specimens of Kaolinite clay, Tokyo bay clay and Kitakyushu clay were subjected to the uni-directional and multi-directional cyclic simple shears under the undrained condition. Then firstly, the effects of cyclic shear direction on the pore water pressure accumulation and secondly, the relationships between the plasticity index of clay and the pore water pressure accumulated during cyclic shear were investigated. In conclusion, it is clarified that when a saturated clay is subjected to uni-directional or multi-directional cyclic simple shear under the undrained condition, the pore water pressure induced by multidirectional cyclic shear increases considerably larger than those generated by the uni-directional one and such a tendency is seen in clays with a wide range of the plasticity indices. The plasticity index of clay...
2012
Cyclic threshold strains in clays versus sands and the change of secant shear modulus and pore water pressure at small cyclic strains A dissertation submitted in partial satisfaction of the requirement for the degree Doctor of Philosophy in Civil Engineering by Ahmad Reza Mortezaie 2012 ii ABSTRACT OF THE DISSERTATION Cyclic threshold strains in clays versus sands and the change of secant shear modulus and pore water pressure at small cyclic strains by Ahmad Reza Mortezaie Doctor of Philosophy in Civil Engineering University of California, Los Angeles, 2012 Professor Mladen Vucetic, Chair When fully saturated soils are subjected to cyclic loading in undrained conditions involving moderate and large cyclic shear strain amplitudes, c , their stiffness and strength decrease and the pore water pressure changes permanently with the number of cycles, N. Such cyclic degradation of stiffness and pore water pressure change are among the most fundamental and important phenomena in soil dynamics. Fully saturated sands are most susceptible to cyclic degradation and significant pore pressure buildup. During cyclic loading, they can completely lose their stiffness and strength while large excess pore pressure develops and they can eventually liquefy. On the other end of the spectrum are fully saturated clays of high plasticity that under significant cyclic loading can lose only a fraction of their original stiffness and
Field measurements of shear strength of an underconsolidated marine clay
Engineering Geology, 2003
This paper presents the observations of cone penetration testing (CPT), in situ vane shear testing and undrained triaxial testing of underconsolidated marine clay in the Craney Island Dredged Material Management Area (CIDMMA), Norfolk, VA. Comparison of vane shear measurements, taken during 1981–1983, to CPT measurements, taken during 1993, indicates a change in undrained shear strength. Both the vane shear and cone penetration resistances are lowest at the mid-heights of the clay layers and the excess pore water pressures are highest at the mid-height of the clay layers, indicating that the clay layer is underconsolidated.
Journal of Geotechnical and Geoenvironmental Engineering, 2013
The effects of the frequency of cyclic shearing and vertical consolidation stress on the cyclic degradation and cyclic pore water pressure in normally-consolidated kaolinite clay having PI 5 28 were investigated with the help of the cyclic strain-controlled Norwegian Geotechnical Institute (NGI) simple shear test. The testing program encompassed three cyclic shear strain amplitudes, g c 5 0:1, 0.25, and 0.5%, two vertical effective consolidation stresses, s vc 9 5 220 and 680 kPa, and three frequencies, f 5 0:001, 0.01, and 0.1 Hz. The results reveal that the cyclic degradation parameter, t, which measures the rate of cyclic degradation with the number of cycles, increases substantially with f and decreases with s vc 9 . If f is increased 10 times, t may increase by 20-50%. If s vc 9 is increased from 220 to 680 kPa, the t parameter may decrease by 20-38%. The cyclic pore water pressure normalized by s vc 9 decreases with f and s vc 9 .