Morten Sjursen | NGI - Academia.edu (original) (raw)
Papers by Morten Sjursen
The quality and reliability of laboratory test data in sensitive clay can significantly be affect... more The quality and reliability of laboratory test data in sensitive clay can significantly be affected by sample disturbance. In turn, sample disturbance may affect key design parameters such as compressibility, preconsolidation stress and undrained shear strength. In this work, samples obtained from a 72 mm thin walled fixed-piston sampler are compared to Sherbrooke Block samples with diameter (Ø) of 160 mm (mini) and 250 mm (standard) for clays from three different locations in Norway (Skatval, Koa and Nybakk-Slomarka). All three clays have plasticity indices varying between 8-25 and water contents varying between 30-40%. Results from triaxial tests (CAUC) and oedometer tests (CRS) are used to study the influence of sampler type and disturbance effect. Sample disturbance from both block samplers is further evaluated using measurements of shear-wave velocity (Vs) performed in the field and in the laboratory. The measurements are correlated to volumetric change values during triaxial testing as a form of evaluating quality of the laboratory tests. RÉSUMÉ : Il est reconnu que les méthodes d'échantillonnage peuvent fortement affecter la qualité des échantillons d'argile molle. De ce fait, les perturbations dues à l'échantillonnage peuvent affecter les paramètres de conception en géotechnique tels que la compressibilité de l'argile, la contrainte de pré-consolidation et la résistance au cisaillement. Dans cette étude, les résultats de laboratoire sur des échantillons obtenu à l'aide d'un échantillonneur à piston de 72 mm sont comparés avec ceux d'échantillons en bloc de 160 mm et 250 mm. Les tests ont été faits sur trois argiles Norvégienne provenant de Skatval, Koa et de Nybakk-Slomarka. Chacune des argiles a un indice de plasticité variant entre 8 et 25, et une gamme de teneur en eau entre 30-40%. Les résultats d'essai triaxiaux en compression (CAUC) ainsi que d'oedomètre (CRS) sont utilisés pour évaluer l'effet des différents échantillonneurs ainsi que la qualité des échantillons. De plus, la qualité des échantillons en bloc est évalué à partir de résultats d'ondes de cisaillement recueillis sur le terrain et au laboratoire. Ces mesures sont aussi corrélées aux changements volumétrique pendant le stade de consolidation dans les essais triaxiaux.
Canadian Geotechnical Journal, 2013
The results of a study with undrained cyclic triaxial and direct simple shear (DSS) tests on high... more The results of a study with undrained cyclic triaxial and direct simple shear (DSS) tests on high-quality undisturbed samples obtained from large blocks of a soft marine Norwegian clay are presented. Several tests with different average shear stresses, shear stress amplitudes, loading frequencies, and sample geometries have been performed on block samples taken from different depths. In tests with small average shear stresses, failure occurred due to large shear strain amplitudes, while large permanent shear strains were observed in tests with higher average shear stresses. Diagrams quantifying the undrained cyclic strength, permanent shear strain, shear strain amplitude, and permanent pore-water pressure dependent on average shear stress, shear stress amplitude, and number of cycles have been developed based on the test results. The undrained cyclic strength was found strongly dependent on loading frequency. Block samples from shallower depth showed a somewhat higher undrained cycl...
Canadian Geotechnical Journal, 2011
Offshore developments for hydrocarbon resources have now progressed to water depths approaching 3... more Offshore developments for hydrocarbon resources have now progressed to water depths approaching 3000 m, with geotechnical design increasingly focused on soft sediments in the upper 30 m or so of the seabed. Due to the difficulties and high cost in recovering high-quality samples from deepwater sites, there is increasing dependence on in situ testing techniques for determining the geotechnical design parameters. This paper summarizes the findings from a joint industry project, undertaken by the Norwegian Geotechnical Institute and the Centre for Offshore Foundation Systems at The University of Western Australia, on the use of in situ testing for the characterization of deepwater soft soils. The project focused on theoretical and empirical studies for the interpretation of piezocone, T-bar, and ball penetration test data, linking the penetration resistance to shear strengths determined from in situ vane tests and laboratory tests on high-quality samples. Guidelines are summarized for ...
Frontiers in Offshore Geotechnics, 2005
Field developments in deep waters with very soft soils have led to increased reliance on the use ... more Field developments in deep waters with very soft soils have led to increased reliance on the use of in situ tests to evaluate soil design parameters. Recently the T-bar has been introduced due to its potential for increasing the reliability of interpreted undrained shear strength relative to the CPTU for soft clays in deep waters. Empirical correlations based on field tests and laboratory tests on samples at one offshore and two onshore soft clay sites indicate that T-bar factors are in a somewhat narrower range compared to cone factors. Recommendations are given in terms of cone and T-bar factors to use, and when T-bar tests should be carried out in addition to CPTU.
Géotechnique, 2010
Difficulties in obtaining high-quality soil samples from deepwater sites have necessitated increa... more Difficulties in obtaining high-quality soil samples from deepwater sites have necessitated increasing reliance on piezocone, T-bar and ball penetration tests to determine soil properties for design purposes. This paper reports the results of an international collaborative project in which a worldwide high-quality database of lightly overconsolidated clays was assembled and used to evaluate resistance factors for the estimation of intact and remoulded undrained shear strength from the penetration resistance of each device. The derived factors were then compared with existing theoretical solutions to evaluate the influence of particular soil characteristics. The overall statistics showed similar levels of variability of the resistance factors, with low coefficients of variation, for all three types of penetrometer. However, correlations of the resistance factors with specific soil characteristics indicated that the resistance factors for the piezocone were more influenced by soil stif...
Géotechnique, 2011
It has been reported in the literature that net cone penetration resistance is normally higher th... more It has been reported in the literature that net cone penetration resistance is normally higher than the penetration resistance measured using full-flow cylindrical (T-bar) or spherical (ball) penetrometers, and also that the ball penetration resistance is generally very close to the T-bar penetration resistance. In this paper, a worldwide high-quality database (three onshore sites and seven offshore sites) was used to identify soil characteristics that contribute to differences in the relative magnitudes of penetration resistance measured with cone, T-bar and ball penetrometers. For soils covered in this database, the ratio of T-bar to net cone penetration resistance (qT-bar/qnet) lay between 0·75 and 1, decreasing with depth from near unity at shallow depths. For the four sites where ball penetrometer data were available, the ratio of ball to T-bar penetration resistance (qball/qT-bar) was found to fluctuate around unity, with an average just greater than 1, but no distinguishable ...
Canadian Geotechnical Journal, 2007
... Introduction The standard procedure in Norway for most commercial projects is to take samples... more ... Introduction The standard procedure in Norway for most commercial projects is to take samples with the Norwegian Geotechnical Institute (NGI, Oslo, Norway) 54 mm composite piston sam-pler (ie, standard piston sampler). ... 1Corresponding author (e-mail: tlu@ngi.no). Page 2. ...
Canadian Geotechnical Journal, 2007
Canadian Geotechnical Journal, 2007
... Introduction The standard procedure in Norway for most commercial projects is to take samples... more ... Introduction The standard procedure in Norway for most commercial projects is to take samples with the Norwegian Geotechnical Institute (NGI, Oslo, Norway) 54 mm composite piston sam-pler (ie, standard piston sampler). ... 1Corresponding author (e-mail: tlu@ngi.no). Page 2. ...
Canadian Geotechnical Journal, 2006
ABSTRACT After many decades of research, the issue of sample disturbance is still important as re... more ABSTRACT After many decades of research, the issue of sample disturbance is still important as regards to determining reliable and representative soil parameters for foundation design in soft clays. Parallel laboratory tests have been carried out on high-quality block samples and ordinary piston tube samples from 12 deposits of soft Norwegian marine clays. Undrained triaxial and direct simple shear (DSS) tests on samples reconsolidated to the in situ effective stresses show that sample disturbance has a significant effect on the measured stress–strain–strength behaviour: the more disturbed the sample, the lower the shear stress at small strains and the higher the shear stress at large strains. Breakdown of the clay structure, including cementation bonds, is the assumed cause of lower shear resistance at small strains, whereas at large strains the shear resistance is governed mainly by the water content, which for soft clay samples, reconsolidated to the in situ effective stresses, will be lower, and the strength thereby higher, the more disturbed the sample. The work described herein also includes the effects of the consolidation procedure; in addition to the reconsolidation technique, both stress history and normalized soil engineering properties (SHANSEP) and delayed consolidation tests have been carried out.Key words: soft clays, sample disturbance, consolidation procedures, stress–strain–strength behaviour, stress–strain–time behaviour.
Géotechnique, 2010
ABSTRACT Difficulties in obtaining high-quality soil samples from deepwater sites have necessitat... more ABSTRACT Difficulties in obtaining high-quality soil samples from deepwater sites have necessitated increasing reliance on piezocone, T-bar and ball penetration tests to determine soil properties for design purposes. This paper reports the results of an international collaborative project in which a worldwide high-quality database of lightly over-consolidated clays was assembled and used to evaluate resistance factors for the estimation of intact and remoulded undrained shear strength from the penetration resistance of each device. The derived factors were then compared with existing theoretical solutions to evaluate the influence of particular soil characteristics. The overall statistics showed similar levels of variability of the resistance factors, with low coefficients of variation, for all three types of penetrometer. However, correlations of the resistance factors with specific soil characteristics indicated that the resistance factors for the piezocone were more influenced by soil stiffness, or rigidity index, than for the T-bar and ball, while the effect of strength anisotropy was only apparent in respect of resistance factors for the T-bar and ball relative to shear strengths measured in triaxial compression. In the correlation between the remoulded penetration resistance and remoulded strength, the resistance factors for remoulded strength were found to be higher than those for intact strength and with a slight tendency to increase with increasing strength sensitivity but insensitive to soil index properties. Based on an assessment of the influence of various soil characteristics, resistance factors are recommended for the estimation of intact and remoulded undrained shear strength from the penetration resistances of each device for soil with strength sensitivity less than six.
Géotechnique, 2011
ABSTRACT It has been reported in the literature that net cone penetration resistance is normally ... more ABSTRACT It has been reported in the literature that net cone penetration resistance is normally higher than the penetration resistance measured using full-flow cylindrical (T-bar) or spherical (ball) penetrometers, and also that the ball penetration resistance is generally very close to the T-bar penetration resistance. In this paper, a worldwide high-quality database (three onshore sites and seven offshore sites) was used to identify soil characteristics that contribute to differences in the relative magnitudes of penetration resistance measured with cone, T-bar and ball penetrometers. For soils covered in this database, the ratio of T-bar to net cone penetration resistance (q(T-bar)/q(net)) lay between 0.75 and 1, decreasing with depth from near unity at shallow depths. For the four sites where ball penetrometer data were available, the ratio of ball to T-bar penetration resistance (q(ball)/q(T-bar)) was found to fluctuate around unity, with an average just greater than 1, but no distinguishable trend with depth. The measured q(T-bar)/q(net) and q(ball)/q(net) followed theoretical trends for the cone resistance to increase with rigidity index, G/s(u), with the best quantitative agreement obtained using a rigidity index defined in terms of the small strain stiffness, G(0), as measured by in situ seismic cone tests. The resistance ratio also followed the theoretical trend predicted with certain assumptions for the effects of strength anisotropy. However, while q(T-bar)/q(net) and possibly q(ball)/q(net) appear to depend slightly on the liquidity index, liquid limit and plasticity index, the resistance ratios appeared independent of other soil parameters, including normalised in situ shear stress, sensitivity and yield stress ratio, for the soils covered in this study.
Canadian Geotechnical Journal, 2007
Canadian Geotechnical Journal, 2009
Canadian Geotechnical Journal, 2007
... Introduction The standard procedure in Norway for most commercial projects is to take samples... more ... Introduction The standard procedure in Norway for most commercial projects is to take samples with the Norwegian Geotechnical Institute (NGI, Oslo, Norway) 54 mm composite piston sam-pler (ie, standard piston sampler). ... 1Corresponding author (e-mail: tlu@ngi.no). Page 2. ...
Canadian Geotechnical Journal, 2006
ABSTRACT After many decades of research, the issue of sample disturbance is still important as re... more ABSTRACT After many decades of research, the issue of sample disturbance is still important as regards to determining reliable and representative soil parameters for foundation design in soft clays. Parallel laboratory tests have been carried out on high-quality block samples and ordinary piston tube samples from 12 deposits of soft Norwegian marine clays. Undrained triaxial and direct simple shear (DSS) tests on samples reconsolidated to the in situ effective stresses show that sample disturbance has a significant effect on the measured stress–strain–strength behaviour: the more disturbed the sample, the lower the shear stress at small strains and the higher the shear stress at large strains. Breakdown of the clay structure, including cementation bonds, is the assumed cause of lower shear resistance at small strains, whereas at large strains the shear resistance is governed mainly by the water content, which for soft clay samples, reconsolidated to the in situ effective stresses, will be lower, and the strength thereby higher, the more disturbed the sample. The work described herein also includes the effects of the consolidation procedure; in addition to the reconsolidation technique, both stress history and normalized soil engineering properties (SHANSEP) and delayed consolidation tests have been carried out.Key words: soft clays, sample disturbance, consolidation procedures, stress–strain–strength behaviour, stress–strain–time behaviour.
Canadian Geotechnical Journal, 2011
Offshore developments for hydrocarbon resources have now progressed to water depths approaching 3... more Offshore developments for hydrocarbon resources have now progressed to water depths approaching 3000 m, with geotechnical design increasingly focused on soft sediments in the upper 30 m or so of the seabed. Due to the difficulties and high cost in recovering high-quality samples from deepwater sites, there is increasing dependence on in situ testing techniques for determining the geotechnical design parameters. This paper summarizes the findings from a joint industry project, undertaken by the Norwegian Geotechnical Institute and the Centre for Offshore Foundation Systems at The University of Western Australia, on the use of in situ testing for the characterization of deepwater soft soils. The project focused on theoretical and empirical studies for the interpretation of piezocone, T-bar, and ball penetration test data, linking the penetration resistance to shear strengths determined from in situ vane tests and laboratory tests on high-quality samples. Guidelines are summarized for interpreting in situ test data, particularly for estimating intact and remoulded undrained shear strengths from the penetration resistance measured by each type of penetrometer. Suggestions are also given for future development of in situ testing techniques to maximize the potential of in situ testing in characterization of deepwater soft soils.
Canadian Geotechnical Journal, 2013
The quality and reliability of laboratory test data in sensitive clay can significantly be affect... more The quality and reliability of laboratory test data in sensitive clay can significantly be affected by sample disturbance. In turn, sample disturbance may affect key design parameters such as compressibility, preconsolidation stress and undrained shear strength. In this work, samples obtained from a 72 mm thin walled fixed-piston sampler are compared to Sherbrooke Block samples with diameter (Ø) of 160 mm (mini) and 250 mm (standard) for clays from three different locations in Norway (Skatval, Koa and Nybakk-Slomarka). All three clays have plasticity indices varying between 8-25 and water contents varying between 30-40%. Results from triaxial tests (CAUC) and oedometer tests (CRS) are used to study the influence of sampler type and disturbance effect. Sample disturbance from both block samplers is further evaluated using measurements of shear-wave velocity (Vs) performed in the field and in the laboratory. The measurements are correlated to volumetric change values during triaxial testing as a form of evaluating quality of the laboratory tests. RÉSUMÉ : Il est reconnu que les méthodes d'échantillonnage peuvent fortement affecter la qualité des échantillons d'argile molle. De ce fait, les perturbations dues à l'échantillonnage peuvent affecter les paramètres de conception en géotechnique tels que la compressibilité de l'argile, la contrainte de pré-consolidation et la résistance au cisaillement. Dans cette étude, les résultats de laboratoire sur des échantillons obtenu à l'aide d'un échantillonneur à piston de 72 mm sont comparés avec ceux d'échantillons en bloc de 160 mm et 250 mm. Les tests ont été faits sur trois argiles Norvégienne provenant de Skatval, Koa et de Nybakk-Slomarka. Chacune des argiles a un indice de plasticité variant entre 8 et 25, et une gamme de teneur en eau entre 30-40%. Les résultats d'essai triaxiaux en compression (CAUC) ainsi que d'oedomètre (CRS) sont utilisés pour évaluer l'effet des différents échantillonneurs ainsi que la qualité des échantillons. De plus, la qualité des échantillons en bloc est évalué à partir de résultats d'ondes de cisaillement recueillis sur le terrain et au laboratoire. Ces mesures sont aussi corrélées aux changements volumétrique pendant le stade de consolidation dans les essais triaxiaux.
Canadian Geotechnical Journal, 2013
The results of a study with undrained cyclic triaxial and direct simple shear (DSS) tests on high... more The results of a study with undrained cyclic triaxial and direct simple shear (DSS) tests on high-quality undisturbed samples obtained from large blocks of a soft marine Norwegian clay are presented. Several tests with different average shear stresses, shear stress amplitudes, loading frequencies, and sample geometries have been performed on block samples taken from different depths. In tests with small average shear stresses, failure occurred due to large shear strain amplitudes, while large permanent shear strains were observed in tests with higher average shear stresses. Diagrams quantifying the undrained cyclic strength, permanent shear strain, shear strain amplitude, and permanent pore-water pressure dependent on average shear stress, shear stress amplitude, and number of cycles have been developed based on the test results. The undrained cyclic strength was found strongly dependent on loading frequency. Block samples from shallower depth showed a somewhat higher undrained cycl...
Canadian Geotechnical Journal, 2011
Offshore developments for hydrocarbon resources have now progressed to water depths approaching 3... more Offshore developments for hydrocarbon resources have now progressed to water depths approaching 3000 m, with geotechnical design increasingly focused on soft sediments in the upper 30 m or so of the seabed. Due to the difficulties and high cost in recovering high-quality samples from deepwater sites, there is increasing dependence on in situ testing techniques for determining the geotechnical design parameters. This paper summarizes the findings from a joint industry project, undertaken by the Norwegian Geotechnical Institute and the Centre for Offshore Foundation Systems at The University of Western Australia, on the use of in situ testing for the characterization of deepwater soft soils. The project focused on theoretical and empirical studies for the interpretation of piezocone, T-bar, and ball penetration test data, linking the penetration resistance to shear strengths determined from in situ vane tests and laboratory tests on high-quality samples. Guidelines are summarized for ...
Frontiers in Offshore Geotechnics, 2005
Field developments in deep waters with very soft soils have led to increased reliance on the use ... more Field developments in deep waters with very soft soils have led to increased reliance on the use of in situ tests to evaluate soil design parameters. Recently the T-bar has been introduced due to its potential for increasing the reliability of interpreted undrained shear strength relative to the CPTU for soft clays in deep waters. Empirical correlations based on field tests and laboratory tests on samples at one offshore and two onshore soft clay sites indicate that T-bar factors are in a somewhat narrower range compared to cone factors. Recommendations are given in terms of cone and T-bar factors to use, and when T-bar tests should be carried out in addition to CPTU.
Géotechnique, 2010
Difficulties in obtaining high-quality soil samples from deepwater sites have necessitated increa... more Difficulties in obtaining high-quality soil samples from deepwater sites have necessitated increasing reliance on piezocone, T-bar and ball penetration tests to determine soil properties for design purposes. This paper reports the results of an international collaborative project in which a worldwide high-quality database of lightly overconsolidated clays was assembled and used to evaluate resistance factors for the estimation of intact and remoulded undrained shear strength from the penetration resistance of each device. The derived factors were then compared with existing theoretical solutions to evaluate the influence of particular soil characteristics. The overall statistics showed similar levels of variability of the resistance factors, with low coefficients of variation, for all three types of penetrometer. However, correlations of the resistance factors with specific soil characteristics indicated that the resistance factors for the piezocone were more influenced by soil stif...
Géotechnique, 2011
It has been reported in the literature that net cone penetration resistance is normally higher th... more It has been reported in the literature that net cone penetration resistance is normally higher than the penetration resistance measured using full-flow cylindrical (T-bar) or spherical (ball) penetrometers, and also that the ball penetration resistance is generally very close to the T-bar penetration resistance. In this paper, a worldwide high-quality database (three onshore sites and seven offshore sites) was used to identify soil characteristics that contribute to differences in the relative magnitudes of penetration resistance measured with cone, T-bar and ball penetrometers. For soils covered in this database, the ratio of T-bar to net cone penetration resistance (qT-bar/qnet) lay between 0·75 and 1, decreasing with depth from near unity at shallow depths. For the four sites where ball penetrometer data were available, the ratio of ball to T-bar penetration resistance (qball/qT-bar) was found to fluctuate around unity, with an average just greater than 1, but no distinguishable ...
Canadian Geotechnical Journal, 2007
... Introduction The standard procedure in Norway for most commercial projects is to take samples... more ... Introduction The standard procedure in Norway for most commercial projects is to take samples with the Norwegian Geotechnical Institute (NGI, Oslo, Norway) 54 mm composite piston sam-pler (ie, standard piston sampler). ... 1Corresponding author (e-mail: tlu@ngi.no). Page 2. ...
Canadian Geotechnical Journal, 2007
Canadian Geotechnical Journal, 2007
... Introduction The standard procedure in Norway for most commercial projects is to take samples... more ... Introduction The standard procedure in Norway for most commercial projects is to take samples with the Norwegian Geotechnical Institute (NGI, Oslo, Norway) 54 mm composite piston sam-pler (ie, standard piston sampler). ... 1Corresponding author (e-mail: tlu@ngi.no). Page 2. ...
Canadian Geotechnical Journal, 2006
ABSTRACT After many decades of research, the issue of sample disturbance is still important as re... more ABSTRACT After many decades of research, the issue of sample disturbance is still important as regards to determining reliable and representative soil parameters for foundation design in soft clays. Parallel laboratory tests have been carried out on high-quality block samples and ordinary piston tube samples from 12 deposits of soft Norwegian marine clays. Undrained triaxial and direct simple shear (DSS) tests on samples reconsolidated to the in situ effective stresses show that sample disturbance has a significant effect on the measured stress–strain–strength behaviour: the more disturbed the sample, the lower the shear stress at small strains and the higher the shear stress at large strains. Breakdown of the clay structure, including cementation bonds, is the assumed cause of lower shear resistance at small strains, whereas at large strains the shear resistance is governed mainly by the water content, which for soft clay samples, reconsolidated to the in situ effective stresses, will be lower, and the strength thereby higher, the more disturbed the sample. The work described herein also includes the effects of the consolidation procedure; in addition to the reconsolidation technique, both stress history and normalized soil engineering properties (SHANSEP) and delayed consolidation tests have been carried out.Key words: soft clays, sample disturbance, consolidation procedures, stress–strain–strength behaviour, stress–strain–time behaviour.
Géotechnique, 2010
ABSTRACT Difficulties in obtaining high-quality soil samples from deepwater sites have necessitat... more ABSTRACT Difficulties in obtaining high-quality soil samples from deepwater sites have necessitated increasing reliance on piezocone, T-bar and ball penetration tests to determine soil properties for design purposes. This paper reports the results of an international collaborative project in which a worldwide high-quality database of lightly over-consolidated clays was assembled and used to evaluate resistance factors for the estimation of intact and remoulded undrained shear strength from the penetration resistance of each device. The derived factors were then compared with existing theoretical solutions to evaluate the influence of particular soil characteristics. The overall statistics showed similar levels of variability of the resistance factors, with low coefficients of variation, for all three types of penetrometer. However, correlations of the resistance factors with specific soil characteristics indicated that the resistance factors for the piezocone were more influenced by soil stiffness, or rigidity index, than for the T-bar and ball, while the effect of strength anisotropy was only apparent in respect of resistance factors for the T-bar and ball relative to shear strengths measured in triaxial compression. In the correlation between the remoulded penetration resistance and remoulded strength, the resistance factors for remoulded strength were found to be higher than those for intact strength and with a slight tendency to increase with increasing strength sensitivity but insensitive to soil index properties. Based on an assessment of the influence of various soil characteristics, resistance factors are recommended for the estimation of intact and remoulded undrained shear strength from the penetration resistances of each device for soil with strength sensitivity less than six.
Géotechnique, 2011
ABSTRACT It has been reported in the literature that net cone penetration resistance is normally ... more ABSTRACT It has been reported in the literature that net cone penetration resistance is normally higher than the penetration resistance measured using full-flow cylindrical (T-bar) or spherical (ball) penetrometers, and also that the ball penetration resistance is generally very close to the T-bar penetration resistance. In this paper, a worldwide high-quality database (three onshore sites and seven offshore sites) was used to identify soil characteristics that contribute to differences in the relative magnitudes of penetration resistance measured with cone, T-bar and ball penetrometers. For soils covered in this database, the ratio of T-bar to net cone penetration resistance (q(T-bar)/q(net)) lay between 0.75 and 1, decreasing with depth from near unity at shallow depths. For the four sites where ball penetrometer data were available, the ratio of ball to T-bar penetration resistance (q(ball)/q(T-bar)) was found to fluctuate around unity, with an average just greater than 1, but no distinguishable trend with depth. The measured q(T-bar)/q(net) and q(ball)/q(net) followed theoretical trends for the cone resistance to increase with rigidity index, G/s(u), with the best quantitative agreement obtained using a rigidity index defined in terms of the small strain stiffness, G(0), as measured by in situ seismic cone tests. The resistance ratio also followed the theoretical trend predicted with certain assumptions for the effects of strength anisotropy. However, while q(T-bar)/q(net) and possibly q(ball)/q(net) appear to depend slightly on the liquidity index, liquid limit and plasticity index, the resistance ratios appeared independent of other soil parameters, including normalised in situ shear stress, sensitivity and yield stress ratio, for the soils covered in this study.
Canadian Geotechnical Journal, 2007
Canadian Geotechnical Journal, 2009
Canadian Geotechnical Journal, 2007
... Introduction The standard procedure in Norway for most commercial projects is to take samples... more ... Introduction The standard procedure in Norway for most commercial projects is to take samples with the Norwegian Geotechnical Institute (NGI, Oslo, Norway) 54 mm composite piston sam-pler (ie, standard piston sampler). ... 1Corresponding author (e-mail: tlu@ngi.no). Page 2. ...
Canadian Geotechnical Journal, 2006
ABSTRACT After many decades of research, the issue of sample disturbance is still important as re... more ABSTRACT After many decades of research, the issue of sample disturbance is still important as regards to determining reliable and representative soil parameters for foundation design in soft clays. Parallel laboratory tests have been carried out on high-quality block samples and ordinary piston tube samples from 12 deposits of soft Norwegian marine clays. Undrained triaxial and direct simple shear (DSS) tests on samples reconsolidated to the in situ effective stresses show that sample disturbance has a significant effect on the measured stress–strain–strength behaviour: the more disturbed the sample, the lower the shear stress at small strains and the higher the shear stress at large strains. Breakdown of the clay structure, including cementation bonds, is the assumed cause of lower shear resistance at small strains, whereas at large strains the shear resistance is governed mainly by the water content, which for soft clay samples, reconsolidated to the in situ effective stresses, will be lower, and the strength thereby higher, the more disturbed the sample. The work described herein also includes the effects of the consolidation procedure; in addition to the reconsolidation technique, both stress history and normalized soil engineering properties (SHANSEP) and delayed consolidation tests have been carried out.Key words: soft clays, sample disturbance, consolidation procedures, stress–strain–strength behaviour, stress–strain–time behaviour.
Canadian Geotechnical Journal, 2011
Offshore developments for hydrocarbon resources have now progressed to water depths approaching 3... more Offshore developments for hydrocarbon resources have now progressed to water depths approaching 3000 m, with geotechnical design increasingly focused on soft sediments in the upper 30 m or so of the seabed. Due to the difficulties and high cost in recovering high-quality samples from deepwater sites, there is increasing dependence on in situ testing techniques for determining the geotechnical design parameters. This paper summarizes the findings from a joint industry project, undertaken by the Norwegian Geotechnical Institute and the Centre for Offshore Foundation Systems at The University of Western Australia, on the use of in situ testing for the characterization of deepwater soft soils. The project focused on theoretical and empirical studies for the interpretation of piezocone, T-bar, and ball penetration test data, linking the penetration resistance to shear strengths determined from in situ vane tests and laboratory tests on high-quality samples. Guidelines are summarized for interpreting in situ test data, particularly for estimating intact and remoulded undrained shear strengths from the penetration resistance measured by each type of penetrometer. Suggestions are also given for future development of in situ testing techniques to maximize the potential of in situ testing in characterization of deepwater soft soils.
Canadian Geotechnical Journal, 2013