Drained strength of bentonite-enhanced sand

Mollins, L. H.; Stewart, Douglas I.; Cousens, T. W.

doi:10.1680/geot.1999.49.4.523

Cited by 31 publications

(11 citation statements)

References 9 publications

(10 reference statements)

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“…Although the impact of fines can be significant, the friction angle is not simply proportional to the fines content. For example, friction angles in most pure quartz sands are 38e40 , but increase up to 44e49 when 5 wt% bentonite (smectite) is added, then decrease to 27e31 when the bentonite content reaches 20 wt% (Mollins et al, 1999). Note in Figure 8B that the DSC subsection of core 20P contains 12e15 wt% smectite, and 69e70 wt% quartzitic sands .…”

Section: Large-strain Properties: Shear Strength and Friction Anglementioning

confidence: 99%

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Hydro-bio-geomechanical properties of hydrate-bearing sediments from Nankai Trough

Santamarina

Dai

Terzariol

et al. 2015

Marine and Petroleum Geology

207

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a b s t r a c tNatural hydrate-bearing sediments from the Nankai Trough, offshore Japan, were studied using the Pressure Core Characterization Tools (PCCTs) to obtain geomechanical, hydrological, electrical, and biological properties under in situ pressure, temperature, and restored effective stress conditions. Measurement results, combined with index-property data and analytical physics-based models, provide unique insight into hydrate-bearing sediments in situ. Tested cores contain some silty-sands, but are predominantly sandy-and clayey-silts. Hydrate saturations S h range from 0.15 to 0.74, with significant concentrations in the silty-sands. Wave velocity and flexible-wall permeameter measurements on neverdepressurized pressure-core sediments suggest hydrates in the coarser-grained zones, the silty-sands where S h exceeds 0.4, contribute to soil-skeletal stability and are load-bearing. In the sandy-and clayey-silts, where S h < 0.4, the state of effective stress and stress history are significant factors determining sediment stiffness. Controlled depressurization tests show that hydrate dissociation occurs too quickly to maintain thermodynamic equilibrium, and pressureetemperature conditions track the hydrate stability boundary in pure-water, rather than that in seawater, in spite of both the in situ pore water and the water used to maintain specimen pore pressure prior to dissociation being saline. Hydrate dissociation accompanied with fines migration caused up to 2.4% vertical strain contraction. The firstever direct shear measurements on never-depressurized pressure-core specimens show hydratebearing sediments have higher sediment strength and peak friction angle than post-dissociation sediments, but the residual friction angle remains the same in both cases. Permeability measurements made before and after hydrate dissociation demonstrate that water permeability increases after dissociation, but the gain is limited by the transition from hydrate saturation before dissociation to gas saturation after dissociation. In a proof-of-concept study, sediment microbial communities were successfully extracted and stored under high-pressure, anoxic conditions. Depressurized samples of these extractions were incubated in air, where microbes exhibited temperature-dependent growth rates.Published by Elsevier Ltd.

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Section: Large-strain Properties: Shear Strength and Friction Anglementioning

confidence: 99%

“…The specimen contains 12e15 wt% smectite . For reference, crosses are plotted for measurements on dry mixtures of quartz sand and 20 wt% smectite (Mollins et al, 1999).…”

Section: P-and S-wave Velocities At Hydrostatic Pressure (Iptc)mentioning

confidence: 99%

Hydro-bio-geomechanical properties of hydrate-bearing sediments from Nankai Trough

Santamarina

Dai

Terzariol

et al. 2015

Marine and Petroleum Geology

207

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“…Thus it is reasonable to assume that there is a matrix of contiguous sand particles within such mixtures. Mollins et al (1999) showed that the peak strength and maximum rate of dilation of saturated BES varied with the sand void ratio in a manner indistinguishable from the behaviour of the sand alone. They concluded that in saturated mixtures containing 5 and 10% bentonite the applied stresses must be supported primarily by a matrix of contiguous sand particles, and that the bentonite made a negligible contribution directly to strength.…”

Section: Discussionmentioning

confidence: 89%

The strength of unsaturated bentonite-enhanced sand

Stewart¹,

Tay²,

Cousens³

2001

Géotechnique

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A modi®cation to Rowe's stress-dilatancy equation is presented that extends its range of application to include unsaturated soil behaviour. The results of a programme of constant water content triaxial tests on unsaturated bentonite-enhanced sand (BES) are reported, together with those of a programme of saturated drained triaxial tests on the sand. It is shown that the variation in the rate of dilation at failure with the sand relative density is similar for the two materials. It is proposed that the packing and friction angle of the sand particles and the degree of saturation control the shear strength of unsaturated BES containing modest amounts of bentonite, and that the shear strength of the bentonite component can be ignored.

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“…Therefore, some researchers have studied the possibility of use of PCC bottom ash in various construction applications, e.g., fill and landfill liners, after modifying its properties by mixing it with various admixtures, e.g., Das et al (1978), Lovell (1990, 1993), Kayabali and Bulus (2000), , Kumar and Stewart (2003a, b), Vaddu (2003, 2004), and Seals et al (1972). There is an ample of literature available on the structural, chemical, and mechanical properties of silty clays and sands amended with various admixtures (e.g., Odell et al, 1960;Sivapullaiah et al, 1996;Abeele, 1986;Chapuis, 1990;Pandian et al 1995;Mollins et al, 1996Mollins et al, , 1999Magistris et al, 1998;Kumar and Yong, 2002). However, studies on morphological analysis of PCC bottom ash-bentonite composite are scarce, if any.…”

Section: Introductionmentioning

confidence: 99%

Morphological and strength analysis of PCC bottom ash amended with bentonite

et al. 2006

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Within the last few years several studies have been completed to evaluate strength, stiffness, and durability properties of pulverized coal combustion (PCC) bottom ash mixed with various admixtures. Studies have shown that strength and stiffness of PCC bottom ash mixed with sodium bentonite changes with the increase in the curing period. Researchers have concluded that this change is due to the chemical composition of the bottom ash and bentonite. In order to understand the reasons for the change in characteristics of bottom ashbentonite mixtures with time, the strength and structural characteristics of bottom ash-bentonite mixtures cured for various periods was evaluated. Results of the strength testing showed increase in strength and stiffness of the mixtures with curing period. The results of structural analysis using environmental scanning electron microscopy show development of fibrous elements which may cause increase in the unconfined compressive strength and stiffness of the mixtures with the curing period. Selected results from this study are presented herein.

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Drained strength of bentonite-enhanced sand

Cited by 31 publications

References 9 publications

Hydro-bio-geomechanical properties of hydrate-bearing sediments from Nankai Trough

Hydro-bio-geomechanical properties of hydrate-bearing sediments from Nankai Trough

The strength of unsaturated bentonite-enhanced sand

Morphological and strength analysis of PCC bottom ash amended with bentonite

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