Enhanced shear strength of sodium bentonite using frictional additives

Conference · Wed Dec 31 04:00:00 EST 1997

OSTI ID:576551

Schmitt, K E ^[1]; Bowders, J J; Gilbert, R B ^[2]; Daniel, D E ^[3]

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1. GeoSyntec Consultants, Huntington Beach, CA (United States)
2. Univ. of Texas, Austin, TX (United States)
3. Univ. of Illinois, Urbana, IL (United States)

One of the most important obstacles to using geosynthetic clay liners (GCLs) in landfill cover systems is the low shear strength provided by the bentonitic portion of the GCL. In this study, the authors propose that granular, frictional materials might be added to the bentonite to form an admixture that would have greater shear strength than the bentonite alone while still raining low hydraulic conductivity. Bentonite was mixed with two separate granular additives, expanded shale and recycled to form mixtures consisting of 20-70% bentonite by weight. In direct shear tests at normal stresses of 34.5-103.5 kPa, effective friction angles were measured as 45{degrees} for the expanded 36{degrees} for the recycled glass, and 7{degrees} for the hydrated granular bentonite. The strength of the expanded shale mixtures increased nearly linearly as the percentage shale in the mixture increased, to 44{degrees} for a bentonite mixture with 80% shale. The addition of recycled glass showed little effect on the shear strength of the mixtures of glass and bentonite. Hydraulic conductivity measurements for both types of mixtures indicated a linear increase with log(k) as the amount of granular additive increased. For applications involving geosynthetic clay liners for cover systems, a mixture of 40% expanded shale and 60% bentonite is recommended, although further testing must be done. The 40/60 mixture satisfies the hydraulic equivalency requirement, with k = 5.1X10{sup -9} cm/sec, while increasing the shear strength parameters of the bentonitic mixture to {phi}{prime} = 17{degrees} and c{prime} = 0.

• Research Organization: USDOE, Washington, DC (United States)
• OSTI ID: 576551
• Report Number(s): CONF-970208--Proc.; ON: DE98001967
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
54 ENVIRONMENTAL SCIENCES
BENTONITE
CONTAINMENT SYSTEMS
FRICTION
HYDRAULIC CONDUCTIVITY
LINERS
POLLUTION CONTROL
SHEAR
STRESSES