ISSN: 1945-7545
CODEN: GTJODJ
Page Count: 16

Compaction of Sand-Processed Clay Soil Mixtures

Howell, JL
Geotechnical engineer, Shepherd Miller, Inc., Fort Collins, CO

Shackelford, CD
Associate professor, Colorado State University, Fort Collins, CO

Amer, NH
Lecturer, Military Technical College, Kobry El-Kobba, Cairo,

Stern, RT
Staff engineer, Golder Assoc., Inc., Lakewood, CO

Abstract

The effects of type of processed clay soil, curing period, and mixing procedure on laboratory compaction of sand-attapulgite clay (S-AC), sand-granular bentonite (S-GB), sand-powdery bentonite (S-PB), and sand-attapulgite clay-granular bentonite (S-AC-GB) mixtures are evaluated. Compaction is evaluated for total clay soil contents of 10, 15, and 20%. Different trends in optimum water content, w_opt, and maximum dry unit weight, γ_dmax, versus clay soil content among the S-AC, S-GB, and S-PB mixtures are attributed, in part, to (1) the greater water sorptivity and lower swelling potential of attapulgite clay relative to the bentonites, (2) the larger particle sizes of the granular bentonite in the air-dried condition relative to the powdery bentonite, and (3) the possible correlation between the w_opt and the plasticity index of the sand-bentonite mixtures. The Δw_opt values and Δγ_dmax values resulting from one-day versus seven-day curing periods before compaction of the S-GB and S-PB mixtures are ∼0.5 percentage points and ≤0.08 kN/m³ (≤0.5 pcf), respectively, and result in different trends in γ_dmax versus bentonite content for the two types of sand-bentonite mixtures. Also, mixing the sand and bentonite in a dry condition before adding water consistently results in greater w_opt and γ_dmax values than mixing the sand with the appropriate amount of water before adding the bentonite regardless of the type of bentonite. Finally, mixing the attapulgite clay and granular bentonite together in small amounts for each individual compaction point for the S-AC-GB mixtures consistently results in higher γ_dmax and w_opt values relative to mixing the attapulgite clay and granular bentonite together in large amounts sufficient to cover all compaction points.

Keywords:
activity, attapulgite, Atterberg limits, bentonite, compaction, curing, granular bentonite, powdery bentonite, sand-attapulgite clay mixtures, sand-bentonite mixtures, sand-clay soil mixtures

Paper ID: GTJ10411J
DOI: 10.1520/GTJ10411J
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