Volume 20, Issue 4 (December 1997)
Compaction of Sand-Processed Clay Soil Mixtures
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, wopt, and maximum dry unit weight, γdmax, 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 wopt and the plasticity index of the sand-bentonite mixtures. The Δwopt values and Δγdmax 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 γdmax 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 wopt and γdmax 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 γdmax and wopt values relative to mixing the attapulgite clay and granular bentonite together in large amounts sufficient to cover all compaction points.