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), sa nd-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, gamma(dmax), versus clay soil content among the S-AC, S-G B, 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 bento nite in the air-dried condition relative to the powdery bentonite, and (3) the possible correlation between the w(opt) and the plasticity in dex of the sand-bentonite mixtures. The Delta w(opt) values and Delta gamma(dmax) values resulting from one-day versus seven-day curing peri ods before compaction of the S-GB and S-PB mixtures are similar to 0.5 percentage points and less than or equal to 0.08 kN/m(3) (less than o r equal to 0.5 pcf), respectively, and result in different trends in g amma(dmax) versus bentonite content for the two types of sand-bentonit e mixtures. Also, mixing the sand and bentonite in a dry condition bef ore adding water consistently results in greater w(opt) and gamma(dmax ) values than mixing the sand with the appropriate amount of water bef ore adding the bentonite regardless of the type of bentonite. Finally mixing the attapulgite clay and granular bentonite together in small a mounts for each individual compaction point for the S-AC-GB mixtures c onsistently results in higher gamma(dmax) and w(opt) values relative t o mixing the attapulgite clay and granular bentonite together in large amounts sufficient to cover all compaction points.