This paper presents the results of a series of tests run on specimens of a low-plasticity clay (LL = 34, PI = 12) with a calcite content of approximately 25 percent by weight. The naturally occurring clay tested is from playa lake deposits in southern Idaho. This test program investigated the strength of labratory compacted specimens as a function of time and curing conditions. Specimens of 33.3 mm (1.3 in.) diameter were prepared using the Harvard miniature kneading compaction device. Specimens for strength testing were prepared with water contents at optimum (16.5 percent) and 4.5 percent dry of optimum (12 percent). The latter value is approximately the water content of the material as-sampled. After compaction, specimens were allowed to cure under either air-dry or moist conditions prior to strength testing. The unconfined strength [ASTM Tests for Unconfined Compressive Strength of Cohesive Soil (D 2166-66)] of replicated specimens was measured at times ranging from several minutes to three months after compaction. The results of these tests showed substantial strength gain with loss of moisture. Most of the increase in strength was experienced within the first 8 h of air-drying while the increase was more gradual for the moist cured specimens. The specimens compacted at optimum water content exhibited higher strengths than those compacted dry of optimum after curing. In the as-molded condition, however, the dry-of-optimum specimens were stronger.

The split-Hopkinson pressure bar (SHPB) technique has been adapted to measure the dynamic response of soil to impulse loads. The experimental technique is relatively simple and can investigate soil response in regimes beyond the capabilities of current equipment used for dynamic soil laboratory investigations. Soils have several characteristics that must be considered in designing a SHPB experiment and evaluating the data (for example, low wave speeds, nonlinear hysteretic behavior, and low unconfined compressive strength compared to the applied loads). Insight has been gained as to how these factors affect experimental accuracy and data reliability. It has been shown that the experimental assumptions can be satisfied and that the experimental results can be replicated.