A study has been made of the precision of the moisture condition test with the aid of ten independent laboratories. Values of repeatability and reproducibility, in terms of the moisture condition value (mcv), were determined for two soils, a heavy clay and a well-graded sand, each at four different test levels. The precision of the test on the sand was considerably poorer than on the heavy clay; the principal reason for this is likely to be the smaller changes in volume associated with the compaction of the more granular, or less cohesive, soils. For the heavy clay the repeatability and reproducibility were respectively 0.8 and 1.6 units of mcv, and these values are considered to apply to soils where the plotted relation between change in penetration of the rammer and number of blows (used in the determination of mcv) has a slope exceeding 8 mm per logarithmic cycle of blows. The equivalent values for the sand were 1.6 and 2.3 units of mcv, considered to apply to soils where the slope of the above-mentioned relation lies in the range of 3 to 8 mm per logarithmic cycle of blows. The study highlighted certain difficulties involving test procedures and the condition of the apparatus, and appropriate amendments have been made to the text of the test procedure to overcome the problems.
Abstract