End Restraint Effects on Cyclic Triaxial Strength of Sand

Cyclic triaxial tests were performed on various soils at different densities and different consolidation pressures, using regular and lubricated ends to explore the possible effect of end restraint. In addition, a number of supplementary tests were also performed, all of which led to the conclusion that for sands tested, the following factors had no measurable effects on the cyclic triaxial strengths: cyclic frequency, load shape, small center dowels at the ends, and sample diameter. The end restraint study showed that the cyclic strength was greater for frictionless ends than for regular ends by amounts ranging from zero for nondilatant soils, to as much as 35% for dense, very dilatant sands. For the usual cases of loose to medium dense sands, for which cyclic tests are most frequently performed, the apparent strength increase is only about 10%, which has already been included in the C_r factor for converting cyclic triaxial results to field strengths.