Volume 31, Issue 1 (January 2008)
Effects of Specimen Size and Some Other Factors on the Strength and Deformation of Granular Soil in Direct Shear Tests
Four direct shear (DS) apparatuses having different sizes with the specimen lengths ranging from 40 to 800 mm were constructed in the study. The vertical and shear stresses acting on the shear zone were measured as accurately as possible confirming its importance. Noticeable effects of specimen shape were observed. The effects of specimen size were evaluated by performing constant pressure DS tests on a fine poorly graded sand (Toyoura sand) in the small, semimedium, medium and large DS apparatuses and a well-graded sandy gravel in the medium DS apparatus. The residual shear strength of Toyoura sand was independent of the specimen size and initial density. Due likely to specimen size effects on both progressive failure and boundary mechanical restraint, the peak strength decreased with an increase in the specimen size. As the specimen size increased with dense Toyoura sand and as the particle size increased in the medium DS tests, the shear displacement at the peak stress and the ultimate volume increase at the residual state consistently increased while the postpeak strain softening became slower. These specimen size effects can be attributed to the thickness of shear zone and the number of shear bands included in the shear zone.