Direct Shear Test on Coarse Gap-Graded Fill: Plate Opening Size and Its Effect on Measured Shear Strength

Abstract

In this paper, three different rock-soil mixtures were reconstituted in laboratory, which were designed to mimic the proportions of coarse and fine particles in the high fill used at the airport construction sites. The shear strength of the reconstituted mixtures was determined by both large-scale direct shear tests (DSTs) with different plate opening sizes and triaxial compression tests. By comparing the test results, the most appropriate plate opening size for DSTs on coarse gap-graded rock-soil mixtures is discussed. The test results indicate that the opening size has a significant effect on the measured shear strength of gap-graded rock-soil mixtures. For DSTs under the same normal stress, the peak strength decreases with increasing plate opening size. For the gap-graded mixture with a small proportion of coarse particles, a plate opening size of one-third to one-quarter of the maximum particle size (dmax) is suitable. With a higher coarse particle content, the opening size should be increased appropriately. If the percentage of gravels (5.0 mm < d < 20.0 mm) is more than 47%, a plate opening size of slightly greater or less than one-half dmax is more appropriate.

Experimental Study on the Reliability of Scaling Down Techniques Used in Direct Shear Tests to Determine the Shear Strength of Rockfill and Waste Rocks

“…For direct shear tests, several standards have been proposed and used in practice. Among them, the ASTM D3080/D3080M-11, hereafter called ASTM, is the most popular and the most used worldwide [2,11,[15][16][17][18][19][20][21][22][23]. It was published as ASTM D3080 in 1972 and updated every eight years by the ASTM technical committees.…”

“…This methodology was followed by several researchers [74,75]. However, their direct shear tests were performed by using a W/d max ratio equal to or even smaller than the minimum required value of 10 stipulated by the ASTM standard, exactly the procedure carried out by other researchers [9,16,[19][20][21][22][23]31,58,59,62,63,73,76]. Recently, Deiminiat et al [10] have shown that the minimum required W/d max ratio of 10, stipulated by the ASTM standard, is too small to eliminate SSEs.…”