ISSN: 0149-6115
Published Online: 16 August 2007
Page Count: 11

Reproducibility of Direct Shear Tests Conducted on Granular Backfill Materials

Bareither, Christopher A.
Graduate Research Assistant,Geological Engineering, University of Wisconsin-Madison,WI,

Benson, Craig H.
Professor and Kellet Fellow,Geological Engineering, University of Wisconsin-Madison,WI,

Edil, Tuncer B.
Professor and Chairman,Geological Engineering, University of Wisconsin-Madison,WI,

(Received 26 October 2006; accepted 17 June 2007)

Abstract

Intra-laboratory and inter-laboratory testing was conducted to assess the bias, repeatability, and reproducibility of the shear strength of compacted granular backfill materials tested in direct shear using AASHTO T 236. Inter-laboratory testing was conducted by ten laboratories using four granular backfill materials. Triaxial compression tests were also conducted on the granular backfill materials to establish a reference friction angle (ϕ^′) for computing bias. Comparison of failure envelopes and friction angles from the intra-laboratory study showed that the test method is highly repeatable (ϕ^′±0.1^°) when conducted in a single laboratory by a single operator using the same equipment. In contrast, data from the inter-laboratory study showed high variability in the failure envelopes and friction angles, with ϕ^′ varying by as much as 18.2° for a given backfill. Analysis of the data from the inter-laboratory study showed that the reproducibility of direct shear tests on granular backfill is 8.8°. The bias in ϕ^′ is −2.5^° when area corrections are not applied and −1.5^° when area corrections are applied.

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Paper ID: GTJ100878
DOI: 10.1520/GTJ100878
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