Journal Published Online: 12 May 2025
Volume 48, Issue 4

Improvement of Large-Scale Direct Shear Apparatus by Cancelling Interface Friction

CODEN: GTJODJ

Abstract

Since the construction of a large-size direct shear (DS) testing apparatus in 1986, the authors’ research team has used the DS test method for shear strength tests on dam materials. This preference is due to its simplicity, controllability, and the clear correlation between test results and shear strength theory compared with the consolidated-drained triaxial compression (TC CD) test. However, this test method has not been fully accepted and put into practical use because the shear strengths from DS tests were usually higher than those from TC CD tests. The aims of this study are as follows: (1) to clarify the reasons why the DS test results show much higher shear strengths compared with those from the TC test; (2) to improve the testing apparatus based on the findings; (3) to conduct verification DS tests using the improved DS apparatus on two coarse-grained materials (material-A and material C-40) in both saturated and air-dried conditions; and (4) to conduct a series of TC tests using the large-size triaxial apparatus to compare both shear strengths and discuss the differences. The main findings are as follows: (1) as the upper shear box of the original apparatus was fixed, the dilatancy-induced friction between the specimen and the sidewall of the shear box during shearing caused an unaccounted excessive vertical load and consequently led to the higher shear strength; (2) after modifying the upper shear box to a movable type with a roller bearing slider, the shear strengths from the DS tests were equivalent to those from the TC tests; and (3) the ratios of specimen dimensions to the maximum grain size Dmax, H/Dmax, L/Dmax, or W/Dmax ≥ 10.7 in the DS tests were sufficient to obtain equivalent shear strengths as those from the TC tests.

Author Information

Suzuki, Sreng Sokkheang
Research and Development Center, Nippon Koei Co., Ltd., Tsukuba, Ibaraki, Japan
Uemura, Kentaro
Research and Development Center, Nippon Koei Co., Ltd., Tsukuba, Ibaraki, Japan
Ishikawa, Hiroki
Sapporo Branch Office, Nippon Koei Co., Ltd., Sapporo, Hokkaido, Japan
Fukuda, Kentaro
Research and Development Center, Nippon Koei Co., Ltd., Tsukuba, Ibaraki, Japan
Li, Liming
Department of Civil Engineering and Engineering Mechanics, Columbia University, New York, NY, USA
Mochizuki, Akitoshi
Department of Civil and Environmental Engineering, Tokushima University, Tokushima, Japan
Pages: 18
Price: $25.00
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Details
Stock #: GTJ20240030
ISSN: 0149-6115
DOI: 10.1520/GTJ20240030