ISSN: 1945-7545
CODEN: GTJODJ
Published Online: 17 December 2003
Page Count: 10

Reduction of Boundary Friction in Model Tests

Fang, YS
Professor and chairman, National Chiao Tung University, Hsinchu, Taiwan

Chen, T-J
Geotechnical Engineer, Sinotech Engineering Consultants Ltd., Taipei, Taiwan

Holtz, RD
Professor, University of Washington, Seattle, WA

Lee, WF
Associate Research Fellow, Geotechnical and Hazard Mitigation Engineering Division, Taiwan Construction Research Institute, Taipei, Taiwan

(Received 10 September 2001; accepted 20 February 2003)

Abstract

To model plane-strain conditions in the laboratory, the frictional resistance between the soil and side walls of the soil box should be reduced as much as possible. Methods commonly employed for this purpose include a latex sheet with silicon grease (“grease method”) or multiple layers of thin plastic sheeting (“plastic sheet method”). Interface friction angles are often measured by direct shear-type tests.

In this paper, a new sliding block testing device for measuring the friction at the interface between soil and different materials at low stress conditions is described. Interface friction angles for eight different methods for reducing boundary friction were investigated using the proposed testing method. Test results indicated that the friction angle obtained with the plastic sheet method is nearly independent of the normal stress. On the other hand, the interface friction angle of the grease method was quite high under low normal stress conditions. Thus, the plastic sheet method appears to be a more appropriate technique under low normal stress conditions to reduce the boundary friction for laboratory scale model tests. As compared with the grease method, advantages of the plastic sheet method include constant friction angles, less time for preparation and cleanup, and lower cost.

To investigate their applicability, both lubrication systems were used in some large-scale laboratory-retaining wall experiments. Earth pressure measurements obtained near the sidewalls indicated that, under a low normal stress, the plastic sheet method was more effective in reducing sidewall friction.

Keywords:
sliding block test, interface friction, laboratory test, plastic sheet, silicone grease, retaining wall, sand

Paper ID: GTJ10812
DOI: 10.1520/GTJ10812
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