A platform for research: civil engineering, architecture and urbanism
A platform for research: civil engineering, architecture and urbanism
Experimental Study on the Effectiveness of Lubricants in Reducing Sidewall Friction
In geotechnical tests, a thin layer of lubricants is usually applied along interfaces between tested soils and the sidewall of a container to minimize interface friction (shear strength). The effectiveness of lubricants in reducing the interface friction has not yet been fully evaluated. In this paper, the effectiveness of several commonly used lubricants in reducing the sidewall friction is presented through backfilling and stress measurement tests performed in a lightly instrumented column. The interface friction angles are back calculated from the measured stresses, using an arching analytical solution. The results show that the most efficient among the tested lubricants is a combination of Teflon and silicone grease, which can reduce the interface friction angle to 16.8°, a value far from being qualified as negligible. For most cases, the application of lubricants has little or no effect in reducing the sidewall friction. For some cases, the application of a lubricant material can even increase the sidewall friction angle. To verify these somehow surprising results, direct shear tests were performed to obtain direct measurements of the interface friction angles between the tested sand and the tested lubricant materials. Very small normal stresses were applied and the sand was gently placed in the shear box to imitate the testing conditions of column filling tests. The good agreement between the directly measured and back-calculated interface friction angles indicates that the column tests and the back-calculated results are reliable. Further analysis reveals that the small cohesion of lubricant materials can become negligible under a high stress state. Under a low stress state, this small cohesion can be translated into high friction. It is concluded that the tested lubricants may be efficient under high stress conditions, but not efficient under low stress conditions. For the latter case, the consideration of zero sidewall friction between the tested soil and lubricated sidewall of the container can lead to inaccurate and even totally wrong results.
Experimental Study on the Effectiveness of Lubricants in Reducing Sidewall Friction
In geotechnical tests, a thin layer of lubricants is usually applied along interfaces between tested soils and the sidewall of a container to minimize interface friction (shear strength). The effectiveness of lubricants in reducing the interface friction has not yet been fully evaluated. In this paper, the effectiveness of several commonly used lubricants in reducing the sidewall friction is presented through backfilling and stress measurement tests performed in a lightly instrumented column. The interface friction angles are back calculated from the measured stresses, using an arching analytical solution. The results show that the most efficient among the tested lubricants is a combination of Teflon and silicone grease, which can reduce the interface friction angle to 16.8°, a value far from being qualified as negligible. For most cases, the application of lubricants has little or no effect in reducing the sidewall friction. For some cases, the application of a lubricant material can even increase the sidewall friction angle. To verify these somehow surprising results, direct shear tests were performed to obtain direct measurements of the interface friction angles between the tested sand and the tested lubricant materials. Very small normal stresses were applied and the sand was gently placed in the shear box to imitate the testing conditions of column filling tests. The good agreement between the directly measured and back-calculated interface friction angles indicates that the column tests and the back-calculated results are reliable. Further analysis reveals that the small cohesion of lubricant materials can become negligible under a high stress state. Under a low stress state, this small cohesion can be translated into high friction. It is concluded that the tested lubricants may be efficient under high stress conditions, but not efficient under low stress conditions. For the latter case, the consideration of zero sidewall friction between the tested soil and lubricated sidewall of the container can lead to inaccurate and even totally wrong results.
Experimental Study on the Effectiveness of Lubricants in Reducing Sidewall Friction
Zheng, Jian (author) / Li, Li (author) / Daviault, Maxime (author)
2021-02-22
Article (Journal)
Electronic Resource
Unknown
Solid lubricants reducing friction in threads
| British Library Online Contents | 1992
Requirements for lubricants and friction-reducing effects of slow-hardening lubricants
| British Library Conference Proceedings | 1998
Voltammetry of the friction contact and tribological effectiveness of lubricants
| British Library Online Contents | 2003
| Taylor & Francis Verlag | 2022