Study on friction characteristic around shield machine using direct shear apparatus.
In shield tunnelling, frictional resistance between the shield and the ground, and that between the segment and the grease are a predominant factor of jack thrust. However, there is no test results about the friction characteristics around shield. Therefore, this research aims to search the friction characteristics between the segment and the grease, and those between the skin plate and the slurry by the direct shear test.
Material 1 (steel and concrete), roughness of steel specimen, material 2 (grease and slurry) , shear speed are adopted as the test parameters. Since the direct shear test is carried out by using the lower and upper box with the gap of 0.2mm, the grease and the slurry are leaked into the gap as increase of confining pressure. Therefore, the calibration for the leakage of the material was applied taking account of the leakage of material 2.
The followings were made clear by this research.
1）The friction of the direct shear apparatus is negligible, compared with the measured shear force. The direct shear test can be done by using the same specimen up to 3 times.
2）Peak strength: Grease and slurry have no peak strength.
3）Shear speed: In case of Material 1:steel, there is no influence on friction force. While in case of Material 1:concrete, the residual shear force under shear speed 0.2 mm/min is larger than that under shear speed 0.5 mm/min. Since the shear displacement-shear stress relation is not so stable for Material 1:concrete, further research is required.
4）Roughness of steel: there is no influence on friction force under Ry < 10mm. In case of Material 1:steel and grease, the residual shear force becomes larger as the steel roughness increases.
5）Materila 1: the residual shear force between steel-grease is larger than that between concrete-grease. Since the shear displacement-shear stress relation is not so stable for Material 1:concrete, further research is required.
6）Leakage of Material 2: The leakage of Material 2 increases as the increase of confining pressure. But from the view points of this test purpose, it is possible to evaluate the residual shear stress under the following conditions: 1) the confining stress keeps constant; 2) the influence of the leakage of Material 2 can be calibrated.
7）In this research, in the case of Material 1:concrete and Material 2: slurry with high confining pressure, the test results has low accuracy.