| Summary: | 碩士 === 淡江大學 === 土木工程學系碩士班 === 106 === The objective of this project is to develop soil nails with knots. By changing the force mechanism of grouted nails, pullout resistance can be more effectively developed when used in poor geological conditions. Large sand box were used to do single nail pull out test. And the results were then compared with those done on the conventional grouted nails to investigate how knot diameters 40 mm, 50 mm, 60mm, 80 mm, and spacing between two knots influenced pullout resistance.
The test results showed that: (1) Conventional grouted nails developed peak pullout force at a displacement of within 10 mm. At the same displacement of 10 mm soil nails with knots already showed higher pullout force than grouted nails. Because of the passive resistance, soil nails with knots needed larger displacement to reach peak pullout force. (2) The soil nails with one knot’s residual of pullout resistance is the same as peak force. When soil nail add to two knots, it can hold at least 93% of its peak resistance. While the residual pullout resistance for grouted nails are 80%~94%. (3) When there is screw exist at the knot active zone where the knots were installed. It will influence the failure mode. Its pullout resistance will have only 75% left. (4) Adding knot on screw can increase pullout resistance, but when the knot’s diameter is too similar to screw’s diameter, the ability of pullout resistance is provided by screw’s friction resistance. Therefore, the diameter of knot and screw can’t be too similar. Or else the passive earth pressure by knot could not be effectively utilized. (5) The smallest Interaction coefficient of soil nail with one knot still have 0.74, higher then grouted nail 0.73. When adding to two knots, its interaction coefficient cause 0.97~1.54. Interaction coefficient can achieve to 1.75 when adding to three knots. (6) Whether the knot diameter, when the spacing of knots is more than twice of knots dimeter, can completely develop knot passive resistance. (7) In the same diameter, the pullout resistance of soil nail with one knot can increase 13%~57% than grouted nail. (8) In the same diameter, the pullout resistance of soil nail with two knots can increase 18%~60% than soil nail with one knot, and can increase 39%~153% than grouted nail. (9) After the research suggest using soil nail with knot that is better than grouted nail. But the test results show that knot diameter 40 mm and 50 mm its effect is limited, so doesn’t recommend small knot diameter.
After the test results, interpreted knot develop percentage (refer to the thesis) to predict soil nail with knots peak pullout force in different spacing. Hope it can serve as a practice reference for the industry.
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