節瘤型土釘之最佳節瘤間距之研究

本研究旨在開發新型節瘤型土釘，改變傳統灌漿釘受力機制與模式，使土釘於地質條件不佳條件下能有效發揮拉出阻抗能力。以大型土釘拉出試驗儀進行單釘試驗，試體分別製作外徑40 mm、50 mm、60 mm與80 mm四種尺寸與傳統灌漿釘做為對比。探討節瘤型土釘之節瘤外徑及間距對拉出阻抗之影響，求得最佳節瘤間距之研究。　　由試驗結果得知: (1)傳統灌漿釘於位移10 mm內可達尖峰拉出力，而節瘤型土釘在位移10 mm時拉出力已高於傳統灌漿釘；而節瘤型土釘因被動阻抗的產生，需更大位移量才會達尖峰拉出力，甚至於30 mm時還未到達尖峰拉出力。(2) 不論何種尺寸之單一節瘤，在大位移時之殘餘拉出力與尖峰值幾乎相同；而當裝有兩顆節瘤時其殘餘拉出力最低仍有有93%以上，優於傳統灌漿釘僅剩餘約80%~94%。 (3)節瘤裝設位置主動區存有螺桿時，會影響到節瘤破壞發展模式，使阻抗力僅剩75%。(4) 純螺桿裝設節瘤時能提升拉出阻抗，但當螺桿直徑與節瘤直徑相差不大時，其主要阻抗能力是來自螺桿的摩擦阻抗，因此節瘤直徑與螺桿直徑不能太相近，否則無法有效發揮節瘤被動阻抗能力。(5)當裝有節瘤時，其互制係數最小仍有0.74高過灌漿釘之最大摩擦係數0.73，於裝設兩顆節瘤時，其互制係數為0.97~1.54，而當裝有三顆節瘤時其互制係數可高達1.75。(6)不論何種節瘤直徑，當節瘤間距相隔達到其直徑兩倍時，能使節瘤完整發揮被動阻抗，不互相影響。(7)節瘤型土釘為單一節瘤時相較同尺寸傳統灌漿釘，其抗拉能力增加13%~57%。(8)當節瘤型土釘裝設兩顆節瘤時，其抗拉能力相較同尺寸單一節瘤提升18% ~ 60%，較傳統灌漿釘提升39%~153%。(9)經過本研究建議工程上採用節瘤型土釘其阻抗效果優於傳統灌漿釘，但節瘤直徑40 mm與50 mm在本研究裡獲得其效益有限，不建議節瘤直徑太小。　　藉由本研究之試驗結果，詮釋節瘤發揮百分比（符號請參照正文）及預測節瘤型土釘在不同節瘤間距下之尖峰拉出力，期可供業界實務之參考使用。

關鍵字

節瘤；土釘；拉出阻抗；間距

並列摘要

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.