土釘加勁技術主要靠密集的土釘打設，使土釘與周圍土壤形成一連貫性實體，並利用土釘抗張的特性對邊坡產生約束作用，然密間距情況下可能導致土釘周圍應力影響範圍重疊，而造成拉出阻抗下降。有鑑於此，本研究以單釘拉出試驗瞭解土釘拉出行為，以描述粗糙因子R與拉出阻抗的關係。透過雙釘及群釘試驗結果，剖析尺寸效應對雙釘及群釘拉出阻抗之影響，並建立雙釘及群釘拉出經驗模式。最後，亦藉由孔穴擴張理論，模擬土釘拉出-位移曲線及探討尺寸效應對土釘拉出阻抗之影響。 經由試驗結果及理論分析得到以下結論：(1)在直徑、牙距及覆土壓力影響下，粗糙釘的尖峰及殘餘視摩擦係數隨直徑增加而遞減，且隨牙距及顆粒增加而遞增，但受覆土壓力影響並不明顯；而光滑釘視摩擦係數則不受直徑影響，僅與兩材料間之界面性質有關。(2)雙釘間互制效應及影響範圍受粗糙因子及土釘直徑影響極為明顯，尖峰狀態下，達到100%雙釘效率所需正規化間距S/D與粗糙因子成正比關係，與土釘直徑則成反比關係。(3)在群釘拉出試驗中，相同間距下兩側釘之拉出行為與雙釘試驗的拉出行為相似，而因中間釘影響範圍重疊區塊較兩側釘複雜，導致群釘效率下降；在相同直徑下，群釘效率低於雙釘效率，而群釘效率與土釘直徑則成反比關係。(4)假設土壤膨脹角與拉出位移為線性關係，利用孔穴擴張理論，獲得模擬曲線的趨勢於峰前符合試驗呈近似線性的結果，而峰後行為於殘餘狀態則與試驗結果略有差異。(5)尺寸效應分析結果顯示，視摩擦係數隨覆土壓力與土釘直徑增加而遞減，覆土壓力與直徑增大則視摩擦係數終將達到定值。 Soil-nailing have been widely used in soil excavation and slope stabilization. Closely spaced nails are buried or drilled into soil to form a reinforced structure. Close space between nails then cause stresses overlap, which may reduce the effectiveness of individual nail. The purpose of this study is to investigate the pullout behavior of the nail through the tests of single. A non-dimensional surface roughness factor R was described the interface between nail and soil. In order to understand mechanical behavior of the group nails, experimental program is performed for the tests of double and three nails. Additionally, the cavity expansion theory is made to construct a theoretical model for modeling the pullout force-displacement behavior. The influence of size effect for the pullout resistances of single and group-nails was concerned. The conclusions via the tests and theoretical analysis are summarized: (1) The peak and residual apparent friction coefficients at the soil-nail interface are increased with increase of the screw pitch and particle size but decreased with increase of the nail diameter. The overburden pressure has not a significant influence on the apparent friction coefficient. Besides, such of smooth nails are not influenced by the nail diameter. (2) The group efficiency of a double nail was shown to be dependent on the surface roughness factor and nail diameter. The minimum required distance for 100% efficiency is increased with increasing the surface roughness factor but reduced with increasing the nail diameter. (3) In the group tests, the pullout behavior of both sides nails is similar a double nail. However, the influence overlap zone of the center nail is complex; the pullout resistance of a center nail is less than a both sides nail in the test results. (4) Using the cavity expansion theory to model the pullout force-displacement behavior is performed by way of the assumption for the linear relationship of soil dilative angle and pullout displacement. (5) Analytical results reveal that the apparent friction coefficient reduced with increasing overburden pressure and nail diameter. Apparent friction coefficient reaches a constant value while the large diameter and/or the higher overburden pressure.
