盤剪為施加一個水平方向之剪應力於試樣,可讓土壤的顆粒產生側向位移和顆粒間的錯動,促使砂土顆粒排列更為緊密。 本研究的主要目的是探討不同盤剪方式對疏鬆砂土相對密度之影響。藉由改變載重、試樣單層厚度及盤轉方式等變因進行一系列盤剪試驗,從中量測試樣壓縮量及圓錐貫入阻抗,以評估盤剪效果與各個變因之關係。本研究使用之圓盤剪力儀系統可自動記錄壓縮量及圓錐貫入阻抗,土樣槽直徑20 cm,土樣為初始相對密度30%之麥寮砂、標準砂及越南砂,以載重20 kPa、60 kPa或100 kPa,進行單向轉角10°、20°、30°、60°及90°之往復式盤剪試驗。 試驗結果顯示,試樣相對密度並因為盤剪累積轉角的增加而增加,且會漸趨近一最大值,此一最大值與載重成正比。試樣初始厚度影響改良後之相對密度,試樣土層厚度較薄之砂土改良效果較好;砂土顆粒形狀偏向片狀多角形且粒徑小者改良效果優於立方體狀且粒徑較大者。盤剪之相對密度改變量與往復剪動的次數關係密切,建議往復盤剪之單向轉角以10°~ 30°較為適宜。
Plate shearing exerts a horizontal shear force to cause lateral displacement and rearrangement of soil grains. In this way, sand grains are closely packed. The purpose of this study is to probe into the effect of type of plate shearing on the relative density and cone penetration resistance of sands. With changing the normal stress, the thickness of specimen, and the type of plate shearing, a series of tests are conducted and the compression and the cone penetration resistance of the specimen are measured. Diameter of the specimen is 20 cm. The specimens of the Mailiao sand, Ottawa sand and Vietnam sand were carried out with initial relative density of 30%. Normal stresses of 20 kPa, 60 kPa and 100 kPa, one-way shear angle 10°, 20°, 30°, 60°, 90°, and different accumulated angle were used. The results of this study show that the relative density of the specimen will increase with the accumulated angle of shearing to a maximum value. This maximum value is directly proportional to the normal stress. The initial thickness of soil specimen affects the improvement of relative density. The smaller thickness of the specimen, the better is the improvement result; flaky and small Mailiao sand is improved better than the chunky and larger Ottawa sand and Vietnam sand. The relationship between the improvement of relative density and the reversal number of times is clear, and it is suggested that one-way shear angle of reversal plate shearing is better at 10°~30°.