砂土於中型土槽中盤剪行為之研究

A Study on the Disc Shearing Behavior of Sands in a Mid-size Soil Tank

黃衍翔(Yan-Xiang Huang)

指導教授 ： 馮道偉

中原大學/工學院/土木工程學系/碩士(2008年)

https://doi.org/10.6840/cycu200900226

摘要

盤剪工法係以圓盤施加一正向應力及轉動之水平剪力於砂土，可讓砂土顆粒產生側向位移而錯動，並具壓實效果，促使砂土顆粒間結合更為緊密，進而提高砂土強度。
本研究主要目的是探討砂土於中型土槽中之盤剪行為，在過去的盤剪試驗中，使用之土樣槽直徑為20 cm，與圓盤直徑19.8 cm之比值約為1，使得在進行盤剪時土樣槽之邊界效應可能對結果造成影響。今於中型土槽中進行盤剪試驗以降低邊界效應，中型土槽內徑為60 cm與圓盤直徑之比值為3。
本研究以麥寮砂及渥太華標準砂二種不同顆粒特性之砂土為土樣，土樣槽內徑為60 cm，盤剪圓盤直徑為20 cm，土樣高度為15 cm，土樣初始相對密度為50 % 。盤剪儀可施加扭力及軸力，實驗中改變載重及圓盤施剪方式，載重為10 ～ 90 kPa，盤剪單位轉角為5∘～45∘，觀察圓盤沉陷量、土樣表面隆起量、側向土壓力、相對密度，並進行圓錐貫入試驗，以推估影響範圍。
試驗結果顯示，相對密度改變量隨載重增加，但改良效果會因砂土顆粒特性不同。由土壓力變化推測盤剪轉角之累積對於砂土相對密度之改良在累積轉角30∘之前效果最為顯著；在累積轉角大於30∘之後，盤剪對於砂土相對密度改良效果趨緩，過多之轉角可能產生塑性破壞而使砂面隆起，且盤剪單位轉角較小者，改良範圍較大，砂土圓錐貫入阻抗值增加較多。盤剪對片狀顆粒土壤之壓縮量較圓狀顆粒效果明顯，麥寮砂在盤剪後圓錐貫入阻抗改變量與試體完成時之比值約為標準砂之2倍。

關鍵字

盤剪 ； 砂土行為

並列摘要

Disc shearing induces a normal stress and a horizontal shear force on the sand samples. This may produce lateral displacement of sand particles to enhance the sand strength and make the sand grains closely packed.
The main purpose of the study is to investigate the disc shearing in sand in the mid-size soil tank. In the previous disc shearing experiments, the caliber ratio between the soil tank and the disc is approximately 1 (20 cm: 19.8 cm). Such a ratio may indicate a boundary effect on test results. The ratio between the internal diameter of the mid-sized tank and the disc caliber is 3. That ratio indicates a reduction in the boundary effect on test results.
In this study, Mailiao sand and Ottawa sand are used as soil samples to include two different grain characteristics. The internal diameter of the soil tank is 60 cm, the diameter of the shearing disc is 20 cm, the height of the soil sample is 15 cm, and the initial relative density of the soil sample is 50%. The shearing instrument can exert both torsion and force to load and shear the disc during the tests. The load varies from 10 to 90 kPa, the shearing unit angle varies from 5∘to 45∘. The disc settlement, the amount of sand surface heave, the lateral earth pressure, and the relative density are observed. The cone penetration test is carried out.
The results show that relative density of sand changes with increasing loads,and is a function of grain characteristics. To estimate the accumulate angles of disc shearing in accordance with the changes of soil pressure, the effect will be the most obvious when the accumulated angles reaches 30∘. When the accumulate angles go over 30∘, disc shearing may not influence as much as they remains under or equal to 30∘. Excessive accumulated angles will produce plastic failure and heaving of sand surface. Less accumulated angles have a larger enhancement range and more increase on cone penetration resistance. Disc shearing enhances flaky grains more than rounded ones. Compared with Ottawa sand, the cone penetration resistance ratio of Mailiao sand is double after disc shearing.

並列關鍵字

Behavior of Sands ； Disc Shearing

參考文獻

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