低塑性粉土因其特殊及敏感之特性，於國內眾多公共工程導致重大工安事故，其中又以深開挖與潛盾隧道施工時引致之管湧災害最為迅速與嚴重；經由相關調查結果可知，災害發生主因大多為敏感性低塑性粉土受內沖蝕效應擾動而産生，然而國內外對此一課題仍未見相關有效之研究。故本研究將利用一系列之分析與試驗，比較現有評估法之優劣，並開發一新式之Flexible Wall Pinhole（簡稱FWP）試驗儀，藉由相關實驗數據來探討內沖蝕效應對低塑性粉土工程性質之影響。
現今用以探討土壤內沖蝕效應方法大致可分為理論與試驗可概分為兩大類，理論法有包含Kenney and Lau（1986）分析原則與管湧理論分析。其中Kenney and Lau（1985）原則雖可考量整體顆粒組成，但無法考量沖蝕水流之作用壓力大小，故仍有不足之處；傳統管湧試驗雖可補足前述之之缺陷，但無法有效地觀察土體內顆粒之孔隙變化，故研究中進一步採用針孔試驗探究其分散性質，但仍因低塑性粉土不具塑性，無法有效分析其內沖蝕效應力影響，且忽略現地有效應力與水壓力之影響，故自行研發FWP試驗儀，以探討內沖蝕效應對低塑性粉土工程性質之影響。
經由FWP試驗結果可知，低塑性粉土之抗內沖蝕能力隨著細粒料含量增加而減少，且隨試體緊密程度提高而加大；由此可知，對於問題低塑性粉土而言，可藉由降低地下水位與提高土層密度等方法，增加其抗內沖蝕效應力能力。

Due to the characteristic of high sensitivity, the low plastic silty sand has induced disasters in several deep excavation projects in Taiwan. The main reason of the disaster can be attributed to the disturbance generating the internal erosion in low plastic silty sand.
There are two main categories to investigate the internal erosion in soils. Kenney and Lau (1986) based on the principle of the piping and considered the whole composition of the particle of the soil, however, the water pore pressure did not take into account in analysis. The traditional piping test may complement the Kenney and Lau’s theory, but the pore change in soil particles was not able to observe effectively in the test. The further developed pinhole test can explore the diffusion properties of soil, however, for a low plastic soil, the data obtained from pinhole test can still not analyze effectively the internal erosion stress and also neglect the influence of in-situ effective stress and water pressure.
In this study, a Flexible Wall Pinhole instrument is developed. The test results shows that the internal erosion resistance decreased and the degree of soil tightness increased as the fine content of the low plastic silty sands increased. And as reducing the groundwater level and increasing the soil density, the internal erosion resistance of low plastic silty sand increased.

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