台灣西南部地區土層富含顆粒細小且不具塑性之低塑性粉土，工程設計上，常將其與黏土一併視為細粒料，或直接視為砂土，故低塑性粉土工程性質一直未受各界關注。1999年集集地震使台灣中部地區發生大規模土壤液化破壞，由相關災害調查結果顯示，多數土壤液化現象發生於低塑性細粒料含量較高之土層，故引起各界對低塑性粉土工程性質之研究興趣。但傳統取樣法不易於敏感及高含水量之低塑性粉土地層取得原狀土樣，故對於原狀低塑性粉土之工程性質研究至今仍未見具體成果；2004至2005年間，台灣南部地區於低塑性粉土地層接連發生嚴重地質災害，其破壞模式為低塑性粉土之顆粒流失引發管湧災害，進而導致隧道與深開挖破壞，然而，受限於傳統試驗法之儀器限制，至今工程界仍無法掌握低塑性粉土之內沖蝕特性。
為瞭解低塑性粉土之完整工程性質，本研究使用新式Gel-Push取樣器，取得高品質未擾動原狀試體。藉由原狀與重模試體之動態試驗結果得知，土壤強度隨低塑性細粒料含量增加而降低，且低塑性粉土易因擾動而軟化，此外，上述現象會隨細粒料含量增加而趨於明顯。
又為探討低塑性粉土內沖蝕性質，研究中結合傳統三軸試驗與針孔試驗開發Flexible Wall Pin Hole試驗儀。由低塑性粉土內沖蝕試驗結果顯示，低塑性粉土之抗內沖蝕能力受試體細粒料含量、緊密程度與圍壓大小所影響，其內沖蝕破壞潛能隨低塑性細粒料含量與孔隙比增加而降低，且圍壓較大時，其內沖蝕破壞潛能較小。
最後，藉由原狀低塑性粉土試體之試驗結果與傳統土壤液化潛能評估法之分析結果比對發現，現行評估法應用於低塑性粉土地層時會低估土層之液化潛能，故於低塑性粉土地層進行土壤液化潛能評估時，應採用室內試驗分析法為佳。

The soil strata in southwestern Taiwan are dominant in low-plasticity silty sand with fine particles and low-plastic. In engineering design, low-plasticity silty sand was considered as general fine-grained soil, so the engineering properties of low-plasticity silty sand were ignored before. During the 1999 Chi-Chi earthquake, serious soil liquefaction damages were observed in central Taiwan. The post-earthquake study indicated that most soil liquefactions were occurred in silty sand deposits with high fines content. Therefore, the engineering properties of low-plasticity silty sand have been of great research interests in soil liquefaction. However, difficulties occurred in undisturbed sampling of sensitive low-plasticity silty sand material with high fines content and high water content. And the undisturbed engineering properties of low-plasticity silty sand have yet to see. In 2004 to 2005, several catastrophic subway construction failures occurred in south Taiwan. Results of forensic investigation indicated that piping failure of non-plastic silty sand is the dominated factor causing serious tunnel and excavation pit collapses. However, because the limitations of traditional test method, so the engineer can’t understand the internal erosion properties of low-plasticity silty sand.
In an effort to investigate the engineering properties of low-plasticity silty sand, this study had adopted a recently developed “Gel-Push” sampling technique to obtain undisturbed soil samples. Results of cyclic triaxail tests on undisturbed and remolded specimens indicate that, higher non-plastic fines content of silty sand would result in lower cyclic liquefaction resistance. Such low-plasticity silty sand deposits would have less liquefaction resistance when they are subjected to disturbance. And this phenomenon would become much more noticeable on the remolded soil specimens.
In order to investigate the internal erosion properties of low-plasticity silty sand, the Flexible Wall Pin Hole Test Device, FWPH, was developed by combining concepts of the conventional Pin Hole test and the triaxial test. Test results of FWPH showed that internal erosion potential of low-plasticity silty sand was affected by its fines content, density and confining pressure. Low-plasticity silty sand at loose state has much higher internal erosion potential than it at dense state. Moreover, when higher confining pressures were maintained, low-plasticity silty sand had less internal erosion potential. Most of all, higher fines content of the low-plasticity silty sand, higher internal erosion potential is clearly observed.
Finally, comparing the triaxial test results of undisturbed specimen with the analysis results of traditional soil liquefaction potential assessment method indicated that the traditional assessment method will underestimate the liquefaction potential in low-plasticity silty sand deposits. Therefore, the triaxial test analysis of undisturbed specimen was recommended to adopt for soil liquefaction potential assessment in low-plasticity silty sand deposits.

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