台灣低塑性粉土質砂工程性質與防制對策研究---子計畫一：S/M(砂/粉土)互層土壤之現場與室內測試

Abstract

台灣粉土細砂受地質背景以及礦物含量之影響其壓縮性遠高於課本或研究論文中常見 均勻級配而乾淨之石英砂，同時台灣粉土細砂顆粒大多成扁平狀而且脆弱，其易碎性也 很高。因此如果要有效的解釋台灣粉土細砂之現地或室內試驗結果必須首先能夠掌握這 些地質背景乃至於顆粒特性對於其工程性質之影響。國內外大地工程界對於粉土質砂土 之研究都屬有限。主持人在近期國科會所贊助研究中使用Laval sampler 於員林粉土或粉 土細砂中取得高品質非擾動試體，進行一系列室內試驗並在取樣現場做SCPTU 試驗。 主持人同時也研發使用Gel-push 取樣器以更經濟的方法於高雄O1 捷運車站工址做非擾 動試體取樣，也在工址進行SCPTU 試驗。非擾動試體試驗與SCPTU 都指出，所測試之 粉土質砂土在現地應該是以砂土/粉土分層的方式呈現，而非如重模試體般均勻攪拌而 成。主持人將分層土壤稱之為S/M 以與均勻攪拌之SM 土壤區別。本子計畫之主要目的 是決定S/M 與SM 土壤在力學行為上之差異以及此一差異與細料含量間之關係。粉土質 砂也是許多填海造地工程所用之主要回填材料，在回填後使用地盤改良方法加以密實 化。由於地盤改良大多對砂土造成過壓密現像，現有知識並無有效方法來評估台灣西部 經過地盤改良，高橫向應力狀態下粉土質砂之液化潛能。本研究之另一主要目的是測試 過壓密S/M 與SM 土壤之力學行為以及此類土壤液化潛能評估的方法。

Because of the differences in geological background and mineral contents, the silty sand typically found inWestern Taiwan is significantly different from the clean quartz sand that is commonly reported in text books. These differences can include compressibility, grain shapes and crushability. It is imperative to have a full understanding of these unique qualities for proper geotechnical engineering design related to this type of soil. Knowledge on the mechanical behavior of silty sand has been limited. The investigator has used the Laval sampler to retrieve high quality silt and silty sand samples in Yuanlin. SCPTU was conducted at the site where soil samples were taken. The investigator also used a Gel-push sampler to retrieve undisturbed samples from the construction site of O1 rapid transit station in Kaohsiun. The cost of Gel-push sampling is much more economical than the Laval sampling. SCPTU was repeated at the O1 station site. The laboratory tests on the natural silty sand samples as well as SCPTU have indicated that the soil at these test sites was likely to be in a layered formation rather than uniformly mixed as it is normally reconstituted in laboratory. The layered soil will be symbolized as the S/M soil to distinguish from the uniformly mixed SM soil. The first objective of this sub-research project is to determine the differences in mechanical behavior between S/M and SM soils and how these differences are related to fines content. The silty sand inWestern Taiwan is often used as a backfill material in land reclamation projects. Upon deposition, the sand is densified by various ground improvement techniques. The densification imposed an effect of overconsolidation. Currently available knowledge is limited in assessing the liquefaction potential for overconsolidated silty sand with high lateral stress state. The second objective of this sub-research project is to ascertain the effects of overconsolidation on the dynamic behavior of S/M and SM soils and procedure for their liquefaction potential assessment.