英文篇名
CASE STUDY ON GROUND IMPROVEMENT EVALUATION BY IN-SITU TESTS
作者
余明山、鍾毓東、陳福成、王傳奇
摘要
位於台灣本島西南海岸的永安液化天然氣接收站是以人工抽砂浚填方式築造的新生地,基地面積廣達72公頃,站內的二期儲槽擴建工程須建造三座容量各為13萬立方米的液化天然氣(Liquefied Natural Gas,LNG)地下儲槽,其編號分別為T-104,T-105及T-106,配置及斷面則示如圖一。新生地的組成,主要為構造疏鬆的沈泥質細砂,並局部夾雜集中沈積的細粒土壤(silt or clay pockets),因此須加以改良,以維護地下儲槽週邊上設施之功能及安全。本文介紹此一地層改良案例,由規劃、設計、模擬施工至正式施工之整體執行程序及其嚴格的品管、檢驗措施供地工同仁參考。文中對夯實砂樁的改良效果、貫入阻力增量及國內常引用之日本經驗設計法的適用性、及改良後土壤顆粒是否粉碎等問題,均深入探討比較。此外,對於使用優良級配的河砂與使用貧級配的海砂做為砂樁回填料所獲致的改良效果是否相同,文中亦舉實例加以探討。
英文摘要
Case study on a hydraulic fill reclaimed site which is improved by compaction sand pile(S.C.P)is presented and discussed for the evaluation of improvement effects on various aspects. The anti-liquefaction design object is achieved by the increase of penetration resistance as well as the high density and permeability of S.C.P itself. The increase of penetration resistance depends on the in-situ confining pressure, the soil type, the depth and the original penetration resistance etc.. For fill sand layer with original qc-value of 35~40 kg/cm2 at depth 2m to 10m, the increase could be around 100%. Comparisons indicate an over-estimation of improvement effect for soil depth below 2m and SPT N-value greater than 5, if the empirical relationship of Japan(JSSMFE,1978 is used. CPT qc-value or DMT M-value seems to be a more propriate index in assessing the improvement effect. Preliminary test result shows a similar improvement effect when sea bed sand, instead of well-graded river sand is used as the S.C.P. fill material. Besides, the installation of S.C.P. makes the fine content of soil stratum increase significantly. As for silt-clay pockets, no obvious improvement effect was found from SPT and CPT test results which were done about 20days after S.C.P. installation. However, the pore water pressure measured by piezocone test shows that the characteristics of soil volumetric change was greatly improved.