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| CYCLIC BEHAVIOR ANALYSIS OF THE SILTY FINE SAND IN CENTRAL WESTERN TAIWAN |
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| 黃安斌、林志平、紀雲曜、古志生、蔡錦松、李德河、林炳森 |
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| 砂土、細料、動態行為、土壤液化、現地試驗、取樣 |
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| 1999年9月21日之集集地震使得台灣中西部地區發生明顯的土壤液化現象，此區域之砂土大多含有不同比例之低至中塑性細料，集集地震為大地工程界提供了一個難得的機會來研究粉土性砂土之抗液化強度。作者在過去六年間針對麥寮砂做一系列之重模試體之室內試驗，包括動、靜態三軸試驗以及圓錐貫入試驗(CPT)之標定，在彰化縣員林鎮設立試驗站從事各種現地試驗與砂土取樣技術之嘗試。根據這些研究結果，作者對於台灣中西部砂土抗液化潛能分析的方法提出我們的看法，並使用集集地震之資料對這些方法做初步之驗證。本文將此期間研究之成果與心得做一報告。 |
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| The Chi Chi earthquake of September 21, 1999 triggered extensive soil liquefaction in Central Western Taiwan. The sand deposits in this area often contain various percentages of low to medium plasticity fines. The earthquake presented a rare opportunity to study the cyclic strength of silty sands. In the past six years, the authors performed a series of laboratory tests on reconstituted Mai Liao Sand specimens, which included monotonic/cyclic triaxial tests and cone penetration (CPT) calibration tests. A test site was established in Yuan Lin Township of Chang Hua County where various in situ testing and sampling techniques were experimented. We offer our views on the analyses that relate to cyclic behavior of the silty sands in this region based on our studies and preliminary verification using the Chi Chi earthquake as a reference. The paper describes the lessons learned from these post earthquake studies. |
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| LIQUEFACTION RESISTANCE DESIGN FOR RAFT FOUNDATION |
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| 謝旭昇、蔡琪駿、盧之偉 |
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| 液化潛能評估、筏式基礎、基礎設計、地盤反力係數、地盤改良 |
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| 台灣地區耐震設計目前使用之地表加速度高達0.23g或0.33g，進行液化潛能分析時常發現SPT N值接近30之中等緊密砂土亦會發生液化。針對基礎下方可能液化之土壤，最直接之方式乃是施作地質改良或甚至採用樁基礎以處理液化衍生之承載力或沉陷量問題，但設計規範亦允許以土壤參數折減之方式進行基礎設計。本文以一筏基設計案例說明如何以參數折減之方式考量液化之影響，並同時討論以低壓劈裂或高壓成型灌漿提高土壤抗液化強度之可能性。 |
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| The current seismic design code stipulates that the peak ground acceleration (PGA) for structure design is either 0.23g or 0.33g in Taiwan area, pending on the geographic location of the construction site. Using the specified PGAs as a design basis, liquefaction potential analysis often found that most sandy materials may liquefy, even for strata with high SPT N values. As a countermeasure, ground improvement or pile foundation may be required. A less costly alternative, which is allowed within the context of the design code, is to adopt a reduced modulus of subgrade reaction for foundation design if the liquefaction hazard is considered minor. This paper presents a case history that uses reduced parameters for raft foundation design. The possibilities of using grouting techniques for liquefaction mitigation are also addressed. |
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| EFFECTS OF GROUND LIQUEFACTION INDUCED LATERAL SPREADING ON PILES |
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| 林三賢、曾玉如、江承家、李維峰 |
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| 側潰、基樁、土壤液化、挫曲 |
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| 本文利用樑在溫氏基礎的方法，考慮非線性土壤行為及非線性的樁身橫斷面彎矩－曲率關係，回算三個由於液化地盤產生側潰後對基樁產生破壞之實際案例，以重新評估其係為受過大彎矩而致破壞或因樁身產生挫曲而致之破壞。此外，日本JRA（1996）及Tokimatsu（2003）所提出之設計分析方法，亦藉此案例分析比較兩法所得結果之差異。 |
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| Three case histories of failure of piles caused by ground lateral spreading are back studied using the beam on Winkler foundation method including nonlinear soil springs and a nonlinear moment-curvature relation for the pile. The lateral spreading effect is modeled by laterally displacing the soil springs support by an amount equal to the free field permanent deformation. Design procedures suggested by Tokimatsu（2003） and by JRA（1996） were also used for case histories evaluation and compared to available observation results. |
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| SIMPLIFIED METHODS FOR ASSESSING LIQUEFACTION POTENTIAL OF SOILS BY USING HYPERBOLIC CYCLIC RESISTANCE CURVES |
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| 黃俊鴻、楊志文、陳正興 |
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| 雙曲線函數、液化、簡易評估法、成功率、安全係數、誤差指標 |
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| 以現地貫入試驗值SPT-N，CPT－qc與震測剪力波速Vs評估土壤液化潛能之方法，稱之為簡易評估法，是工程界最常使用的液化評估方法。本研究根據以往地震之液化與非液化案例資料的整理與分析，發現以雙曲線函數迴歸判斷液化與否之臨界液化強度曲線，可以合理預測集集地震與世界上其他地震之液化與非液化案例，而雙曲線液化強度曲線法不但公式簡單，且其參數具有明顯的物理意義，建議可作為本土化的液化評估方法。利用集集地震與世界上其他地震之液化與非液化案例資料，本研究以評估方法之判定成功率與至少安全係數誤差指標為評估指標，比較雙曲線液化強度曲線法與世界上其他簡易評估法的適用性。評估結果顯示，無論是SPT-N，CPT－qc與震測Vs法，以雙曲線液化強度曲線為基礎的評估方法，皆不遜於世界上現有的其他簡易評估法，建議可供工程界參考使用。 |
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| To assess the liquefaction potential of soil during earthquakes, the simplified procedures by using the value of SPT-N，CPT－qc and seismic Vs are the most prevailing methods applied in the engineering practices. Basically, these methods were deduced from the worldwide data of liquefaction and non-liquefaction cases reported in the past major earthquakes. In Taiwan, large amount of liquefaction data were retrieved from the devastating Chi-Chi earthquake in 1999. Therefore, it is valuable to use the Taiwan data to evaluate the performances of those simplified methods commonly used, and to deduce an improved method, if possible, to take into account the effects of local soils. Based on investigations on all data, this paper proposed a method by using the hyperbolic functions to fit the critical cyclic resistance curves, a boundary curve for judging liquefaction or non-liquefaction, in the CSR-(N1)60, CSR-qc1N, and CSR-Vs plots, respectively. The advantage of using the hyperbolic function is that it is simple in form to have physical quantities as parameters. The performances of the Hyperbolic method along with other simplified methods are then thoroughly investigated in comparison studies. From the results of two assessment indices, the prediction success rate and the error of at-least safety factor, it is shown that the proposed Hyperbolic methods performed very well as compared to the other simplified SPT-N，CPT－qc and seismic Vs methods. |
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| DETERMINATION OF PEAK GROUND ACCELERATION FOR LIQUEFACTION ANALYSIS |
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| 黃富國、王淑娟 |
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| 土壤液化、場址效應、設計地震、最大考量地震 |
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| 土壤液化為發生於軟弱地盤上之地質震害。如何考慮場址效應，決定適當之最大地表加速度，為液化分析時之重要課題。本研究從加速度衰減律、經驗關係與規範係數，及地盤反應分析等三方面進行探討，並以嘉南平原一場址為例，比較新版規範「設計地震」及「最大考量地震」(MCE)所決定之地震力，以及由地震危害度分析(SHA)搭配地盤反應分析(GRA)所推估之地震力，對液化損害評估結果之影響及差異。結果顯示，規範對場址效應之考慮可能不夠保守，或過於保守，視震度而定；直接進行地盤反應分析，是決定具液化潛能土層地表最大加速度之較佳方式。 |
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| Seismic-induced soil liquefaction causes damages on soft ground. It is an important issue to decide peak ground acceleration(PGA) appropriately for liquefaction analysis considering site effects. These subjects are divided into three parts in this paper, including PGA attenuation law, empirical relationships and amplification coefficients in the code, and site-specific response analysis. A case study of Chianan Plain is implemented. PGA and liquefaction potential estimated from Design Earthquake and Maximum Considered Earthquake(MCE) according to newly-revised building codes in Taiwan are compared to those from seismic hazard analysis(SHA) and ground response analysis(GRA). It is shown that site effects estimated from codes may be un-conservative or over-conservative depending on seismic intensity. Performing a site-specific ground response analysis is the best way to decide PGA on soft ground for liquefaction analysis |
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| DISTURBANCE AND SPECIMEN QUALITY DESIGNATION OF COHESIVE SOIL |
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| 胡逸舟、秦中天、吳筱寒 |
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| 擾動、樣品品質指標、主要壓密完成壓密 |
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| 大地工程師所經常面對和處理的工程材料，大多數為岩石與土壤之類的自然材料。在實務上，工程師經常需要從有限的現場以及室內試驗結果，來評估研判於構造物構築過程中可能面對的問題，以及完工後能否滿足設計需求。其中最關鍵的課題便是工程師如何從有限的試驗結果中釐出可靠、合理的參數，以作為設計、分析、施工、乃至於完工後營運階段的構造物安全管理的依據。本文首先將討論擾動對土壤試驗結果之影響，接著介紹一個可以作為量化評估樣品品質優劣的標準－樣品品質指標(Specimen Quality Designation，SQD)，並收集台北盆地內現有工程之壓密試驗結果，計算各試驗結果之樣品品質指標，藉以探討國內目前的不擾動土樣之取樣品質，並說明採用合適的室內試驗決定樣品品質。 |
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| Geotechnical engineers usually deal with the natural materials, such as rocks and soils, and shall carry out their works according to very limited test results. A better sample quality becomes very important and essential in every aspect for a good test, no matter laboratory or field test. Especially for laboratory mechanics test, it is necessary to insure the samples are in “undisturbed” conditions. Disturbance will directly affect the test result, which might mislead the design or analysis results. This paper collects consolidation test results of some currently undergoing projects in Taipei basin and studies their specimen quality based on “Specimen Quality Designation”(SQD). It is anticipated to introduce a reasonable way to decide the specimen quality for so called “undisturbed” samples. |
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