不排水剪力強度Su為黏土層中進行工程穩定分析最重要的強度參數，依據前人研究結果，顯示不排水剪力強度Su隨試驗種類有很大的差異，但選用何種才較接近現場工程的情況，目前尚無較具體的結論。為研究台北盆地黏性土壤不排水剪力強度特性，本研究收集台北盆地黏性土壤不同Su試驗資料，包含常用之室內及現地試驗，依台北盆地工程地質分區，以統計方法分析台北盆地各地質分區黏性土壤不排水剪力強度特性，分別統計得各地質分區不同Su試驗與地表高程之關係式，而依此統計關係式，建立不同試驗間之相關性。 為研究求得代表現地Su值之方法，本研究收集台北盆地內工程災變案例，利用路堤填築破壞與深開挖隆起破壞案例資料，反算台北粉土現地平均不排水剪力強度Su(in-situ)，並與室內Su(UC)試驗值比較，得出以無圍壓縮試驗強度估計現地不排水剪力強度之經驗關係。另外，亦收集樁載重試驗案例，推算達極限狀態之樁周單位摩擦應力，據以建立樁側單位摩擦應力與Su(UC)之比值關係α（即黏著係數，adhesion factor）隨Su值之變化關係。上述研究成果可供爾後於台北盆地進行黏土工程穩定分析選用不排水剪力強度之參考。 The undrained shear strength Su is the most important strength parameter in stability analysis of soft clay engineering. It was found that Su of different tests have great differences in accordance with previous research. At present, there are no definite conclusions about which type of undrained shear strength tests matches the in-situ condition best. In order to go deep into the Su characteristics of clayey soils in Taipei basin, this study collect Su data of different types of in-situ and laboratory test and compile their Su characteristics statistics based on the engineering geological zoning of Taipei basin. The relations of Su and elevation of different zones are established. The correlations of Su of different test types are also deduced. For sake of obtaining the most representative in-situ Su , failure cases of embankment and deep excavation are amassed to back calculate the average in-situ undrained shear strength Su(in-situ) of clayey soils in Taipei basin. After that, empirical relation of Su(in-situ) and Su(UC) from unconfined compression test is established. Furthermore, cases of pile load tests are also collected to deduce the ultimate unit friction along pile shaft. Variation of adhesion factor α ( defined as ultimate unit friction divided by Su(UC) ) with Su(UC) is derived. The results of this study can provide a useful guide to selection of undrained shear strength for stability analysis in soft clay engineering.
