非均質土體上淺基礎傾斜量與差異沉陷量之估計方法

Abstract

在大地工程中面對的材料往往是自然產生而非均質的。但實務上為求方便，許多計算皆是建立在均質假設上，因此要如何簡便而又不失準確性的找出能代表非均質性質的單一數值便十分重要。 Vanmarcke (1977) 表示，具空間變異性的土壤性質可視為隨機場。考慮水平與鉛直方向具有相同關聯性長度的土體，Ching and Hu (2017) 使用有限元素分析提出pseudo incremental energy model，以加權幾何平均來估計受到均勻沉陷量的剛性淺基礎「感受到的」土體的等效楊氏模數。對於向上連接著柱的淺基礎來說，由於受到上部結構的約束，均勻沉陷而不會傾斜的假設是合理的，而此時除了沉陷量之外，差異沉陷量也是必須考量的；相對的，在筏式基礎的情形中，則應假設淺基礎能有傾斜發生。本研究建立在pseudo incremental energy model上，試圖估計出淺基礎的差異沉陷量與傾斜量，考慮到筏式基礎的傾斜與兩相鄰淺基礎的差異沉陷之間的相似性，本研究會先尋找差異沉陷量的估計方式，再判斷估計之差異沉陷量是否與傾斜量有明確的關係，能做簡單修正後當作傾斜量的估計。 結果發現，兩個受到相同荷載的等寬剛性不傾斜淺基礎，其間的差異沉陷量可以用兩基礎在「只有自己基礎上的荷載存在時」各自的沉陷量的差值來估計，即便沒有考慮另一個荷載造成的影響而不能準確的代表各自真正的沉陷量，其差值能很有效的估計差異沉陷量。本研究並發現，運用此方法估計兩基礎相鄰時的差異沉陷量，其值的2.581倍即大約是單一基礎的傾斜量。

The materials we face in geotechnical engineering are often resulting from natural process, and thus heterogeneous. However, for the purpose of convenience, many calculations are based on homogeneity hypothesis. So it is important to have a representative estimate of the value. To estimate effective Young’s modulus, Ching and Hu (2017) introduced the pseudo incremental energy model to calculate the weights and the weighted geometric average Young’s modulus. Based on their result, this study focus on the tilt and differential settlement. Due to the similarity, the two values might have strong relation or similar estimation process. As a result, one can estimate the settlement of a shallow foundation caused only by the load on it by pseudo incremental energy model, and the difference between the two values would be almost the same as the differential settlement when both the loads exist. Also, by viewing as two foundations, the tilt of foundation can be estimated by the differential settlement times 2.581.