場鑄樁於不排水土層受側向載重之 p-y 曲線法評估

Evaluation of p-y Curve for Drilled Shafts in Undrained Soils under Lateral Loading

管浩(Hao Guan)

指導教授 ： 陳逸駿

中原大學/工學院/土木工程研究所/碩士(2019年)

https://doi.org/10.6840/cycu201900436

摘要

在橋樑工程、輸配電構造物及高樓結構等，場鑄樁基礎常為設計者所採用的主要深基礎形式，以抵抗側向載重。於眾多側向承載力分析法中，p-y 曲線法已廣泛地應用於工程界。為能有系統地評估 p-y 曲線法於不排水土層的應用，本研究蒐集相當數量的現地場鑄樁側向樁載重試驗資料，評估 p-y 曲線法對場鑄樁於不排水土層條件下預測側向載重之精準度，並依其結果加以改良以提高預測精準度。分析之資料採用世界各地代表性之場鑄樁側向載重試驗，分析所用的地工參數則選擇能真正反應現地土壤在受力時之行為模式，以提高研究結果之可靠度。
依轉折深度以上之土壤性質及其所佔權重，將不排水土層分為軟弱黏土層與堅實黏土層兩大類後，再參考場鑄樁之剛柔性，將其分為柔性以及剛性場鑄樁兩種類型以方便爾後設計分析者使用。分析結果顯示柔性場鑄樁以軟弱黏土之原始 p-y 曲線對側向載重進行預測時，其總體平均預測差異值 ΔQ/Qm 約為 -28% ，表示其預測結果相較現地量測結果存在低估之現象。而剛性場鑄樁以軟弱黏土之原始 p-y 曲線對側向載重進行預測時，其總體平均預測差異值 ΔQ/Qm 約為 -24% ，表示其預測結果相較現地量測結果也存在低估之現象。至於柔性場鑄樁以堅實黏土之原始 p-y 曲線對側向載重進行預測時，當其側向變位小於等於 0.5% 樁徑時，平均預測差異值 ΔQ/Qm 介於 4% ～ 32% 之間，存在高估現象；而當側向變位大於0.5% 樁徑時，平均預測差異值則 ΔQ/Qm 介於 -3% ～ -16% 之間，存在低估現象。剛性場鑄樁以堅實黏土之原始 p-y曲線對側向載重進行預測亦出現同樣趨勢，當其側向變位小於等於 1% 樁徑時，平均預測差異值 ΔQ/Qm 介於 6% ～ 62% 之間，存在高估現象；而當側向變位大於 1% 樁徑時，平均預測差異值 ΔQ/Qm 則介於 -17% ～ -28% 之間，存在低估現象。經過對不排水土層的 p-y 曲線進行改良後，柔性場鑄樁及剛性場鑄樁於軟弱黏土層受側向加載預測之平均誤差值分別收斂至 -1.41% 與 -0.4% 。而柔性場鑄樁及剛性場鑄樁於堅實黏土層受側向加載預測之平均誤差值則分別收斂至 -0.86% 與 -2.56% 。

關鍵字

場鑄樁 ； 側向載重-位移曲線 ； 黏聚性土層 ； p-y 曲線 ； 軟弱黏土層 ； 堅實黏土層

並列摘要

For bridge structures, electrical transmission line structures, high-rise building, etc., drilled shaft foundations are the most commonly used type deep foundation to resist lateral loading. Among various lateral analytical models, the p-y curve method is the most widely used method especially in engineering practice. This study was conducted to evaluate the p-y curve method for drilled shafts by utilizing a wide variety of field lateral load test data of different undrained soil conditions and using LPile as a software for the analysis. These collected data were then divided into soft clay and stiff clay. According to the flexibility of piles, the data were further divided into flexible piles and rigid piles in soft clay and stiff clay, respectively to provide better consistency of the analysis.
Results of the analysis showed that the average difference of flexible piles in soft clay for the predicted versus measured results for ΔQ/Qm is -28%, which means that the prediction were underestimated. For rigid piles in soft clay, the analysis showed that the average difference of the predicted versus measured results for ΔQ/Qm is -24%, which means that the prediction result is also underestimated.
For flexible piles in stiff clay, when the lateral displacement is less than or equal to 0.5% of the pile diameter, the average result for ΔQ/Qm is between 4% and 32%, which means that the prediction result is overestimated. On the other hand, when the lateral displacement is greater than 0.5% of the pile diameter, the average result for ΔQ/Qm is between -3% and -16%, which means that the prediction result is underestimated. For rigid piles in stiff clay, when the lateral displacement is less than or equal to 1% of the pile diameter, the average result of ΔQ/Qm ranges between 6% and 62%, which means that the prediction result is overestimated. When the lateral displacement is greater than 1% of the pile diameter, the average result ΔQ/Qm is between -17% and -28%, which means that the prediction result is underestimated.
Finally, the p-y curves were then back-analyzed using the measured stress-strain results of the collected field load tests, where statistical analysis was applied to optimize these curves. After refining the p-y curve, the maximum prediction difference was improved to -1.41% and -0.4% for flexible and rigid drilled piles in soft clay, respectively. Additionally, the maximum prediction difference for flexible and rigid drilled piles in the stiff clay was improved to -0.86% and -2.56%, respectively.

並列關鍵字

drilled shafts ； lateral load-displacement curve ； cohesive soils ； p-y curve ； soft clays ； stiff clays

參考文獻

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