黏土空間變異性對主動土壓力之影響

Impact of Spatial Variability in Clay on Active Lateral Force

胡毓港(Yu-Gang Hu)

指導教授 ： 卿建業

國立臺灣大學/工學院/土木工程學研究所/博士(2014年)

https://doi.org/10.6342/NTU.2014.00643

摘要

本研究探討黏土不排水剪力強度的空間變異性(spatial variability)對主動土壓力之力學機制影響。研究發現不排水剪力強度的空間變異性無法完全僅以固定滑動面之空間平均(spatial average)剪力強度所解釋(例如：沿著固定滑動面之線平均剪力強度或固定滑動面上之區域平均剪力強度)，因為臨界滑動面搜尋弱面的機制也扮演著很重要的角色。假若忽略此搜尋弱面的機制將可能低估主動土壓力，使得結果偏向不保守。除此之外，單純的空間平均也無法描述具空間變異性之土動土壓力的複雜行為(比如：critical scale of fluctuation (critical SOF)的現象)。然而，研究發現此critical SOF的現象卻與空間平均效應(spatial averaging effect)存在著密切的關係。例如：線平均效應明顯較面積平均效應來得弱，所以前者臨界滑動面搜尋弱面之行為較後者顯著，因此critical SOF的現象也較為顯著。由此可見，僅考慮單純的空間平均將可能忽略或抑制critical SOF之發生，導致結果偏向不保守º單純的空間平均無法解釋critical SOF的現象是因為其無法量化臨界滑動面搜尋弱面的機制，因此本研究進一步探討與量化此搜尋弱面的機制，並且提出一套可供模擬主動土壓力樣本的簡單程序，而此程序不需要透過額外的隨機場有限元素分析或極限平衡法。

關鍵字

大地工程 ； 主動土壓力 ； 空間變異性 ； 空間平均 ； 隨機場 ； 臨界關聯性長度 ； 隨機模擬

並列摘要

This study explores the mechanism of the active lateral force in undrained clay when there is a spatial variability in the clay. It is shown that the effect of such spatial variability cannot be fully explained by the pure spatial averaging over a prescribed area or line; the tendency to seek the weak path for the critical slip curve is also important. Ignoring this important mechanism is risky, rendering the active lateral force estimate smaller than the actual value. Furthermore, pure spatial averaging cannot capture the phenomenon of the critical scale of fluctuation (critical SOF). However, it is found that the phenomenon of the critical SOF is connected to the nature of the spatial averages. The line averaging effect is significantly weaker than the area averaging effect, so the tendency for the critical slip curve to seek for a favorable location is stronger. Hence, the phenomenon of the critical SOF is more pronounced. It implies that if a strong pure spatial averaging is mistaken, the critical SOF can probably be ignored. This makes pure spatial averaging methods unconservative. Pure spatial averaging cannot capture this phenomenon of the critical SOF, because it cannot quantify the tendency of seeking the weak path. Therefore, the mechanism of seeking the weak path is explored in this study, and a probability distribution model for the active lateral force is proposed to characterize this sophisticated mechanism. Furthermore, a simplified procedure based on the distribution model is proposed to simulate the active lateral force samples without the use of the random finite element method or limit equilibrium method.

並列關鍵字

geotechnical engineering ； active lateral force ； spatial variability ； spatial average ； random field ； critical scales of fluctuation ； stochastic simulation

參考文獻

Breysse, D., Niandou, H., Elachachi, S., Houy, L., 2005, “A generic approach to soil-structure interaction considering the effects of soil heterogeneity,” Geotechnique, Vol. 55, No. 2, pp. 143-150.

Cherubini, C., 2000, “Reliability evaluation of shallow foundation bearing capacity on c–ϕ soils,” Canadian Geotechnical Journal, Vol. 37, No. 1, pp. 264–269.

Cho, S. E., 2007, “Effect of spatial variability of soil properties on slope stability,” Engineering Geology, Vol. 92, pp. 97-109.

Cho, S.E., Park, H.C., 2010, “Effect of spatial variability of cross-correlated soil properties on bearing capacity of strip footing,” International Journal for Numerical and Analytical Methods in Geomechanics, Vol. 34, No. 1, pp. 1–26.

Ching, J., Hu, Y.G., Yang Z.Y., Shiau, J.Q., Chen, J.C., Li, Y-S., 2010, “Reliability-based design for allowable bearing capacity of footings on rock masses by considering angle of distortion,” International Journal of Rock Mechanics and Mining Sciences, Vol. 45, No. 5, pp. 728-740.