砂性土壤中擴座基樁之抗拉拔承載力的評估方法

An Estimate about the Uplift Force of the Belled Pile in Sandy Soil

許師瑜(Shi-Yu Hsu) ； 林炤圭(Jaw-Guei Lin) ； 林三賢(San-Shyan Lin)

《海洋工程學刊》 14卷4期 (2014/12) Pp. 233-251

https://doi.org/10.6266/JCOE.2014.1404.03

摘要

本文藉由重新檢討螺旋錨碇基樁以及錨碇版破壞的型式與物理行為，發現增加考慮砂性土壤中擴座基樁受到上拉拔力時由擴大基座的存在以及對其上方土壤擠壓所造成的影響，可以更準確地估算基樁的抗拉拔力。本研究假設當擴座基樁受到向上拉拔力時，由於基座上方土壤受到上方土重及向上拉拔力的聯合擠壓而發生土壤組構的變化，致使剪力破壞面的發展偏離直樁表面，本文利用37組實驗室或現場實測值對現有的抗拉拔力的經驗公式進行測試發現其與實測值的平均相對誤差都大於50%，而若不限制破壞面的起始位置的話，平均相對誤差可以降到8.5%以下，顯示擴座基樁的拉拔剪力破壞面並非從直樁部分的底部開始發展，也證實估算擴座基樁的上拉拔力時必須考慮土壤的壓密行為。但考量實際的工程應用，本研究建議土壤剪力破壞面可假設自0.67倍擴大基座半徑處開始發展。測試結果顯示本研究所提出之經驗公式較現有理論的估算值為佳，與實測值之平均相對誤差低於25%，而如果剔除可能因量測或土壤特性估算誤差導致相對誤差偏大的8組，平均相對誤差可以降到約17%左右。如果能夠進一步考慮海床土壤的特性，可將本研究延伸至海上擴座基樁的抗拉拔力的估算。

關鍵字

擴座基樁 ； 抗拉拔力 ； 剪力破壞面

並列摘要

This study reexamined the previous studies about the ultimate pullout capacity and the development of resultant failure surface of screw pile of anchor plate, and found that the estimations of ultimate pullout capacity can be more accurate if taken into account the existence of the enlarged base and the influence from the soil consolidation behavior above the enlarged base induced by the upward motion of the belled pile. Such phenomena might cause the initiate location of the resultant failure surface be detached from the surface of the vertical pile. Under this assumption, by using 37 data sets of the laboratory tests or the field tests, this study found estimated ultimate pullout capacity from the previous theories all have more than 50% relative error in average against the test data. If allow the initiate location of failure surface developed within the radius of vertical pile and enlarged base, the average relative error can be reduced to less than 8.5%, which proves that the failure surface does not develop from the surface of the vertical pile, and the soil consolidation due to the uplift of the pile must be taken into account. For practical use, the initiate location of the failure surface is suggested develop from 0.67 of the radius of enlarged base, and the average relative error of 37 data sets is below 25%, and if omitting the 8 data sets which contain relative error larger than 20%, the averaged relative error can be reduced to around 17%. If introducing the soil properties of the seabed soil, this research can be extended to estimate the ultimate uplift capacity of the offshore belled pile.

並列關鍵字

belled pile ； ultimate pullout capacity ； resultant failure surface