以超載減少軟弱粘土二次壓縮之研究

A Study on Surcharging to Reduce A Study on Surcharging to Reduce Secondary Compression of Natural Soft Clays

李淑芳(Shu- Fang Li)

指導教授 ： 馮道偉

中原大學/工學院/土木工程研究所/碩士(2002年)

https://doi.org/10.6840/cycu200200280

摘要

中文摘要
超載工法為眾多地盤改良工法之一，常被用來改良軟弱土壤，不僅可增加土壤的強度，並可避免建物完成後因不均勻的沉陷而衍生問題，但是對於地盤受超載改良後的回脹與再壓縮性質一直無法確實的了解。
為探討軟弱粘土於超載移除後的回脹與再壓縮性質，本研究利用傳統單向度壓密試驗儀對六種土樣分別進行三種超載比的超載單向度壓密試驗，並分析所得結果，分析方法包括:1)評估後超載割線二次壓縮指數;2)評估修正後超載割線二次壓縮指數，將後超載的時間原點改為由加載起始時起算;3)評估二次壓縮再現時間與超載比的關係;4)評估後超載二次壓縮應變速率之特性。
根據研究的結果顯示:1)超載比愈大，後超載割線二次壓縮指數所受到的折減愈大，表示對軟弱粘土的二次壓縮沉陷量改良效果愈好;2)修正之後超載割線二次壓縮指數亦隨超載比的增加而折減;3)二次壓縮再現時間與超載比的關係顯示，增加超載比會延遲二次壓縮再現的時間並可將分析結果以一均值曲線表示; 4)對後超載應變速率分析發現在相同最終載重，未受超載作用與受超載作用的二次壓縮應變速率呈現一雙對數的線性關係。
雖然超載比愈大對軟弱粘土二次壓縮沉陷改良的效果愈好，但是超載工法實際設計應用時尚須考慮地盤承載力、經濟效益及現地是否可實行等問題。

關鍵字

後超載二次壓縮應變速率 ； 後超載割線二次壓縮指數 ； 後超載二次壓縮量 ； 地盤改良 ； 超載工法

並列摘要

ABSTRACT

Surcharging is one of the exsiting ground improvement techniques. It could be used to reduce long term settlement and also used to increase soil strength. But the rebound and recompression properties after surcharge removal are not well established.
In order to unsterdand the properties of rebound and recompression, this study carried out oedometer tests for six soft clays with three surcharge ratios to simulate surcharging. Properties analyzed in this thesis include: 1) post–surcharge secant secondary compression index; 2) amended post- surcharge secant secondary compression index in which the time starts from load application; 3) time at which secondary compression reappears; 4) post-surcharge secondary compression strain rate.
The results of this study indicate that: 1) the post–surcharge secant secondary compression index decrease with the increase in surcharge ratio; 2) the amended post-surcharge secant secondary compression index also decrease with the increase in surcharge ratio; 3) time at which secondary compression reappears increases with the increase in surcharge ratio; 4) the post-surcharge secondary compression strain rate under the same final load with surcharging and without surcharging have a linear logarithm to logarithm relationship.
Although increase the surcharge ratio will decrease the long term settlement, the ground strength and economy must be considered when the surcharge ratio is selected.

並列關鍵字

post–surcharge secant secondary compression ind ； ground improvement ； post-surcharge secondary compression strain rate ； Surcharging

參考文獻

4. Mullins, B. and Mullins, M. B. (1848), “On the Origin and Reclamation of Peat Bog, with Some Observation on the Construction of Roads, Railways, and Canals in Bog.” Institution of Civil Engineers of Ireland, Transcations, Vol. 2, pp. 1-48.

1. Magnan, J. P. (1994), “Methods to Reduce the Settlement of Embankments on Soft Clay: a review.” Vertical and horizontal displacements of foundations and embankments, ASCE Geotechnical Special Publication, Vol. 1, No. 40, pp. 77-91.

3. Kerisel, J. (1975), “Old Structures in Relation to Soil Conditions.” Geotechnique, Vol. 25, No. 3, pp.433-483.

7. Legget, R. F. and Peckover, F. L. (1973), “Foundation Performance of a 100-year-old Bridge.” Canadian Geotechnical Journal, Vol. 10, No. 3, pp. 504-519.

17. Nash, D. F. T. (2001), “Modelling the Effects of Surcharge to Reduce Long Term Settlement of Reclamations over Soft Clays: a numerical case study.” Soils and Foundations, Vol. 41, No. 5, pp. 1-13.