夯實土壤之直接張力試驗與其影響因子之研究

Direct Tension Test on Compacted Sand-Clay Mixture with Different Ratio of Sand to Clay and Factors Affecting Its Measurements

童連致齊(Lian-Zhi-Qi Tong)

指導教授 ： 葛宇甯

國立臺灣大學/工學院/土木工程學研究所/碩士(2016年)

https://doi.org/10.6342/NTU201602953

摘要

在大地工程設計與分析中，土壤之張力強度常被忽略，因為土壤之張力強度遠低於其壓力強度或剪力強度，但在許多工程問題上土壤的張力強度是需要被考慮的，尤其是應用在預測土壩的裂縫行為、道路或鋪面以及邊坡穩定的張力裂縫。土壤在受直接拉力試驗後之行為如今還沒有一致的試驗儀器和理論來探討土壤之張力阻抗，目前大多使用間接張力試驗來求得土壤之張力強度，但在間接試驗下，是無法直接獲得土壤受張力下應力應變之歷時曲線，因此直接張力試驗是值得研究的。
本研究參考前人發展之直接張力儀器為基礎，改良後建立了新的直接張力儀器。根據過往之研究結果，施加拉力的速率以及夯實土壤之夯實層數較與土壤之張力強度無關，但在試體模具的選用上，至今仍然無相關之研究，因此討論在分別為10°、20°和30°之三角形楔型塊的試驗邊界條件下對量測土壤張力強度之影響。除了試驗邊界條件的改變，試體高度對土壤張力強度之影響也做了一系列的試驗，試驗之試體高度分別為3 cm、6 cm、9 cm和12 cm。最後在不同的砂黏土配比下，對土壤張力強度在不同幾何條件下進行試驗與討論。本研究之試體是以其最佳含水量 (OMC) 和最大乾密度條件下之石英砂和高嶺土以3:1和4:1重量比配製而成之低黏性夯實土壤，並使用吻合試體表面形狀之特殊夯捶夯實，以達到試體均勻夯實之效果，既能減少試驗之誤差更能加快實驗速度。
本研究除了使用強度分析之外，還加入了能量分析法，並且比較兩者分析之結果。根據試驗之結果，能量分析法在不同之試驗條件下是可以得到較一致的趨勢，這是強度分析無法達到的，因此後續之分析會著重於能量分析法。

關鍵字

土壤張力強度 ； 夯實土壤 ； 直接張力試驗 ； 強度分析 ； 能量分析

並列摘要

In geotechnical engineering practice, the tensile strength of soil is generally ignored during design and safety assessment. Compared to the compressive strength of soil and the shear strength of soil, the tensile strength of soil is too small to be considered. Furthermore, uncommon testing apparatuses and techniques for measuring the tensile strength of soil and uncompleted theories have not been adequately developed and studied. Currently, the methods of measuring the tensile strength of soil can be categorized into direct and indirect methods. Compared to direct method, the indirect methods, such as the Brazilian test, the split tension test, double punch test, unconfined penetration test, etc. have been developed. All the indirect tension tests have a defect that the orientation of tensile strain cannot be directly obtained during experiment. Therefore, in this study, direct tension method is modified and the tensile behavior of compacted lightly cemented sand is examined.
The modified direct tension apparatus was developed. To examine the geometric influence in direct tension test, three affecting factors, the effect of the specimen sizes, the effect of boundary condition and the effect of the clay-sand mixed ratios, respectively, were discussed in this study. First affecting factor was examined by changing the height of specimen, 3 cm, 6 cm, 9 cm and 12 cm, respectively. Second affecting factor was examined only by triangular wedges with three different angles, 10°, 20° and 30°, respectively. The higher the triangular wedge angle, the less cross sectional area is, and the higher grabbing ability is. Therefore, the specimen size and shape should be discussed. The last affecting factor was examined by 4:1 and 3:1 mixed ratio of sand to clay by weight. All the specimens were prepared at its maximum dry density and optimum moisture content, and compacted by the tampers which fit the shape of the specimen. In addition, this direct tension apparatus was modified firstly in this study due to the unsolved problems in the previous study, such as the non-uniform compaction, the friction of guide rails and the eccentric problem during the experiment.
From the results of the direct tension tests, the specimen with different fines contents could strongly influence their behavior at different geometric conditions. Besides the strength analysis, the energy analysis was used to describe the tensile behavior of soil.

並列關鍵字

Tensile strength ； compacted soil ； direct tension test ； energy analysis ； strength analysis

參考文獻

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