十字葉片剪力強度與室內試驗不排水剪力強度之半經驗關係

A Semi-Empirical Undrained Shear Strength Relationship between Field Vane Test and Laboratory Tests

蘇世豐(Shi-Fon Su)

《中國土木水利工程學刊》 23卷3期 (2011/09) Pp. 329-337

https://doi.org/10.6652/JoCICHE.201109_23(3).0009

摘要

本研究根據異向性不排水強度準則與協合流律，來決定垂直方向無應變增量之圓柱剪力態，並憑此一圓柱剪力態來描述十字葉片周圍土壤之破壞應力態，隨後再配合試驗數據來反推圓柱剪力態的主剪應力，以及十字葉片不排水剪力強度。無論如何，本文所建議的現場十字葉片試驗與室內試驗之不排水剪力強度比，它們是半經驗關係式且未考慮應變軟化（或硬化）、現地應力係數以及應變速率等影響因素。藉由15 種不同土壤的試驗數據比較，本文建議的現場十字葉片試驗與三軸CKoU軸向壓縮試驗之不排水剪力強度半經驗式，其一般估計誤差是多數介於 ±20%，且這個強度比是隨著塑性指數與強度異向性比的減少而減少。最後，本文建議的半經驗式若應用於低塑性黏土（譬如PI小於20%），則此預測的十字葉片不排水剪力強度是可能高過Mesri經驗圖。

關鍵字

異向性 ； 不排水剪力強度 ； 十字葉片阻抗和黏

並列摘要

The analysis of shear resistance mobilized by the vane into clay is based on an anisotropic strength criterion, the associated flow rule and the simplifying assumption that the stress state around a rotating vane is similar to the cylindrical shearing condition and with no increase in vertical strain. Experimental data were used for back analysis and the principal shear stress under the cylindrical shearing condition could be obtained from the data. So can the vane shear strength. However, the proposed method is semi-empirical; the influences of strain hardening-softening behavior, the coefficient of in situ stress, and strain rate on the strength analysis are not considered. In order to verify the suitability of the proposed method, the predicted strength ratios were compared with experimental data for 15 different soils. The difference between the predicted and observed strength ratio is generally on the order of ± 20%. The results show that the shear strength ratio of the field vane test to the axial compression test decreases with a decrease in the plasticity index and with a decrease in the strength anisotropy ratio. Finally, the calculated undrained shear strength from field vane test is found to be possibly higher than the charts produced by Mesri (1989) when the plasticity index of the clay is less than 20%.

並列關鍵字

anisotropy ； undrained shear strength ； vane shear resistance ； clay