低黏性砂土張力強度之驗證

Abstract

在過去學者的研究當中，有許多方法可以決定土壤的張力強度，依據是否可直接量測拉力與否，可分為直接法與間接法。直接法主要是以直接拉力試驗 ( direct tensile test ) 為主，且可再分為水平或垂直施加拉力；而間接法常採用的方法有，例如 ： 劈裂試驗 ( split tensile test ) 、無圍壓縮貫入試驗 ( unconfined penetration test ) 或稱為雙貫入棒試驗 ( double punch test )。 本研究以複合驗證法求取低黏性砂土的張力強度，採用高嶺土與越南石英砂土混合之複合土壤 SC，分別進行兩大部分試驗，第一部份試驗，選定土樣 SC (S-石英砂 80% 與 C-高嶺土 20%) 為試驗土樣，主要為土壤張力強度間接法之相關試驗，分別依序進行 ： 直接剪力試驗、無圍壓縮試驗與無圍壓縮貫入試驗；第二部份試驗，選定土樣 SC (S-石英砂 80% 與 C-高嶺土 20%) 為試驗土樣，主要為土壤張力強度直接法試驗及壓力平板試驗。 在不同含水量下，直接張力試驗之有效張力強度的相對偏差很小，故含水量並不會影響不飽和土壤之有效張力強度，且由 Lu et al. (2006、2010) 所提出的的不飽和土壤有效應力架構計算直接張力試驗之有效張力強度，其值在含水量 w = 9%、11% 時相當接近，代表直接張力試驗有很高之準確性。

There are many methods of determining the tensile strength of soil. Depending on whether the specimen can be directly pulled in tension, it can be categorized into direct and indirect methods. In the direct methods, the specimen can be horizontally or vertically loaded. In the indirect methods, the split tensile test and the unconfined penetration test (double punch test) are often used. In this study, compacted clayed sandy specimens (with 80% of sand and 20% of caly by weight) were prepared for a series of the tests. The first part of tests is related to the indirect test of soil tensile strength, including direct shear test, unconfined compression test, and unconfined penetration test. The second part of tests is related to the direct test of soil tensile strength, including direct tension test and pressure plate test. The direct tension test of the effective stress varies slightly at different water contents, indicating the effective tensile strength of unsaturated soil was unaffected by the water contents. The direct tension test of the effective stress is quite close when the water content is at 9 and 11 percent, which suggests that the direct tension test be quite accurate in determining the tensile strength of lightly cemented sand.