Development of Direct Shear Apparatus and Liquefaction Strength Tests

ABSTRACT This article aimed to introduce a novel direct shear (DS) test system including three apparatuses developed by the authors, type-I for the monotonic loading test, type-II for the liquefaction test, and type-III with a two-dimensional specimen for the observation of the shear deformation; to show that the test results obtained using each test apparatus are equivalent to the triaxial test results; and to demonstrate the usefulness and reliability of the DS test method. Historically, the triaxial test method expanded rapidly in the 1960s after Bishop and Henkel’s pioneering work because of its clear theoretical framework; it is still in the mainstream nowadays. Meanwhile, Mikasa adopted the concept from Taylor and developed a DS apparatus that can perform consolidated undrained (CU) tests with the constant volume control, as well as CD tests. However, the Mikasa-type DS apparatus had a drawback in CD testing to avoid the friction effect on the measured strength. To address this, the authors developed the type-I DS apparatus with a reaction block that combines double jacks and load cells for measuring the strength accurately. For low-stress range tests such as liquefaction tests, the type-II DS apparatus was developed to enhance further the test accuracy. Detailed shear deformation was observed by using the type-III DS apparatus to define the criterion of the liquefaction strength with the aid of the image analysis on the shear strain. The CU and CD strengths obtained with the type-I DS apparatus were confirmed to be equivalent to the triaxial test results. Next, the liquefaction strengths obtained with the type-II DS apparatus were coincident with the cyclic triaxial test results and identified that the DS test method was less susceptible to the sample disturbance. The DS test was concluded to be a reliable method for evaluating the soil strengths under either monotonic or cyclic loading.