Development of an auto compensation system in cyclic triaxial apparatus for liquefaction analysis

When performing cyclic triaxial tests, the connection process between loading piston and specimen could have significant effect on the test results. Tensile pre-shearing effect occurs during saturation and consolidation stages in screw-based configurations and compressive pre-shearing stress is induced while making the connection between loading piston and specimen in vacuum-based configurations. In order to overcome these technical problems, a special auto compensation system was incorporated into an existing cyclic triaxial apparatus, allowing: (1) no physical contact between loading piston and specimen to achieve an isotropic consolidation state, (2) the later connection between these two components to be easily accomplished with almost insignificant disturbance on the specimen (maximum 100 N in axial force). To assess the performance of this auto compensation system, two experiments of same dense reference sand specimens were respectively conducted, and the results were found to be similar, showing the good repeatability. Moreover, as compared with screw-based configuration, the test specimen did not undergo an adverse tensile pre-shearing. As a result, the test specimen became more resistant to cyclic mobility. On the contrary, as compared with another vacuum-based configuration (without auto compensation) well-documented in the literature, the obtained result was less stable since the employment of auto compensation system ensured that there was no beneficial compressive pre-shearing during the connection stage. The results obtained in this study showed the good performance of the developed auto compensation system in the triaxial test apparatus for liquefaction analysis. •An innovative auto compensation system was incorporated into an existing triaxial device allowing a true isotropic consolidation state prior to shearing stage.•An almost harmless connection between loading piston and upper triaxial base was achievable with the auto compensation system.•Compared with conventional triaxial devices, neither adverse tensile nor beneficial compressive pre-shearing took place with the use of auto compensation system.