Numerical investigation of failure modes and mechanical characteristics of remolded loess using unconfined penetration test

Tensile strength is one of the important mechanical parameters for controlling the development of cracks in the Loess Plateau. However, the tensile strength of soil is difficult to be precisely measured due to the lack of satisfying laboratory techniques. Unconfined penetration test (UPT) is commonly used as an indicator to predict soil tensile strength characteristics, while there has been less research study about test parameter values range of UPT and micromechanical characteristics at failure. This study finished 50 groups of UPTs of remolded loess with different disk diameters (12.36–27.81 mm) at various sample heights (37–87 mm) based on Q2loess in Lintong areas, and the crack development and failure essence in the different failure modes process were investigated by the discrete element modeling. The results showed that disk diameters and sample height were closely correlated with the failure mode. The failure of remolded loess in the UPT is not only tensile failure, which also can occur compression failure and tensile–compression coupling failure. Among them, when the ratio of disk diameters to sample height is about in the range of 0.189–0.309, the sample appears tensile failure. In addition, the ratio of compressive and tensile crack numbers in the sample is 0.16–0.22 in the tensile failure mode. The numerical simulation method provides a way for the observation of failure process and crack development, thereby improving the understanding of failure essence in UPT. The findings will provide a reference way to improve test theory and method of loess tensile strength.