Effect of Height-to-Diameter Ratio on the Compression Test Results of Remodeled Loess and Its Mechanism

The confined compression test is the most widely used test to study the compressive deformation of soil in a laboratory, and the height-diameter (H/D) ratio has a significant effect on the confined compression test results. However, there has been limited research on the effect of the H/D ratio on loess compression deformation. In this work, a series of confined compression tests were carried out on the remolded loess samples using a modified oedometer to explore the effect of the H/D ratio on the compression deformation. Scanning electron microscopy (SEM) tests were used to investigate the variation of the microstructure in soils with different H/D ratios along the sample height. The results showed that the axial strain of the remolded loess decreases with the increase in the H/D ratio. The influence of the H/D ratio on the compression deformation is not obvious at lower pressures and compaction degrees, but it is significantly enhanced when the H/D ratio is beyond 0.65. The compression curves of the remolded loess samples with different H/D ratios fit the Gompertz equation well, and the transition point of the compression curves becomes difficult to identify with the increase in the H/D ratio. The compression index (C-c) decreases exponentially as a function of the H/D ratio, while the compressive yield stress (P-c) increases linearly with the increase in the H/D ratio. SEM analysis showed that, with the increase in the H/D ratio, the compression deformation of the sample changed from the whole sample involved in compression to the part of the soil in contact with the pressure. The compression of loess is mainly dominated by the compression of macropores and mesopores. The development of the soil-ring wall friction on the compression deformation induced by the H/D ratio was analyzed based on the change in microstructure, and a three-stage development of the soil-ring wall friction was established. These results and analysis established the connection between the specification and the literature, providing strong support for the rationality of the confined compression test results.