Anatomy of incremental behaviour of granular materials induced by loading reversal: a stress probing analysis

In practical geotechnical engineering, soil elements in the ground often experience varying stress paths involving loading reversals. To better understand the incremental behaviour of granular material under these conditions and enhance associated constitutive formulations, a series of probing tests was conducted on granular specimens at various stages of loading and unloading. The stress probing test, used in conjunction with the discrete-element method, can effectively capture the strain response of granular specimens subjected to stress increments in different directions. Using this technique, the evolution of strain response envelopes during various stages of loading reversal was obtained and analysed. The test results indicated that, during the initial stage of loading reversal, the plastic modulus increases dramatically, while the plastic flow direction remains nearly unchanged from its value prior to reversal. The plastic modulus and plastic flow direction were derived from the probing tests, which guided the development of a constitutive model within the bounding surface framework. Three strategies for relocating the projection centre upon loading reversal were considered, and their performance under different test conditions was presented and evaluated.