Influence of acidic environment and temperature on mechanical behavior of cement-treated Masado and numerical modeling with a thermoelasto-viscoplastic model

Cement-treated Masado (CTM), as a common cement-mixed geomaterial, is usually only used in ground improvement for temporal structures in Japan. However, in recent years, it has been used for new permanent structures, such as the supporting ground of pile foundations and direct foundations. Masado, a completely decomposed granite, is distributed widely in Japan. However, the long-term stability of CMT has not been thoroughly investigated, despite that it has the risk of exposure to environmental changes in acid conditions and temperature, which are very common in volcanic areas in Japan. In this study, to investigate the influence of acidic environments and temperatures on the mechanical behavior of CMT, a systematic test program using uniaxial and triaxial tests was conducted on CMT specimens under different acidic environments, temperatures, and confining pressures. To avoid the extra influence of water on the mechanical behavior of CMT, a special double-cell was designed within the pressure chamber of the triaxial loading device so that the volumetric strain of the specimens completely sealed with rubber sleeve can be accurately measured in triaxial compression and creep tests. In addition, the chemical components of all the tested specimens are investigated by X-ray fluorescence spectrometry analysis to identify the influence of calcium leaching and hydration reactions in the curing period. Combined with the influence of the initial confining pressure, the influence of the acidic environment and temperature on the strength and dilatancy of CMT is carefully investigated. Based on the test results, a relation between the stress ratio at the critical state and the influential factors, including the initial confining pressure, acidic environment and temperature, is proposed by regression analyses. Meanwhile, an existing thermoelasto-viscoplastic model is modified to properly describe the influence of the abovementioned influential factors on the mechanical behavior CMT. The applicability of the modified model is then verified by triaxial compression and creep tests.