Experimental study on unloading creep of sandstone under temperature-seepage coupling conditions

Environmental factors (such as temperature and water) and their coupling effects will change the unloading creep properties of surrounding rock after tunnel excavation, threatening the stability of surrounding rock and the safety maintenance of construction sites. To analyze the effects of temperature, seepage flow, and their coupling on the creep characteristics of sandstone unloading, the triaxial unloading creep test was carried out on the sandstone specimen (φ50 mm×100 mm) by using the self-designed temperature control system and the improved pore water conduction specimen sealing device. The results show that during the creep time of 300 min after unloading the confining stress, the axial compression and radial expansion creep speed increase gradually and then slow down. The strain is mainly radial creep. The decrease in temperature leads to the increase in axial creep deformation and the decrease in radial creep deformation of the dry and saturated specimens. With the increase in seepage water pressure, the axial strain reduces, and the seepage water pressure suppresses the axial creep deformation, while the radial strain increases significantly, and the expansion phenomenon is obvious. Seepage water pressure promotes radial creep deformation. With the increase of seepage water pressure, the axial unloading creep rate decreases and the radial unloading creep rate increases. Under the coupling effect of temperature and seepage, the creep rate curve of unloading is divided into the attenuation stage and the stable stage, and the deformation in the attenuation stage is dominant. The radial creep rate is higher than the axial creep rate; the fluctuation amplitude of the radial creep rate is small, which reaches stability fast. This study can provide scientific information for the stability evaluation of surrounding rock in deep underground engineering.