Xiao Yun

In order to study the creep characteristics and mechanism of red-bed soft rock under the water–rock interaction, fluid–structure coupling triaxial compression tests and creep tests under stepwise loading were carried out. Furthermore, the influences of seepage pressure and stress on creep deformation, long-term strength, Poisson’s ratio, and seepage velocity were analyzed. According to the experimental results, the influence of seepage on the creep of soft rock cannot be ignored. The results show that the seepage leads to a decrease in triaxial strength and long-term strength, and an increase in instantaneous deformation and creep deformation. The failure mode of triaxial compression changes from shear failure to tension-shear conjugate failure, whereas the long-term strength of fluid–structure coupling creep is 60%~70% of the triaxial strength. When the stress level and seepage pressure are relatively small, the Poisson’s ratio of creep increases with the increase of seepage pressure, and the radial creep deformation response lags behind the axial creep deformation. However, at a high stress level and osmotic pressure, the Poisson’s ratio and seepage velocity increase rapidly, and the duration of the accelerated creep is obviously shortened. Through the analysis of the influence of seepage pressure on the seepage velocity, with the increase in the seepage velocity, the seepage velocity changes and fluctuations are more obvious, which further confirms the damaging effect of seepage pressure and erosion on the internal structure. In the field monitoring of actual engineering, the rapid change of seepage velocity can be used as a precursor signal to predict the instability. Therefore, the water–rock interaction cannot be ignored in the analysis of mechanical properties and long-term stability of red-bed soft rocks.

The rheological energy characteristics and evolution law of fractured sandstone strengthened with CFRP (carbon fiber reinforced plastic) were studied to solve the problem of rheological failure of rock after engineering excavation disturbance. In this paper, the graded loading rheological tests of fractured sandstone after reinforcement are carried out. The results show that the failure rheological stress of sandstone increases with the increase of the area strengthened by CFRP. When the reinforcement area is from 3140 mm² to 4710 mm², the failure rheological stress of rock mass is increased from 65 MPa to 75 MPa, approximately 15.4%. Except for the initial rheological stage, the elastic energy is decreasing and the dissipative energy is increasing. The elastic energy is fully released, and the dissipative energy is provided by the total energy when the rock is destroyed. The energy dissipation ratio (U_d/U) of sandstone under the two reinforcement areas reached the minimum value at the stable rheological stage, which was 0.26 (A = 3140 mm²) and 0.42 (A = 4710 mm²) respectively. The energy mechanism of CFRP is that CFRP stores energy mainly and consumes energy secondly before the energy inflexion. However, CFRP switches to consuming energy mainly and storing energy secondly after the energy inflexion. The energy storage coefficient of CFRP can directly describe the function of elastic energy or dissipative energy of CFRP under arbitrary stress. When the energy storage coefficient T > 1, the damage of CFRP is small. Further, the energy storage coefficient reaches the maximum value of 5 at the energy inflection point (55 MPa). When the energy storage coefficient T < 1, the damage of CFRP is large, and the energy storage coefficient reaches the minimum value of 0.005 at the stress of 40 MPa. During the rheological process of fractured sandstone strengthened with CFRP, the energy evolution shows the relationship between elastic energy and dissipated energy. The energy mechanism of CFRP explains the working mechanism of the reinforced structure in the rheological process and plays a guiding role in the analysis of the rheological failure of the reinforced rock in the practical engineering.