Research on Rheological Energy Characteristics of Fractured Sandstone Strengthened with CFRP

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 (Ud/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.