Short-term and creep tests were performed on saturated silty mudstone obtained from the Three Gorges Reservoir area. Based on the triaxial creep test results, the variations of creep strain and creep rate of silty mudstone with time were analyzed in detail, and the differences between the axial and lateral creep parameters were quantitatively studied at different deviatoric stress levels. The longterm strength of silty mudstone was obtained. The results demonstrate that the lateral creep characteristics are more significant than the axial creep characteristics for silty mudstone in the tests. Analysis of the lateral creep characteristics of the rock is a reasonable approach to determine whether creep failure occurs in the silty mudstone. The long-term strength of silty mudstone decreases remarkably, and it is actually the lateral long-term strength of the rock. According to the triaxial creep curves of silty mudstone, a new nonlinear viscoelasto-plastic creep model was proposed by connecting in series the nonlinear viscoplastic body with the sixcomponent model. Comparing the model curves with test results, this model was determined to reflect the creep properties of silty mudstone accurately. Finally, the selection of the creep model parameters was achieved by considering the axial and lateral creep characteristics of silty mudstone.

This study investigates the effect of prefabricated fissures on the creep mechanical strength and acoustic emission (AE) characteristics of sandstone. Under the same test conditions, indoor uniaxial compression creep AE tests were performed on intact and artificially fissured sandstone specimens using a rock rheometer and a PCI-Ⅱ AE tester controlled with an RLJW-2000 microcomputer. The variation characteristics of strain, long-term strength, number of AE events, AE ringing count, AE energy, and RA value of the two specimens were then analyzed to determine the effect of prefabricated fissures on the creep mechanical properties and AE characteristics of sandstone. The results show that under the same stress level, the instantaneous strain, creep strain, and total strain of the prefabricated fissures specimen was larger than the corresponding values of the intact specimen. The prefabricated fissures exhibited the most significant influence on the creep strain of the specimen, followed by the total strain. The fissures showed the least influence on the instantaneous strain of the specimen. Furthermore, the long-term strength of the prefabricated fissures specimen was only 37.5% of that of the intact specimen. Owing to the influence of the prefabricated fissures, the long-term strength of the sandstone was significantly reduced. In engineering practice, fissures should be noted and analyzed for the potential failure of a formation. Moreover, as the stress level increases, the number of AE events of the specimen also increases. The number of AE events and cumulative AE events generated by the prefabricated fissures specimen at various stress levels is significantly higher than the corresponding values of the intact specimen. The maximum ringing count of the prefabricated fissures specimen was 7.3 times that of the intact specimen, and the maximum AE energy was 3.8 times that of the intact specimen. The cumulative AE ringing count was 1.5 times that of the intact specimen, and the cumulative energy was 4.5 times that of the intact specimen. The prefabricated fissures significantly affect the maximum AE ringing count, maximum AE energy, cumulative AE ringing count, and cumulative AE energy of the specimen. Finally, tensile fissures were the main microcracks generated inside the intact specimen during creep, and shear cracks were secondary. The microcracks generated inside the prefabricated fissures specimen consisted of mixed tension-shear cracks, but mainly consisted of shear cracks with fewer tension cracks. The RA value correlates well with the observed internal microcracks, indicating that the RA value can be used to characterize fractures in sandstone specimens. The RA value has a guiding significance for characterizing the type of internal microcracks in the process of rock creep.

Instability failure of bolted fractured rock masses is not typically observed at the beginning stage. Instead, their deformation continuously adjusts over time in response to the continuous application of a constant load, resulting in creep failure. The presence of bolt influences the failure of rock by changing the stress distribution within the rock mass. To reveal the influence of bolts on fractured rock masses, double-fractured sandstone specimens reinforced with 0, 1, and 2 horizontal bolts were fabricated. The mechanical properties, deformation failure modes, AE characteristics, and instability precursor data of unbolted, single-bolted, and double-bolted specimens were compared and analyzed. The results show that: (1) The mechanical properties of bolted fractured rock mass have been significantly improved. The long-term strength of single-bolted and double-bolted specimens was 35.93% and 49.88% higher than that of unbolted specimens, respectively; (2) Compared with the unbolted specimen, the axial strain of the double-bolted specimen decreased by 20.55% and 32.97% at stress levels of 40 and 60 MPa, respectively, indicating that the bolt effectively restrained specimen deformation; (3) The AE energy, cumulative ring count, and peak frequency of bolted fractured rock samples decreased at the same stress level, with the AE energy of the double-bolted sample being only 0.6 times that of the unbolted sample; (4) An analysis of the AE ratio of the ring count to the duration and the rise time to amplitude (AF-RA) value, along with the macroscopic failure characteristics, revealed the reinforcement mechanism of the bolt. As the number of bolts increased, the final failure mode transitioned from shear failure to tensile shear failure; (5) Based on the critical slowing down features of AE signals, a sudden and significant increase in both variance and autocorrelation coefficient can serve as an early warning signal for rock failure. It can be used to determine the long-term strength and predict short-term failure of bolted fractured sandstone. This presented study can provides a basis for the analysis of the creep process in bolted fractured rock masses.