Deep rock structures are often subjected to complex cyclic disturbances generated by earthquakes and blasting vibrations. The rocks will resist disturbance with multiple stress levels, and the research on mechanical response is still insufficient under such conditions. A series of multi-level cyclic loading experiments were subjected to limestone specimens to obtain the stress–strain relation and fracture behavior. This study explored the effect of amplitude and cycle times on rocks. A Discrete Element Method model of rock specimens was established in Particle Flow Code 2D (PFC2D). The simulation results are coincidental with the experiment results. The results show that loading with low cycles can strengthen the rock, but loading with high cycles will present deteriorated effect on the rock. In the numerical simulation test, the initial crack will appear earlier with the amplitude increase. More micro cracks will be induced as the number of cycles per level increases. Moreover, tensile cracks are mainly distributed around the specimen when shear cracks widely appear in the central area. With the increase of amplitude, failure modes with mixed shear and tensile cracks will become universal.
Deep rock structures are often subjected to complex cyclic disturbances generated by earthquakes and blasting vibrations. The rocks will resist disturbance with multiple stress levels, and the research on mechanical response is still insufficient under such conditions. A series of multi-level cyclic loading experiments were subjected to limestone specimens to obtain the stress-strain relation and fracture behavior. This study explored the effect of amplitude and cycle times on rocks. A Discrete Element Method model of rock specimens was established in Particle Flow Code 2D (PFC2D). The simulation results are coincidental with the experiment results. The results show that loading with low cycles can strengthen the rock, but loading with high cycles will present deteriorated effect on the rock. In the numerical simulation test, the initial crack will appear earlier with the amplitude increase. More micro cracks will be induced as the number of cycles per level increases. Moreover, tensile cracks are mainly distributed around the specimen when shear cracks widely appear in the central area. With the increase of amplitude, failure modes with mixed shear and tensile cracks will become universal.
Soil–cement–bentonite (SCB) backfill has been widely used in constructing cut-off walls to inhibit groundwater movement in contaminated sites. This study prepares SCB backfill with fixed fluidity. We conducted a series of experiments to investigate the engineering characteristics and microscopic mechanism of the backfill. The results indicate that the water content in the slurry was more sensitive to the bentonite content. The unconfined compression strength (UCS) value increased with an increase in the cement content, and the change with an increase in bentonite content was not noticeable. The permeability coefficient decreased distinctly with an increase in the cement and bentonite contents. The porosity of the SCB backfill increased with increasing bentonite content and decreased with increasing cement content. The UCS of SCB backfill was linearly and negatively correlated with the porosity; the permeability coefficient was not significantly related to the porosity. The percentage of micro- and small-pore throats in the backfill increased with increasing bentonite and cement contents. As cement and bentonite content increased by 6% in the backfill, the proportion of micro- and small-pore throats increased by 0.7% and 1.2%, respectively. The percentage of micro- and small-pore throats is deduced to be more suitable as a characterization parameter for the permeability of the SCB backfill. The overall results of this study show that the reasonably proportioned SCB backfill has potential as an eco-friendly and cost-effective material. Based on the requirements of strength and permeability coefficient (UCS > 100 kPa, 28 days permeability coefficient <1 × 10−7 cm/s), we suggested using a backfill with 12% bentonite and 9% cement as the cut-off wall mix ratio.
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