Study on the Rock Size Effect of Quasistatic and Dynamic Compression Characteristics

Abstract

To study the size effect of rock under quasistatic and dynamic conditions, the changes in compressive strength with the change in specimen size are measured. Cylindrical granite specimens with length-diameter ratios in the range of 0.5∼1 are used for uniaxial compression tests using an RMT testing machine and an SPHB impact testing machine. Under quasistatic loading, the failure modes of the specimens with different length-diameter ratios are different. The larger the size of the specimen structure is, the greater the probability of defects such as joints and micro cracks is and the smaller the influence of the specimen on the distribution of a three-dimensional stress state is. The rock strength decreases with increasing length-diameter ratio. Using the improved Weibull formula, the size of the specimen is expressed by the volume, and the calculated rock strength of different volumes is similar to the compressive strength from the quasistatic tests. Under dynamic loading, the dynamic compressive strengths of the specimens with different length-diameter ratios are similar, and the failure mode of the specimens is different from that under quasistatic loading. Soon after a crack appears in a specimen, the specimen splits. As the size of the specimens decreases, the fragments size to approach the millimeter scale. By improving the Weibull distribution formula and considering variation in strain rate caused by the size of the specimen, the dynamic compressive strength of rocks of different volumes is calculated by introducing the critical strain rate and related parameters, and the results are similar to the experimental dynamic compressive strength obtained. The improved Weibull formula based on the strength size effect can accurately describe the quasistatic and dynamic compressive strength laws.

Study on the influence of rock bridge angle on the size effect of rock uniaxial compression

“…Eq (10) is suitable for estimating the UCS of rocks with different rock sizes. However, when measuring the size, it is necessary to maintain a fixed 2:1 side length ratio, which limits its applicability.…”

“…Scholars have studied it from the aspects of loading conditions, ratio of height to diameter, water content, rock type, and strain rate. For example, Zhou et al [10] used an RMT testing machine to study the relationship between rock size and UCS under quasistatic and dynamic conditions, and accurately derived their patterns by improving the Weibull distribution formula. Fu et al [11] used granite and limestone for laboratory uniaxial compression test and found that the height-diameter ratio had a significant effect on UCS.…”

Influence of dynamic load and water on energy accumulation and dissipation in sandstone

“…Deep mining operations expose rock masses to a complex geological milieu characterized by elevated temperature, pressure, osmotic forces, and disturbances 1 – 6 . A thorough understanding of the mechanical response of the rock mass in this challenging environment is gained in the support of underground engineering initiatives 7 – 11 . Nevertheless, the energy conversion mechanisms governing sandstone under the combined effects of water and dynamic loading remain largely uncharted.…”