Dynamic Mohr-Coulomb and Hoek -Brown strength criteria of sandstone at high in rates

Significance 

Among the available strength criteria used in the analysis of rock mechanics, Mohr-Coulomb and Hoek-Brown strength criteria are commonly used. Unfortunately, validating the applicability and reliability of the above criteria have been a great challenge. This can be attributed to the assumption that the parameters in the strength criteria are constant under static loading. In the recently published literature, rocks are equally subjected to dynamic loads that exhibit different mechanical response from that of static loads. Therefore, under dynamic rock failure, the above strength criteria with constant parameter under static loading do not take into consideration the strain rate effects and thus are unsuitable for the rock mechanics analysis. As such development of alternative dynamic strength criteria for rocks taking into account the rate effects are highly desirable.

Up to now, various researchers have performed a series of dynamic uniaxial compression tests on various materials including granite and marble under different strain rates and confining pressures. For instance, dynamic M-C strength criterion showed good applicability in low confining pressure conditions while H-B strength criterion exhibited good applicability in both low and high confining pressure conditions. However, determining rock dynamic strength criterion at high strain rates is still a challenge. Presently, the split Hopkinson pressure bar (SHPB) devise is used to evaluate rock strength at high strain rates. This has pioneered the establishment of an M-C strength criterion taking into consideration the loading rate and the uniaxial compression strength. As such, recent studies have shown the importance of dynamic uniaxial and triaxial compressive strength of rocks under various confining pressures and high strain rates in developing the dynamic strength criterion.

To this note, Central South University researchers: Xuefeng Si (PhD candidate), Associate professor Dr. Fengqiang Gong, Professor Xibing Li, and Song Luo (PhD candidate) together with Professor Shanyong Wang at the University of Newcastle in Australia investigated the dynamic M-C and H-B strength criteria under high strain rates and low confining pressure. Fundamentally, the triaxial compression tests and the dynamic uniaxial of sandstone were conducted with a modified triaxial SHPB and a conventional SHPB system respectively. The experimental data were analyzed under varying strain rates and confining pressure ranging from 40-160s-1 and 5.0-15.0MPa respectively. The work is published in International Journal of Rock Mechanics and Mining Sciences.

The authors observed that the strain rate logarithm exhibited a positive and negative linear correlation with the cohesion and internal friction angle respectively. However, change in the cohesion was more dominant than the internal friction. Additionally, the rock parameter m, internal friction, and cohesion changed with an increase in the strain rate because they were not constant. To validate the study, the established expression of the dynamic M-C and H-B strength criteria was used to determine the strength of the sandstone. Interestingly, it proved effective for applications at both high strain rates and low confining pressure. This was also justified by the similarities in the theoretical and actual experimental strengths. Altogether, the study can be extended for analysis of various types of rocks.

Dynamic Mohr-Coulomb and Hoek -Brown strength criteria of sandstone at high in rates - Advances in Engineering
Experimental system sketch of modified triaxial SHPB apparatus

About the author

Fengqiang Gong is an associate professor at School of Resources and Safety Engineering, Central South University, China. His main research interests include rock strength criterion, rock dynamic fracture characteristics, deep rock mechanical behavior and characteristics, and geotechnical reliability theory. He has published more than 100 papers and owned 20 patents. He served as the Editorial Board Members of 《Chinese Journal of Rock Mechanics and Engineering》and 《Journal of Mining and Strata Control Engineering》.

About the author

Xuefeng Si is a PhD student at the Central South University, China, and engaged in the research of rock strength criterion and deep rock mechanics.

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About the author

Xibing Li is a Professor at School of Resources and Safety Engineering, Central South University, China. His main research interests focus on rock dynamic and mining engineering. He proposed an innovative approach based on SHPB system with half sine wave loading. He has published about 200 scientific papers on rock failure mechanisms and mining engineering, and he is the author of ten books of rock mechanics and mining engineering. He served as the Editorial Board Members of 《Chinese Journal of Rock Mechanics and Engineering》,《Journal of Mining and Strata Control Engineering》, 《Journal of Central South University》,《Journal of Mining & Safety Engineering》and 《Journal of Vibration and Shock》.

About the author

Shanyong Wang is a full professor at the department of civil engineering of the University of Newcastle. His expertise and research interests lie in advanced computational analysis of soft soil deformation and improvement and fractures evolution in brittle materials such as concrete and rock by the finite element and discrete element methods, as well as the experimental study of loose fill slopes and pile foundations subject to grouting. Since 2002, he has published, or has had accepted for publication, 134 refereed international journal articles and 45 conference papers.

About the author

Song Luo a PhD student at the Central South University, China. His research interests include the rock mechanics and energy law.

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Reference

Si, X., Gong, F., Li, X., Wang, S., & Luo, S. (2019). Dynamic Mohr–Coulomb and Hoek–Brown strength criteria of sandstone at high strain ratesInternational Journal of Rock Mechanics and Mining Sciences115, 48-59.

Go To International Journal of Rock Mechanics and Mining Sciences

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