Strength criteria of gas hydrate-containing coal under high confining pressure

Abstract

The conventional triaxial loading tests were conducted under different saturation(50%, 80%) and confining pressures (12 MPa, 16 MPa, 20 MPa) to explore the applicability of Mohr-Coulomb(M-C) criterion, Hoek-Brown (H-B) criterion as well as Generalized Hoek-Brown(GH-B) criterion to gas hydrate-containing coal under high confining pressure condition. The stress-strain curves were analyzed, and the variation of the main principal stress with the confining pressure was fitted by using the formulas of three strength criteria. Meanwhile, the root mean square deviation RMSE and correlation coefficient were introduced to evaluate the applicability of different strength criteria for gas hydrate-containing coal. The results show that the stress-strain curves exhibit strain hardening characteristics under the condition of high confining pressure. The higher the confining pressure and saturation, the higher the peak strength. The confining pressure has a significant effect on the peak strength. M-C and GH-B criteria are proved to have good fitting effect on the test data, with higher correlation coefficient and lower RMSE value than H-B criterion. The linear fitting line between the predicted value and the test value is very close to the 1∶1 gradient line, indicating that the two criteria have good applicability to gas hydrate-containing coal. The correlation coefficient of H-B criterion is lower than M-C and GH-B criterion. The RMSE value is larger, and the applicability of H-B criterion to gas hydrate-containing coal is slightly lower than M-C criterion and GH-B criterion.

Keywords

• high confining pressure
• gas hydrate-containing coal
• stress-strain curve
• strength criteria
• saturation