Abstract
AbstractCreep behavior is one of the most important mechanical behaviors of coal. In the present study, we systematically carried out a series of creep experiments of briquette samples under triaxial compression and gas pressure. The experimental results showed that the creep deformation characteristics of coal were related to deviatoric stress and gas pressure. The accelerating creep stage initiated when the deviatoric stress reached or exceeded the yield stress until failure took place. In contrast, when the deviatoric stress was less than the yield strength, only transient and steady creep stage occurred. Besides, gas pressure played a positive role in the creep process of coal. The axial strain of coal slightly increased with gas pressure (range from 0.13 to 0.40 MPa) when the effective triaxial stress remained constant. For example, in the steady creep stage (σ1 = 9 MPa, p = 0.13 MPa), the axial strain of sample S1 is 2.710% and that of sample S2 is 3.361%, that is, coal samples with high gas pressure have higher axial strain. Moreover, gas pressure has two main effects on the mechanical behavior of coal. One is that the coal adsorbs gas molecules resulting in swelling strain and swelling stress, and the other is that the gas pressure may compress the coal particles. Considering the swelling stress and gas pressure, we intensively studied the effective stress formula of coal containing gas. Then, the effective stress was taken into consideration in the nonlinear Nishihara creep model. Furthermore, the tertiary creep factor n was introduced in the nonlinear model to control the creep deformation evolution with time so that the nonlinear model could accurately describe the full creep stage of coal. In contrast, due to the lack of such a controlling parameter, the Nishihara model failed to reproduce the accelerating creep stage.
Highlights
Creep behavior is one of the fundamental mechanical properties of coal or rock, associated with the stability of many buildings and underground structures in mining and rock engineering, such as roadways, tunnels, and dams
When the deviatoric stress was less than the yield strength, only transient and steady creep stage occurred
One is that the coal adsorbs gas molecules resulting in swelling strain and swelling stress, and the other is that the gas pressure may compress the coal particles
Summary
Creep behavior is one of the fundamental mechanical properties of coal or rock, associated with the stability of many buildings and underground structures in mining and rock engineering, such as roadways, tunnels, and dams. Based on the analysis of rheological test data, the empirical model describing the relationship between creep strain and time is established via the fitting results. Based on the unsaturated creep tests of weak intercalated soils, an improved Mesri creep model was established by Zhu and Yu9 using GDS triaxial apparatus. They subsequently carried out the compressive trials of two kinds of gangue and found that the logarithmic function is suitable for describing its equal‐time stress‐strain relationship. The empirical models with simple creep equation forms and only a few parameters appear to have the capability to describe the creep behaviors of specific rock or coal fairly well and may play an important role in engineering practice. The empirical models have an obvious defect that the physical meaning of model parameters is still unknown
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