Abstract
In the current work a new equation for initial damage assessment of limestone based on plane strain theory is proposed. Detailed investigations of the static and dynamic characteristics of limestone with different initial damage degree, using longitudinal wave speed, and static-dynamic compression tests are performed. This study investigated the static and dynamic characteristics of limestone with different initial damage degree, using longitudinal wave speed, and static-dynamic compression tests. Experimental results show that the degree of initial damage decreases with increasing longitudinal wave speed, which reaches the minimum when the longitudinal wave speed is approximately 6000 m/s, and the smaller the longitudinal wave velocity, the greater the degree of initial damage. The static and dynamic compressive strengths of limestone increase with the longitudinal wave velocity and strain rate, but the elastic modulus and Poisson’s ratio do not change significantly. Finally, based on the experimental results, the definitions of damage threshold value and strain softening are proposed, which further verify the influence of strain rate and initial damage on rock compression characteristics. The present study sheds light on the importance of initial damage for the mechanical state of rock in underground engineering.
Highlights
Natural rock contains microcracks, micropores, and other defects
Many scholars have since chosen parameters that are related to the rock mechanics in order to characterize the initial damage, such as the number, spacing, direction of microcracks [13,14,15,16], crack volumetric strain [17], X-ray, computed tomographic scan number [18,19], ratio of initial compression and yield strength [20,21], the acoustic emission signals [22,23,24,25], and the rock’s acoustic wave speed [26,27,28,29,30,31]
The yield-stage strain values of the four initial damage values in Figure 13a obtained by the longitudinal wave velocity method are on average 2% larger than those obtained from the loading-unloading method
Summary
Micropores, and other defects. The initial stress release and redistribution during the construction of underground structures lead to the further development of original microcracks and micropores in rock. Many scholars have since chosen parameters that are related to the rock mechanics in order to characterize the initial damage, such as the number, spacing, direction of microcracks [13,14,15,16], crack volumetric strain [17], X-ray, computed tomographic scan number [18,19], ratio of initial compression and yield strength [20,21], the acoustic emission signals [22,23,24,25], and the rock’s acoustic wave speed [26,27,28,29,30,31]. The relevant experimental data regarding initial damage are quite scarce, especially those in terms of high strain rate These above investigations have provided insights into the compression static and dynamic characteristics of limestone with different initial levels of damage. The presentation of the results in this study is helpful to better understanding the mechanical properties in order to develop a proper constitutive model of limestone with initial damage
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