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Nonlinear shear constitutive model for peak shear-type joints based on improved Harris damage function

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Xie S. , Lin H. , Wang Y. , Cao R. , Yong R. , Du S. , Li J.

Archives of Civil and Mechanical Engineering

2020

tom Vol. 20, no. 3

454--467

The majority of jointed rock mass failures mainly occur along the joints in shear mode, which promotes a wide investigation on the proposal of a reasonable and reliable shear constitutive model of rock joints. In this paper, based on Improved Harris function and laboratory shear tests, a new constitutive model of saw-tooth joints was proposed. Firstly, a series of laboratory direct shear tests were carried out on saw-tooth joint specimens made of rock-like materials (cement mortar) to obtain the shear stress-displacement curves. Subsequently, the test results were divided into sliding failure type and peak shear type according to whether there is a significant stress drop between peak stress and residual stress. It is assumed that rock elements can be divided into undamaged parts and damaged parts during the shearing process. The stress-displacement relation of the undamaged part satisfies Hooke’s law, while the damaged part provides residual stress. Via the comparison with commonly used micro-element failure probability density functions, the Improved Harris distribution function was selected as the standard to characterize the strength of micro rock units. Finally, derived from the theory of damage statistical mechanics, a damage statistical constitutive model was proposed, which can reflect the deformation characteristics of rock joints. Compared with previous models and experimental data, the model proposed in this paper can represent the trend of peak shear curve variation with higher accuracy, the parameters are easy to be solved and have obvious physical significance, which verifies the advantages and applicability of this model.

Investigation of the correlation between crack propagation process and the peak strength for the specimen containing a single pre-existing flaw made of rock-like material

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Yang H. , Lin H. , Wang Y. , Cao R. , Li J. , Zhao Y.

Archives of Civil and Mechanical Engineering

2021

tom Vol. 21, no. 2

458--478

This paper investigated the relationship between the strength of fractured rock and the crack propagation process. A series of uniaxial compression tests were carried out on the rock-like material specimens with single pre-fabricated flaw. Moreover, DIC (digital image correlation) technology was utilized to monitor and analyze the failure process of specimens. The initiation of each crack was defined as a key event, and the relationship between several key events and the axial load of the specimen during the crack propagation was quantitatively analyzed. The time-sequence analysis of crack propagation was also conducted by selecting benchmark points on the both sides of major cracks. It can be found that only the wing crack propagation occurs and there is no obvious shear crack before the peak strength. When the first secondary crack initiated, the specimen reached its peak strength and the wing crack just reached its critical length. Beyond the peak strength, secondary cracks initiated and coalesced rapidly, which leads to the sudden failure of fractured rock. Therefore, the peak strength of the specimen can be assessed by taking the critical length of the steadily propagating wing crack as the condition which determines whether the specimen reaches the peak strength. Furthermore, the discrete element numerical simulation was also implemented to confirm the experimental results.