Stabilization of Gob-Side Entry with an Artificial Side for Sustaining Mining Work
A concrete artificial side (AS) is introduced to stabilize a gob-side entry (GSE). To evaluate the stability of the AS, a uniaxial compression failure experiment was conducted with large and small-scale specimens. The distribution characteristics of the shear stress were obtained from a numerical simulation. Based on the failure characteristics and the variation of the shear stress, a failure criterion was determined and implemented in the strengthening method for the artificial side. In an experimental test, the distribution pattern of the maximum shear stress showed an X shape, which contributed to the failure shape of the specimen. The shear stress distribution and failure shape are induced by a combination of two sets of shear stresses, which implies that failure of the AS follows the twin shear strength theory. The use of anchor bolts, bolts, and anchor bars enhances the shear strength of the artificial side. When this side is stable, the components can constrain the lateral deformation as well as improve the internal friction angle and cohesion. When the AS is damaged, the components prevent the sliding of broken blocks along the shear failure plane and improve the residual strength of the artificial side. When reinforced with an anchor bar, the AS is still stable even after mining operations for three years.
COMPARISON OF YIELD STRENGTH THEORIES WITH EXPERIMENTAL RESULTS
On the basis of the testing data of the yield strength of various types of plastic metals under biaxial and triaxial combined tensile-compressive principal stress, the relative errors calculated using Tresca strength theory, Mises strength theory, Mohr-Coulomb strength criterion, Beltrami's maximum energy theory and limiting strain energy strength theory(LSEST) are analyzed, respectively. The result shows that the errors according to LSEST are within 10%, being the minimum. The errors calculated by Tresca strength theory, Mises strength theory and Mohr-Coulomb strength criterion are -36%, -27% and -23%, respectively. The calculating results are on the conservative side compared with the test ones. For materials with equal tensile and compressive yield strength, Tresca strength theory and Mises strength theory could not be applied either, and the theoretical shear yield strength is 2~(1/2)/2 times of the tensile yield strength. LSEST could be used to calculate the strength under biaxial and triaxial combined tensile-compressive principal stress, which is consistent with Rankine strength theory under a full tensile and a full compressive principal stress state, which suggests that LSEST has a prospect and value for engineering applications.
A review of nonlinear dynamics applications to structural health monitoring
The process of implementing a damage detection strategy for aerospace, civil and mechanical engineering infrastructure is referred to as structural health monitoring (SHM). In many cases damage causes a structure that initially behaves in a predominantly linear manner to exhibit nonlinear response when subject to its operating environment. The formation of cracks that subsequently open and close under operating loads is an example of such damage. The damage detection process can be significantly enhanced if one takes advantage of these nonlinear effects when extracting damage‐sensitive features from measured data. This paper will provide a review of examples from nonlinear dynamical systems theory and from nonlinear system identification techniques that are used for the feature‐extraction portion of the damage detection process. This paper is not intended as a comprehensive review of all damage detection methods rooted in nonlinear dynamics, but rather to provide a number of illustrations of complimentary approaches where damage‐sensitive data features are based on nonlinear system response. These features, in turn, can either be used as a direct diagnosis of damage or as input to statistical damage classifier. Copyright © 2007 John Wiley & Sons, Ltd.