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Zhang X.,CAS Institute of Geology and Geophysics | Wang S.,CAS Institute of Geology and Geophysics | Han G.,CAS Institute of Geology and Geophysics | Zhang B.,State Key Laboratory of Shield Machine and Boring Technology
Yanshilixue Yu Gongcheng Xuebao/Chinese Journal of Rock Mechanics and Engineering

To study the progressive failure of schistose rock, three stress thresholds, i.e. crack initiation stress σci, crack damage stress σcd and uniaxial compression peak strength σf, and their relationship between each other are summarized and discussed systematically. Based on the uniaxial compression axial stress-axial/radial strain curves of Danba quartz mica schist, analysis of stress thresholds of schistose rock in progressive failure process are firstly applied to schistose rock. Stress thresholds under the three conditions of schistose foliation oriented perpendicular, parallel, and at 30° to loading direction respectively are obtained, which are compared with those of other sorts of rock in references. Results show that the crack propagation are related to rock type. Grain size of mineral, cement bond quality between mineral grains and schistose and joint plane development are all the factors to influence the progressive failure process of rock. Different stress threshold ranges of different types of rock are then got accordingly. Experimental research results of quartz mica schist indicate that due to the joint plane developments, strong anisotropy exists in the schistose rock crack propagation under uniaxial compression. This distinguishing characteristics should be considered quantitatively during underground excavation and support design. Source

Qi G.,Xian Jiaotong University | Zhengying W.,Xian Jiaotong University | Hao M.,Xian Jiaotong University | Qiao C.,State Key Laboratory of Shield Machine and Boring Technology
Journal of Mechanical Science and Technology

A common drawback presented by several numerical rock-breaking studies was that the rocks beneath disc cutters were cut off excessively while the rocks between disc cutters remained, which usually resulted in a smaller cutter spacing than the proper value. To overcome this limitation, the constitutive equations of different rock parts were defined separately using VUMAT, an ABAQUS-based material subroutine. The constitutive model of rock was an application of the Drucker-Prager yield criterion coupled with the Lemaitre damage model. Full-scale rock-breaking tests on a rotary cutting machine were conducted, and 25 groups of orthogonal numerical simulations were carried out. By comparing the normal force, rolling force, and specific energy of numerical results with those of experimental results, the optimal values of the defined parameters Dc1, k, and B were determined to be 9☓10-4, 0.1 and 0.8, respectively. With the presented numerical method and the determined parameters, the influences of cutter spacing on normal force, rolling force, and specific energy were studied. Both the normal and rolling forces of the first cutting generally remained constant, whereas the forces of the second cutting generally increased linearly with the cutter spacing. The optimal cutter spacing for the studied rock type (Hard sand rock collected from West Qinling tunnel) was approximately 72 mm, which was in accordance with the cutter spacing of the tunnel boring machine applied in this tunnel project. © 2016, The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg. Source

Sun W.,Dalian University of Technology | Guo L.,Dalian University of Technology | Zhou J.-J.,State Key Laboratory of Shield Machine and Boring Technology | Huo J.-Z.,Dalian University of Technology
Meitan Xuebao/Journal of the China Coal Society

To investigate rock fragmentation process under disc cutter and how cutter-ring structure affects cutter-rock interaction, a 3D cutter-rock interaction model based on discrete element method was build. Contact force, micro crack development and crack balls during cutting process were studied. Furthermore effect of cutter edge width and angle on rock fragmentation was analyzed, and the mapping relationship between ring structure and cutting efficiency was established. Results show that the micro failure of rock is mainly due to tensile crack, and fragmentation is an acceleration process. Cutter edge width affects cutter-rock interaction more than cutter edge angle, with cutter force and crack rock volume increase obviously when cutter edge width increases. Based on the mapping relationship, the ring structure for 17″ disc cutter was designed, and the optimized edge width and angle were obtained. ©, 2015, China Coal Society. All right reserved. Source

Lu Y.-F.,China Three Gorges University | Lu Y.-F.,Wuhan University | Lu T.,China Three Gorges University | Zhou J.-J.,State Key Laboratory of Shield Machine and Boring Technology | And 2 more authors.
Yantu Lixue/Rock and Soil Mechanics

The classification as three types is proposed for the load-displacement relation curve of the rock-soil mass at first; a criterion of high earth pressure is defined. A new constitutive theory is at first proposed; the complete-process relation of stress-strain can be described under different normal stresses (or different confining pressures) by this theory. There only exist three mechanical parameters describing the geomaterial and stress state. It describes not only the mechanical behavior of geomaterial, but also of the complex material and of the surface between different media, the arbitrary deformation can be obtained. The relationship of stress-strain for the different rock-soil masses and the surface between rock-soil layer and pile are described by the proposed constitutive theory. The testing data of pile foundation of Changshawan bridge are simulated; the results show: that the mechanical properties of different rock-soil masses and interlayer between rock-soil mass and pile can be presented by this constitutive theory. Source

Zhu H.-Y.,Shanxi Railway Institute | Li H.-B.,State Key Laboratory of Shield Machine and Boring Technology | Zhang H.-P.,State Key Laboratory of Shield Machine and Boring Technology | Ren Y.-Y.,State Key Laboratory of Shield Machine and Boring Technology
Zhendong yu Chongji/Journal of Vibration and Shock

TBM tools have to be replaced frequently because of wear. There is a lack of an effective method to evaluate the tool condition in underground construction. The acoustic emission technology is applied to detect the health condition of the TBM tool. Single or multiple acoustic emission features were used to estimate the wear trend according to the acoustic emission signals from a TBM mode at different levels of wear. An improved CRITIC method to evaluate hob wear was put up. The disc cutter wear test showed that the improved CRITIC method is more sensitive to the tool wear levels. The new method is more efficient to evaluate and predict tool wear, and it provides guidance for repairing and maintaining of the cutting tool. © 2016, Editorial Office of Journal of Vibration and Shock. All right reserved. Source

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