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Numerical Research On Zonal Disintegration Of Rock Mass Around Deep Tunnel
Zhang, Y.B. (State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology) | Tang, C.A. (Center for Rock Instability & Seismicity Research, Dalian University of Technology) | Liang, Z.Z. (Center for Rock Instability & Seismicity Research, Dalian University of Technology) | Zuo, Y.J. (Research Center for Numerical Tests on Material Failure, Dalian University) | Zhang, Y.J. (Research Center for Numerical Tests on Material Failure, Dalian University)
ABSTRACT Zonal disintegration of rock mass around underground engineering is a hot research topic since discovery of it. It concerns with the stability and support of engineering at deep level. The numerical method of simulation on three dimensional models is involved. The numerical models with a circle hole and two holes taking rock heterogeneity into account under loading are adopted. The meshes for the model consists of 90×180×180=291,6000 8-nodal hexahedron elements with a geometry of 90×180×180mm in size. With the code named RFPA3D-Parallel (3-Dimensional Parallel Rock Failure Process Analysis) based on finite element method running on Lenovo 1800 Cluster with 64 CPUs, the whole process of rock fracturing of zonal disintegration (fracture spacing) is obtained. It provides a powerful numerical tool to study the problem of zonal disintegration in rock mass. The numerical results indicate that the higher axial principle stress may be one of the most important factors caused spacing fracture in rock mass around deep tunnel. 1. Introduction With economic and engineering developing, underground space's exploitation is going to deep level. Main results of in-situ tests of the behavior of rocks around underground workings at large depth have been published earlier. Rock mass at large depths is in the situation of high crustal stress, high temperature and high seepage pressure. The mechanical behaviors of rock mass in deep tunnels are different from those shallow tunnels. The phenomenon of zonal disintegration (see Fig.1) alternately successive distribution of fractured zone and unfractured zone around rock mass of tunnel or working face at large depthsobserved by E.I. Shemyakin et.al.[1] is one of important and interested problems in deep rock engineering and mechanics theory. It has key influence to the excavation and supporting of tunnels and working faces. Many researchers with interests have done some work on it. And a lot of explanations about its formation have been put forward by various theories and experiments. A.M. Kozel[2] considered the relationship the development of zonal disintegration and the dynamic process of drivage and blasting. G.G. Mirzaev[3] related fractures parallel tunnel contour to seismic wave called Hopkinson failure. E.I. Shemyakin et al.[1,4] carried out experimental tests in their laboratory with similar material and research on engineering practical application of zonal disintegration. Their study showed that rock mechanical property, rock structure, tunnel shape and support pattern have influence on zonal disintegration and that the stress changes around tunnel not the blasting caused zonal disintegration around deep tunnel. L.S.Metlor, A.F.Morozov and M.P.Zborshchik[5] revealed physics basics of rock fracture around tunnel with nonequilibrium thermodynamics, and represented the revolution process rock failure from elastic situation to zonal fracture structure. As viewed from energy, V.N.Reva[6] presented an evaluation method to tunnel stability on the condition of appearing zonal disintegration. 2.1. Numerical Method The RFPA3D code is based on the theory of elastic-damage mechanics and FEM (finite element method). In RFPA3D, the solid or material is assumed to be composed of many elements (8-nodal hexahedral isoparametric element at present) with the same size.
Crack Propagation Modeling Of Rock-Like Materials From Surface Flaw Under Uniaxial Compression
Tang, S.B. (School of Civil and Hydraulic Engineering, Dalian University of Technology, Dalian) | Tang, C.A. (School of Civil and Hydraulic Engineering, Dalian University of Technology, Dalian) | Liang, Z.Z. (School of Civil and Hydraulic Engineering, Dalian University of Technology, Dalian) | Zhang, Y.B. (School of Civil and Hydraulic Engineering, Dalian University of Technology, Dalian) | Li, L.C. (School of Civil and Hydraulic Engineering, Dalian University of Technology, Dalian) | Ma, T.M. (School of Civil and Hydraulic Engineering, Dalian University of Technology, Dalian) | Wong, R.H.C. (Department of Civil and Structural Engineering, The Hong Kong Polytechnic University)
ABSTRACT Crack propagation processes of rock-like material containing a single pre-existing surface flaw under uniaxial compression are numerically investigated by the Realistic Failure Process Analysis(RFPA3D) code. Heterogeneity feature of rock sample is simulated by Weibull distribution. Numerical simulated results indicate that three types of cracks emerged from the surface flaw under uniaxial compression, namely wing cracks, anti-wing cracks and petal cracks. Anti-wing crack is the primary crack and developed by the growth of tensile cracks from the surface of the sample extending into the interior of the sample. The heterogeneity consideration in the RFPA3D code result in unsmooth crack path and unsymmetrical crack growth of the two antiwing cracks at the left and right lateral of pre-existing flaw, which are recognized to be realistic for heterogeneous materials. Numerical simulations in this studies show the failure process very clearly including the growth of wing cracks, anti-wing cracks, and petal cracks, especially the inside crack growth process which is difficult to observe in the conventional experiment. It provides a better understanding on crack development around a surface flaw. 1. Introduction Extensive research has been done on crack propagation in different brittle or quasi-brittle materials with a single pre-existing flaw under uniaxial compression loading. To investigate the growth mechanism of these cracks, plenty of studies are documented by laboratory tests[1–6]. And found that primary cracks which also named wing cracks appear first, and they are tensile cracks which start at the tips of the flaw and propagate in a curvilinear path as the loading is increased. Generally, wing cracks grow in a stable manner since an increase in load is necessary to lengthen the cracks and align with the direction of the most compressive load[1]. The secondary cracks appear later and propagate in coplanar of the flaw or with an inclination similar to the wing cracks but in the opposite direction. It can be seen from the previous studies about flaw movement that they much focused on the cracks initiation and propagation of simplified 2- D or internal 3-D pre-existing flaw, ignoring a type of flaw which penetrates into the sample a finite depth which named surface flaw(see Fig.2). Recent experiments of crack growth with a single pre-existing surface flaw under uniaxial compression showed that a new type of crack quite obviously occurred in the opposite direction of wing cracks, which named anti-wing cracks[[7–9]]. And it is found that the depth of the flaw significantly influence the crack pattern, i.e. 2. Numerical Methodology The heterogeneity of rock is regard as the source of nonlinear mechanical behavior of rock. And failures in heterogeneous material not only occurred at the high-stress site, but also start at the weaker locations due to the presence of micro-cracks and grain boundaries.
- Research Report > New Finding (1.00)
- Research Report > Experimental Study (0.69)
Three-Dimensional Damage Model For Heterogeneous Rock Failure Process And Numerical Tests
Liang, Z.Z. (School for Civil and Hydraulic Engineering) | Tang, C.A. (School for Civil and Hydraulic Engineering) | Li, L.C. (School for Civil and Hydraulic Engineering) | Zhang, Y.B. (School for Civil and Hydraulic Engineering)
ABSTRACT A three-dimensional damage model was established combined with statistical mechanics to simulate failure process of heterogeneous rocks. The heterogeneities on mesoscopic scale were considered by assigning element mechanical properties randomly by following a certain statistical distribution function. It was assumed that each element kept elastic before reaching to the failure threshold, and it may fail in either in tensile failure mode or shear failure mode according to a shear failure criterion combined with a tension cut-off. Uniaxial compression test, uniaxial tension test, three bending test and conventional triaxial compression test are carried out to calibrate the model. The simulated crack initiation and propagation as well as the whole progressive fracture process are compared with the theoretical results, the experimental observations and other numerical simulation results. It can be found that heterogeneity plays an important role in rock failure process. Numerical tests for the typical mechanical experiments also indicate the developed damage model is a valuable numerical tool for research on the rock failure progressive fracture. 1. Introduction Analysis of a wide range of problems in rock mechanics and engineering requires knowledge of the failure process in rock. This includes tunnel design, rock slope design and other engineering applications as well as geophysical problems such as earthquake prediction. Though experimental observations have provided a great deal of insight into the complicated failure process, the mechanism of rock fracture under mechanical loading, the details of the failure mechanisms, including the microfracture initiation, propagation, and coalescence, is not fully understood. Rocks are non-transparent and it is difficult to trace the propagation of the rock fracture and fragmentation within the rock. The evolution of the fracture progressive process cannot be successively and visually shown in experimental observations. Besides, it is too expensive to conduct a large number of experiments. On one hand, real fracture processes are 3D and not 2D, and the problems encountered in rock mechanics and engineering are almost all three dimensional to some extent. On the other hand, the two-dimensional analysis is intrinsically limited. There are many loading cases which cannot be simulated in 2D (for instance biaxial loading cases which fail out of plane, or triaxial tests), and even for those which can, it would be desirable to evaluate the importance of the three-dimensional effect because, strictly speaking, 2D calculations would correspond to arrangements of aggregates or particles of prismatic shape in the third dimension [1]. Further, tension experiments on concrete have shown that the fracture process is rarely uniform in the third direction, since cracks generally propagate from one corner, rather than uniformly through the entire depth of a specimen [2]. In addition, neither in plane strain nor in axisymmetric triaxial loading conditions can the intermediate principal stress be taken into consideration. RFPA2D have been successfully used to model the failure of brittle materials and the associated microseismicities. The work presented in this paper is the further study of the work of RFPA2D. and the mesoscopic elastic damage model.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (0.88)