Pre-existing discontinuities change the mechanical properties of rock masses,and further influence failure behavior around an underground opening.In present study,the failure behavior in both Inner and Outer zones aro...Pre-existing discontinuities change the mechanical properties of rock masses,and further influence failure behavior around an underground opening.In present study,the failure behavior in both Inner and Outer zones around a circular opening in a non-persistently jointed rock mass under biaxial compression was investigated through numerical simulations.First,the micro parameters of the PFC^(3D) model were carefully calibrated using the macro mechanical properties determined in physical experiments implemented on jointed rock models.Then,a parametrical study was undertaken of the effect of stress condition,joint dip angle and joint persistency.Under low initial stress,the confining stress improves the mechanical behavior of the surrounding rock masses;while under high initial stress,the surrounding rock mass failed immediately following excavation.At small dip angles the cracks around the circular opening developed generally outwards in a step-path failure pattern;whereas,at high dip angles the surrounding rock mass failed in an instantaneous intact rock failure pattern.Moreover,the stability of the rock mass around the circular opening deteriorated significantly with increasing joint persistency.展开更多
In this paper numerical analysis of underground structures, taking account the transverse isotropy system of rocks, was done using CAST 3M code by varying the shape of excavation and the coefficient of earth pressure ...In this paper numerical analysis of underground structures, taking account the transverse isotropy system of rocks, was done using CAST 3M code by varying the shape of excavation and the coefficient of earth pressure k. Numerical results reveal that the anisotropy behavior, the shape of hole and the coefficient of earth pressure k have significant influence to the mining induced stress field and rock deformations which directly control the stability of underground excavation design. The magnitude of horizontal stress obtained for the horse shoe shape excavation(25.2 MPa for k = 1; 52.7 MPa for k = 2)is lower than the magnitude obtained for circular hole(26.4 MPa for k = 1; 59.5 MPa for k = 2).Therefore, we have concluded that the horse shoe shape offers the best stability and the best design for engineer. The anisotropy system presented by rock mass can also influence the redistribution of stresses around hole opened. Numerical results have revealed that the magnitude of redistribution of horizontal stresses obtained for transverse isotropic rock(12.1 MPa for k = 0.5; 25.2 MPa for k = 1 and52.7 MPa for k = 2) is less than those obtained in the case of isotropic rock(27.6 MPa for k = 1;48.6 MPa for k = 2 and 90.81 MPa for k = 2). The more the rock has the anisotropic behavior, the more the mass of rock around the tunnel is stable.展开更多
The pollen morphology of lbur species from the genus Trigonella L. （Fabaceae） distributed in Tunisia （T. foenum-graecum, T. maritima, T. stellata and T. monspeliaca） was studied with light and scanning electron ...The pollen morphology of lbur species from the genus Trigonella L. （Fabaceae） distributed in Tunisia （T. foenum-graecum, T. maritima, T. stellata and T. monspeliaca） was studied with light and scanning electron microscope （SEM）. Results showed that the pollen morphology of these four species was not homogenous in relation to shape, dimensions and ornamentation. The pollen grains were 3-zonocolporate, radially symmetrical, isopolar, prolate to perprolate type （P/E = 1.45-2.09）. Medium in size, elliptical or rectangular-obtuse-convex in equatorial view and circular in polar view. Ectoapertures-colpi： long, medium width, with acute ends, endoapertures-pork large, circular to lolongate, protruding in mesocolpium. The rectum was reticulate to perforate reticulate with ± irregular pattern of muri, except for T. monspeliaca which ornamentation was relatively homogeneous with a loose network and psilate area. Ornamentation with lumina different in size was most clearly expressed in mesocolpium while the apocolpium and the area just along the apertures was psilate or with small scattered puncta. The exine thickness was 1.10-2.42 μtm.展开更多
基金supported by the National Basic Research Program of China (No.2013CB036003)the Graduate Research and Innovation Program of Jiangsu Province (No.CXLX13_943)
文摘Pre-existing discontinuities change the mechanical properties of rock masses,and further influence failure behavior around an underground opening.In present study,the failure behavior in both Inner and Outer zones around a circular opening in a non-persistently jointed rock mass under biaxial compression was investigated through numerical simulations.First,the micro parameters of the PFC^(3D) model were carefully calibrated using the macro mechanical properties determined in physical experiments implemented on jointed rock models.Then,a parametrical study was undertaken of the effect of stress condition,joint dip angle and joint persistency.Under low initial stress,the confining stress improves the mechanical behavior of the surrounding rock masses;while under high initial stress,the surrounding rock mass failed immediately following excavation.At small dip angles the cracks around the circular opening developed generally outwards in a step-path failure pattern;whereas,at high dip angles the surrounding rock mass failed in an instantaneous intact rock failure pattern.Moreover,the stability of the rock mass around the circular opening deteriorated significantly with increasing joint persistency.
文摘In this paper numerical analysis of underground structures, taking account the transverse isotropy system of rocks, was done using CAST 3M code by varying the shape of excavation and the coefficient of earth pressure k. Numerical results reveal that the anisotropy behavior, the shape of hole and the coefficient of earth pressure k have significant influence to the mining induced stress field and rock deformations which directly control the stability of underground excavation design. The magnitude of horizontal stress obtained for the horse shoe shape excavation(25.2 MPa for k = 1; 52.7 MPa for k = 2)is lower than the magnitude obtained for circular hole(26.4 MPa for k = 1; 59.5 MPa for k = 2).Therefore, we have concluded that the horse shoe shape offers the best stability and the best design for engineer. The anisotropy system presented by rock mass can also influence the redistribution of stresses around hole opened. Numerical results have revealed that the magnitude of redistribution of horizontal stresses obtained for transverse isotropic rock(12.1 MPa for k = 0.5; 25.2 MPa for k = 1 and52.7 MPa for k = 2) is less than those obtained in the case of isotropic rock(27.6 MPa for k = 1;48.6 MPa for k = 2 and 90.81 MPa for k = 2). The more the rock has the anisotropic behavior, the more the mass of rock around the tunnel is stable.
文摘The pollen morphology of lbur species from the genus Trigonella L. （Fabaceae） distributed in Tunisia （T. foenum-graecum, T. maritima, T. stellata and T. monspeliaca） was studied with light and scanning electron microscope （SEM）. Results showed that the pollen morphology of these four species was not homogenous in relation to shape, dimensions and ornamentation. The pollen grains were 3-zonocolporate, radially symmetrical, isopolar, prolate to perprolate type （P/E = 1.45-2.09）. Medium in size, elliptical or rectangular-obtuse-convex in equatorial view and circular in polar view. Ectoapertures-colpi： long, medium width, with acute ends, endoapertures-pork large, circular to lolongate, protruding in mesocolpium. The rectum was reticulate to perforate reticulate with ± irregular pattern of muri, except for T. monspeliaca which ornamentation was relatively homogeneous with a loose network and psilate area. Ornamentation with lumina different in size was most clearly expressed in mesocolpium while the apocolpium and the area just along the apertures was psilate or with small scattered puncta. The exine thickness was 1.10-2.42 μtm.
