Coal pillar deformation is typically nonlinear and time-dependent. The accurate prediction of this defor- mation has a vital importance for the successful implementation of mining techniques. These methods have proven...Coal pillar deformation is typically nonlinear and time-dependent. The accurate prediction of this defor- mation has a vital importance for the successful implementation of mining techniques. These methods have proven very important as a way to excavate coal resources from under buildings, railways, or water bodies. Elastic and visco-elastic theory are employed with a Maxwell model to formulate an analytic solution for displacement of coal pillars in room and pillar mine. These results show that the visco-elastic solution adequately predicts the coal pillar deformation over time. We conclude that the visco-elastic solution can predict the coal pillar and roadway displacement from the measured geological parameters of the conditions in situ. Furthermore, this method would be useful for mine design, coal pillar support optimization, ground subsidence prediction, and coal pillar stability analysis.展开更多
Geogrids are used as reinforcement materials widely in geotechnical and civil engineering fields. In this paper, a series of comparative tests on creep behavior of specific geoOgrids are conducted in the laboratory un...Geogrids are used as reinforcement materials widely in geotechnical and civil engineering fields. In this paper, a series of comparative tests on creep behavior of specific geoOgrids are conducted in the laboratory under different combinations of loading levels and environmental temperature. Based on the test results,comparative analyses are made to study long-term behaviors of isochronous load-strain curves, creep curves and relaxation curves for the specified geogrids. Furthermore, a constitutive model based on theory of visco-elasticity and tests results is proposed for geogrids and a rational procedure is presented in detail for determining the relevant parameters of the proposed model. Finally, the effect of tests temperature on model parameter values is investigated.展开更多
At the first time,the finite element method was used to model and analyze the free vibration and transient response of non-uniform thickness bi-directional functionally graded sandwich porous(BFGSP)skew plates.The who...At the first time,the finite element method was used to model and analyze the free vibration and transient response of non-uniform thickness bi-directional functionally graded sandwich porous(BFGSP)skew plates.The whole BFGSP skew-plates is placed on a variable visco-elastic foundation(VEF)in the hygro-thermal environment and subjected to the blast load.The BFGSP skew-plate thickness is permitted to vary non-linearly over both the length and width of the skew-plate,thereby faithfully representing the real behavior of the structure itself.The analysis is based on a four-node planar quadrilateral element with eight degrees of freedom per node,which is approximated using Lagrange Q_(4)shape function and C^(1)level non-conforming Hermite shape function based on refined higher-order shear deformation plate theory.The forced vibration parameters of the non-uniform thickness BFGSP skew-plate are fully determined using Hamilton's principle and the Newmark-βdirect integration technique.Accuracy of the calculation program is validated by comparing its numerical results with those from reputable sources.Furthermore,a thorough assessment is conducted to determine the impact of various parameters on the free and forced vibration responses of the non-uniform thickness BFGSP skew-plate.The findings of the paper may be used in the development of civil and military structures in situations that are prone to exceptional forces,such as explosions and impacts load.展开更多
The dynamic ground subsidence due to underground mining is a complicated time-dependent and rate- dependent process. Based. on the theory of rock rheology and probability integral method, this study developed the supe...The dynamic ground subsidence due to underground mining is a complicated time-dependent and rate- dependent process. Based. on the theory of rock rheology and probability integral method, this study developed the superposltlOn model for the prediction and analysis of the ground dynamic subsidence in mining area of thick !oose layer. The model consists of two parts （the prediction of overlying bedrock and the prediction of thick loose layer）. The overlying bedrock is regarded as visco-elastic beam, of which the dynamic subsidence is predicted by the Kelvin visco-elastic rheological model. The thick loose layer is regarded as random medium, and the ground dynamic subsidence, is predicted by the probability integral model. At last, the two prediction models are vertically stacked in the same coordinate system, and the bedrock dynamic subsidence is regarded as a variable mining thickness input into the prediction model of ground dynamic subsidence. The prediction results obtained were compared w^th actual movement and deformation data from Zhao I and Zhao II mine, central China. The agreement of the prediction results with the. field measurements.show that the superposition model （SM） is more satisfactory and the formulae obtained are more effective than the classical single probability Integral model（SPIM）, and thus can be effectively used for predicting the ground dynamic subsidence in mining area of thick loose layer.展开更多
Elastic and strength properties （proportional-limit stress （O＇prop）, Young＇s modulus （E）, breaking stress （O＇max） in static bending parallel to grain in a longitudinal direction）, as well as stress relaxati...Elastic and strength properties （proportional-limit stress （O＇prop）, Young＇s modulus （E）, breaking stress （O＇max） in static bending parallel to grain in a longitudinal direction）, as well as stress relaxation in air-dried condition and water-saturated conditions at seven different constant temperatures and increasing and decreasing temperatures were investigated for wood from Chinese-fir and poplar plantations. The results show that hygrothermal conditions considerably affect these mechanical properties. The higher the moisture content （MC） or temperature, the lower the strength of wood. Further investigation of the effects of constant temperature on stress relaxation indicates that high temperature specimens have low relaxation moduli and high fluidity. In the case of increasing temperature the range of the modulus of relaxation is larger than in the case of a reduction in temperature, while the residual moduli do not show large differences. This is because the modulus at high temperatures decreases more than that at low temperatures. The fluidity of specimens in a state of water desorption increases slowly at the beginning, increases quickly until the MC reaches an equilibrium moisture content （EMC） and then becomes stable, which is quite different from that in a water-saturated state. Fluidity in a desorption state is much higher than in a water-saturated state. This is probably due to the fact that the former is in an unstable state which can be interpreted as a state with internal strain and has therefore a greater potential to release strain.展开更多
基金provided by the National Basic Research Program of China (No. 2005CB221502)the Major Program of National Natural Science Foundation of China (No.50490273)+3 种基金the Postdoctoral Subject Foundation of the State Key Laboratory of Geomechanics & Deep Underground Engineering(No. PD1005)the Research Foundation of Heze University (No.XY10BS04)the TransCentury Training Program Foundation forthe Talents by the State Education Commission (No. NCET-08-0837)the National Natural Science Foundation of China (No.50834005)
文摘Coal pillar deformation is typically nonlinear and time-dependent. The accurate prediction of this defor- mation has a vital importance for the successful implementation of mining techniques. These methods have proven very important as a way to excavate coal resources from under buildings, railways, or water bodies. Elastic and visco-elastic theory are employed with a Maxwell model to formulate an analytic solution for displacement of coal pillars in room and pillar mine. These results show that the visco-elastic solution adequately predicts the coal pillar deformation over time. We conclude that the visco-elastic solution can predict the coal pillar and roadway displacement from the measured geological parameters of the conditions in situ. Furthermore, this method would be useful for mine design, coal pillar support optimization, ground subsidence prediction, and coal pillar stability analysis.
文摘Geogrids are used as reinforcement materials widely in geotechnical and civil engineering fields. In this paper, a series of comparative tests on creep behavior of specific geoOgrids are conducted in the laboratory under different combinations of loading levels and environmental temperature. Based on the test results,comparative analyses are made to study long-term behaviors of isochronous load-strain curves, creep curves and relaxation curves for the specified geogrids. Furthermore, a constitutive model based on theory of visco-elasticity and tests results is proposed for geogrids and a rational procedure is presented in detail for determining the relevant parameters of the proposed model. Finally, the effect of tests temperature on model parameter values is investigated.
文摘At the first time,the finite element method was used to model and analyze the free vibration and transient response of non-uniform thickness bi-directional functionally graded sandwich porous(BFGSP)skew plates.The whole BFGSP skew-plates is placed on a variable visco-elastic foundation(VEF)in the hygro-thermal environment and subjected to the blast load.The BFGSP skew-plate thickness is permitted to vary non-linearly over both the length and width of the skew-plate,thereby faithfully representing the real behavior of the structure itself.The analysis is based on a four-node planar quadrilateral element with eight degrees of freedom per node,which is approximated using Lagrange Q_(4)shape function and C^(1)level non-conforming Hermite shape function based on refined higher-order shear deformation plate theory.The forced vibration parameters of the non-uniform thickness BFGSP skew-plate are fully determined using Hamilton's principle and the Newmark-βdirect integration technique.Accuracy of the calculation program is validated by comparing its numerical results with those from reputable sources.Furthermore,a thorough assessment is conducted to determine the impact of various parameters on the free and forced vibration responses of the non-uniform thickness BFGSP skew-plate.The findings of the paper may be used in the development of civil and military structures in situations that are prone to exceptional forces,such as explosions and impacts load.
基金provided by the National Natural Science Foundation of China Youth Found of China (No.41102169)the doctoral foundation of Henan Polytechnic University of China (No. B2014-056)
文摘The dynamic ground subsidence due to underground mining is a complicated time-dependent and rate- dependent process. Based. on the theory of rock rheology and probability integral method, this study developed the superposltlOn model for the prediction and analysis of the ground dynamic subsidence in mining area of thick !oose layer. The model consists of two parts （the prediction of overlying bedrock and the prediction of thick loose layer）. The overlying bedrock is regarded as visco-elastic beam, of which the dynamic subsidence is predicted by the Kelvin visco-elastic rheological model. The thick loose layer is regarded as random medium, and the ground dynamic subsidence, is predicted by the probability integral model. At last, the two prediction models are vertically stacked in the same coordinate system, and the bedrock dynamic subsidence is regarded as a variable mining thickness input into the prediction model of ground dynamic subsidence. The prediction results obtained were compared w^th actual movement and deformation data from Zhao I and Zhao II mine, central China. The agreement of the prediction results with the. field measurements.show that the superposition model （SM） is more satisfactory and the formulae obtained are more effective than the classical single probability Integral model（SPIM）, and thus can be effectively used for predicting the ground dynamic subsidence in mining area of thick loose layer.
基金funded by the Special Funded Project for Basic Scientific Research of the Nationallevel Research Institute for Public Welfare(No.CAFINT2007C03)
文摘Elastic and strength properties （proportional-limit stress （O＇prop）, Young＇s modulus （E）, breaking stress （O＇max） in static bending parallel to grain in a longitudinal direction）, as well as stress relaxation in air-dried condition and water-saturated conditions at seven different constant temperatures and increasing and decreasing temperatures were investigated for wood from Chinese-fir and poplar plantations. The results show that hygrothermal conditions considerably affect these mechanical properties. The higher the moisture content （MC） or temperature, the lower the strength of wood. Further investigation of the effects of constant temperature on stress relaxation indicates that high temperature specimens have low relaxation moduli and high fluidity. In the case of increasing temperature the range of the modulus of relaxation is larger than in the case of a reduction in temperature, while the residual moduli do not show large differences. This is because the modulus at high temperatures decreases more than that at low temperatures. The fluidity of specimens in a state of water desorption increases slowly at the beginning, increases quickly until the MC reaches an equilibrium moisture content （EMC） and then becomes stable, which is quite different from that in a water-saturated state. Fluidity in a desorption state is much higher than in a water-saturated state. This is probably due to the fact that the former is in an unstable state which can be interpreted as a state with internal strain and has therefore a greater potential to release strain.
