Foundation settlement is of great significance for high-fill engineering in collapsible loess areas.To predict the construction settlement of Lüliang Airport located in Shanxi Province,China,a plane strain finite...Foundation settlement is of great significance for high-fill engineering in collapsible loess areas.To predict the construction settlement of Lüliang Airport located in Shanxi Province,China,a plane strain finite element method considering the linear variation in the modulus,was carried out in this paper based on the results of geotechnical tests.The stress and deformation of four typical sections caused by layered fill are simulated,and then the settlement of the high-fill airport is calculated and analyzed by inputting three sets of parameters.The relative soft parameters of loess geomaterials produce more settlement than the relatively hard parameters.The thicker the filling body is,the greater the settlement is.The filling body constrained by mountains on both sides produces less settlement than the filling body constrained by a mountain on only one side even the filling thickness is almost the same.The settlement caused by the original subbase accounts for 56%−77%of the total settlement,while the fill soils themselves accounts for 23%−44%of the total settlement,which is approximately consistent with the field monitoring results.It provides a good reference for predicting the settlement of similar high-fill engineering.展开更多
The collapse of rock masses in fault-developed zones poses significant safety challenges during the excavation of high-stress underground caverns. This study investigates the spatiotemporal evolution of the collapse m...The collapse of rock masses in fault-developed zones poses significant safety challenges during the excavation of high-stress underground caverns. This study investigates the spatiotemporal evolution of the collapse mechanisms of the cavern in the Yebatan Hydropower Station through using microseismic (MS) monitoring and displacement measurements. We developed a multi-parameter deformation early warning model that integrates three critical indicators: deformation rate, rate increment, and tangential angle of the deformation time curve. The results of the early warning model show a significant and abrupt increase in the deformation of the rock mass during the collapse process. The safety and stability of the local cavern in the face of excavation-induced disturbances are meticulously assessed utilizing MS data. Spatiotemporal analysis of the MS monitoring indicates a high frequency of MS events during the blasting phase, with a notable clustering of these events in the vicinity of the fault. These research results provide a valuable reference for risk warnings and stability assessments in the fault development zones of analogous caverns.展开更多
Experimental quasi-static crushing tests were conducted by using a universal testing machine format kenaf-epoxy composite elliptical cones. The work focused on the vertex angle's effects on energy absorption capab...Experimental quasi-static crushing tests were conducted by using a universal testing machine format kenaf-epoxy composite elliptical cones. The work focused on the vertex angle's effects on energy absorption capability; the vertex angles vary from 0° to 24° in 6 increments. The failure modes of the kenaf fibre epoxy composite elliptical cones were observed utilising delegate photos taken during the quasistatic crushing test. Load-deformation curves and deformation histories of typical specimens are presented and discussed. Moreover, the effects of cone vertex angles on the load carrying capacity and the energy absorption capability are also discussed. The results show that the energy absorption abilities significantly influence the ellipticity vertex angle as the load carrying capacity. We concluded that the quasi-static axial crushing behaviour of elliptical mat laminated composite cones is strongly affected by their structural geometry and the specific energy absorbed by the composite elliptical cones with vertex angles of 6°, 12°, 18°, and 24°, which is more than an elliptical cone with the vertex angle of 0°(the elliptical tube) at any given deformation. However, the specific energy absorption for the elliptical composite cone showed a positive correlation, i.e., the more the angle increased, the more energy was absorbed. In this regard, an elliptical composite cone with a 24° angle exhibited the best energy absorption capability.展开更多
Gob-area roof rupture movement is a key disturbance factor for gob-side entry retaining.The characteristics of gob-area sequential roof collapse of overlying strata and superposed disturbance mechanism for gob-side en...Gob-area roof rupture movement is a key disturbance factor for gob-side entry retaining.The characteristics of gob-area sequential roof collapse of overlying strata and superposed disturbance mechanism for gob-side entry retaining are obtained via physical simulation and theoretical analysis,in which the scope of disturbed strata is enlarged from main roof to fracture zone.The experiment reveals that as a working face advances,roof strata sequentially collapse from bottom to top and produce multiple disturbances to gob-side entry retaining.Key strata among the overlying strata control each collapse.Main roof subsidence is divided into three stages:flexure subsidence prior to rupture,rotational subsidence during rupture and compressive subsidence after rupture.The amounts of deformation evident in each of the three stages are 15%,55%and 30%,respectively.After the master stratum collapses,main roof subsidence approaches its maximum value.The final span of the key stratum determines the moment and cycling of gob-side entry retaining disturbances.Main roof subsidence influences the load on the filling wall.The sequential roof collapse of overlying strata results in fluctuations in the gob-side entry retaining deformation.Calculation formulae for the final span of the key stratum and the filling wall load are obtained via theoretical analysis.A control method for the stability of the gob-side entry retaining’s surrounding rock is proposed,which includes 3 measures:a“dual-layer”proactive anchorage support,roadside filling with dynamic strength matching and auxiliary support during disturbance.Finally,the gob-side entry retaining of the Xiaoqing mine E1403 working face is presented as an engineering case capable of verifying the validity of the research conclusions.展开更多
The custom of hybridization fibre composite in energy absorption tube application has gained the attention of structural crashworthiness in composite material industry. Thus, the approach of this review is to understa...The custom of hybridization fibre composite in energy absorption tube application has gained the attention of structural crashworthiness in composite material industry. Thus, the approach of this review is to understand the effect in hybridization within metal/synthetic fibre composite, synthetic/synthetic fibre composite and nature/synthetic fibre composite as energy absorption tube, which reflects on the energy absorption characteristics and crashworthiness behaviors in previous the study. By way of instance, a wide range of methodology and particular parameter in previous study such as the effect in fibre arrangement, matrix polymer, technique of fabrication, fibre treatment(natural fibre), design in geometry/cross-section and others mechanism of hybrid fibre composite tube are highlighted which to comprehend the capability of the mechanical performance and collapsible behavior as sacrificial structure in high-performance structure applications. Moreover, in the recently studies there have been many of the research regarding structural materials as energy absorption tube has been introduced such as metal/matrix composites, new alloy metals and polymer composites which intended to evaluate the performance of these materials into circumstance in loading and impact characteristic. Therefore, this review article is trying to explore the research articles related to the effect of hybridization fibres and thermoset polymer as reinforcement for energy absorption tube research and expected would provide an information and idea which to expend the knowledge in future study of hybridization effect for energy absorption tube, moreover the development for future potential as new hybrid composite fibre materials from the natural/synthetic fibres reinforced composite material in employing of high-performance energy absorption tube application is still less discover and highlighted.展开更多
The state of roof collapse in tunnels is actually three-dimensional, so constructing a three-dimensional failure collapse mechanism is crucial so as to reflect the realistic collapsing scopes more reasonably. Accordin...The state of roof collapse in tunnels is actually three-dimensional, so constructing a three-dimensional failure collapse mechanism is crucial so as to reflect the realistic collapsing scopes more reasonably. According to Hoek-Brown failure criterion and the upper bound theorem of limit analysis, the solution for describing the shape of roof collapse in circular or rectangular tunnels subjected to seepage forces is derived by virtue of variational calculation. The seepage forces calculated from the gradient of excess pore pressure distribution are taken as external loading in the limit analysis, and it is of great convenience to compute the pore pressure with pore pressure coefficient. Consequently, the effect of seepage forces is taken as a work rate of external force and incorporated into the upper bound limit analysis. The numerical results of collapse dimensions with different rock parameters show great validity and agreement by comparing with the results of that with two-dimensional failure mechanism.展开更多
Reliable prediction of the potential collapse region of rock mass is a key challenge for deep underground cavity excavation, especially if a concealed karst cave is located above the excavated cavity. Because of the e...Reliable prediction of the potential collapse region of rock mass is a key challenge for deep underground cavity excavation, especially if a concealed karst cave is located above the excavated cavity. Because of the effect of the blast vibration, a possible collapse would occur at a certain region between the concealed karst cave and the excavated cavity. This paper aims to study the roof collapse of a deep buried cavity induced by a concealed karst cave base on a two-dimensional failure mechanism by using upper bound theorem. The failure mechanism is constituted by arbitrary curves which is similar to the collapse observed in an actual cavity excavation. The shape and range of the collapse block is determined by virtual work equation in conjunction with variational approach. The results obtained by the presented approach are approximate with the numerical results provided by finite difference code, which indicates that the proposed method in this work is valid.展开更多
A new horn failure mechanism was constructed for tunnel faces in the soft rock mass by means of the logarithmic spiral curve. The seismic action was incorporated into the horn failure mechanism using the pseudo-static...A new horn failure mechanism was constructed for tunnel faces in the soft rock mass by means of the logarithmic spiral curve. The seismic action was incorporated into the horn failure mechanism using the pseudo-static method. Considering the randomness of rock mass parameters and loads, a three-dimensional (3D) stochastic collapse model was established. Reliability analysis of seismic stability of tunnel faces was presented via the kinematical approach and the response surface method. The results show that, the reliability of tunnel faces is significantly affected by the supporting pressure, geological strength index, uniaxial compressive strength, rock bulk density and seismic forces. It is worth noting that, if the effect of seismic force was not considered, the stability of tunnel faces would be obviously overestimated. However, the correlation between horizontal and vertical seismic forces can be ignored under the condition of low calculation accuracy.展开更多
For different kinds of rocks,the collapse range of tunnel was studied in the previously published literature.However,some tunnels were buried in soils,and test data showed that the strength envelopes of the soils foll...For different kinds of rocks,the collapse range of tunnel was studied in the previously published literature.However,some tunnels were buried in soils,and test data showed that the strength envelopes of the soils followed power-law failure criterion.In this work,deep buried highway tunnel with large section was taken as objective,and the basic expressions of collapse shape and region were deduced for the highway tunnels in soils,based on kinematical approach and power-law failure criterion.In order to see the effectiveness of the proposed expressions,the solutions presented in this work agree well with previous results if the nonlinear failure criterion is reduced to a linear Mohr-Coulomb failure criterion.The present results are compared with practical projects and tunnel design code.The numerical results show that the height and width of tunnel collapse are greatly affected by the nonlinear criterion for the tunnel in soil.展开更多
The nonlinear Hoek-Brown failure criterion was introduced to limit analysis by applying the tangent method. Based on the failure mechanism of double-logarithmic spiral curves on the face of deep rock tunnels, the anal...The nonlinear Hoek-Brown failure criterion was introduced to limit analysis by applying the tangent method. Based on the failure mechanism of double-logarithmic spiral curves on the face of deep rock tunnels, the analytical solutions of collapse pressure were derived through utilizing the virtual power principle in the case of pore water, and the optimal solutions of collapse pressure were obtained by using the optimization programs of mathematical model with regard of a maximum problem. In comparison with existing research with the same parameters, the consistency of change rule shows the validity of the proposed method. Moreover, parametric study indicates that nonlinear Hoek-Brown failure criterion and pore water pressure have great influence on collapse pressure and failure shape of tunnel faces in deep rock masses, particularly when the surrounding rock is too weak or under the condition of great disturbance and abundant ground water, and in this case, supporting measures should be intensified so as to prevent the occurrence of collapse.展开更多
Failure data from oilfield showed that casings which were designed according to API standards were deformed and collapsed in salt formations. The main reason for decrease in strength may be caused by non-uniform loadi...Failure data from oilfield showed that casings which were designed according to API standards were deformed and collapsed in salt formations. The main reason for decrease in strength may be caused by non-uniform loading(NUL) that was not considered in traditional casing collapsing strength design or that the designing method should be improved and developed. Obviously, the calculation of casing collapse strength is one of the key factors in casing design. However, the effect of NUL on casing collapse strength was generally neglected in the present computational methods. Therefore, a mechanical model which can calculate casing collapse strength under NUL was established based on the curved beam theory of the elasticity and was solved using displacement method. Simultaneously, three anti-collapse experiments were performed on C110 casing under NUL, and the strain and deformation laws of three casings in the process of collapse were obtained by the electrical method. Yield limit of every casing was obtained by analyzing those data. Experimental results are consistent with the results of calculation of new model. It indicates that the model can be used to calculate yield limit loading of casings under NUL.展开更多
Ceramic balls represent a new type of damaging element,and studies on their damaging power of composite armor are required for a comprehensive evaluation of the effectiveness of various types of weapons.The goal of th...Ceramic balls represent a new type of damaging element,and studies on their damaging power of composite armor are required for a comprehensive evaluation of the effectiveness of various types of weapons.The goal of this study was to determine the impact ofφ7 mm toughened Al2 O3 ceramic balls on a composite ceramic/metal armor.The influences of the ceramic panel and the thickness of the metal backing material on the destroying power of the ceramic balls were first determined.Based on the agreement between numerical simulation,experimental results,and calculation models of the target plate resistance,the response mechanism of the ceramic balls was further analyzed.The results indicate that for a back plate of Q235 steel,with an increasing thickness of the ceramic panel,the piercing speed limit of the ceramic balls gradually increases and the diameter of the out-going hole on the metal back decreases.Different conditions were tested to assess the effects on the piercing speed,the diameter of the out-going hole,the micro-element stress,and the integrity of the recovered ceramic bowl.展开更多
In research of the characteristics of the cavity evolution, the pressure, and the liquid spurt in hydrodynamic ram, the experiment of the high-velocity fragment impacting the water-filled container had been conducted....In research of the characteristics of the cavity evolution, the pressure, and the liquid spurt in hydrodynamic ram, the experiment of the high-velocity fragment impacting the water-filled container had been conducted. The relationships between the above three characteristics have been researched. The evolution of the cavity can be divided into three processes according to its shape characteristics. The first liquid spurt occurred in Process Ⅱ and the rest of it occurred in Process Ⅲ. The duration of the second liquid spurt is longer than the first liquid spurt. When the impact velocity of the fragment is less than996 m/s, the velocity of the second liquid spurt is the highest. When the velocity of the fragment is greater than 996 m/s, the velocity of the first liquid spurt is the highest. The maximum velocities of the first and second liquid spurt are 111 m/s and 94 m/s respectively. The pressure fluctuated sharply in Processes Ⅰ and Ⅲ. The maximum peak pressures in the shock and the cavity oscillation phases are15.51 MPa and 7.96 MPa respectively. The time interval of the two adjacent pressure pulses increases with the increase of the fragment velocity.展开更多
Based on the target scatterer density, the range-spread target detection of high-resolution radar is addressed in additive non-Gaussian clutter, which is modeled as a spherically invariant random vector. Firstly, for ...Based on the target scatterer density, the range-spread target detection of high-resolution radar is addressed in additive non-Gaussian clutter, which is modeled as a spherically invariant random vector. Firstly, for sparse scatterer density, the detection of target scatterer in each range cell is derived, and then an M/K detector is proposed to detect the whole range-spread target. Se- condly, an integrating detector is devised to detect a range-spread target with dense scatterer density. Finally, to make the best of the advantages of M/K detector and integrating detector, a robust detector based on scatterer density （DBSD） is designed, which can reduce the probable collapsing loss or quantization error ef- fectively. Moreover, the density decision factor of DBSD is also determined. The formula of the false alarm probability is derived for DBSD. It is proved that the DBSD ensures a constant false alarm rate property. Furthermore, the computational results indi- cate that the DBSD is robust to different clutter one-lag correlations and target scatterer densities. It is also shown that the DBSD out- performs the existing scatterer-density-dependent detector.展开更多
To explore the influence of karst cavity pressure on the failure mechanisms of rock layers above water-filled caves, novel blow-out and collapse mechanisms are put forward in this study. The proposed method uses the n...To explore the influence of karst cavity pressure on the failure mechanisms of rock layers above water-filled caves, novel blow-out and collapse mechanisms are put forward in this study. The proposed method uses the nonlinear optimization to obtain the failure profiles of surrounding layered rock with water-filled cave at the bottom of the tunnel. By referring to the functional catastrophe theory, stability analysis with different properties in different rock layers is implemented with considering the incorporation of seepage forces since the groundwater cannot be ignored in the catastrophe analysis of deep tunnel bottom. Also the parametric analysis is implemented to discuss the influences of different rock strength factors on the failure profiles. In order to offer a good guide of design for the excavation of deep tunnels above the water-filled caves, the proposed method is applied to design of the minimum effective height for rock layer. The results obtained by this work agree well with the existing published ones.展开更多
According to the stress state of the crack surface, crack rock mass can be divided into complex composite tensile-shear fracture and composite compression-shear fracture from the perspective of fracture mechanics. By ...According to the stress state of the crack surface, crack rock mass can be divided into complex composite tensile-shear fracture and composite compression-shear fracture from the perspective of fracture mechanics. By studying the hydraulic fracturing effect of groundwater on rock fracture, the tangential friction force equation of hydrodynamic pressure to rock fracture is deduced. The hydraulic fracturing of hydrostatic and hydrodynamic pressure to rock fracture is investigated to derive the equation of critical pressure when the hydraulic fracturing effect occurs in the rock fracture. Then, the crack angle that is most prone to hydraulic fracturing is determined. The relationships between crack direction and both lateral pressure coefficient and friction angle of the fracture surface are analyzed. Results show that considering the joint effect of hydrodynamic and hydrostatic pressure, the critical pressure does not vary with the direction of the crack when the surrounding rock stationary lateral pressure coefficient is equal to 1.0. Under composite tensile-shear fracture, the crack parallel to the direction of the main stress is the most prone to hydraulic fracturing. Under compression-shear fracture, the hydrodynamic pressure resulting in the most dangerous crack angle varies at different lateral pressure coefficients; this pressure decreases when the friction angle of the fracture surface increases. By referring to the subway tunnel collapse case, the impact of fractured rock mass hydraulic fracturing generated by hydrostatic and hydrodynamic pressure joint action is calculated and analyzed.展开更多
Prediction of the state of roof collapse is a big challenge in tunnel engineering, while the limit analysis theory makes it possible to derive the analytical solutions of the collapse mechanisms. In this work, an exac...Prediction of the state of roof collapse is a big challenge in tunnel engineering, while the limit analysis theory makes it possible to derive the analytical solutions of the collapse mechanisms. In this work, an exact solution of collapsing shape in shallow underwater tunnel is obtained by using the variation principle and the upper bound theorem based on nonlinear failure criterion. Numerical results under the effect of river water and supporting pressure are derived and discussed. The maximum water depth above the river bottom surface is determined under a given buried depth of shallow cavities and the critical depth of roof collapse is obtained under a constant river depth. In comparison with the previous results, the present solution shows a good agreement with the practical results.展开更多
基金Project(2020M670604)supported by the China Postdoctoral Science FoundationProject(41790434)supported by the National Natural Science Foundation of China。
文摘Foundation settlement is of great significance for high-fill engineering in collapsible loess areas.To predict the construction settlement of Lüliang Airport located in Shanxi Province,China,a plane strain finite element method considering the linear variation in the modulus,was carried out in this paper based on the results of geotechnical tests.The stress and deformation of four typical sections caused by layered fill are simulated,and then the settlement of the high-fill airport is calculated and analyzed by inputting three sets of parameters.The relative soft parameters of loess geomaterials produce more settlement than the relatively hard parameters.The thicker the filling body is,the greater the settlement is.The filling body constrained by mountains on both sides produces less settlement than the filling body constrained by a mountain on only one side even the filling thickness is almost the same.The settlement caused by the original subbase accounts for 56%−77%of the total settlement,while the fill soils themselves accounts for 23%−44%of the total settlement,which is approximately consistent with the field monitoring results.It provides a good reference for predicting the settlement of similar high-fill engineering.
基金Projects(52209132, 52309156) supported by the National Natural Science Foundation of ChinaProject(BK20251905) supported by the Natural Science Foundation of Jiangsu Province,China+2 种基金Project(252102320037) supported by the Henan Province Science and Technology Research,ChinaProject(CKWV20231173/KY) supported by the CRSRI Open Research Program,ChinaProject(2023KSD15) supported by the Open Research Fund of Hubei Provincial Key Laboratory of Construction and Management in Hydropower Engineering,China。
文摘The collapse of rock masses in fault-developed zones poses significant safety challenges during the excavation of high-stress underground caverns. This study investigates the spatiotemporal evolution of the collapse mechanisms of the cavern in the Yebatan Hydropower Station through using microseismic (MS) monitoring and displacement measurements. We developed a multi-parameter deformation early warning model that integrates three critical indicators: deformation rate, rate increment, and tangential angle of the deformation time curve. The results of the early warning model show a significant and abrupt increase in the deformation of the rock mass during the collapse process. The safety and stability of the local cavern in the face of excavation-induced disturbances are meticulously assessed utilizing MS data. Spatiotemporal analysis of the MS monitoring indicates a high frequency of MS events during the blasting phase, with a notable clustering of these events in the vicinity of the fault. These research results provide a valuable reference for risk warnings and stability assessments in the fault development zones of analogous caverns.
基金the Universiti Putra Malaysia for the financial support for this research programme using HiCoE Grant,Ministry of Higher Education,Malaysia
文摘Experimental quasi-static crushing tests were conducted by using a universal testing machine format kenaf-epoxy composite elliptical cones. The work focused on the vertex angle's effects on energy absorption capability; the vertex angles vary from 0° to 24° in 6 increments. The failure modes of the kenaf fibre epoxy composite elliptical cones were observed utilising delegate photos taken during the quasistatic crushing test. Load-deformation curves and deformation histories of typical specimens are presented and discussed. Moreover, the effects of cone vertex angles on the load carrying capacity and the energy absorption capability are also discussed. The results show that the energy absorption abilities significantly influence the ellipticity vertex angle as the load carrying capacity. We concluded that the quasi-static axial crushing behaviour of elliptical mat laminated composite cones is strongly affected by their structural geometry and the specific energy absorbed by the composite elliptical cones with vertex angles of 6°, 12°, 18°, and 24°, which is more than an elliptical cone with the vertex angle of 0°(the elliptical tube) at any given deformation. However, the specific energy absorption for the elliptical composite cone showed a positive correlation, i.e., the more the angle increased, the more energy was absorbed. In this regard, an elliptical composite cone with a 24° angle exhibited the best energy absorption capability.
基金Project(51404251)supported by the National Natural Science Foundation of ChinaProject(BK20140198)supported by the Natural Science Foundation of Jiangsu Province,China+1 种基金Project(PPZY2015A046)supported by the Top-notch Academic Programs Project of Jiangsu Higher Education Institutions,ChinaProject supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions,China
文摘Gob-area roof rupture movement is a key disturbance factor for gob-side entry retaining.The characteristics of gob-area sequential roof collapse of overlying strata and superposed disturbance mechanism for gob-side entry retaining are obtained via physical simulation and theoretical analysis,in which the scope of disturbed strata is enlarged from main roof to fracture zone.The experiment reveals that as a working face advances,roof strata sequentially collapse from bottom to top and produce multiple disturbances to gob-side entry retaining.Key strata among the overlying strata control each collapse.Main roof subsidence is divided into three stages:flexure subsidence prior to rupture,rotational subsidence during rupture and compressive subsidence after rupture.The amounts of deformation evident in each of the three stages are 15%,55%and 30%,respectively.After the master stratum collapses,main roof subsidence approaches its maximum value.The final span of the key stratum determines the moment and cycling of gob-side entry retaining disturbances.Main roof subsidence influences the load on the filling wall.The sequential roof collapse of overlying strata results in fluctuations in the gob-side entry retaining deformation.Calculation formulae for the final span of the key stratum and the filling wall load are obtained via theoretical analysis.A control method for the stability of the gob-side entry retaining’s surrounding rock is proposed,which includes 3 measures:a“dual-layer”proactive anchorage support,roadside filling with dynamic strength matching and auxiliary support during disturbance.Finally,the gob-side entry retaining of the Xiaoqing mine E1403 working face is presented as an engineering case capable of verifying the validity of the research conclusions.
基金Universiti Putra Malaysia for financial support via the Graduate Research Fellowship (GRF) scholarship through the School of Graduate Study (UPM/SPS/ GS47054) for providing a scholarship to the principal author to carry out this research projectHiCOE grant (6369107) from Ministry of Higher Education Malaysia
文摘The custom of hybridization fibre composite in energy absorption tube application has gained the attention of structural crashworthiness in composite material industry. Thus, the approach of this review is to understand the effect in hybridization within metal/synthetic fibre composite, synthetic/synthetic fibre composite and nature/synthetic fibre composite as energy absorption tube, which reflects on the energy absorption characteristics and crashworthiness behaviors in previous the study. By way of instance, a wide range of methodology and particular parameter in previous study such as the effect in fibre arrangement, matrix polymer, technique of fabrication, fibre treatment(natural fibre), design in geometry/cross-section and others mechanism of hybrid fibre composite tube are highlighted which to comprehend the capability of the mechanical performance and collapsible behavior as sacrificial structure in high-performance structure applications. Moreover, in the recently studies there have been many of the research regarding structural materials as energy absorption tube has been introduced such as metal/matrix composites, new alloy metals and polymer composites which intended to evaluate the performance of these materials into circumstance in loading and impact characteristic. Therefore, this review article is trying to explore the research articles related to the effect of hybridization fibres and thermoset polymer as reinforcement for energy absorption tube research and expected would provide an information and idea which to expend the knowledge in future study of hybridization effect for energy absorption tube, moreover the development for future potential as new hybrid composite fibre materials from the natural/synthetic fibres reinforced composite material in employing of high-performance energy absorption tube application is still less discover and highlighted.
基金Project(2013CB036004) supported by the National Basic Research Program of ChinaProject(51178468) supported by the National Natural Science Foundation of ChinaProject(2013zzts235) supported by Innovation Fund of Central South University of China
文摘The state of roof collapse in tunnels is actually three-dimensional, so constructing a three-dimensional failure collapse mechanism is crucial so as to reflect the realistic collapsing scopes more reasonably. According to Hoek-Brown failure criterion and the upper bound theorem of limit analysis, the solution for describing the shape of roof collapse in circular or rectangular tunnels subjected to seepage forces is derived by virtue of variational calculation. The seepage forces calculated from the gradient of excess pore pressure distribution are taken as external loading in the limit analysis, and it is of great convenience to compute the pore pressure with pore pressure coefficient. Consequently, the effect of seepage forces is taken as a work rate of external force and incorporated into the upper bound limit analysis. The numerical results of collapse dimensions with different rock parameters show great validity and agreement by comparing with the results of that with two-dimensional failure mechanism.
基金Projects(51878074,51678071)supported by the National Natural Science Foundation of China
文摘Reliable prediction of the potential collapse region of rock mass is a key challenge for deep underground cavity excavation, especially if a concealed karst cave is located above the excavated cavity. Because of the effect of the blast vibration, a possible collapse would occur at a certain region between the concealed karst cave and the excavated cavity. This paper aims to study the roof collapse of a deep buried cavity induced by a concealed karst cave base on a two-dimensional failure mechanism by using upper bound theorem. The failure mechanism is constituted by arbitrary curves which is similar to the collapse observed in an actual cavity excavation. The shape and range of the collapse block is determined by virtual work equation in conjunction with variational approach. The results obtained by the presented approach are approximate with the numerical results provided by finite difference code, which indicates that the proposed method in this work is valid.
基金Projects(51804113,51434006,51874130)supported by the National Natural Science Foundation of ChinaProject(E51768)supported by the Doctoral Initiation Foundation of Hunan University of Science and Technology,China+1 种基金Project(E61610)supported by the Postdoctoral Research Foundation of Hunan University of Science and Technology,ChinaProject(E21734)supported by the Open Foundation of Work Safety Key Lab on Prevention and Control of Gas and Roof Disasters for Southern Coal Mines,China
文摘A new horn failure mechanism was constructed for tunnel faces in the soft rock mass by means of the logarithmic spiral curve. The seismic action was incorporated into the horn failure mechanism using the pseudo-static method. Considering the randomness of rock mass parameters and loads, a three-dimensional (3D) stochastic collapse model was established. Reliability analysis of seismic stability of tunnel faces was presented via the kinematical approach and the response surface method. The results show that, the reliability of tunnel faces is significantly affected by the supporting pressure, geological strength index, uniaxial compressive strength, rock bulk density and seismic forces. It is worth noting that, if the effect of seismic force was not considered, the stability of tunnel faces would be obviously overestimated. However, the correlation between horizontal and vertical seismic forces can be ignored under the condition of low calculation accuracy.
基金Project(2013CB036004)supported by the National Basic Research Program of ChinaProject(51378510)supported by the National Natural Science Foundation of China
文摘For different kinds of rocks,the collapse range of tunnel was studied in the previously published literature.However,some tunnels were buried in soils,and test data showed that the strength envelopes of the soils followed power-law failure criterion.In this work,deep buried highway tunnel with large section was taken as objective,and the basic expressions of collapse shape and region were deduced for the highway tunnels in soils,based on kinematical approach and power-law failure criterion.In order to see the effectiveness of the proposed expressions,the solutions presented in this work agree well with previous results if the nonlinear failure criterion is reduced to a linear Mohr-Coulomb failure criterion.The present results are compared with practical projects and tunnel design code.The numerical results show that the height and width of tunnel collapse are greatly affected by the nonlinear criterion for the tunnel in soil.
基金Project(2013CB036004)supported by National Basic Research Program of ChinaProjects(51178468,51378510)supported by National Natural Science Foundation of ChinaProject(CX2013B077)supported by Hunan Provincial Innovation Foundation for Postgraduate,China
文摘The nonlinear Hoek-Brown failure criterion was introduced to limit analysis by applying the tangent method. Based on the failure mechanism of double-logarithmic spiral curves on the face of deep rock tunnels, the analytical solutions of collapse pressure were derived through utilizing the virtual power principle in the case of pore water, and the optimal solutions of collapse pressure were obtained by using the optimization programs of mathematical model with regard of a maximum problem. In comparison with existing research with the same parameters, the consistency of change rule shows the validity of the proposed method. Moreover, parametric study indicates that nonlinear Hoek-Brown failure criterion and pore water pressure have great influence on collapse pressure and failure shape of tunnel faces in deep rock masses, particularly when the surrounding rock is too weak or under the condition of great disturbance and abundant ground water, and in this case, supporting measures should be intensified so as to prevent the occurrence of collapse.
基金Projects(51074135,51274170,51004084)supported by the National Natural Science Foundation of China
文摘Failure data from oilfield showed that casings which were designed according to API standards were deformed and collapsed in salt formations. The main reason for decrease in strength may be caused by non-uniform loading(NUL) that was not considered in traditional casing collapsing strength design or that the designing method should be improved and developed. Obviously, the calculation of casing collapse strength is one of the key factors in casing design. However, the effect of NUL on casing collapse strength was generally neglected in the present computational methods. Therefore, a mechanical model which can calculate casing collapse strength under NUL was established based on the curved beam theory of the elasticity and was solved using displacement method. Simultaneously, three anti-collapse experiments were performed on C110 casing under NUL, and the strain and deformation laws of three casings in the process of collapse were obtained by the electrical method. Yield limit of every casing was obtained by analyzing those data. Experimental results are consistent with the results of calculation of new model. It indicates that the model can be used to calculate yield limit loading of casings under NUL.
文摘Ceramic balls represent a new type of damaging element,and studies on their damaging power of composite armor are required for a comprehensive evaluation of the effectiveness of various types of weapons.The goal of this study was to determine the impact ofφ7 mm toughened Al2 O3 ceramic balls on a composite ceramic/metal armor.The influences of the ceramic panel and the thickness of the metal backing material on the destroying power of the ceramic balls were first determined.Based on the agreement between numerical simulation,experimental results,and calculation models of the target plate resistance,the response mechanism of the ceramic balls was further analyzed.The results indicate that for a back plate of Q235 steel,with an increasing thickness of the ceramic panel,the piercing speed limit of the ceramic balls gradually increases and the diameter of the out-going hole on the metal back decreases.Different conditions were tested to assess the effects on the piercing speed,the diameter of the out-going hole,the micro-element stress,and the integrity of the recovered ceramic bowl.
基金the National Natural Science Foundation of China(Grant No.11572159)the National Defense Science and Technology Foundational Enhancement Program Technology Field Foundation(No.2020-JCJQ-JJ-401)for providing the financial support for this study.
文摘In research of the characteristics of the cavity evolution, the pressure, and the liquid spurt in hydrodynamic ram, the experiment of the high-velocity fragment impacting the water-filled container had been conducted. The relationships between the above three characteristics have been researched. The evolution of the cavity can be divided into three processes according to its shape characteristics. The first liquid spurt occurred in Process Ⅱ and the rest of it occurred in Process Ⅲ. The duration of the second liquid spurt is longer than the first liquid spurt. When the impact velocity of the fragment is less than996 m/s, the velocity of the second liquid spurt is the highest. When the velocity of the fragment is greater than 996 m/s, the velocity of the first liquid spurt is the highest. The maximum velocities of the first and second liquid spurt are 111 m/s and 94 m/s respectively. The pressure fluctuated sharply in Processes Ⅰ and Ⅲ. The maximum peak pressures in the shock and the cavity oscillation phases are15.51 MPa and 7.96 MPa respectively. The time interval of the two adjacent pressure pulses increases with the increase of the fragment velocity.
基金supported by the National Natural Science Foundation of China (61102166)the Scientific Research Foundation of Naval Aeronautical and Astronautical University for Young Scholars (HY2012)
文摘Based on the target scatterer density, the range-spread target detection of high-resolution radar is addressed in additive non-Gaussian clutter, which is modeled as a spherically invariant random vector. Firstly, for sparse scatterer density, the detection of target scatterer in each range cell is derived, and then an M/K detector is proposed to detect the whole range-spread target. Se- condly, an integrating detector is devised to detect a range-spread target with dense scatterer density. Finally, to make the best of the advantages of M/K detector and integrating detector, a robust detector based on scatterer density （DBSD） is designed, which can reduce the probable collapsing loss or quantization error ef- fectively. Moreover, the density decision factor of DBSD is also determined. The formula of the false alarm probability is derived for DBSD. It is proved that the DBSD ensures a constant false alarm rate property. Furthermore, the computational results indi- cate that the DBSD is robust to different clutter one-lag correlations and target scatterer densities. It is also shown that the DBSD out- performs the existing scatterer-density-dependent detector.
文摘To explore the influence of karst cavity pressure on the failure mechanisms of rock layers above water-filled caves, novel blow-out and collapse mechanisms are put forward in this study. The proposed method uses the nonlinear optimization to obtain the failure profiles of surrounding layered rock with water-filled cave at the bottom of the tunnel. By referring to the functional catastrophe theory, stability analysis with different properties in different rock layers is implemented with considering the incorporation of seepage forces since the groundwater cannot be ignored in the catastrophe analysis of deep tunnel bottom. Also the parametric analysis is implemented to discuss the influences of different rock strength factors on the failure profiles. In order to offer a good guide of design for the excavation of deep tunnels above the water-filled caves, the proposed method is applied to design of the minimum effective height for rock layer. The results obtained by this work agree well with the existing published ones.
基金Project(50908234)supported by the National Natural Science Foundation of ChinaProject(2011CB710604)supported by the Basic Research Program of China
文摘According to the stress state of the crack surface, crack rock mass can be divided into complex composite tensile-shear fracture and composite compression-shear fracture from the perspective of fracture mechanics. By studying the hydraulic fracturing effect of groundwater on rock fracture, the tangential friction force equation of hydrodynamic pressure to rock fracture is deduced. The hydraulic fracturing of hydrostatic and hydrodynamic pressure to rock fracture is investigated to derive the equation of critical pressure when the hydraulic fracturing effect occurs in the rock fracture. Then, the crack angle that is most prone to hydraulic fracturing is determined. The relationships between crack direction and both lateral pressure coefficient and friction angle of the fracture surface are analyzed. Results show that considering the joint effect of hydrodynamic and hydrostatic pressure, the critical pressure does not vary with the direction of the crack when the surrounding rock stationary lateral pressure coefficient is equal to 1.0. Under composite tensile-shear fracture, the crack parallel to the direction of the main stress is the most prone to hydraulic fracturing. Under compression-shear fracture, the hydrodynamic pressure resulting in the most dangerous crack angle varies at different lateral pressure coefficients; this pressure decreases when the friction angle of the fracture surface increases. By referring to the subway tunnel collapse case, the impact of fractured rock mass hydraulic fracturing generated by hydrostatic and hydrodynamic pressure joint action is calculated and analyzed.
基金Foundation item： Project（2013CB036004） supported by the National Basic Research Program of China Project（51178468） supported by the National Natural Science Foundation of China Project（2013zzts235） supported by Research Foundation of Central South University, China
文摘Prediction of the state of roof collapse is a big challenge in tunnel engineering, while the limit analysis theory makes it possible to derive the analytical solutions of the collapse mechanisms. In this work, an exact solution of collapsing shape in shallow underwater tunnel is obtained by using the variation principle and the upper bound theorem based on nonlinear failure criterion. Numerical results under the effect of river water and supporting pressure are derived and discussed. The maximum water depth above the river bottom surface is determined under a given buried depth of shallow cavities and the critical depth of roof collapse is obtained under a constant river depth. In comparison with the previous results, the present solution shows a good agreement with the practical results.
