To understand the mechanical response pattern of the existing structure and ground due to the construction of metro tunnels underneath,the finite difference method is adopted to study the torsional deformation and str...To understand the mechanical response pattern of the existing structure and ground due to the construction of metro tunnels underneath,the finite difference method is adopted to study the torsional deformation and stress variation of the existing structure and the effect of underground carriageway structures on the surface subsidence.The curves of the maximum differential subsidence,torsion angle,and distortion of the cross-section of the existing structure show two peaks in succession during traversing of two metro tunnels beneath it.The torsion angle of the existing structure changes when the two tunnels traverse beneath it in opposite directions.The first traversing of the shield tunnel mainly induces the magnitude variation in torsional deformation of the existing structure,but the second traversing of the subsurface tunnel may cause a dynamic change in the magnitude and form of torsional deformation in the existing structure.The shielding effect can reduce the surface subsidence caused by metro tunnel excavation to a certain extent,and the development trend of subsidence becomes slower as the excavation continues.展开更多
The response displacement method(RDM)is recommended for the seismic analysis of underground structures in the transverse direction for many codes,including bases for design of structures-seismic actions for designing ...The response displacement method(RDM)is recommended for the seismic analysis of underground structures in the transverse direction for many codes,including bases for design of structures-seismic actions for designing geotechnical works(ISO 23469)and code for seismic design of urban rail transit structures(GB 50909-2014).However,there are some obvious limitations in the application of RDM.Springs and the shear stress of the soil could be approximately evaluated for the structures having a simple cross section,such as rectangular and circular structures.It is necessary to propose simplified seismic analysis methods for structures with complex cross sections.This paper refers to the idea of RDM and proposes three generalized response displacement methods(GRDM).In GRDM1,a part of the soil surrounding a structure is selected to generate a generalized underground structure with a rectangular cross section,and the same analysis model as RDM is applied to analyze the responses of the structure.In GRDM2,a hollow soil model without a generalized structure is used to compute the equivalent load caused by the relative displacement of the soil,and the soil-structure interaction model is applied to calculate the responses of the structure.In GRDM3,a continuous soil model is applied to compute the equivalent load caused by the relative displacement and shear stress of the soil,and the soil-structure interaction model is applied to analyze the responses of the structure,which is the same as the model used in GRDM2.The time-history analysis method(THAM)is used to evaluate the accuracy of the proposed simplified methods.Results show that the error of GRDM1 is about 20%,while the error is only 5%for GRDM2 and GRDM3.Among the three proposed methods,GRDM3 has obvious advantages regarding calculation efficiency and accuracy.Therefore,it is recommended to use GRDM3 for the seismic response analysis of underground structures that have conventional simple or complex cross sections.展开更多
This paper describes a commonly used pseudo-static method in seismic resistant design of the cross section of underground structures. Based on dynamic theory and the vibration characteristics of underground structures...This paper describes a commonly used pseudo-static method in seismic resistant design of the cross section of underground structures. Based on dynamic theory and the vibration characteristics of underground structures, the sources of errors when using this method are analyzed. The traditional seismic motion loading approach is replaced by a method in which a one-dimensional soil layer response stress is differentiated and then converted into seismic live loads. To validate the improved method, a comparison of analytical results is conducted for internal forces under earthquake shaking of a typical shallow embedded box-shaped subway station structure using four methods: the response displacement method, finite element response acceleration method, the finite element dynamic analysis method and the improved pseudo-static calculation method. It is shown that the improved finite element pseudo-static method proposed in this paper provides an effective tool for the seismic design of underground structures. The evaluation yields results close to those obtained by the finite element dynamic analysis method, and shows that the improved finite element pseudo-static method provides a higher degree of precision.展开更多
A semi-analytical method of solving the problem of dynamic stress concentration of arbitrary underground structure under the effect of blast waves was introduced. Using the Fourier transform theory, the shock waves (...A semi-analytical method of solving the problem of dynamic stress concentration of arbitrary underground structure under the effect of blast waves was introduced. Using the Fourier transform theory, the shock waves (in the forms of SH-waves) can be converted into frequency bands. After employing complex functions and conformal mapping, the admittance functions of various underground structures were obtained. Then, the problem of the time domain dynamic stress response of underground structure can be easily solved through the Fourier inverse transform. At last, the results and curves of the dynamic stress for the square, triangle and horseshoe cavity were presented.展开更多
In this paper, the bolt- and cable-supported structures mainly refer to anchored cables, anchored bolts, soil nails and other commonly used reinforcing and supporting structures in geotechnical engineering, as well as...In this paper, the bolt- and cable-supported structures mainly refer to anchored cables, anchored bolts, soil nails and other commonly used reinforcing and supporting structures in geotechnical engineering, as well as reinforced soil structures in permanent works. They are often used in combination, or formed into composite bolt-and cable-supported structures, with other traditional construction methods and relevant measures. Distinct characteristics of such structures are that they are most often invisible, exposed to more severe underground corrosive environments and with strict durability requirements. A number of serious durability problems of underground structures are discussed and major achievements and advances in China and abroad in terms of durability and reinforcement measures for underground structures are reviewed, followed by comprehensive analyses. Some suggestions for those problems are put forward.展开更多
In this paper, the generalized variational principle of dynamic analysis for the blast-resistant underground structures is established, and the corresponding generalized functional of elastoplastic analysis for underg...In this paper, the generalized variational principle of dynamic analysis for the blast-resistant underground structures is established, and the corresponding generalized functional of elastoplastic analysis for underground structures is derived, and the generalized variational principle of nonconservative system is given, thus the fundamental of dynamical analysis for underground structures to resist blast is proposed. Finally, for the underground cylindrical structure to resist blast, dynamical calculations are made, and compared with the test results.展开更多
Chloride diffusion coefficient and water penetration depth of 3 types concrete were studied. The experimental results show that the concrete permeability decreases itself in the order as follow: pure portland cement c...Chloride diffusion coefficient and water penetration depth of 3 types concrete were studied. The experimental results show that the concrete permeability decreases itself in the order as follow: pure portland cement concrete(CO), concrete added with fly ash(C1), concrete added with both fly ash and silica fume(C2). SEM and microhardness analyses show that the properties of interfacial zone are significantly influenced by silica fume. With the improvement of interfacial zone properties, the permeability especially the Chloride ion diffusivity of concrete significantly decreases.展开更多
A design procedure for improving the seismic performance of unequal-span underground structures by installing isolation devices at the top end of columns is proposed based on the seismic failure mode of frame-type und...A design procedure for improving the seismic performance of unequal-span underground structures by installing isolation devices at the top end of columns is proposed based on the seismic failure mode of frame-type underground structures and the design concept of critical support columns.A two-dimensional finite element model(FEM)for a soil-underground structure with an unequal-span interaction system was established to shed light on the effects of a complex subway station with elastic sliding bearings(ESB)and lead rubber bearings(LRB)on seismic mitigation.It was found that the stiffness and internal force distribution of the underground structure changed remarkably with the installation of isolation devices at the top end of the columns.The constraints of the beam-column joints were significantly weakened,resulting in a decrease in the overall lateral stiffness and an increase in the structural lateral displacement.The introduction of the isolation device effectively reduces the internal force and seismic damage of the frame column;however,the tensile damage to the isolation structure,such as the roof,bottom plate,and sidewall,significantly increased compared to those of the non-isolation structure.Although the relative slip of the ESB remains within a controllable range under strong earthquake excitation as well as frame columns with stable vertical support and self-restoration functions,the LRB shows a better performance during seismic failure and better lateral displacement response of the unequal-span underground structure.The analysis results provide new ideas and references for promoting the application of seismic isolation technology in underground structures.展开更多
In this study,A time-domain seismic response analysis method and a calculation model of the underground structure that can realize the input of seismic P,SV and Rayleigh waves are established,based on the viscoelastic...In this study,A time-domain seismic response analysis method and a calculation model of the underground structure that can realize the input of seismic P,SV and Rayleigh waves are established,based on the viscoelastic artificial boundary elements and the boundary substructure method for seismic wave input.After verifying the calculation accuracy,a comparative study on seismic response of a shallow-buried,double-deck,double-span subway station structure under incident P,SV and Rayleigh waves is conducted.The research results show that there are certain differences in the cross-sectional internal force distribution characteristics of underground structures under different types of seismic waves.The research results show that there are certain differences in the internal force distribution characteristics of underground structures under different types of seismic waves.At the bottom of the side wall,the top and bottom of the center pillar of the underground structure,the section bending moments of the underground structure under the incidences of SV wave and Rayleigh wave are relatively close,and are significantly larger than the calculation result under the incidence of P wave.At the center of the side wall and the top floor of the structure,the peak value of the cross-sectional internal force under the incident Rayleigh wave is larger than the calculation result under SV wave.In addition,the floor of the underground structure under Rayleigh waves vibrates in both the horizontal and vertical directions,and the magnification effect in the vertical direction is more significant.Considering that the current seismic research of underground structures mainly considers the effect of body waves such as the shear waves,sufficient attention should be paid to the incidence of Rayleigh waves in the future seismic design of shallow underground structures.展开更多
Soils with spatial variability are the product of natural history.The mechanical properties tested by soil samples from boreholes in the same soil layer may be different.Underground structure service in surrounding so...Soils with spatial variability are the product of natural history.The mechanical properties tested by soil samples from boreholes in the same soil layer may be different.Underground structure service in surrounding soils,their seismic response is controlled by the deformation of the surrounding soils.The variability of soil mechanical parameters was not considered in the current research on the seismic response of underground structures.Therefore,a random field model was established to describe the spatial variability of surrounding soils based on the random field theory.Then the seismic response of underground structures in the random field was simulated based on the time-domain explicit global FEM analysis,and the soil mechanical parameters and earthquake intensity influencing the seismic response of surrounding soils and underground structures were studied.Numerical results presented that,the randomness of soil parameters does not change the plastic deformation mode of surrounding soils significantly.The variation coefficients of inter-story deformation of structures and lateral deformation of columns are much smaller than that of mechanical parameters,and the randomness of soil parameters has no obvious effect on the structural deformation response.展开更多
The pushover method for underground structures is a seismic analysis method featured by high calculation accuracy and a simple implementation process.The method has been widely used in seismic design and other related...The pushover method for underground structures is a seismic analysis method featured by high calculation accuracy and a simple implementation process.The method has been widely used in seismic design and other related scientific research;however,the influence of different soil-structure flexibility ratios on the accuracy of this method is still not well understood.In this study,we select the cross-section structures beneath the Daikai subway station as the research object and establish 12 finite element analysis models with different soil-structure flexibility ratios using ABAQUS.All models are computed by the dynamic time-history method or the pushover method.Furthermore,the dynamic time-history solution result is taken as the standard solution,and the precision and application of the pushover analysis method are discussed based on the parameters of peak interlayer displacement and peak internal force of the middle column section.The results show that the soil-structure flexibility ratio has a significant influence on the calculation accuracy of the pushover method,and the calculation accuracy of this method is the most ideal when the soil-structure flexibility is equal to 1.The research results can provide significant references for the seismic design of underground structures or the improvement of simplified seismic analysis methods.展开更多
Based on a centrifuge model test and distinct element method(DEM), this study provides new insights into the uplift response of a shallow-buried structure and the liquefaction mechanism for saturated sand around the s...Based on a centrifuge model test and distinct element method(DEM), this study provides new insights into the uplift response of a shallow-buried structure and the liquefaction mechanism for saturated sand around the structure under seismic action. In the centrifuge test, a high-speed microscopic camera was installed in the structure model, by which the movements of particles around the structure were monitored. Then, a two-dimensional digital image processing technology was used to analyze the microstructure of saturated sand during the shaking event. Herein, a numerical simulation of the centrifuge experiment was conducted using a two-phase(solid and fl uid) fully coupled distinct element code. This code incorporates a particle-fl uid coupling model by means of a "fi xed coarse-grid" fl uid scheme in PFC3D(Particle Flow Code in Three Dimensions), with the modeling parameters partially calibrated based on earlier studies. The physical and numerical models both indicate the uplifts of the shallow-buried structure and the sharp rise in excess pore pressure. The corresponding micro-scale responses and explanations are provided. Overall, the uplift response of an underground structure and the occurrence of liquefaction in saturated sand are predicted successfully by DEM modeling. However, the dynamic responses during the shaking cannot be modeled accurately due to the restricted computer power.展开更多
In this paper the Capon spectral estimation method,i.e.the maximun likelihood method,was applied to the analysis of the short periodic geomagnetic events occurred from January to March,1986 at the Chinese Great Wall S...In this paper the Capon spectral estimation method,i.e.the maximun likelihood method,was applied to the analysis of the short periodic geomagnetic events occurred from January to March,1986 at the Chinese Great Wall Station on Antarctic(CGWSA) and the complex transfer functions A and B for Peneds T=45 s-160 min were calculated,derived from the medulus|A| of A and its phase angle,it seems that there are two structural layers in the subterranean electric conductivity under the CGWSA,the corresponding periods at the interface being around 20-26 minutes.We also compared the Capon spectral estimation method with the Fast Fourier Trasformation(FFT).The former appeared to be better than the latter.展开更多
A numerical framework was proposed for the seismic analysis of underground structures in layered ground under inclined P-SV waves.The free-field responses are first obtained using the stiffness matrix method based on ...A numerical framework was proposed for the seismic analysis of underground structures in layered ground under inclined P-SV waves.The free-field responses are first obtained using the stiffness matrix method based on plane-wave assumptions.Then,the domain reduction method was employed to reproduce the wavefield in the numerical model of the soil–structure system.The proposed numerical framework was verified by providing comparisons with analytical solutions for cases involving free-field responses of homogeneous ground,layered ground,and pressure-dependent heterogeneous ground,as well as for an example of a soil–structure interaction simulation.Compared with the viscous and viscous-spring boundary methods adopted in previous studies,the proposed framework exhibits the advantage of incorporating oblique incident waves in a nonlinear heterogeneous ground.Numerical results show that SV-waves are more destructive to underground structures than P-waves,and the responses of underground structures are significantly affected by the incident angles.展开更多
The underground structure in coral sand is threatened by earthquake.The special dynamic characteristics of coral sand were realized by finite difference program.Specifically,the stress–strain loops,shear modulus atte...The underground structure in coral sand is threatened by earthquake.The special dynamic characteristics of coral sand were realized by finite difference program.Specifically,the stress–strain loops,shear modulus attenuation and hysteresis behaviour of coral sand were simulated using hysteresis damping.On this basis,numerical models were established to study the seismic response of the rectangular underground structure in coral sand,and the fluid–solid coupling and soil-structure interaction were considered.The results illustrate that the increasing relative density of coral sand foundation reduces the excess pore water pressure(EPWP),but amplifies the horizontal dynamic soil pressure of the coral sand-underground structure system.The increase in the permeability coefficient of coral sand reduces the EPWP accumulation,which leads to an increase of the stiffness and a decrease of the acceleration amplification of coral sand sites.展开更多
Underground structures are susceptible to float and move upward during earthquakes when located in a liquefiable soil deposit.There are examples of this phenomenon in past major earthquake events.In this study,the upl...Underground structures are susceptible to float and move upward during earthquakes when located in a liquefiable soil deposit.There are examples of this phenomenon in past major earthquake events.In this study,the uplift of circular tunnels in a liquefiable sand layer was investigated with a series of shaking table tests.The research has focused on the buried depth of the tunnel,tunnel diameter,tunnel weight,liquefaction extent,uplift mechanism,and factor of safety against liquefaction-induced uplift.According to the test results,the shallow buried depth,larger diameter,and lower weight can intensify the tunnel uplift,so the displacement in post-liquefaction time continues at the same rate as during the shaking time.Due to the shear-induced dilation,pore water pressure generation around the tunnel was reduced compared with that of the free field.The excess pore water pressure dissipation in the soil overlying the uplifted tun-nel was significant,which leads to suction in the soil deposit.Furthermore,the acceleration response of overlying soil with the uplifted tunnel was similar to that of the free field.However,the soil acceleration response around the tunnel without uplift was similar to the base motion.展开更多
Seismic response of underground structure in liquefiable soils was analyzed by means of fully coupled dynamic finite element method.The soils were simulated by a cyclic mobility constitutive model,which is developed a...Seismic response of underground structure in liquefiable soils was analyzed by means of fully coupled dynamic finite element method.The soils were simulated by a cyclic mobility constitutive model,which is developed at the base of modified Cam-Clay model with some concepts such as stress induced anisotropy,overconsolidation and structure.It is verified that the constitutive model can perfectly described the dynamic character of both liquefiable sand and non-liquefiable clay.Special emphasis was given for the influence of thickness of liquefiable soil on the seismic response.Results showed that soils at both sides of the structure flowed toward the bottom of the underground structure with the occurrence of liquefaction,which led to the uplift of structure.The uplift of underground structure increased with the increasing of thickness of liquefiable soils.展开更多
Based on the domain reduction idea and artificial boundary substructure method,this paper proposes an FK-FEM hybrid approach by integrating the advantages of FK and FEM(i.e.,FK can efficiently generate high-frequency ...Based on the domain reduction idea and artificial boundary substructure method,this paper proposes an FK-FEM hybrid approach by integrating the advantages of FK and FEM(i.e.,FK can efficiently generate high-frequency three translational motion,while FEM has rich elements types and constitutive models).An advantage of this approach is that it realizes the entire process simulation from point dislocation source to underground structure.Compared with the plane wave field input method,the FK-FEM hybrid approach can reflect the spatial variability of seismic motion and the influence of source and propagation path.This approach can provide an effective solution for seismic analysis of underground structures under scenario of earthquake in regions where strong earthquakes may occur but are not recorded,especially when active faults,crustal,and soil parameters are available.Taking Daikai subway station as an example,the seismic response of the underground structure is simulated after verifying the correctness of the approach and the effects of crustal velocity structure and source parameters on the seismic response of Daikai station are discussed.In this example,the influence of velocity structure on the maximum interlayer displacement angle of underground structure is 96.5%and the change of source parameters can lead to the change of structural failure direction.展开更多
Effect of Explosion on underground structures where drilled on the stony materials can be affected by explosive strength and rock mass properties of tunnel. In this paper, it has been studied on effect of explosion of...Effect of Explosion on underground structures where drilled on the stony materials can be affected by explosive strength and rock mass properties of tunnel. In this paper, it has been studied on effect of explosion of 10 tons TNT on the round tunnel (diameter: 10 m) in 25 m depth in the mass rocks (RMR > 90) to estimate stability of tunnel to construct underground structure. Regarding to the studied stones, geo-mechanical indices of rock mass have been found to use as strength criteria in UDEC. In the next step, tunnel in real dimensions and founded indices is modeled with UDEC and analyzed stably. Explosion wave indices are found by UFC Instruction and other experimental relations to administer force from explosion wave on the model. Finally, on the base of FISH, indices of explosion wave are administrated in UDEC and tunnel is analyzed dynamically. According to modeling in depth of 25 m, amount of displacement of drilled tunnel in mass rocks (RMR < 90) is very lower than standard criterion and the tunnel is very stable. Development of plastic zone, vertical and horizontal displacement of rock mass around the tunnel, speed variations and stress from explosion wave are modeled and recorded as the graphs and figures.展开更多
基金National Natural Science Foundation of China,Grant/Award Numbers:51878060,52078046。
文摘To understand the mechanical response pattern of the existing structure and ground due to the construction of metro tunnels underneath,the finite difference method is adopted to study the torsional deformation and stress variation of the existing structure and the effect of underground carriageway structures on the surface subsidence.The curves of the maximum differential subsidence,torsion angle,and distortion of the cross-section of the existing structure show two peaks in succession during traversing of two metro tunnels beneath it.The torsion angle of the existing structure changes when the two tunnels traverse beneath it in opposite directions.The first traversing of the shield tunnel mainly induces the magnitude variation in torsional deformation of the existing structure,but the second traversing of the subsurface tunnel may cause a dynamic change in the magnitude and form of torsional deformation in the existing structure.The shielding effect can reduce the surface subsidence caused by metro tunnel excavation to a certain extent,and the development trend of subsidence becomes slower as the excavation continues.
基金National Natural Science Foundation of China under Grant No.52108453Natural Science Foundation of Jiangxi Province of China under Grant No.20212BAB214014+1 种基金National Key R&D Program of China under Grant No.2018YFC1504305Joint Funds of the National Natural Science Foundation of China under Grant No.U1839201。
文摘The response displacement method(RDM)is recommended for the seismic analysis of underground structures in the transverse direction for many codes,including bases for design of structures-seismic actions for designing geotechnical works(ISO 23469)and code for seismic design of urban rail transit structures(GB 50909-2014).However,there are some obvious limitations in the application of RDM.Springs and the shear stress of the soil could be approximately evaluated for the structures having a simple cross section,such as rectangular and circular structures.It is necessary to propose simplified seismic analysis methods for structures with complex cross sections.This paper refers to the idea of RDM and proposes three generalized response displacement methods(GRDM).In GRDM1,a part of the soil surrounding a structure is selected to generate a generalized underground structure with a rectangular cross section,and the same analysis model as RDM is applied to analyze the responses of the structure.In GRDM2,a hollow soil model without a generalized structure is used to compute the equivalent load caused by the relative displacement of the soil,and the soil-structure interaction model is applied to calculate the responses of the structure.In GRDM3,a continuous soil model is applied to compute the equivalent load caused by the relative displacement and shear stress of the soil,and the soil-structure interaction model is applied to analyze the responses of the structure,which is the same as the model used in GRDM2.The time-history analysis method(THAM)is used to evaluate the accuracy of the proposed simplified methods.Results show that the error of GRDM1 is about 20%,while the error is only 5%for GRDM2 and GRDM3.Among the three proposed methods,GRDM3 has obvious advantages regarding calculation efficiency and accuracy.Therefore,it is recommended to use GRDM3 for the seismic response analysis of underground structures that have conventional simple or complex cross sections.
基金China Earthquake Administration Association Fund Under Grant No. 106060 and Institute of Engineering Mechanics Director Fund
文摘This paper describes a commonly used pseudo-static method in seismic resistant design of the cross section of underground structures. Based on dynamic theory and the vibration characteristics of underground structures, the sources of errors when using this method are analyzed. The traditional seismic motion loading approach is replaced by a method in which a one-dimensional soil layer response stress is differentiated and then converted into seismic live loads. To validate the improved method, a comparison of analytical results is conducted for internal forces under earthquake shaking of a typical shallow embedded box-shaped subway station structure using four methods: the response displacement method, finite element response acceleration method, the finite element dynamic analysis method and the improved pseudo-static calculation method. It is shown that the improved finite element pseudo-static method proposed in this paper provides an effective tool for the seismic design of underground structures. The evaluation yields results close to those obtained by the finite element dynamic analysis method, and shows that the improved finite element pseudo-static method provides a higher degree of precision.
文摘A semi-analytical method of solving the problem of dynamic stress concentration of arbitrary underground structure under the effect of blast waves was introduced. Using the Fourier transform theory, the shock waves (in the forms of SH-waves) can be converted into frequency bands. After employing complex functions and conformal mapping, the admittance functions of various underground structures were obtained. Then, the problem of the time domain dynamic stress response of underground structure can be easily solved through the Fourier inverse transform. At last, the results and curves of the dynamic stress for the square, triangle and horseshoe cavity were presented.
基金Supported by the National Natural Science Foundation of China (50279054 and 10772199)
文摘In this paper, the bolt- and cable-supported structures mainly refer to anchored cables, anchored bolts, soil nails and other commonly used reinforcing and supporting structures in geotechnical engineering, as well as reinforced soil structures in permanent works. They are often used in combination, or formed into composite bolt-and cable-supported structures, with other traditional construction methods and relevant measures. Distinct characteristics of such structures are that they are most often invisible, exposed to more severe underground corrosive environments and with strict durability requirements. A number of serious durability problems of underground structures are discussed and major achievements and advances in China and abroad in terms of durability and reinforcement measures for underground structures are reviewed, followed by comprehensive analyses. Some suggestions for those problems are put forward.
文摘In this paper, the generalized variational principle of dynamic analysis for the blast-resistant underground structures is established, and the corresponding generalized functional of elastoplastic analysis for underground structures is derived, and the generalized variational principle of nonconservative system is given, thus the fundamental of dynamical analysis for underground structures to resist blast is proposed. Finally, for the underground cylindrical structure to resist blast, dynamical calculations are made, and compared with the test results.
文摘Chloride diffusion coefficient and water penetration depth of 3 types concrete were studied. The experimental results show that the concrete permeability decreases itself in the order as follow: pure portland cement concrete(CO), concrete added with fly ash(C1), concrete added with both fly ash and silica fume(C2). SEM and microhardness analyses show that the properties of interfacial zone are significantly influenced by silica fume. With the improvement of interfacial zone properties, the permeability especially the Chloride ion diffusivity of concrete significantly decreases.
基金the research funding provided by the National Natural Science Foundation of China(NSFC,No.51978333)the SINOMACH Science and Technology Major Project(SINOMAST-ZDZX-2020-03)。
文摘A design procedure for improving the seismic performance of unequal-span underground structures by installing isolation devices at the top end of columns is proposed based on the seismic failure mode of frame-type underground structures and the design concept of critical support columns.A two-dimensional finite element model(FEM)for a soil-underground structure with an unequal-span interaction system was established to shed light on the effects of a complex subway station with elastic sliding bearings(ESB)and lead rubber bearings(LRB)on seismic mitigation.It was found that the stiffness and internal force distribution of the underground structure changed remarkably with the installation of isolation devices at the top end of the columns.The constraints of the beam-column joints were significantly weakened,resulting in a decrease in the overall lateral stiffness and an increase in the structural lateral displacement.The introduction of the isolation device effectively reduces the internal force and seismic damage of the frame column;however,the tensile damage to the isolation structure,such as the roof,bottom plate,and sidewall,significantly increased compared to those of the non-isolation structure.Although the relative slip of the ESB remains within a controllable range under strong earthquake excitation as well as frame columns with stable vertical support and self-restoration functions,the LRB shows a better performance during seismic failure and better lateral displacement response of the unequal-span underground structure.The analysis results provide new ideas and references for promoting the application of seismic isolation technology in underground structures.
基金supported by National Natural Science Foundation of China(Grant no.U1839201)China National Postdoctoral Program of Innovative Talents(Grant no.BX20200192)+1 种基金China Postdoctoral Science Foundation,China(2020M680575)Shuimu Tsinghua Scholar Program(Grant no.2020SM005)。
文摘In this study,A time-domain seismic response analysis method and a calculation model of the underground structure that can realize the input of seismic P,SV and Rayleigh waves are established,based on the viscoelastic artificial boundary elements and the boundary substructure method for seismic wave input.After verifying the calculation accuracy,a comparative study on seismic response of a shallow-buried,double-deck,double-span subway station structure under incident P,SV and Rayleigh waves is conducted.The research results show that there are certain differences in the cross-sectional internal force distribution characteristics of underground structures under different types of seismic waves.The research results show that there are certain differences in the internal force distribution characteristics of underground structures under different types of seismic waves.At the bottom of the side wall,the top and bottom of the center pillar of the underground structure,the section bending moments of the underground structure under the incidences of SV wave and Rayleigh wave are relatively close,and are significantly larger than the calculation result under the incidence of P wave.At the center of the side wall and the top floor of the structure,the peak value of the cross-sectional internal force under the incident Rayleigh wave is larger than the calculation result under SV wave.In addition,the floor of the underground structure under Rayleigh waves vibrates in both the horizontal and vertical directions,and the magnification effect in the vertical direction is more significant.Considering that the current seismic research of underground structures mainly considers the effect of body waves such as the shear waves,sufficient attention should be paid to the incidence of Rayleigh waves in the future seismic design of shallow underground structures.
基金supported by the Beijing Natural Science Foundation(8212007)the Pyramid Talent Training Project of Beijing University of Civil Engineering and Architecture(JDYC20200311)。
文摘Soils with spatial variability are the product of natural history.The mechanical properties tested by soil samples from boreholes in the same soil layer may be different.Underground structure service in surrounding soils,their seismic response is controlled by the deformation of the surrounding soils.The variability of soil mechanical parameters was not considered in the current research on the seismic response of underground structures.Therefore,a random field model was established to describe the spatial variability of surrounding soils based on the random field theory.Then the seismic response of underground structures in the random field was simulated based on the time-domain explicit global FEM analysis,and the soil mechanical parameters and earthquake intensity influencing the seismic response of surrounding soils and underground structures were studied.Numerical results presented that,the randomness of soil parameters does not change the plastic deformation mode of surrounding soils significantly.The variation coefficients of inter-story deformation of structures and lateral deformation of columns are much smaller than that of mechanical parameters,and the randomness of soil parameters has no obvious effect on the structural deformation response.
基金sponsored by the National Natural Science Foundation of China(52008206)the China Postdoctoral Science Foundation(2021M690279)。
文摘The pushover method for underground structures is a seismic analysis method featured by high calculation accuracy and a simple implementation process.The method has been widely used in seismic design and other related scientific research;however,the influence of different soil-structure flexibility ratios on the accuracy of this method is still not well understood.In this study,we select the cross-section structures beneath the Daikai subway station as the research object and establish 12 finite element analysis models with different soil-structure flexibility ratios using ABAQUS.All models are computed by the dynamic time-history method or the pushover method.Furthermore,the dynamic time-history solution result is taken as the standard solution,and the precision and application of the pushover analysis method are discussed based on the parameters of peak interlayer displacement and peak internal force of the middle column section.The results show that the soil-structure flexibility ratio has a significant influence on the calculation accuracy of the pushover method,and the calculation accuracy of this method is the most ideal when the soil-structure flexibility is equal to 1.The research results can provide significant references for the seismic design of underground structures or the improvement of simplified seismic analysis methods.
基金National Natural Science Foundation of China under Grant Nos.41272296 and 51208294
文摘Based on a centrifuge model test and distinct element method(DEM), this study provides new insights into the uplift response of a shallow-buried structure and the liquefaction mechanism for saturated sand around the structure under seismic action. In the centrifuge test, a high-speed microscopic camera was installed in the structure model, by which the movements of particles around the structure were monitored. Then, a two-dimensional digital image processing technology was used to analyze the microstructure of saturated sand during the shaking event. Herein, a numerical simulation of the centrifuge experiment was conducted using a two-phase(solid and fl uid) fully coupled distinct element code. This code incorporates a particle-fl uid coupling model by means of a "fi xed coarse-grid" fl uid scheme in PFC3D(Particle Flow Code in Three Dimensions), with the modeling parameters partially calibrated based on earlier studies. The physical and numerical models both indicate the uplifts of the shallow-buried structure and the sharp rise in excess pore pressure. The corresponding micro-scale responses and explanations are provided. Overall, the uplift response of an underground structure and the occurrence of liquefaction in saturated sand are predicted successfully by DEM modeling. However, the dynamic responses during the shaking cannot be modeled accurately due to the restricted computer power.
文摘In this paper the Capon spectral estimation method,i.e.the maximun likelihood method,was applied to the analysis of the short periodic geomagnetic events occurred from January to March,1986 at the Chinese Great Wall Station on Antarctic(CGWSA) and the complex transfer functions A and B for Peneds T=45 s-160 min were calculated,derived from the medulus|A| of A and its phase angle,it seems that there are two structural layers in the subterranean electric conductivity under the CGWSA,the corresponding periods at the interface being around 20-26 minutes.We also compared the Capon spectral estimation method with the Fast Fourier Trasformation(FFT).The former appeared to be better than the latter.
基金supported by the National Natural Science Foundation of China(Grant Nos.41922059,42177134,and 51778487)Fundamental Research Funds for the Central Universities,CHD(300102262506)Top Discipline Plan of Shanghai Universities-Class I.
文摘A numerical framework was proposed for the seismic analysis of underground structures in layered ground under inclined P-SV waves.The free-field responses are first obtained using the stiffness matrix method based on plane-wave assumptions.Then,the domain reduction method was employed to reproduce the wavefield in the numerical model of the soil–structure system.The proposed numerical framework was verified by providing comparisons with analytical solutions for cases involving free-field responses of homogeneous ground,layered ground,and pressure-dependent heterogeneous ground,as well as for an example of a soil–structure interaction simulation.Compared with the viscous and viscous-spring boundary methods adopted in previous studies,the proposed framework exhibits the advantage of incorporating oblique incident waves in a nonlinear heterogeneous ground.Numerical results show that SV-waves are more destructive to underground structures than P-waves,and the responses of underground structures are significantly affected by the incident angles.
基金supported by the National Natural Science Foundation of China(Grant Nos.52178312,51878103,51778092,41831282)Innovation Group Science Foundation of the Natural Science Foundation of Chongqing,China(Grant No.cstc2020jcyj-cxttX0003).
文摘The underground structure in coral sand is threatened by earthquake.The special dynamic characteristics of coral sand were realized by finite difference program.Specifically,the stress–strain loops,shear modulus attenuation and hysteresis behaviour of coral sand were simulated using hysteresis damping.On this basis,numerical models were established to study the seismic response of the rectangular underground structure in coral sand,and the fluid–solid coupling and soil-structure interaction were considered.The results illustrate that the increasing relative density of coral sand foundation reduces the excess pore water pressure(EPWP),but amplifies the horizontal dynamic soil pressure of the coral sand-underground structure system.The increase in the permeability coefficient of coral sand reduces the EPWP accumulation,which leads to an increase of the stiffness and a decrease of the acceleration amplification of coral sand sites.
文摘Underground structures are susceptible to float and move upward during earthquakes when located in a liquefiable soil deposit.There are examples of this phenomenon in past major earthquake events.In this study,the uplift of circular tunnels in a liquefiable sand layer was investigated with a series of shaking table tests.The research has focused on the buried depth of the tunnel,tunnel diameter,tunnel weight,liquefaction extent,uplift mechanism,and factor of safety against liquefaction-induced uplift.According to the test results,the shallow buried depth,larger diameter,and lower weight can intensify the tunnel uplift,so the displacement in post-liquefaction time continues at the same rate as during the shaking time.Due to the shear-induced dilation,pore water pressure generation around the tunnel was reduced compared with that of the free field.The excess pore water pressure dissipation in the soil overlying the uplifted tun-nel was significant,which leads to suction in the soil deposit.Furthermore,the acceleration response of overlying soil with the uplifted tunnel was similar to that of the free field.However,the soil acceleration response around the tunnel without uplift was similar to the base motion.
基金the National Natural Science Foundation of China (No. 50679041)the Shanghai Leading Academic Discipline Project (No.B208)the Shang-hai Pujiang Program (No. 08PJ1406600)
文摘Seismic response of underground structure in liquefiable soils was analyzed by means of fully coupled dynamic finite element method.The soils were simulated by a cyclic mobility constitutive model,which is developed at the base of modified Cam-Clay model with some concepts such as stress induced anisotropy,overconsolidation and structure.It is verified that the constitutive model can perfectly described the dynamic character of both liquefiable sand and non-liquefiable clay.Special emphasis was given for the influence of thickness of liquefiable soil on the seismic response.Results showed that soils at both sides of the structure flowed toward the bottom of the underground structure with the occurrence of liquefaction,which led to the uplift of structure.The uplift of underground structure increased with the increasing of thickness of liquefiable soils.
基金supported by Open Foundation of National Engineering Laboratory for High Speed Railway Construction(No.HSR202006)National Natural Science Foundation of China(Grant Nos.52178495,52078498).
文摘Based on the domain reduction idea and artificial boundary substructure method,this paper proposes an FK-FEM hybrid approach by integrating the advantages of FK and FEM(i.e.,FK can efficiently generate high-frequency three translational motion,while FEM has rich elements types and constitutive models).An advantage of this approach is that it realizes the entire process simulation from point dislocation source to underground structure.Compared with the plane wave field input method,the FK-FEM hybrid approach can reflect the spatial variability of seismic motion and the influence of source and propagation path.This approach can provide an effective solution for seismic analysis of underground structures under scenario of earthquake in regions where strong earthquakes may occur but are not recorded,especially when active faults,crustal,and soil parameters are available.Taking Daikai subway station as an example,the seismic response of the underground structure is simulated after verifying the correctness of the approach and the effects of crustal velocity structure and source parameters on the seismic response of Daikai station are discussed.In this example,the influence of velocity structure on the maximum interlayer displacement angle of underground structure is 96.5%and the change of source parameters can lead to the change of structural failure direction.
基金supported by the National Natural Science Foundation of China(41004020)the Director Foundation of Institute of Seismology,China Earthquake Administration(IS200926044)
文摘Effect of Explosion on underground structures where drilled on the stony materials can be affected by explosive strength and rock mass properties of tunnel. In this paper, it has been studied on effect of explosion of 10 tons TNT on the round tunnel (diameter: 10 m) in 25 m depth in the mass rocks (RMR > 90) to estimate stability of tunnel to construct underground structure. Regarding to the studied stones, geo-mechanical indices of rock mass have been found to use as strength criteria in UDEC. In the next step, tunnel in real dimensions and founded indices is modeled with UDEC and analyzed stably. Explosion wave indices are found by UFC Instruction and other experimental relations to administer force from explosion wave on the model. Finally, on the base of FISH, indices of explosion wave are administrated in UDEC and tunnel is analyzed dynamically. According to modeling in depth of 25 m, amount of displacement of drilled tunnel in mass rocks (RMR < 90) is very lower than standard criterion and the tunnel is very stable. Development of plastic zone, vertical and horizontal displacement of rock mass around the tunnel, speed variations and stress from explosion wave are modeled and recorded as the graphs and figures.