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
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
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
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
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
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
After reviewing the studies on the lateral artificial boundaries in dynamic soil-structure interactions,the free field boundary was theoretically analyzed in asymmetric-and symmetric-matrix forms.First,the lumped mass...After reviewing the studies on the lateral artificial boundaries in dynamic soil-structure interactions,the free field boundary was theoretically analyzed in asymmetric-and symmetric-matrix forms.First,the lumped mass system was combined with viscous or viscoelastic elements to obtain a lumped mass-free field boundary.Second,typical examples were implemented using the finite element software ABAQUS.The incident shear wave was taken to be perpendicular to the bottom to verify the effectiveness of the lumped mass-free field under various sites:underground structures,uniform sites,and layered sites.Finally,the accuracy of the lumped mass-free field boundary was compared with those of the viscoelastic and roller boundaries on different calculation scales,soil damping ratios,structure sizes,and ground motion characteristics.Subsequently,the engineering design values for different damping ratios are given.The results show that the precision of the lumped mass-free field boundary was reasonable,and the operation was simple within the same engineering application.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
The assessment of the seismic safety of underground structures,either tunnels or large station boxes,should not be overlooked especially in densely populated areas,even with low to moderate seismicity.For underground ...The assessment of the seismic safety of underground structures,either tunnels or large station boxes,should not be overlooked especially in densely populated areas,even with low to moderate seismicity.For underground structures,an important issue is the estimation of the seismic actions acting on the structure;only few experimental evidences are available for multi-level propped walls.For tunnels,it is generally assumed that their seismic behavior in soft ground is governed by the surrounding soil,while the inertial load contribution of the underground structure itself is negligible.In both cases,recent numerical studies proved that advanced dynamic analyses can provide satisfactory interpretation of non-linear soil-structure interaction during earthquakes.In this paper,a real case study,represented by a large open multi-propped excavation and a circular segmented tunnel in a densely urbanized area of the city center in Napoli,has been used to investigate some of the mentioned aspects.Accurate geotechnical characterization and choice of the reference input motions lead to a first estimate of the free-field ground motion,which was subsequently used for pseudo-static decoupled analyses.For the complexity of both excavation geometry and staged construction,a full dynamic analysis was considered neither affordable nor reliable for the multi-propped station box;thus two conventional pseudo-static analyses,applying either a displacement-based or a force-based approach,were carried out.In the case of the tunnel,the seismic increments of internal forces in the lining could be calculated through both a simplified pseudostatic analysis and a full dynamic analysis,showing a satisfying agreement.Overall,the results of the study demonstrated that the seismic increments of internal forces in the diaphragm walls of the station and in the segmented lining of the tunnel were quite significant.The case study encourages improving the reliability of simplified methods based on the more advanced dynamic approaches.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
A disadvantage of the conventional quasi-static test method is that it does not consider the soil restraint effect.A new method to test the seismic performance of prefabricated specimens for underground assembled stru...A disadvantage of the conventional quasi-static test method is that it does not consider the soil restraint effect.A new method to test the seismic performance of prefabricated specimens for underground assembled structures is proposed,which can realistically reflect the strata restraint effect on the underground structure.Laboratory work combined with finite element(FE)analysis is performed in this study.Three full-scale sidewall specimens with different joint forms are designed and fabricated.Indices related to the seismic performance and damage modes are analyzed comprehensively to reveal the mechanism of the strata restraint effect on the prefabricated sidewall components.Test results show that the strata restraint effect effectively improves the energy dissipation capacity,load-bearing capacity,and the recoverability of the internal deformation of the precast sidewall components.However,the strata restraint effect reduces the ductility of the precast sidewall components and aggravates the shear and bending deformations in the core region of the connection joints.Additionally,the strata restraint effect significantly affects the seismic performance and damage mode of the prefabricated sidewall components.An FE model that can be used to conduct a seismic performance study of prefabricated specimens for underground assembled structures is proposed,and its feasibility is verified via comparison with test data.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
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 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.
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.
基金Natural Science Foundation of Henan Province under Grant No.222300420415。
文摘After reviewing the studies on the lateral artificial boundaries in dynamic soil-structure interactions,the free field boundary was theoretically analyzed in asymmetric-and symmetric-matrix forms.First,the lumped mass system was combined with viscous or viscoelastic elements to obtain a lumped mass-free field boundary.Second,typical examples were implemented using the finite element software ABAQUS.The incident shear wave was taken to be perpendicular to the bottom to verify the effectiveness of the lumped mass-free field under various sites:underground structures,uniform sites,and layered sites.Finally,the accuracy of the lumped mass-free field boundary was compared with those of the viscoelastic and roller boundaries on different calculation scales,soil damping ratios,structure sizes,and ground motion characteristics.Subsequently,the engineering design values for different damping ratios are given.The results show that the precision of the lumped mass-free field boundary was reasonable,and the operation was simple within the same engineering application.
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.
基金This work was carried out as part of WP3‘Tunnels’of the sub-project on‘Earthquake Geotechnical Engineering’,in the framework of the research programme funded by Italian Civil Protection through the ReLUIS Consortium.Dr.Lorenza Evangelista is warmly acknowledged for the help provided in preparing the map in Fig.1.
文摘The assessment of the seismic safety of underground structures,either tunnels or large station boxes,should not be overlooked especially in densely populated areas,even with low to moderate seismicity.For underground structures,an important issue is the estimation of the seismic actions acting on the structure;only few experimental evidences are available for multi-level propped walls.For tunnels,it is generally assumed that their seismic behavior in soft ground is governed by the surrounding soil,while the inertial load contribution of the underground structure itself is negligible.In both cases,recent numerical studies proved that advanced dynamic analyses can provide satisfactory interpretation of non-linear soil-structure interaction during earthquakes.In this paper,a real case study,represented by a large open multi-propped excavation and a circular segmented tunnel in a densely urbanized area of the city center in Napoli,has been used to investigate some of the mentioned aspects.Accurate geotechnical characterization and choice of the reference input motions lead to a first estimate of the free-field ground motion,which was subsequently used for pseudo-static decoupled analyses.For the complexity of both excavation geometry and staged construction,a full dynamic analysis was considered neither affordable nor reliable for the multi-propped station box;thus two conventional pseudo-static analyses,applying either a displacement-based or a force-based approach,were carried out.In the case of the tunnel,the seismic increments of internal forces in the lining could be calculated through both a simplified pseudostatic analysis and a full dynamic analysis,showing a satisfying agreement.Overall,the results of the study demonstrated that the seismic increments of internal forces in the diaphragm walls of the station and in the segmented lining of the tunnel were quite significant.The case study encourages improving the reliability of simplified methods based on the more advanced dynamic approaches.
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The authors gratefully acknowledge the financial support provided by the National Key R&D Program of China(No.2018YFC0808705)the National Natural Science Foundation of China(Grant No.51678033)the Technology Research and Development Project of China Railway Siyuan Survey and Design Group Co.,Ltd.(No.2021K026).
文摘A disadvantage of the conventional quasi-static test method is that it does not consider the soil restraint effect.A new method to test the seismic performance of prefabricated specimens for underground assembled structures is proposed,which can realistically reflect the strata restraint effect on the underground structure.Laboratory work combined with finite element(FE)analysis is performed in this study.Three full-scale sidewall specimens with different joint forms are designed and fabricated.Indices related to the seismic performance and damage modes are analyzed comprehensively to reveal the mechanism of the strata restraint effect on the prefabricated sidewall components.Test results show that the strata restraint effect effectively improves the energy dissipation capacity,load-bearing capacity,and the recoverability of the internal deformation of the precast sidewall components.However,the strata restraint effect reduces the ductility of the precast sidewall components and aggravates the shear and bending deformations in the core region of the connection joints.Additionally,the strata restraint effect significantly affects the seismic performance and damage mode of the prefabricated sidewall components.An FE model that can be used to conduct a seismic performance study of prefabricated specimens for underground assembled structures is proposed,and its feasibility is verified via comparison with test data.
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.
