Currently,there is a lack of research on the impact of excavation damage on the stability of underground compressed air energy storage(CAES)chambers.This study presents a comprehensive analytical framework for evaluat...Currently,there is a lack of research on the impact of excavation damage on the stability of underground compressed air energy storage(CAES)chambers.This study presents a comprehensive analytical framework for evaluating the elastic and elastoplastic stress fields in CAES chambers surrounding rock,incorporating excavation-induced centripetal reduction of rock stiffness and strength.A proposed model introduces exponential reduction functions for the deformation modulus and cohesion within the excavation disturbed zone(EDZ),deriving analytical solutions for both elastic and elastoplastic stress distributions.A case study of a practical engineering project validates the theoretical formulations through comparative analysis with numerical simulations,demonstrating strong consistency in stress field predictions.The main findings indicate that the EDZ causes a significant non-monotonic variation in the elastic hoop stress distribution.While it does not significantly affect the range of the plastic zone,it reduces the permeability and bearing capacity of the surrounding rock,highlighting the necessity of integrating the centripetal reduction of mechanical properties and strictly controlling excavation-induced damage in the design practice.Furthermore,this study provides a new approach for the selection of lining materials and structural design for CAES chambers:the radial stiffness smoothly increases to match the EDZ surrounding rock stiffness,and the cohesion exceeds that of the surrounding rock,which can significantly optimize the overall system's stress distribution.This study provides valuable insights and references for the selection of excavation methods,stability assessment,and support structure design for CAES engineering,and holds significant importance for improving the CAES technology system.展开更多
An elastoplastic method for analyzing the 3D deformation, stress and transverse distribution of tension stress during cold strip rolling is developed. The analysis is based on the elastoplastic variational principle i...An elastoplastic method for analyzing the 3D deformation, stress and transverse distribution of tension stress during cold strip rolling is developed. The analysis is based on the elastoplastic variational principle in which a kinematically admissible velocity field is constructed with the lateral flow function as an unknown function. The stress distribution and volume strain distribution are obtained by solving the simultaneous equations formed by the longitudinal differential equation of equilibrium and constitutive equations. The lateral flow function is determined by minimizing the total energy dissipation rate. Experimental investigation was carried out on a reversible cold mill. The front tension stress distributions in cold rolled strips were measured by a multi roll segmented tension sensing shapemeter. The calculated results are in good agreement with the measured ones.展开更多
The equivalent stress fundamental solution for the elastoplastic dynamic plane strain problem is proposed to transform the virtual work in the third direction to the plane.Subsequently,based on Betti reciprocal theore...The equivalent stress fundamental solution for the elastoplastic dynamic plane strain problem is proposed to transform the virtual work in the third direction to the plane.Subsequently,based on Betti reciprocal theorem,by adopting the time dependent fundamental solutions in terms of displacement,traction and equivalent stress,the boundary integral equations for dynamic elastoplastic analysis for the plane strain problem are established.The establishment procedures for the displacement and the stress boundary integral equations,together with the stress equation at boundary points,are presented in details,while the standard discretization both in time and space under the frame of time domain boundary element method(TD-BEM)and the solution of the algebraic equations are also briefly stated.Two verification examples are presented from different viewpoints,for elastic and elastoplastic analysis,for 1-D and 2-D geometries,and for finite and infinite domains.The TD-BEM formulation for dynamic elastoplastic analysis is presented for the plane strain problem as an example,where the formulation is also applicable for the plane stress problem by properly transforming the elastic constants and adopting the corresponding fundamental solutions.展开更多
The knee bracing steel frame (KBF) is a new kind of energy dissipating frame, which combines excellent ductility and lateral stiffness. As the structural fuse of the frame, the knee element will yield first during a s...The knee bracing steel frame (KBF) is a new kind of energy dissipating frame, which combines excellent ductility and lateral stiffness. As the structural fuse of the frame, the knee element will yield first during a severe earthquake so that no damage occurs to the major structural members and the rehabilitation is easy and economical. To help fully understand the relations be- tween its seismic performance and the structural parameters, systematic elastoplastic analysis of the KBF structure with finite element method was conducted in this work. Finally, general design recommendations were made according to the results of the analysis.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
Accelerated proximal gradient methods have recently been developed for solving quasi-static incremental problems of elastoplastic analysis with some different yield criteria.It has been demonstrated through numerical ...Accelerated proximal gradient methods have recently been developed for solving quasi-static incremental problems of elastoplastic analysis with some different yield criteria.It has been demonstrated through numerical experiments that these methods can outperform conventional optimization-based approaches in computational plasticity.However,in literature these algorithms are described individually for specific yield criteria,and hence there exists no guide for application of the algorithms to other yield criteria.This short paper presents a general form of algorithm design,independent of specific forms of yield criteria,that unifies the existing proximal gradient methods.Clear interpretation is also given to each step of the presented general algorithm so that each update rule is linked to the underlying physical laws in terms of mechanical quantities.展开更多
When a tunnel is excavated below the groundwater table,groundwater flows in through the excavated wall of the tunnel and seepage forces act on it.These forces significantly affect the ground reaction curve,which is de...When a tunnel is excavated below the groundwater table,groundwater flows in through the excavated wall of the tunnel and seepage forces act on it.These forces significantly affect the ground reaction curve,which is defined as the relationship between the internal pressure and radial displacement of the tunnel wall.This study investigates analytical solutions for seepage forces acting on the lining of a circular tunnel under steady-state groundwater flow.Considering the tunnel’s construction or service period and boundary conditions,the direction of maximum principal stress changes,and the input stress of the Mohr-Coulomb criterion varies.The stress distribution and yield range of the surrounding soils and linings are studied.The first,second,and third critical inner pressures are defined and evaluated.The influence of the seepage field on the plastic radius,first critical pressure,and stress distribution of the tunnel is analyzed.It is shown that during the construction period,the seepage force promotes the expansion of the yield area,whereas during the service period,the opposite is the case.The first critical pressure increases nearly linearly with the distant water pressure.The radial stress distribution decreases clearly in comparison with that when the seepage force is not considered,and the reduction is more prominent when internal pressure increases.The tangential stress distribution increases clearly compared with that when the seepage force is not considered.展开更多
The constitutive equation was deduced. The results were obtained from theelastic and elastoplastical analysis of the cylinder sample applied with different ratios ofload on both the inner and outer sides and different...The constitutive equation was deduced. The results were obtained from theelastic and elastoplastical analysis of the cylinder sample applied with different ratios ofload on both the inner and outer sides and different moduli ratio. The factors affecting thedevelopment of the plastic field of the cylinder with finite radius were shown. The resultsshow that the different moduli ratio is the most important factor in the development of theplastic zone. The slight fluctuation of the ratio will bring multiplied increment of the displacement, which may result in the final destruction of the engineering material.展开更多
Impermeable bentonite or its mixtures have been proposed as candidate materials to be used in the geotechnical disposal of radioactive nuclear waste. These materials are filled in the space between a canister containi...Impermeable bentonite or its mixtures have been proposed as candidate materials to be used in the geotechnical disposal of radioactive nuclear waste. These materials are filled in the space between a canister containing radioactive nuclear waste and an underground chamber to absorb the radionuclide emitting from the canister and simultaneously retard its migration accompanying the perrneation of underground water to prevent the surrounding environment from po1lution. On the basis of the established elastoplastic strain-hardening mechanical model considering the material’s dilatancy character,the authors carry out the stress-strain analysis of a thick-wa1l cylinder in a plane strain state subJected to a pressure difference between internal and external pressures. The analysis may be expected to be a theoretical basis for developing a coupled shear and permeability test apparatus for conducting a permeability test along a sheared plane in a specimen. The apparatus will be used to study the effects of shear strain on the variation of geotechnical materials’ permeability coefficient in order to evaluate the influence of shear strain caused by nonuniform deformation and/or earthquake on the long-term safety of the disposal system of radioactive nuclear waste. The theoretlcal analysls methods in this paper can be directly spread to the analysis of the deformation and stability of tunnels or roadways driven in soft soils or high moisture-bearing soft rocks.展开更多
In this paper, the stress-strain curve of material is fitted by polygonal line composed of three lines. According to the theory of proportional loading in elastoplasticity, we simplify the complete stress-strain relat...In this paper, the stress-strain curve of material is fitted by polygonal line composed of three lines. According to the theory of proportional loading in elastoplasticity, we simplify the complete stress-strain relations, which are given by the increment theory of elastoplasticity. Thus, the finite element equation with the solution of displacement is derived. The assemblage elastoplastic stiffness matrix can be obtained by adding something to the elastic matrix, hence it will shorten the computing time. The determination of every loading increment follows the von Mises yield criteria. The iterative method is used in computation. It omits the redecomposition of the assemblage stiffness matrix and it will step further to shorten the computing time. Illustrations are given to the high-order element application departure from proportional loading, the computation of unloading fitting to the curve and the problem of load estimation.展开更多
The lining and surrounding rock around tunnels constructed in cold areas exhibit nonuniform material properties due to the existence of a temperature field.This study considered the effects of these properties on the ...The lining and surrounding rock around tunnels constructed in cold areas exhibit nonuniform material properties due to the existence of a temperature field.This study considered the effects of these properties on the integrity of tunnel structures.By establishing an elastoplastic mechanical model,analytical solutions to the stress and displacement under five different elastoplastic states were derived and compared based on distinct yield criteria.The findings showed that with increasing relative radius,the displacement in the lining elastic zone initially decreased before increasing,whereas the shift in the plastic zone continued to increase.The displacement in the elastic zone of the frozen surrounding rock intensified with increasing relative radius,whereas the shift in the plastic zone experienced a gradual decline.The displacement of the inner wall of the lining was always greater than that of the outer wall,and this phenomenon occurred only after the frozen surrounding rock exhibited a plastic zone.The maximum displacements of the liner in its elastically limited and plastically limited states were 1.39,1.77,2.28,and 2.37 mm and 15.93,25.51,44.28,and 48.58 mm based on the Drucker-Prager(DP),Mohr-Coulomb(MC),Tresca,and double-shear strength criteria,respectively;the maximum limit displacements of the frozen surrounding rock were 12.74,20.41,35.43,and 38.87 mm and 85.32,103.38,569.23,and 680.43 mm,respectively.With increasing relative radius,the radial stresses within both the lining and the frozen surrounding rock intensified;and the tangential stress in the elastic zone of the lining decreased whereas the opposite change rule was observed in the plastic zone.The tangential stresses in the frozen surrounding rock and lining exhibited the same variation trend.Based on calculations with four distinct strength criteria,the elastic and plastic ultimate bearing capacities of the lining were 1.81,2.31,2.95,and 3.07 MPa,and 3.31,4.84,7.48,and 8.05 MPa,while those of the frozen surrounding rock were 8.52,13.24,22.17,and 24.18 MPa,and 16.76,32.46,74.15,and 85.64 MPa.In addition,with the expansion of the plastic zone,the phenomenon of a sudden change in the tangential stress at location r2 became progressively attenuated.The study findings can provide some theoretical guidance for the design and construction of tunnels in cold areas.展开更多
In the period of rapid development of urban rail transit,the traditional transportation hub has become increasingly unable to meet the needs of people's travel due to the lack of rationality and efficiency of land...In the period of rapid development of urban rail transit,the traditional transportation hub has become increasingly unable to meet the needs of people's travel due to the lack of rationality and efficiency of land use,the monotonous structure and other reasons,resulting in a series of new three-dimensional transportation hub.The Huangmugang comprehensive transportation hub in Shenzhen is a complex four-story underground station with different spans.The station adopts a large-diameter and large-angle V-column structure system.In this paper,a simplified seismic analysis method suitable for the V-pillar structure of subway station is proposed,and the two-dimensional finite element model and dynamic time history analysis of subway station are completed in combination with practical engineering cases.The influence of buried depth change of station on the response law of subway station is studied.The seismic response results of station under three different buried depths are analyzed,and the stress and deformation law of key components such as V-pillar,side wall and station floor of station structure are compared and analyzed.The main conclusions are as follows:with the increase of the buried depth of the station,the constraint effect of the surrounding soil on the station structure is obviously enhanced,which is manifested by the increase of the constraint effect of the soil on the side wall of the station and the decrease of the displacement of the side wall.However,with the further increase of the buried depth of the station,the constraint effect of the surrounding soil on the station tends to be stable.At the same time,due to the increase of the thickness of the overlying soil,the self-weight stress transmitted by the soil of the station increases,which makes the deformation of the side wall of the station increase.展开更多
基金Science and Technology Commission of Shanghai Municipality,Grant/Award Number:22dz1205300。
文摘Currently,there is a lack of research on the impact of excavation damage on the stability of underground compressed air energy storage(CAES)chambers.This study presents a comprehensive analytical framework for evaluating the elastic and elastoplastic stress fields in CAES chambers surrounding rock,incorporating excavation-induced centripetal reduction of rock stiffness and strength.A proposed model introduces exponential reduction functions for the deformation modulus and cohesion within the excavation disturbed zone(EDZ),deriving analytical solutions for both elastic and elastoplastic stress distributions.A case study of a practical engineering project validates the theoretical formulations through comparative analysis with numerical simulations,demonstrating strong consistency in stress field predictions.The main findings indicate that the EDZ causes a significant non-monotonic variation in the elastic hoop stress distribution.While it does not significantly affect the range of the plastic zone,it reduces the permeability and bearing capacity of the surrounding rock,highlighting the necessity of integrating the centripetal reduction of mechanical properties and strictly controlling excavation-induced damage in the design practice.Furthermore,this study provides a new approach for the selection of lining materials and structural design for CAES chambers:the radial stiffness smoothly increases to match the EDZ surrounding rock stiffness,and the cohesion exceeds that of the surrounding rock,which can significantly optimize the overall system's stress distribution.This study provides valuable insights and references for the selection of excavation methods,stability assessment,and support structure design for CAES engineering,and holds significant importance for improving the CAES technology system.
基金granted by China Postdoctoral Science Foundation
文摘An elastoplastic method for analyzing the 3D deformation, stress and transverse distribution of tension stress during cold strip rolling is developed. The analysis is based on the elastoplastic variational principle in which a kinematically admissible velocity field is constructed with the lateral flow function as an unknown function. The stress distribution and volume strain distribution are obtained by solving the simultaneous equations formed by the longitudinal differential equation of equilibrium and constitutive equations. The lateral flow function is determined by minimizing the total energy dissipation rate. Experimental investigation was carried out on a reversible cold mill. The front tension stress distributions in cold rolled strips were measured by a multi roll segmented tension sensing shapemeter. The calculated results are in good agreement with the measured ones.
基金The authors would like to acknowledge the financial support provided by Hebei Education Department(Grant QN2020135)the National Key R&D Program of China(Grants 2019YFC1511105 and 2019YFC1511104)the National Natural Science Foundation of China(Grant 51778193).
文摘The equivalent stress fundamental solution for the elastoplastic dynamic plane strain problem is proposed to transform the virtual work in the third direction to the plane.Subsequently,based on Betti reciprocal theorem,by adopting the time dependent fundamental solutions in terms of displacement,traction and equivalent stress,the boundary integral equations for dynamic elastoplastic analysis for the plane strain problem are established.The establishment procedures for the displacement and the stress boundary integral equations,together with the stress equation at boundary points,are presented in details,while the standard discretization both in time and space under the frame of time domain boundary element method(TD-BEM)and the solution of the algebraic equations are also briefly stated.Two verification examples are presented from different viewpoints,for elastic and elastoplastic analysis,for 1-D and 2-D geometries,and for finite and infinite domains.The TD-BEM formulation for dynamic elastoplastic analysis is presented for the plane strain problem as an example,where the formulation is also applicable for the plane stress problem by properly transforming the elastic constants and adopting the corresponding fundamental solutions.
基金Project (No. 2002CB412790) supported by the National BasicResearch Program (973) of China
文摘The knee bracing steel frame (KBF) is a new kind of energy dissipating frame, which combines excellent ductility and lateral stiffness. As the structural fuse of the frame, the knee element will yield first during a severe earthquake so that no damage occurs to the major structural members and the rehabilitation is easy and economical. To help fully understand the relations be- tween its seismic performance and the structural parameters, systematic elastoplastic analysis of the KBF structure with finite element method was conducted in this work. Finally, general design recommendations were made according to the results of the analysis.
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Accelerated proximal gradient methods have recently been developed for solving quasi-static incremental problems of elastoplastic analysis with some different yield criteria.It has been demonstrated through numerical experiments that these methods can outperform conventional optimization-based approaches in computational plasticity.However,in literature these algorithms are described individually for specific yield criteria,and hence there exists no guide for application of the algorithms to other yield criteria.This short paper presents a general form of algorithm design,independent of specific forms of yield criteria,that unifies the existing proximal gradient methods.Clear interpretation is also given to each step of the presented general algorithm so that each update rule is linked to the underlying physical laws in terms of mechanical quantities.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.51278467,2015M582204 and 2016T90681).
文摘When a tunnel is excavated below the groundwater table,groundwater flows in through the excavated wall of the tunnel and seepage forces act on it.These forces significantly affect the ground reaction curve,which is defined as the relationship between the internal pressure and radial displacement of the tunnel wall.This study investigates analytical solutions for seepage forces acting on the lining of a circular tunnel under steady-state groundwater flow.Considering the tunnel’s construction or service period and boundary conditions,the direction of maximum principal stress changes,and the input stress of the Mohr-Coulomb criterion varies.The stress distribution and yield range of the surrounding soils and linings are studied.The first,second,and third critical inner pressures are defined and evaluated.The influence of the seepage field on the plastic radius,first critical pressure,and stress distribution of the tunnel is analyzed.It is shown that during the construction period,the seepage force promotes the expansion of the yield area,whereas during the service period,the opposite is the case.The first critical pressure increases nearly linearly with the distant water pressure.The radial stress distribution decreases clearly in comparison with that when the seepage force is not considered,and the reduction is more prominent when internal pressure increases.The tangential stress distribution increases clearly compared with that when the seepage force is not considered.
文摘The constitutive equation was deduced. The results were obtained from theelastic and elastoplastical analysis of the cylinder sample applied with different ratios ofload on both the inner and outer sides and different moduli ratio. The factors affecting thedevelopment of the plastic field of the cylinder with finite radius were shown. The resultsshow that the different moduli ratio is the most important factor in the development of theplastic zone. The slight fluctuation of the ratio will bring multiplied increment of the displacement, which may result in the final destruction of the engineering material.
文摘Impermeable bentonite or its mixtures have been proposed as candidate materials to be used in the geotechnical disposal of radioactive nuclear waste. These materials are filled in the space between a canister containing radioactive nuclear waste and an underground chamber to absorb the radionuclide emitting from the canister and simultaneously retard its migration accompanying the perrneation of underground water to prevent the surrounding environment from po1lution. On the basis of the established elastoplastic strain-hardening mechanical model considering the material’s dilatancy character,the authors carry out the stress-strain analysis of a thick-wa1l cylinder in a plane strain state subJected to a pressure difference between internal and external pressures. The analysis may be expected to be a theoretical basis for developing a coupled shear and permeability test apparatus for conducting a permeability test along a sheared plane in a specimen. The apparatus will be used to study the effects of shear strain on the variation of geotechnical materials’ permeability coefficient in order to evaluate the influence of shear strain caused by nonuniform deformation and/or earthquake on the long-term safety of the disposal system of radioactive nuclear waste. The theoretlcal analysls methods in this paper can be directly spread to the analysis of the deformation and stability of tunnels or roadways driven in soft soils or high moisture-bearing soft rocks.
文摘In this paper, the stress-strain curve of material is fitted by polygonal line composed of three lines. According to the theory of proportional loading in elastoplasticity, we simplify the complete stress-strain relations, which are given by the increment theory of elastoplasticity. Thus, the finite element equation with the solution of displacement is derived. The assemblage elastoplastic stiffness matrix can be obtained by adding something to the elastic matrix, hence it will shorten the computing time. The determination of every loading increment follows the von Mises yield criteria. The iterative method is used in computation. It omits the redecomposition of the assemblage stiffness matrix and it will step further to shorten the computing time. Illustrations are given to the high-order element application departure from proportional loading, the computation of unloading fitting to the curve and the problem of load estimation.
基金supported by the Natural Science Foundation of Anhui Province(2408085ME147)Engineering Research Center of the Ministry of Education for Underground Mining Engineering(JYBGCZX2022103)+3 种基金the Key Laboratory of Building Structure and Underground Engineering of Anhui Province(KLBSUE-2023-02)the Key Laboratory of Underground Engineering and Disaster Prevention and Control of Henan Province(KFKT 2023-06)supported by National Natural Science Foundation of China(No.52378384)Natural Science Foundation of Anhui Province(No.2308085ME188).
文摘The lining and surrounding rock around tunnels constructed in cold areas exhibit nonuniform material properties due to the existence of a temperature field.This study considered the effects of these properties on the integrity of tunnel structures.By establishing an elastoplastic mechanical model,analytical solutions to the stress and displacement under five different elastoplastic states were derived and compared based on distinct yield criteria.The findings showed that with increasing relative radius,the displacement in the lining elastic zone initially decreased before increasing,whereas the shift in the plastic zone continued to increase.The displacement in the elastic zone of the frozen surrounding rock intensified with increasing relative radius,whereas the shift in the plastic zone experienced a gradual decline.The displacement of the inner wall of the lining was always greater than that of the outer wall,and this phenomenon occurred only after the frozen surrounding rock exhibited a plastic zone.The maximum displacements of the liner in its elastically limited and plastically limited states were 1.39,1.77,2.28,and 2.37 mm and 15.93,25.51,44.28,and 48.58 mm based on the Drucker-Prager(DP),Mohr-Coulomb(MC),Tresca,and double-shear strength criteria,respectively;the maximum limit displacements of the frozen surrounding rock were 12.74,20.41,35.43,and 38.87 mm and 85.32,103.38,569.23,and 680.43 mm,respectively.With increasing relative radius,the radial stresses within both the lining and the frozen surrounding rock intensified;and the tangential stress in the elastic zone of the lining decreased whereas the opposite change rule was observed in the plastic zone.The tangential stresses in the frozen surrounding rock and lining exhibited the same variation trend.Based on calculations with four distinct strength criteria,the elastic and plastic ultimate bearing capacities of the lining were 1.81,2.31,2.95,and 3.07 MPa,and 3.31,4.84,7.48,and 8.05 MPa,while those of the frozen surrounding rock were 8.52,13.24,22.17,and 24.18 MPa,and 16.76,32.46,74.15,and 85.64 MPa.In addition,with the expansion of the plastic zone,the phenomenon of a sudden change in the tangential stress at location r2 became progressively attenuated.The study findings can provide some theoretical guidance for the design and construction of tunnels in cold areas.
文摘In the period of rapid development of urban rail transit,the traditional transportation hub has become increasingly unable to meet the needs of people's travel due to the lack of rationality and efficiency of land use,the monotonous structure and other reasons,resulting in a series of new three-dimensional transportation hub.The Huangmugang comprehensive transportation hub in Shenzhen is a complex four-story underground station with different spans.The station adopts a large-diameter and large-angle V-column structure system.In this paper,a simplified seismic analysis method suitable for the V-pillar structure of subway station is proposed,and the two-dimensional finite element model and dynamic time history analysis of subway station are completed in combination with practical engineering cases.The influence of buried depth change of station on the response law of subway station is studied.The seismic response results of station under three different buried depths are analyzed,and the stress and deformation law of key components such as V-pillar,side wall and station floor of station structure are compared and analyzed.The main conclusions are as follows:with the increase of the buried depth of the station,the constraint effect of the surrounding soil on the station structure is obviously enhanced,which is manifested by the increase of the constraint effect of the soil on the side wall of the station and the decrease of the displacement of the side wall.However,with the further increase of the buried depth of the station,the constraint effect of the surrounding soil on the station tends to be stable.At the same time,due to the increase of the thickness of the overlying soil,the self-weight stress transmitted by the soil of the station increases,which makes the deformation of the side wall of the station increase.
