Ultimate Bearing Capacity Of Utility Tunnel Structure With Corrugated Steel Pipe Under Complex Loads

The Utility Tunnel Structure(UTS)made of Corrugated Steel Pipe(CSP)is a new type of underground structure,which has only been researched and applied in China in recent years.Since the CSP is provided inside the pipe gallery,the corrugated steel not only bears the external earth pressure,but also bears the local load,and there are few related studies at home and abroad.In this paper,the ultimate bearing capacity of the pipe gallery with brackets is studied by finite element method.Firstly,the characteristics of the model,the constitutive relation of the selected materials and the nonlinear mechanical properties are mainly introduced;including the constitutive relationship of steel,yield criterion and soil constitutive relation,soil-arch interaction,and the model construction process is introduced in detail.The engineering example is selected to compare the measured values of the project with the finite element analysis values,and the CHBDC specification is used to verify the parameters.The parameters of the finite element model are selected reasonably,which lays a foundation for the simulation analysis of the ultimate bearing capacity of corrugated steel arches under complex loads.Then,the finite element method is used to study the deformation and ultimate bearing capacity of corrugated steel pipe structure under different load combinations,including dead load,dead load + pipeline load,dead load + live load,dead load + live load + pipeline load.Load combination.The results show that when the dead load is applied,the soil is filled on the pipe side,the top of the pipe is upturned,and the stress and deformation of the pipe wall are not large;the top fill of the pipe,the stress and deformation of the pipe top are positively correlated with the height of the fill,and the corrugated steel structure is in the backfill.When a certain height is reached,the soil arching effect is formed.At this time,the stress anddisplacement of the corrugated steel structure tend to be stable,and the growth rate becomes slow.When the dead load + pipeline load acts,the corrugated steel pipe wall connected with the bracket generates stress concentration phenomenon.The pipe wall at the joint connection reaches the yield first,and the influence range is about three waves.When the height of the bracket is different,where is the support position.First yield,the higher the position of the bracket,the lower the ultimate bearing capacity of the corrugated steel arch.When the dead load + live load is applied,the top of the pipe reaches the yield first under the full-span live load;when the half-span is stressed,the large shear deformation occurs in the middle part of the soil,the shoulder is first yielded,and the ultimate bearing capacity is compared with the full span.When the load is reduced,the corrugated steel is flattened on the half-span side.The half-span stress is the most unfavorable,and the half-span force should be avoided.When the dead load + live load + pipeline load,under the half-span load,the pipeline load is applied.When the height of the bracket is different,the shoulder of the pipe reaches the yield first.As the height of the bracket increases,the stress at the top of the pipe increases faster than that of the arch line.When the bracket is 45°,the stress at the top of the pipe exceeds the arching line,indicating that the bracket is only a local load,which has an effect on the local stress of the corrugated steel.Secondly,under the combination of dead load + live load + pipeline load,considering the elastic modulus,internal friction angle,Poisson's ratio,steel strength and steel plate thickness of the backfill,the finite element analysis is carried out to obtain the limit of corrugated steel structure.The bearing capacity increases with the increase of the elastic modulus and internal friction angle of the backfill soil,and increases with the increase of the strength and thickness of the steel.However,the Poisson's ratio has little effect on the bearing capacity,and the most influential is the strength of the steel itself.Finally,verify the reliability of the formula.For the bending moment and axial force at the corrugated steel pipe wall at the support,the finite element value of the model analysis is compared with the calculation formula of the bearing capacity proposed by the research group.The difference between the two data is less than 5%,and the formula can be usedunder complex loads.Calculation of bearing capacity of corrugated steel structures with brackets.It is recommended to adopt the formula proposed by the research group to calculate the bearing capacity of corrugated steel supports.In view of the limitations of this model,the paper concludes with some suggestions for the shortcomings of this paper.