Research On The Effect Of Structure-soil Relative Stiffness On Uneven Settlement Of Underground Structure

With the rapid development of socio-political and economic development,along with the increase of urban population and the expansion of urban scale,people’s demand for travel convenience has gradually increased.Because transportation is an important factor in urban development,the underground integrated transportation hub is an inevitable product of the role of urban development.During the construction and operation of underground transportation hubs,uneven settlement often occurs in underground structures due to regional ground settlement,lateral and longitudinal inhomogeneities in the ground,train loads,and differences of the underground structure-soil relative stiffness.Severe uneven settlement can lead to safety problems and pose a threat to people’s lives and property.In this paper,the comprehensive transportation hub of Xiong’an intercity station is used as a reference.By means of theoretical study and numerical simulation,the settlement deformation of the underground structure under the action of static load and train load is studied.The influence of structure-soil relative stiffness on the uneven settlement of the underground structure is analyzed,and methods to reduce the uneven settlement are proposed according to the research laws,and the main work and results are as follows:(1)Through theoretical analysis and derivation of the structure-soil relative stiffness calculation formula,the factors affecting the structure-soil relative stiffness are analyzed.First,two-dimensional model of single-span underground structure is established to calculate the structure-soil relative stiffness,and then a three-dimensional model is established to investigate its settlement deformation law on the underground structure.The results show that the maximum settlement value of the structure decreases as the structure-soil relative stiffness increases.The maximum settlement value of the structure increases with the increase of the structure size,and decreases first and then increases with the increase of the width-to-height ratio.The settlement is the smallest when the width-to-height ratio is 1.(2)Two multi-span frame structures,the throat area structure and the national railway garage structure,are selected for the Xiong’an intercity station.Through finite element calculations,the influence law of structure-soil relative stiffness on the settlement of underground frame structures is investigated.For the factors affecting the uneven settlement of the structure,the methods to reduce the uneven settlement are compared and analyzed.The results show that the settlement value decreases with the increase of the structure-soil relative stiffness,and the settlement value of the structure increases with the increase of the structure size.When the relative stiffness increases to 10,the settlement of the structure is particularly small and tends to be stable.The settlement difference between the structure in the throat area and the structure in the national railway garage decreases with the increase of the structureground relative stiffness.Therefore,the overall settlement of both structures can be reduced by simultaneously increasing the throat area structure-soil relative stiffness in the and the structuresoil relative stiffness in the national railway garage.It is also possible to reduce the uneven settlement by increasing the structure-soil relative stiffness in the national railway garage or decreasing the structure-soil relative stiffness the throat area,so that the settlement values of the two structures are equal.(3)For the inter-station open cut tunnel and transition section structure,the effects of tunnel depth,structural lining thickness and tunnel-soil relative stiffness on the uneven settlement of the underground structure are analyzed by theoretical calculations and finite element numerical simulations,taking into account the train vibration load.The results show that the soil elastic modulus and Poisson’s ratio affect the magnitude of the structure-soil relative stiffness,and the structural settlement decreases with the increase of the structure-soil relative stiffness.Along the direction of leaving the station,the buried depth of the tunnel increases continuously,and the settlement of the structure increases first,then tends to be stable,and finally decreases gradually.When the buried depth of the tunnel is 12 m to 16 m,the settlement value of the structure is the largest;Along the direction of the station,the lining thickness of the tunnel structure increases continuously,and the settlement of the structure increases first,then tends to be stable,and finally decreases.When the lining thickness is 1.4m,the settlement value of the structure is the largest;For underground tunnel structures with different cross-sectional clearances,the structure-soil relative stiffness decreases and then increases along the direction of the station,and there is a situation where the structure-soil relative stiffness is equal.Comparing and analyzing the settlement magnitude of different structures in this case,it can be found that the settlement amounts are only slightly different.Therefore,for the study of uneven settlement of underground structures under complex conditions,the structure-soil relative stiffness can well reflect the relationship between it and the settlement of the structure,and it is of reference significance for the relevant projects.