Research On Assembled Steel Structure Supporting Technology Of Circular Shaft Based On Active Preloading

With the rapid development of urbanization,Urban land and social resources are becoming increasingly tense in China.In order to solve the problem of insufficient floor space,the infrastructure has been transferred to underground.The underground shafts have become more and more demanding as construction tunnels for underground projects.At present,the supporting structure of the underground shaft mainly depends on shotcrete.The concrete construction is facing a severe test with the improvement of people's environmental awareness.Since 2016,China has vigorously developed assembled structure to reduce environmental pollution caused by construction.Therefore,this paper proposed a set of preloaded,recyclable and assembled circular shaft steel structure support equipment based on the concept of assembled steel structure design.The support structure is verified by theoretical calculation,numerical simulation,field loading test and construction application.The main results are as follows:1.A circular pre-tightening support structure was designed based on the speciality(large number,shallow depth(within 10m),small diameter,relatively fixed size and temporary characteristics,etc.)of the construction shaft in the urban municipal pipe network project.The support structure consists of steel pipe and steel plate.The circular supporting structure layer is formed by the structure unit and the pre-tightening screw.The longitudinal direction of the support structure is reinforced by the longitudinal connecting component.The supporting structure is a cylindrical structure after completion of construction.The supporting structure has the advantages of safety,rapid,environmental,recyclable,economical.2.For the characteristics of the active pre-tightening support structure,the earth pressure calculation formula in the non-limit state was derived considering the soil arching effect.The mechanical properties of the supporting structure were analyzed too.The results show the supporting structure mainly bears the circumferential axial force.The component stress,the strength of pre-tightening screw and the bolt were verified under the axial force.The entire structural force system is clear,which is convenient for engineering calculation and design.3.The stress mechanism of the structure unit(including steel pipes,blocks and steel plates)was analyzed by SAP2000 finite element software.The analysis results show that the deformation of the steel plate and the existence of the block will cause to generate torque and bending moment in the steel pipe,which is bad for the structure.It is necessary to optimize the spacing of the block and the rigidity of the steel plate during the design process.4.The loading test shows that the stratum around the shaft is deformed to the outside of the shaft as the supporting structure expands outward,and the stress in the steel pipe increases linearly with the external expansion of supporting structure.It indicates that the expansion of the supporting structure can cooperate with the surrounding soil and play a positive role in suppressing surface settlement.5.The field application shows that the construction process of the structure is simple,and the construction period is short with the average construction period of 3.0 m/day.The construction site does not cause environmental pollution,and the structure can be completely recycled and reused.The structure has obvious economic and social benefits.