The Analysis Of Some Main Questions In Structural Design Of A Large-scale Underground Construction

With the continuous development of the national economy,science and technology,the underground,air and underwater space is continuously included as usable city space apart from the traditional ground space.Exploitation of the underground has an irreplaceable role in solving problems such as heavy traffic,shortage of city space,improving city environment,protecting city landscape,decreasing the waste of the land resources,etc.Subsurface construction can effectively separate people from vehicles to improve both the city static and dynamic transportation situation and relieve traffic buildup.The transportation facilities,such as the underground walkway,have the ability to separate massive amounts of people from vehicles.Therefore,the exploitation and utilization of underground construction is getting more attention from different departments in different areas.The large-scale underground walkway has the features such as a long uncracked length,large load resistance capacity,and complicated mechanics,and therefore is much more difficult to repair than an superstructure due to potential safety hazards.Since this structure is extremely susceptible to deformation,all factors that affect it must be fully considered during the design process.Compared to the exposed superstructure,more attention must be given to the elaborate design of the subsurface structure.In this study,the subsurface walkway construction project on NANSHA LINSHAN Island is taken as an example to analyze some of the key design technology ot the large-size underground structure features in detail.This study consists of the following aspects:⑴ The study of seismic resistance performance of the ultra-long subsurface structure in various soil layersAccording to the available provision and code in our country,the major methods of analyzing the superstructure are based on the built-in pile head model and built-in basement roof model.But for the subsurface structure(especially in soft soil),it is obviously not accurate enough to use these models.In the study,a static and dynamic analysis by using elastic foundation connection modeling are carried out to analyze the stress of the overall object consisting of the superstructure and pile foundation with piles of different length.A corresponding construction detail technology and control method is proposed.⑵ Analysis of the stress of the flat slab floor system with trough subsidenceSince a flat slab floor system is usually utilized in large underground spaces and the subsidence trough is set on the slab for the need of installation of the equipment and pipelines,it definitely will cause a change in the stress distribution.The slab stresses caused by different trough layouts are analyzed and discussed.And the corresponding design method is suggested.⑶ The study of the design method for the retaining system as the combination of retaining component and superstructureUnderground construction usually connects different areas by the Sunken Plaza.This Plaza usually utilize a cantilever retaining system for the external walls with a height of 10 to 12 meters,but at the same time,the thickness of the external wall must be restrained to some reasonable range.Therefore,it requires a great deal of skill.For these features of the project,a lattice retaining system is presented.This system create a connection between the supporting piles and side walls of the superstructure with the rib-wall in order to take full advantage of the resistance capacity of the retaining piles.A corresponding calculation model,design method and construction detail scheme is presented.