The Optimization Of Approaching Construction Method For New Subway Works Based On Settlement Controlling

With the acceleration of urbanization process in China, metro engineering has developed vigorously in order to deal with urban public transport issue. More and more subway tunneling projects are built in flourishing and bustling cities, whose construction is adjacent to or undercrossing towards inevitably overground or underground structures and buildings. And meanwhile there is a great deal of problem on geotechnical engineering and construction technique to spring up. Ground surface subsidence induced by the excavation of the tunneling may endanger the safety of overground and underground structures and buildings, which gives rise to grave losses of economy and even calamities of injuries and deaths, and then what leads up to is bad social influence. As a result, during the construction progress, it's an important realistic issue how to keep off landslide and groud surface settlement induced by tunneling is forecasted reliably and controlled effectively so as to endure the safety of superstructures and substructures along the project line, which must be solved in the urban MTR construction.Seen from current engineering practices and scholarly researches in China, in the aspects on damages and their countermeasures of approaching structures and buildings produced by the underground engineering excavation, at present however there isn't a complete evaluation criterion about construct damages aroused by MTR excavation and relevant academic reserches are also less. General solution is to supply with a settlement limit value. It's said that not to exceeding this limit is workable.For example, such as Beijing and Shenzhen cities, generally stipulating the upper limit of the ground surface settlement controls within 30mm and the lower limit of the surface upheaval limit is within 10mm. However, these values are based on experiences, and its working out has not systematical theoretical researching base. Even if within the range of 30mm, different structures have different mechanical responsestructures and different damage degrees too. To some tunneling works, it may be overconversative but to another is not safe.Therefore, taking reinforcement measures to adjacent buildings and structures according to this criterion is not always appropriate and maybe not reasonable in engineering economics.The paper very based on tutor's task of Technical Requirements on Underground Engineering Undercrossing Existing Transportation Facilities and combined with the construction reality situation of Beijing underground diametrical line tunneling, which is large cross-section in high-water-level and soft wall rock from Beijing railway station to Beijing west railway station.In six aspects, such as the settlements of earth surface, tunnel roof and floor, close-to existing buildings and subway line and underground pipeline and the level deformation of tunnel sides, this paper goes over and talks over more deepgoingly on above-mentioned problems, classifies the studies of ground surface settlement in details and puts forward raft foundation stress more pointedly. Hence it can provide with engineering analogy reference evidence for this kind of works so as to make such construction control more applicable, secure and economic. Fist of all, in line with really adopted double side drift method in diametrical line engineering, numerical simulation models are presented to match with its construction ways.And then, the settling curve of ground surface and existing buildings, the settling convergent curve of tunnel roof and the level convergent curve obtained from field monitoring data are put into use in testing and verifying the numerical models until they couple with the above monitoring data curve by means of adjusting the parameters of rock and soil solid elements and structure grid cells in modeling. As a consequence, the approximate two-dimensional initial state or the true three-dimensional of country rock at engineering site are simulated and presented. On that basis, 35 forms of structure section added up to 126 kinds of construction ways for both side heading method, cavern-pile method, CRD method, CD method, single side drift method and bench method are simulated in plane. Analyzing their deformation tendency of the modeling above, it turned out at first step that opticonstructed double side drift method, hole-pile method and CRD method are beneficial to settlement controlling. Thereout, 3D simulating the above three typical methods is to further study detailed classification control of settlement deformations. Finally comprehensively analyzing those cases above, it comes to conclusion that the construction optimum proposal is cavern-pile method and detailed classification control indexes are proposed correspondingly.The project of Technical Requirements on Underground Engineering Undercrossing Existing Transportation Facilities calls for a great number of engineering analogy cases. With metro tunneling engineering constructed in large scale in our country, there will be more and more and complex more cases of underground adjacent engineerings, so one may well say their research is in the ascendant. It hopes to throw a minnow to catch a whale so that scholars can go deep into research such problems in the future, drawing our country's utilization of underground space resources and development of underground engineering into the way of sustainable development according to the principle of inheritance and development.