The Research Of The Deformation Regularity Of Tunnels Constructed By The PBA Method

With the process of urbanization in our country accelerating, some large and medium-sizedcities have been taken part in the urban subway construction actively due to relieve the problemof city traffic and promote city construction as well. Although subway construction has beenlaunched rapidly, it has sprung up several kinds of problems which we should not ignore. Inflourishing cities, constructing the subways owning to some factors such as construction andgeological conditions will not only threaten the security of the surrounding buildings and theunderground pipelines, but also influence people’s daily life. Therefore, how to improveconstruction method used to focus on control surface subsidence and how to maintain thesurrounding buildings and the underground pipelines have become major problems which weshould solve as soon as possible.Dating back from the ground excavation to the undercutting applied for concealed-diggingunderground construction, the subway construction technology in our country has developedcontinuous. By using twin side heading method to middle tunnel method, people from now onare widely used of PBA method. All these construction methods are considered settlement-based,which reflects both operability and benefit.Compared with a great number of sallow buried-tunneling methods, the PBA method notonly can better control by constructors, but also can conquer sallow buried-tunneling methodswhich depend on geological conditions. PBA method in construction, moreover, has processedseveral characteristics such as simple operation, high construction efficiency and less wasteproject. Hence, PBA method has accepted by engineering when it has appeared for several years.In order to improve PBA method influence on surface subsidence and complete the constructionway of PBA method, this thesis will make an analysis the whole procedure through combine themonitoring data from Jiu Long Shan Station in Beijing subway line14with the result of FLACnumerical simulation, striving to grasp the settlement discipline of PBA method and thenobtaining excavation in process of construction during critical period. Also, putting forward thenecessary control measures by using the settlement discipline of PBA method is able tocommand the amount of surface subsidence effectively and operate the surface buildings and the underground pipelines safely.Since the larger settlement stage has reflected on flexible retaining excavation stage, thequantity of surface subsidence in excavation stage is very important for the total amount ofsettlement. If a project can be better controlled the excavation phase of the settlement, the totalexcavation phase must be controlled. Through two modes of FLAC numerical simulation and onthe basis of viability, this article analyzes the different between two excavation methods indifferent sections to make a comparison through the quantity of settlement and security.Moreover, this thesis will mention control factors and key monitoring object in each stage inorder to service actual project and attribute to our society.