Research On The Influence Of Excavation Construction Of Subway Station To Adjacent Buildings

Metro lines and stations have been built in35cities of China, which is one of the countries with the most metro projects in the world. The excavations of numerous metro stations have some impacts on the surrounding environment, especially the settlement and deformation of those existing building. For the geological conditions, excavation programs and building structures are difficult to be reflected by traditional theories and empirical methods, the influence principle of excavation to surrounding buildings is very complicated. Accordingly, it is difficult to predict the subsidence and deformation or judge the risk of those buildings.The impact of excavation in sand and stiff clay to surrounding high-rise buildings are studied based on numerical simulation, measurement and analysis, parametric inversion and fuzzy risk assessment, the methods of which are applied in the excavations of subway stations. Aiming at the uncertainty of prediction results of building settlements, this paper is written according to the technical route of "finding problem, measurement verification, increasing accuracy, fuzzy risk assessment", and the major contents and achievements of this study are as follows:(1) Numerical simulation. The empirical methods in simulating excavation and surrounding buildings were summarized and analysed to confirm the simulation schemes of key contents, such as soil constitutive model, building, computational domain, enclosure structure and ground stress. The combination of different schemes was used to simulate those uncertain contents. The software Abaqus was used to establish three finite element models of the excavation of a subway station, and some significant simulation conclusions were obtained in this application.Achievements:A procedure of dimension calculation of excavation model was proposed. Different schemes were used to simulate the uncertain elastic modulus of soil, seepage, inner support. The uncertain value ranges of building settlements and inclinations were revealed by the application results. The simulation factors of building settlements in descending order were the schemes of precipitation, soil parameters and inner support, and there might be inverse relationship between building settlements and elastic modulus of soil.(2) Measurement and analysis. The measured data of groundwater level, lateral displacement of diaphragm wall, ground settlements, building settlements and inclinations of a subway station were analysed statistically, and were contrasted with simulation results and relevant statistics experiences.Achievements:The simulation schemes and conclusions of this study were proved to be reasonable. The measured settlements and inclinations of buildings adjacent to excavation were smaller in the dual structure of sand and stiff clay. There were inverse relationship between the maximum settlements, differential settlements and the length-width ratios of buildings, but proportional relationship between the maximum inclinations, deflection ratios of buildings and the distances from buildings to excavation.(3) Parametric inversion and settlements forecast. The characteristics of different methods of experimental design were contrasted. Based on the advantage of principle and application, the simulation experiments were performed in terms of uniform design. Based on the relationship between simulation settlements and elastic modulus of soil, the simple and reasonable method was choised to regress parameters. To forecast the settlements outside excavation in subsequent construction stages, numerical simulation and parametric inversion were applied in the construction monitoring of a subway station.Achievements:Uniform design was introduced into parametric inversion and settlements forecast of excavation for the first time, and the advantage of uniform design and numerical simulation was reflected by reducing test number with high precistion. There were linear relationships between elastic modulus of soil and simulation settlements of some measuring points, when other conditions were unchanged. The accuracy of forecasting settlements outside excavation was higher than that of traditional experience.(4) Fuzzy risk assessment. The risk of building was synthetically evaluated by the maximum settlements, inclinations, damage coefficient of building. The interval numbers of three parameters were introduced to describe the uncertainty of evaluation indexes. Based on the characteristics of building risk and interval numbers of three parameters, an evaluation procedure of building risk was proposed. Risk assessment was applied in the masonry structure which was nearest to a subway station.Achievements:A simplified risk judgment model of buildings adjacent to excavation was proposed. The damage coefficient was introduced and revised by relevant standards to describe the damage condition of building. The interval numbers of three parameters were introduced to describe evaluation indexes, and the integral solutions of possibility degree were calculated. The fuzzy membership functions of S-type were proposed. The super weight method was introduced and revised. The clear, uniform and reasonable result in risk judgment application was better than that of traditional experience.