تحلیل رانش زمین به دلیل عبور ایستگاه مترو با بزرگ شدن تونل های حفاظ تحت ساخت و تجزیه و تحلیل حساسیت پارامتر آن

Using expanding excavation based on shield tunnel can be regarded as a new approach to construct a metro station, especially when traditional methods cannot be implemented. This paper focuses on the ground movement property caused by shield tunneling and expanding construction. Ground movement property and construction influence scope, which happens during the construction process, are obtained by large numbers of numerical calculations and monitoring measurements. Results show that expanding excavation is the main factor which affects ground movement, and its influence will increase as the stability of surrounding rock deteriorates. Besides, horizontal displacement and vertical displacement (uneven settlement) are the two important factors which lead to building deformation and cracks; therefore, more attention should be given to these areas where the maximum displacement may occur during the construction process. Analysis of the two parameters, length to diameter ratio and depth to diameter ratio, indicates their relationship with safety of tunnel and building. Influence degree and scope of ground settlement are obtained due to change of the two parameters. The practical importance of this analysis is that we can judge whether building and tunnel are in a dangerous zone and thereby adopt relevant pre-reinforcements to ensure their safety. Later with the comparison of numerical simulation and in-situ data, we verify the accuracy of simulation.

At present, when building a metro station, conventional processes and technologies cannot be implemented smoothly because of restrictions caused by surrounding environment (e.g., launching and receiving shafts cannot be constructed on the line because of the existence of buildings and underground utilities). However, these problems can be effectively solved when the shield tunneling method or the expanding shield tunnels method are utilized to construct a metro station directly. Meanwhile, construction period can be shortened significantly and construction quality will also be improved, which will definitely bring practical and economic significance (Lu, 2007, Li, 2007 and Liu, 2010). Both shield tunneling and expanding construction will induce disturbance to the surrounding rock and cause ground movement; however, what exactly the two processes “contribute” to the ground movement is still unknown; besides, considering the existence of a building, when H/D and L/D change (H is the depth of tunnel, L is the horizontal distance between tunnel and building, D is diameter of shield tunnel), the influence of two construction processes on stratum movement is also unknown. Currently, some published papers, which are related to this subject, are mostly about construction schemes. For example, Nakamura et al. (2003) introduced a method to excavate a rectangular cross-section for the Kyoto Municipal Subway. Shirai et al. (2005) reported a new technology, namely using the large-diameter curved pipe roof construction method to construct large underground spaces. Kunihiko and Kenichi et al. (2006) presented that a large diameter shield tunnel was used for the construction of subway, and he also described a non-cut-and-cover method which was used for cutting the ground between two large-diameter shield tunnels. Hiroshi et al. (2006) showed that shield tunneling is utilized to build the Central Circular Shinjuku Route of Tokyo Metropolitan Expressway, and the space enlargement method was adopted to construct branch connections and ramps. Hiroshi (2007) described an Open-Cut Method which was used for the construction of enlarging road shield tunnel. However, there is little research about the effect of this construction method on the ground movement property are few. This paper presents a detailed research on such problems, with the background of a left line platform tunnel of Dongshankou metro station Guangzhou metro line 6 in China.

In this article, at first we analyse the ground movement property caused by shield tunneling and expanding excavation. Considering the different formation condition of China, we chose three different formation conditions to analyse; and then we conducted some research on parameter sensitivity analysis about L/D and H/D under existence of building. Finally, accuracy of numerical simulation is verified by comparing with in situ monitoring data. The results of the present study are summarized below: – For the two factors of shield driving and expanding excavation, expanding excavation is the principal factor which influences ground movement. This influence is particularly obvious when the stability of surrounding rock becomes deteriorated. E.g., for different formation condition, ground settlement caused by expanding construction account for 60% (IV-grade), 70% (V-grade) and 75% (VI-grade) of the total settlement, see Table 4. – Research indicates that building deformation and cracks are mainly caused by uneven settlement, stretch and squeeze of stratum. Therefore, monitoring measurement is extremely important, especially for these positions where the maximum displacement happened, see Table 3. – By comparing with Table 5, it is easy for us to predict and judge the safety of a tunnel and any adjacent building before construction, which is particularly important in urban area. Further, this study can help us to determine whether it is essential to take some relevant pre-reinforcement measures to ensure construction safety. At present, we have successfully applied this conclusion to Dongshankou metro station. – Analysis is performed on the basis of both in situ data and numerical simulation, which can assist us to verify the accuracy of numerical data and to understand the influence of construction on ground movement. The use of shield tunneling and expanding excavation for metro station construction is a new construction method in China. Besides, Dongshankou station is the first station which adopts this method to construct a metro station. There are not too many experiences which can be used for reference; therefore, we hope we can supply some useful information to the following projects.