Analysis of ground movement due to metro station driven with enlarging shield tunnels under building and its parameter sensitivity analysis

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Abstract

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.

Highlights

► We get the ground movement property caused by shield tunneling and expanding excavation. ► Ground movement property happened in different geological conditions are obtained. ► Relationship between length to diameter ratio, depth to diameter ratio and safety of tunnel and building are gained.

Introduction

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, 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.

Section snippets

Engineering situation

The use of expanding excavation based on shield tunnels is adopted in an under-construction left line platform tunnel of Dongshankou metro station Guangzhou metro line 6, China. The distance from the tunnel vault to the ground surface is 18.800–19.845 m, and the distance between invert and ground is 27.045–27.534 m. The left line of station crosses a six storied building of the Second Light Industry Group. The terrane through which the left line platform tunnel passes consists mainly of

Model building

According to the construction scheme and geological data, FLAC3D is used to build a three-dimensional model. Model dimension is 98 m × 50 m × 35 m, number of grid cells are 89,000, see Fig. 2. When modeling, shell element and cable element are used to simulate primary lining and rock bolts; besides we adopt beam element to simulate columns and beams. The live load of every floor is according to the code for design of building foundation (The National Standards Compilation Group of People’s Republic of

Ground movement property induced by shield tunneling and expanding excavation

In urban areas, it is essential to protect pre-existing structures and underground utilities from damage due to ground movement caused by the construction of a metro station. Therefore, it is particularly important to know the influence degree and scope as a result of a metro station construction. This section will focus on this problem.

Parameter sensitivity analyses of ground movement under existence of building

As indicated before, length to diameter ratio (L/D) and depth to diameter ratio (H/D) are the two important factors which have a close relationship with ground movement. In this section parameter sensitivity analysis of these two factors is analysed in detail and relevant conclusions are obtained. The so-called “parameter sensitivity” that is, when one parameter is fixed, the research objective will change with variation of other parameters. Some researchers have carried out similar research on

Layout of measuring points

The station is located in the intersection between Shuqian Road and Zhongshan Road, while the platform tunnel is under the buildings of Shuqian Road. Measuring points are difficult to fix as the design drawing because of heavy traffic flow. Therefore, we make some adjustments when arranging the monitoring points, see Fig. 16.

Monitoring Results

According to exploration data, the distance between the platform tunnel of the left line and the surface is 18.80–19.85 m (H/D 2.9–3.1). The building is on the top of

Conclusions

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

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