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Ground movements due to tunneling are becoming increasingly critical as buildings are located around construction sites. This study proposes a new combined reinforcement method using a foundation grouting oblique pipe roof. The former improves the bearing capacity of the subsoil, and the latter blocks the transmission of soil deformation, which weakens the influence of construction during overlapped tunnel under-crossing. Based on this new method, a case study of the shield tunneling response to an old building in Line 6 of China’s Chengdu Metro is presented. Additionally, three-dimensional numerical models without reinforcement, traditional foundation grouting reinforcement, and the new combined reinforcement schemes were compared. The numerical simulation performance was verified using a set of field instrumentation data, which demonstrated that the old building response to the overlapped tunnels was under control, and the maximum deformation, angular distortion, and principal tensile strain of the building were 5.25 mm, 5.10 × 10–6 rad/m, and 0.0081%, respectively. Compared with the traditional reinforcement scheme, the deformation, angular distortion, and principal tensile strain in the combined reinforcement scheme were reduced by 54.78%, 71.02%, and 70.22%, respectively. These results have important implications for the design and construction of shield tunnels and their response to old buildings.

A dense network of underground tunnels usually makes subsequent tunnels cross existing tunnels in the process of urbanization. In this study, we mainly study the deformation of the subway line 11 caused by the under-crossing of the Qianhai–Nanshan Integrated Drainage Deep Tunnel in Shenzhen. We analyzed the process of displacement during the subsequent tunnel under-crossing the subway line 11 according to the displacement monitoring data. Our results demonstrate that deformation detection is an effective measure for controlling the impact of the subsequent tunnel under-crossing subway tunnels. The aim of this paper may provide guidelines for some existing tunnels that are under-crossed by subsequent tunnels with similar conditions. [ABSTRACT FROM AUTHOR]

Extra care should be taken when new tunnels pass through an existing tunnel. If it is not handled properly, this will affect the operation safety of the existing line, and bring security risks to the train's operation. In order to study the impact of an under-crossing parallel double-line shield tunnel on the existing shield tunnel structure, the influence of tunnel construction on the deformation of overlying strata was analyzed, and the formula for estimating the formation settlement at depth Z below the surface, caused by the excavation of a double-tunnel parallel tunnel, was deduced. Then, a series of three-dimensional finite element numerical simulations were carried out. We analyzed and systematically studied the adverse effects of the tunnel structure of Guangzhou subway Line 5, caused by the tunneling of subway Line 18, evaluated its structure and operational safety, and provided suggestions for site construction. This research demonstrates the following conclusions. (1) The tunnel structures of subway Line 5 and Line 18 are mainly in the strongly weathered argillaceous siltstone stratum, and lightly weathered argillaceous siltstone stratum, respectively, and the stratum where the Line 18 tunnel is located is relatively safe. (2) According to three-dimensional finite element numerical simulation analysis, during the shield-tunneling process of subway Line 18, the maximum X horizontal displacement, the maximum Y horizontal displacement, and the maximum Z vertical displacement of the tunnel structure in subway Line 5 are 1.09, 3.50, and 4.55 mm, respectively. It is considered that the impact of the shield-tunnel penetration of subway Line 18 on the tunnel structure of subway Line 5 is relatively controllable, and does not affect the structure and operational safety. (3) It is suggested that settlement monitoring should be strengthened within the range of 12 m (about 1.5 tunnel diameter D). before and after the excavation axis of the underpass tunnel, and it is necessary to carry out local reinforcement treatment, to prevent adverse effects on the operation of the existing tunnel. [ABSTRACT FROM AUTHOR]

Extra care should be taken when new tunnels pass through an existing tunnel. If it is not handled properly, this will affect the operation safety of the existing line, and bring security risks to the train’s operation. In order to study the impact of an under-crossing parallel double-line shield tunnel on the existing shield tunnel structure, the influence of tunnel construction on the deformation of overlying strata was analyzed, and the formula for estimating the formation settlement at depth Z below the surface, caused by the excavation of a double-tunnel parallel tunnel, was deduced. Then, a series of three-dimensional finite element numerical simulations were carried out. We analyzed and systematically studied the adverse effects of the tunnel structure of Guangzhou subway Line 5, caused by the tunneling of subway Line 18, evaluated its structure and operational safety, and provided suggestions for site construction. This research demonstrates the following conclusions. (1) The tunnel structures of subway Line 5 and Line 18 are mainly in the strongly weathered argillaceous siltstone stratum, and lightly weathered argillaceous siltstone stratum, respectively, and the stratum where the Line 18 tunnel is located is relatively safe. (2) According to three-dimensional finite element numerical simulation analysis, during the shield-tunneling process of subway Line 18, the maximum X horizontal displacement, the maximum Y horizontal displacement, and the maximum Z vertical displacement of the tunnel structure in subway Line 5 are 1.09, 3.50, and 4.55 mm, respectively. It is considered that the impact of the shield-tunnel penetration of subway Line 18 on the tunnel structure of subway Line 5 is relatively controllable, and does not affect the structure and operational safety. (3) It is suggested that settlement monitoring should be strengthened within the range of 12 m (about 1.5 tunnel diameter D). before and after the excavation axis of the underpass tunnel, and it is necessary to carry out local reinforcement treatment, to prevent adverse effects on the operation of the existing tunnel.

A section of closely spaced twin tunnels at Shangmeilin station on Shenzhen metro line 9 was excavated by the shield tunneling method. Part of this section lies closely beneath the tunnel servicing Metro line 4. Due to restrictions on ground surface to control the extra settlement of the existing tunnel in the area, an in-tunnel grouting protection method was adopted in combination with the shield method. This method greatly reduced the effect on the existing tunnels when building the twin tunnels underneath. The settlement of and stress on the existing tunnels associated with the construction of the new tunnels were systematically monitored. Because of the twice under-crossing process, the excavation of twin tunnels had a superposed influence on the existing tunnel and surrounding soil. The behavior of the overlying tunnel was analyzed based on instrumentation records obtained from the project. The settlement profile of the existing structure displayed a “V” shape after the first under-crossing but a “W” shape after the second. The hoop stress of the existing tunnel induced by shield tunneling below had beneficial effects on the stress state of the tunnel structure. By contrast, the longitudinal stress exerts a bending moment on the existing tunnel, with a large tensile stress that had adverse effects on its structure. Based on the monitored data, three deformation modes are proposed to describe the behavior of the existing tunnel. In addition, the differences between the two under-crossing processes are discussed; both the ground loss ratio and width parameter of the settlement trough in the second profile were larger than those of the first profile due to the decrease in soil stability. [ABSTRACT FROM AUTHOR]

• A model of a large-diameter slurry shield crossing an existing tunnel is developed. • Shield crossing obliquely causes an offset of existing tunnel settlement trough. • The solution of semi-infinite saturated soil is applied to deformation prediction. • Safety indicators are provided as a preliminary evaluation tool for tunnel design. With the expansion of underground space networks, new tunnels especially large-diameter shields under-crossing existing tunnels have been commonly practiced. To obtain a better understanding of the effect of large-diameter slurry shield under-crossing on the existing tunnel and provide a quick and effective tool for evaluating the deformation behaviors of the existing tunnel before construction, in this study a simplified analytical method is proposed. Based on the two-stage method, and considering the characteristics of construction factors such as additional thrust on the shield excavation face of the slurry shield machine, friction force of the shield shell, and grouting pressure of the shield tail, deformation of the existing tunnel caused by the crossing of the large-diameter slurry shield in saturated soil is calculated. The proposed method is verified with field measurement data from a case study. A parametric analysis is conducted to study the influence of typical factors on tunnel responses, including longitudinal bending stiffness, elastic modulus, clearance between two tunnels, and shield crossing angle. The parametric study indicates a significant influence of the crossing angle on maximum settlement and the influence range of settlement of the existing tunnel. Recommendations for safe values of shield crossing clearance are given. The proposed analytical solution can be used as a reference to predict the potential risk of new large-diameter slurry shield crossing on the existing tunnel in engineering practices. [ABSTRACT FROM AUTHOR]