Optimization Analysis of Controlled Blasting for Passing through Houses at Close Range in Super‐Large Section Tunnels

The urban shallow tunnelling process in silty soil is easy to cause large displacement of surface and tunnel. Obviously, if the strata and the tunnel face are not treated by reasonable reinforcement method, instability and collapse phenomenon will be encountered during the tunnel excavation. There are a series of studies on construction methods of shallow tunnels, but these methods have limitations in silty soil. In this study, a comprehensive construction plan of the urban shallow tunnel in silty soil was proposed and applied to a case study in Fuzhou, Fujian Province in South China. The in situ monitoring tests and numerical simulation were employed to address displacement characteristics of surface and tunnel. Results indicated that the urban shallow tunnelling process could achieve good effect by dewatering of silty soil, reinforcing surface by vertical jet grouting piles, and advanced small pipes and circumferential grouting in the tunnel face; surface settlement during dewatering process accounted for about 30% of total surface settlement in silty soil; the excavation of the top heading, the middle, and lower benches had great effect on displacement of surface and tunnel for three-bench seven-step excavation method in silty soil; surface settlement troughs in silty soil were deeper and wider; lock-feet bolts had good effect on restricting horizontal convergence; and ratio of total crown settlement and total horizontal convergence was in range of 1.43∼1.59 when b/h was 0.88 in silty soil. The construction plan proposed in this paper is helpful for further study of shallow tunnel tunnelling process in silty soil.

Section: Calculation Parameters Of the Numerical Modelmentioning

confidence: 84%

Displacement Characteristics of an Urban Tunnel in Silty Soil by the Shallow Tunnelling Method

Zhang

Qiu

et al. 2020

“…e supporting structure of vault is mainly concentrated in tensile stress, and the maximum tensile stress is 4.44∼4.76 MPa. erefore, during the construction process, it is necessary to strengthen the deformation monitoring of connection between steel supporting and initial supporting [33,34,36,38], thus improving the load strength of supporting structure and resistance ability of deformation of surrounding rock. Figure 14(e) shows the relationship between the maximum principal stress of the supporting structure of the CK9 + 462 section and the excavation face distance (L 3 ).…”

Section: Horizontal Deformation Characteristics Of Caverns ①mentioning

confidence: 99%

“…erefore, it is of great significance to effectively control the excavation spacing of different caverns to guide the safe construction of large-section and neighborhood tunnels. However, there is little research on the optimization of parallel tunnel construction parameters [4,[34][35][36].…”

Section: Introductionmentioning

confidence: 99%

Optimization of Construction Parameters and Deformation Characteristics of Large‐Section Loess Tunnel: A Case Study from Xi’an Metro

Zhao

Cheng

Song

et al. 2021

Self Cite

Loess geological tunnels are characterized by weak geological structure and poor self-stability of surrounding rock, so effectively controlling the excavation face distances of different caverns is of great significance for guiding the safe construction of large-section tunnels. Based on the excavation of large-section loess tunnel from Xi’an Metro Line 4, the optimal excavation face distance is determined based on Midas numerical model. Then, the surface settlement and horizontal deformation are analyzed based on monitoring data, and, finally, the rationality of excavation face distance is verified. The results show that the influence of excavation face distance on surface settlement, vault settlement, and horizontal deformation is consistent. The surface settlement mainly occurs in the range of −20∼20 m from the tunnel centerline and the settlement trough formed has asymmetric characteristics. The vault settlement and horizontal deformation undergo first a rapid settlement and then a slow settlement. The connection between initial support and middle partition is mainly tensile stress and the middle and bottom parts of the supporting structure are mainly compressive stress. Numerical results suggest that the optimal excavation faces distance of L1, L2, and L3 which can be 4, 9, and 9 m, respectively. Construction monitoring data show that the double-sides heading method has a significant effect on surface settlement, vault settlement, and horizontal deformation. The surface settlement occurs within the range of −17∼6 m from the tunnel centerline. The maximum vault settlement and horizontal deformation are 73.00% and 65.50% of the maximum allowable. It can be seen that the actual excavation parameters optimized by Midas numerical model have high reliability.

“…erefore, in order to ensure the safety of pile structure, it is essential to take some measures, among which shield construction parameters should be optimized first. According to previous experience and references [55][56][57][58], the disturbance of shield tunneling to soils can be reduced by controlling the face support pressure (200 kPa), synchronous grouting pressure (250 kPa), and jacking force (3500 kPa). In addition, the effective schemes to substantially reduce the influence caused by tunneling are reinforcement of soil or adjacent pile itself, isolation, and pile foundation underpinning.…”

Section: Selection Of Protective Schemesmentioning

confidence: 99%

A Comparative Study of Protective Schemes for Shield Tunneling Adjacent to Pile Groups

Lai

et al. 2020

Shield tunneling adjacent to pile groups is always an unavoidable problem in urban metro construction. A case was found in the project of Tianjin Metro Line 7, where a shield tunnel would be constructed near the existing pile groups of Shiyou Bridge. The whole shield tunnel is close to pile groups, and the minimum distance is only 0.8 m. Therefore, four kinds of protective schemes are proposed in this paper. It is vital to select an appropriate protective scheme to guarantee the safety during the tunnel construction. In this study, the main mechanical characteristic and physical parameters of site soil were obtained through laboratory tests. Besides, the three-dimensional finite element method was carried out to compare and analyze the effectiveness of the protective schemes in mitigating the effects of tunneling on adjacent pile groups. The results show that the deep-hole grouting scheme has better control effect on the lateral deformation and bending moment of piles, while the pile foundation underpinning scheme has better effectiveness on reducing the settlement of bridge structure and ground deformation. Finally, the deep-hole grouting reinforcement scheme will be adopted to ensure the shield passing through the pile groups smoothly.