Earth pressure balance shield tunneling in sandy gravel deposits: a case study of application of soil conditioning
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ORIGINAL PAPER
Earth pressure balance shield tunneling in sandy gravel deposits: a case study of application of soil conditioning Yingjie Wei 1,2,3 & Yuyou Yang 1
&
Mingjiang Tao 4 & Duli Wang 3 & Yuxin Jie 2
Received: 1 November 2019 / Accepted: 20 May 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Earth pressure balance shield (EPBS) tunneling techniques originally developed for fine-grained soil deposits have been adopted in a growing number of tunneling projects where challenging geological conditions, such as those with coarse-grained soils, are encountered. However, successful application of EPBS tunneling with soil conditioning could fully address technical challenges during tunneling in coarse-grained strata, such as tunnel face instability, blocking or clogging, severe wear of cutting tools, and low-effiency tunneling. In this paper, a comprehensive case study is presented that EPBS tunneling was successfully used in Beijing Metro Xijiao line with the aid of soil conditioning, where sandy gravel deposit with unfavorable particle size distribution, poor flowabilty, high permeability, and high abrasiveness was encountered. A series of both laboratory and in situ testing was carried to evaluate foaming agents, develop soil conditioning schemes, and verify their effectiveness of modifying the sandy gravel for EPBS tunneling purpose. The homogeneity, workability, permeability, and abrasivity of foamed soils were tested in the laboratory to develop soil conditioning schemes while the effectiveness of soil conditioning schemes during in situ tunneling was further evaluated with slump test and visual inspection. Parameters, such as foam expansion ratio (FER), half-life period, and foam injection ratio (FIR), which are used to evaluate the behavior of foaming agent and performance of conditioning schemes and tunneling schemes, were also discussed. Keywords Sandy gravel . EPBS . Foam agent . Soil conditioning . Grey system theory
Introduction Various tunnel boring machines (TBMs), especially closed mode shield machines with earth pressure support (namely, earth pressure balance shield (EPBS)), have been increasingly used in urban areas in China because of the rapid development of metro and utility tunnel construction in recent years. In soft ground tunneling, an EPBS machine can be used to excavate soils quickly by using various cutting tools (e.g., nose cone, * Yuyou Yang [email protected] Yingjie Wei [email protected] Mingjiang Tao [email protected]
knife bit, scraper, disc cutter, ripper tooth), during which the tunnel face is steadily supported through the use of the excavated soils with earth pressure in the chamber. Meanwhile, the pressurized soils in the chamber can be transported into the area of the atmospheric pressure through a screw conveyor. Therefore, there is a pressure difference between inside and outside of the chamber when EPBS advances during the process of excavating soils at the tunnel face and expelling soils through a screw conveyor. EPBS machines and
