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Geomechanics and Engineering Volume 34, Number 5, September10 2023 , pages 491-505 DOI: https://doi.org/10.12989/gae.2023.34.5.491 |
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Stability of rectangular tunnel in improved soil surrounded by soft clay |
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Siddharth Pandey and Akanksha Tyagi
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| Abstract | ||
| The practical usage of underground space and demand for vehicular tunnels necessitate the construction of non-circular wide rectangular tunnels. However, constructing large tunnels in soft clayey soil conditions with no ground improvement can lead to excessive ground deformations and collapse. In recent years, in situ ground improvement techniques such as jet grouting and deep cement mixing are often utilized to perform cement-stabilisation around the tunnel boundary to prevent large deformations and failure. This paper discusses the stability characteristics and failure behaviour of a wide rectangular tunnel in cement-treated soft clays. First, the plane strain finite element model is developed and validated with the results of centrifuge model tests available in the past literature. The critical tunnel support pressures computed from the numerical study are found to be in good agreement with those of centrifuge model tests. The influence of varying strength and thickness of improved soil surround, and cover depth are studied on the stability and failure modes of a rectangular tunnel. It is observed that the failure behaviour of the tunnel in improved soil surround depends on the ratio of the strength of improved soil surround to the strength of surrounding soil, i.e., qui/qus, rather than just qui. For low qui/qus ratios, the stability increases with the cover; however, for the high strength improved soil surrounds with qui >> qus, the stability decreases with the cover. The failure chart, modified stability equation, and stability chart are also proposed as preliminary design guidelines for constructing rectangular tunnels in the improved soil surrounded by soft clays. | ||
| Key Words | ||
| cement-treated clays; cover; failure behaviour; rectangular tunnel; stability | ||
| Address | ||
| Siddharth Pandey and Akanksha Tyagi: Department of Civil Engineering, Indian Institute of Technology Roorkee, India, 247667 | ||