Abstract
In multi-arch tunnels, the increased rock load on the concrete lining of the main tunnel and side walls due to the excavation of adjacent tunnels is critical and must be considered in the design stage. Therefore, this study estimates the rock load of a multi-arch tunnel using two-dimensional numerical analysis, considering rock mass classifications, overburden, and construction steps. The rock load is estimated using two criteria: the factor of safety and stress variable. The rock load is underestimated when the factor of safety is applied to rock mass class III. However, the stress variable method reveals a reasonable rock load as overburden increases. Particularly, the rock load is estimated to be equal to the overburden in shallow tunnels and approximately 0.7 times the tunnel width in deep tunnels. Additionally, the crack-induced rock load is computed using back analysis at the excavation completion stage of adjacent tunnels, yielding the relation between the rock load height and the deformation modulus of the rock mass. Therefore, an accurate estimation of the rock load of multi-arch tunnels emphasizes the importance of a more economical and realistic design and must be addressed in the process of performance-based tunnel design.
Highlights
In conventional tunneling, the rock load typically acts on sprayed shotcrete and installed rock bolts in the case of single-tunnel excavation
The stress variable exclusively emphasizes that, when the overburden is less than the tunnel width (H < D), the rock load must be considered equal to the overburden value, even for rock mass class III
The following conclusions are obtained from this study: 1. A multi-arch tunnel consists of multiple tunnels connected parallel to each other, and it has a
Summary
The rock load typically acts on sprayed shotcrete and installed rock bolts in the case of single-tunnel excavation. It is necessary to select a criterion to estimate the the rockbehavior and lining, complex construction steps, geometric conditions, and plastic behavior of the rock rock load for concrete lining and compare it with the numerical analysis results. It is necessary to select a criterion to estimate the rock load for concrete lining for single tunnels have been a few studies theyfor must be extended to multiand compare it with thedeveloped numerical in analysis results. The construction of a three-arch tunnel, the initial support is typically provided in the form shotcrete and rock bolts. System in a more engineered way and to potentially advance the current three-arch tunnel design
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