Abstract
The large deformation of soft rock tunnel is one of the key problems to be overcome in the tunnel construction stage. In the present study, the deformation mechanism of a representative tunnel and some related countermeasures are investigated using field tests and engineering geological analysis. Owing to the scarce performances of methods based on other criteria such as small pipe spacing, anchor bolt length and steel frame spacing, a new support scheme is implemented and optimized. Results show that shear failure and bedding sliding are produced under high horizontal stress conditions. The low strength of the surrounding rock results in the uneven convergence of both sides of the tunnel. With the aforementioned new support scheme, however, most of such problems can be mitigated leading to good stability properties and ensuing economic advantages.
Highlights
The large deformation of soft rock often occurs in numerous tunnels during the tunnel development in the world [1,2], which can lead to the impediment of the construction schedule and delay the construction period
The pressure of the surrounding rock at the left arch foot decreased at the 29th day, and it tended to be stable at about the 33rd day
The main conclusions are as following: 1. The horizontal convergence of the deformation in the tunnel is large and it is asymmetric convergence on the left and right waists, which is caused by the effect of the rock strength, the insitu stress, and the parameters of the support scheme
Summary
The large deformation of soft rock often occurs in numerous tunnels during the tunnel development in the world [1,2], which can lead to the impediment of the construction schedule and delay the construction period. Due to the difference of geological environments, the large deformation of soft rock tunnel has its own characteristics, so it is necessary to study the deformation mechanism and associated supporting measures of the tunnel. Hoek et al [2] defined the soft rock as rock with uniaxial compressive strength less than 25 MPa in 1981. He [3] further proposed the definition of the soft rock systematically and summarized the deformation causes of different soft rocks. They proposed that the large deformation mechanism of the soft rock can be divided into three categories including thirteen subcategories, which were physicochemical expansion, stress expansion and structural deformation. The large deformation mechanism and support problems of the soft rock tunnels are still required to be further studied
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