Study on model test and numerical simulation of layered soft rock tunnel construction with different large deformation grades
To explore the asymmetric failure characteristics of layered soft rock tunnels in complex and difficult mountainous areas,and to propose reasonable construction deformation control technologies for layered soft rock tunnels under different large deformation grades,by taking a typical layered soft rock tunnel of Jiuzhaigou—Mianyang expressway,a large deformation grade classification standard for layered soft rock tunnels in complex and difficult mountainous areas was established as the engineering background.Then a series of studies were conducted on the influence of construction methods and support patterns on the mechanical behavior of layered soft rock tunnels under different large deformation grades through model tests and numerical simulations.The research results indicate that the most unfavorable position for the spatial asymmetric distribution of stress and deformation in layered soft rock tunnels is located in the normal or tangential position of the bedding plane due to the coupling effect of stress field and soft bedding direction,and the asymmetric mechanical characteristics of the tunnel become more obvious with the increase of large deformation grade(slight,medium and strong).Additionally,there are differences in the improvement effects of construction methods and support patterns on the deformation and stress of layered soft rock tunnels under different large deformation grades.Therefore,for three types of layered soft rock tunnels with large deformation grades,the recommended construction deformation control technologies for two-step construction+single-layer primary support+short rock bolt support,three-step construction+single-layer primary support+long and short rock bolt support,and three-step reserved core soil construction+double-layer primary support+long and short rock bolt support were proposed separately.
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