| Up to now,there are more than 35000 tunnels with a total length of 37000 kilometers in China,which constitute a super transportation network,with the total mileage ranking the first in the world.Due to many uncertainties in geotechnical engineering,there are many rock engineering problems in tunnel construction,such as large deformation of soft rock tunnel,low strength of soft rock,weak rock quality and poor bearing capacity,which greatly increases the difficulty of tunnel construction.Another problem is the failure mechanism of layered tunnel surrounding rock.Layered strata are very common in nature,whose deformation and strength characteristics are obviously different from those of homogeneous rock mass.Moreover,the research on deformation and fracture mechanism of layered strata is rather complex.For example,the deformation and fracture of layered surrounding rock with gentle dip angle(0°<α<30°)is more complex than that of horizontal and steep dip angle.The construction of tunnel cannot avoid the complex geological environment of soft and gently inclined layered rock mass.Due to the double bad geological environment,the interaction between soft rock and gently inclined layered,it is difficult to study the deformation and failure law of tunnel surrounding rock.In this paper,the combination of digital photography measurement technology and similar model test,as well as numerical simulation and theoretical analysis methods,was used to explore the deformation law of the surrounding rock in soft and gently inclined layered tunnel.The main research results are as follows:(1)Through the image calculation and analysis of Photo Infor based on digital photogrammetry,the whole process of detailed deformation and fracture of the specimen in the basic mechanical test was obtained.At the same time,the Poisson’s ratio of similar materials was obtained by the data extraction function of Post Viewer,which provided a new way to obtain the Poisson’s ratio.(2)Using the motor biaxial loading test machine,which independently developed by the research group,and combining with digital photography technology,the evolution characteristics and failure modes of surrounding rock deformation and fracture of soft and gently inclined layered tunnel were obtained.The main performance is that: firstly,the cracks and blocks appear at the vertical bedding plane of the rock layer at the vault of the layered tunnel;secondly,shear cracks appear at the spandrel of the tunnel;finally,the shear cracks develop into shear wedge by connecting with the bedding plane and the vault cracks,and then collapse.Meanwhile,the surrounding rock damage on the left side(bias side)of the tunnel is more serious because of the bedding bias.(3)According to the stress characteristics of the surrounding rock in soft and gently inclined layered tunnel in different test stages,the first layer of roof,spandrel and the second layer of roof in three failure stages were respectively simplified as mechanical models of simply supported beam,cantilever beam and simply supported beam under uniformly distributed load.Based on this,the evolution process of deformation and fracture of surrounding rock in soft and gently inclined layered tunnel was deduced intuitively.(4)Through Rhino modeling and Griddle mesh generation,the limitation of FLAC3 D modeling and the influence of the dense mesh around the tunnel hole on the calculation results can be solved.The results of numerical calculation show that the distribution of plastic zone of the surrounding rock in soft and gently inclined layered tunnel is in the shape of central symmetry with the tunnel as the center.Meanwhile,with the increase of dip angle,the plastic zone develops gradually and presents the deformation and fracture characteristics of "Z" shape distribution.From the point of view of the stress on the surrounding rock and structural surface around the tunnel,the reasons for the failure of surrounding rock around the soft and gently inclined layered tunnel were explained.Combined with the comparative analysis of model test,a better verification was obtained.The research results of this paper have a certain reference value for the related research on the deformation and fracture mode and mechanism of the surrounding rock in soft and gently inclined layered tunnel,which also has a certain guiding role in the differential design of supporting structure in such surrounding rock,as well as the safety construction of the engineering site.There are 81 figures,11 tables and 106 references in this dissertation. |
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