| As a special soil in geotechnical engineering,loess has obvious characteristics of structure,collapsibility and anisotropy.With the development of economy,a large number of loess tunnels and underground engineering have been built in the loess region.During the construction of loess tunnels,the arch settlement is large and the palm surface is prone to collapse.Therefore,the deformation control of loess tunnels is one of the hot research directions in the tunnel field.At present,the design and construction schemes used in engineering are generally based on the anisotropy theory,ignoring the influence of loess anisotropy on the mechanical response during tunnel excavation.With Mianchi Highway to Xichuan Highway as the research background,the deformation control technology of loess tunnel was studied by laboratory experiment,theoretical derivation,constitutive model development and numerical simulation,considering the influence of loess anisotropy on the mechanical response of loess tunnel.The main research work and achievements of this paper are as follows:(1)The samples of YK35+957 section of Kolewan Tunnel in western Henan Province were taken from horizontal and vertical directions respectively.The differences of deformation parameters and strength parameters of undisturbed loess in horizontal and vertical directions were analyzed through laboratory consolidation tests and triaxial shear tests.The results show that the anisotropy of the loess in western Henan is significant.Under the same normal pressure,the compressibility in the horizontal direction is greater than that in the vertical direction,and the deformation modulus in the vertical direction is 1.8 times of that in the horizontal direction.The cohesion in vertical direction is 35.46% larger than that in horizontal direction,and the internal friction Angle in vertical direction is 5.05% larger than that in horizontal direction.The difference of shear strength parameters is mainly reflected in the cohesion.(2)The anisotropic constitutive model of rock and soil mass was summarized.It can be divided into anisotropic elastic model and anisotropic elastoplastic model.Transverse isotropic constitutive model is widely used in numerical simulation software.The secondary development and numerical verification of FLAC3 D ubiquitous joint constitutive model were carried out by Visual Studio 2015 platform and C++ language.The self-defined constitutive model can reflect the strength and deformation anisotropy characteristics of loess.(3)The self-defined anisotropic constitutive model was used to simulate the excavation and support process of Kolewan tunnel,and the results were compared with the isotropic model.The results show that the surrounding rock deformation is larger when loess anisotropy is considered,and the surrounding rock deformation is asymmetrical in space,and the stress concentration is obvious.(4)Based on the analysis of the control principle of tunnel surrounding rock deformation,three kinds of deformation occur in tunnel surrounding rock: face advance displacement;Face extrusion displacement;Displacement behind the face of the palm.Combined with the results of numerical simulation,the deformation control measures of surrounding rock of loess tunnel were put forward.The deformation control measures of surrounding rock in loess tunnel are as follows: applying small guide pipe and pipe shed;Face spray concrete,reserve core soil;Using step excavation method;Strengthen the initial support. |
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