Development Of Anisotropic Constitutive Model Of Phyllite And Its Application In Tunnel Engineering

Phyllite strata has significant properties of strength anisotropy and deformation anisotropy,which has an important impact on the construction mechanical characteristics of phyllite tunnel.At present,the design and construction methods in engineering are generally based on the isotropy theory and the influence of stratum anisotropy on mechanical behavior of tunnel excavation is neglected.Take the tunnel engineering with high geostress and steeply dipping phyllite strata as the background,using X-ray Diffraction(XRD),Scanning Electron Microscope(SEM)and Transmission Electron Microscope(TEM),by means of theoretical derivation,constitutive model development,disaster investigation and numerical simulation,the mechanical behavior of tunnel in phyllite strata is studied in depth.The main research works and achievements in this paper are summarized as follows:(1)The main mineral components of chlorite phyllite are quartz,chlorite and illite,etc.The phyllite has a "thin sheet" microstructure and phyllite can be assumed to laminated material cemented with one type of thin isotropic mineral sheet,which makes the macroscopic mechanical behaviors of phyllite showing transversely isotropic anisotropic characteristics;(2)The theoretical elaboration,further development and numerical verification of a incremental elastio-plastic constitutive model(transversely isotropic elastio-plastic ubiquitous-joint model),which is capable of reproducing the strength anisotropy and deformation anisotropy of stratified rock mass,are carried out.The results are shown that the constitutive model can accurately reproducing the phyllite's features;(3)The validity about the single plane of weakness theory for the description of strength anisotropy of stratified rock mass is discussed.The theoretical formulas of directional elastic modulus surface and elastic deformation anisotropic curve of transversely isotropic materials are derived.And it is also explained that the elastic deformation anisotropy curve type of stratified rock mass is mainly influenced by the cross shear modulus;(4)The theory is applied to Yangjiaping tunnel of Cheng-Lan railway.The construction process of railway tunnel with steeply dipping phyllite strata,whose initial stress state is dominated by horizontal geostress perpendicular to the tunnel axis,is simulated using three-dimensional numerical method.The destruction mechanism of the tunnel with steeply dipping phyllite strata was revealed and the validity of this model was verified;(5)Based on the single plane of weakness theory,the equation of ultimate lateral pressure coefficient of stratified rock mass is derived.Based on the constitutive model developed in this paper,the mechanical behavior of unsupported circular tunnels in phyllite strata with different lateral pressure coefficient and stratum occurrence is analyzed and its mechanical behavior under second stress state is summarized.The research results in this paper can provide useful references for the similar underground engineering in phyllite strata.