Mechanical Characteristics of Tunnel Structure after Softening of Gently Inclined Layered Phyllite Surrounding Rock with Water
Layered phyllite have the characteristics of orthorhombic anisotropy,and water-softening and argillization.The strength of the rock mass will be greatly attenuated under the water-rock interaction,leading to increased load on the support structure and deterioration of its load-bearing performance,posing a huge challenge to the safety of tunnel structures.In this paper,the X-ray diffraction(XRD),scanning electron microscopy(SEM),and disintegration characteristics tests on layered phyllite are carried out to find out the softening characteristics of layered phyllite when encountering water.A concrete damaged plasticity(CDP)model is introduced to characterize the damage and deterioration behavior of concrete,a cohesive zone model(CZM)is introduced to characterize the shear slip behavior of bedding planes,and then the numerical models of gently inclined layered rock mass are established.Considering the strength decrease caused by the water-softening effect of layered phyllite,the evolution of mechanical behavior and bearing capacity of tunnel structure are analyzed under the water-softening effect of the layered surrounding rock with different bedding plane angles.The research results show that the high content of clay minerals in phyllite provides a material basis for its softening when exposed to water.The clay minerals in the cracks absorb water and expand,causing the cracks to further open and extend,cutting the rock sample into fragments.After the surrounding rock softens,there is significant stress concentration in the inverted arch and the tunnel feet on both sides.There is a significant asymmetry in the distribution of compressive stresses in the lining structure.The maximum compressive stress of the lining structure significantly increases after the surrounding rock softens,with an increase of over 40％.The increase in inclination angle of the rock layer increases the compression damage of the lining after softening the surrounding rock.The use of advanced reinforcement can effectively reduce the deformation of tunnels when surrounding rock encountering water,and the reinforcement effect of advanced grouting is better than that of advanced bolts.
tunnel engineeringgently inclined layered phyllitewater-softeningtunnel structuremechanical characteristicsconcrete damaged plasticitycohesive zone model
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