Seismic Damage Mechanism of Portal Slope and Lining in Mountain Tunnels
In order to explore the seismic damage mechanism of portal section of mountain tunnel and to provide reference for its rehabilitation and anti-vibration measures,a series of numerical simulations were conducted to analyze the earthquake dynamic response of the portal slope and lining of the tunnel and to study the damage mechanism,including slope cracking and slipping,rockfall and collapse,and lining cracking based on Longxi tunnel which was seriously damaged in 5.12 Wenchuan Earthquake.The results show that:1)Slope cracks were due to the horizontal seismic inertial force which exceeds the tensile strength of slope;2)The slope slipping is caused by the crack penetration where the oblique component of horizontal seismic inertia force exceeds the shear strength of slope;3)The rockfall and collapse are caused by the cumulative tensile stress in loose soil and rock which exceed the tensile strength of slope;4)The lining transverse cracks were due to the repeated tensile and compressive action of the seismic load along the axial direction,which makes the lining tensile strain accumulates and exceeds the concrete ultimate strength;5)As for the longitudinal lining cracking,the transverse seismic load makes a rapid change of additional bending moment in lining caused by direction alternates,leading to the strength reduction of concrete.
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