Study on Mechanism and Prevention of Slope Instability at Shallow-buried,Bedding and Unsymmetrically Loaded Tunnel Portal
Understanding the evolution mechanism of slope instability at the bedding and unsymmetrically loaded tunnel portal and studying the relationship between slope retaining structure stress and tunnel burial depth is cru-cial for slope protection.During the construction of the Shiliangzi Tunnel,the slope instability and failure occurred at the shallow-buried,bedding and unsymmetrically loaded tunnel portal.Geological mapping,borehole drilling,surface displacement monitoring,numerical simulation,and other methods were used to clarify the slope structure,physical-mechanical parameters,and deformation characteristics.Based on this,the instability mechanism of the slope at the tunnel portal was analyzed,the protection methods and measures for the slope at the bedding and unsym-metrically loaded tunnel portal were studied.Results show that the instability evolution of the slope at the shallow-buried,bedding and unsymmetrically loaded tunnel portal goes through four stages:1)reduction of interlayer shear strength,2)formation of bedding and unsymmetrical loading,3)local failure of lower slope body leading to retrogres-sive creep and cracking of back slope,4)exacerbation of deformation leading to thrust load-caused failure of the slope at the tunnel portal.With the installation of anti-slide piles and a tunnel burial depth of 16 m on the moun-tain side,the slope stability is achieved.At this depth,control over landslide deformation and pile shear force is sig-nificant.However,the effectiveness decreases significantly when the burial depth exceeds 16 m.
Bedding and unsymmetrical loadDeformation characteristicsInstability mechanismNumerical simu-lationPrevention
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