Stability Analysis Of Palm Face In Overhanging Section Of Transverse Passage With Shallow Buried And Concealed Excavation Method

During the excavation of the main line of metro,when the surface space around the main line is limited,engineers need to excavate cross passages with elevation section in order to provide multiple excavation faces for the main line.Because of the particularity of the elevation section of the transverse passage,the pre-supporting structure has the same elevation angle as the elevation section.During the excavation of the face,the surrounding rock above the oblique face tends to slide downward,and the ability of the pre-support structure with the upward lifting angle to resist the downward sliding of the surrounding rock decreases,which has a negative impact on the stability of the upper step face of the lifting section.At present,there is no relevant research on the stability of the upper step face of the upper segmental section in the middle-lift section of weak soil layer at home and abroad.Based on the construction background of the elevation section of No.1 crossing passage in Mujie Section of Bid 01 of Beijing Metro Line 19,this paper studies the pre-support mode suitable for the elevation section of the crossing passage through Midas GTS numerical simulation software,and studies the elevation angle and surrounding rock of the elevation section under this support mode.The influence of internal friction angle and cohesion of surrounding rock on the stability of upper step face of upper partition in lifting section.The following conclusions are drawn:(1)Compared with the pre-supporting structure of advance small pipe grouting,the presupporting structure of pipe shed grouting can greatly improve the stability of the upper step face for the upper partition of the lifting section.(2)When pipe roof grouting is used as pre-supporting structure,with the increase of the elevation angle of the cross-channel elevation section,the surrounding rock in the plastic yield state in front of the face increases;the surrounding rock failure in the tensile failure state at the bottom of the face extends obliquely above the face with the increase of the elevation angle.The instability of palm surface occurs in the form of shear failure at the bottom of palm surface.(3)Longitudinal extrusion displacement of palm face increases with the increase of elevation angle.The larger the lifting angle is,the more significant the change of cohesion and internal friction angle per unit scale has on the longitudinal extrusion displacement of the palm face.(4)In order to provide a theoretical basis for the construction of the elevation section of the cross passage in the future,this paper summarizes the variation law of the extrusion displacement of the face of the elevation section under different surrounding rock cohesion and internal friction angle.