Study On Secondary Excavation Stability And Supporting Technology Of Existing Stratified Rocky Cutting High Slope In Expressway Reconstruction And Extension

In the reconstruction and expansion project of highway,the secondary excavation problem of existing high slope is often encountered,which is affected by the types of slope rock and soil,engineering and hydrogeological characteristics,excavation and support methods,and road operation safety.The secondary excavation stability and deformation control of high slope is a very special and complicated geotechnical engineering problem.This paper combines the secondary excavation of a high-slope rock with Bedding gentle dip in the reconstruction and expansion project of Laiwu-Linyi section of Beijing-Shanghai Expressway.The high-slope is studied twice by field bolt pull-out test and numerical simulation.The stability,deformation and stress variation characteristics during the excavation process are proposed.Below are key research findings:(1)After the unloading of the full-length cemented anchor,the drawing process shows a “secondary drawing” phenomenon.When the pulling force is applied until the unloading and retracting amount recovers,the working load of the bolt is reached,and the anchor head deforms more than the grouting body.After the deformation limit,it will enter the yield-destruction stage.During the 20-year operation period,the ultimate bearing capacity loss of the bolt is 23.93%~31.94%.(2)After the excavation of the gently inclined bedding slope,the horizontal deformation is mainly caused by the horizontal deformation.The deformation mode is the combined failure of the trailing edge stepped-slip-sliding and the leading edge arc-sliding sliding.The excavation of the slope reduces the stability of the slope,and the stability after the slope is improved by about 10%.To a certain extent,the bolt support constrains the slope,tendency of instability.(3)The slope significantly changes the original stress state during an excavation process,forming a stepped rock layer fracture-sand layer slip deformation zone,and the step deformation zone transfers the gravity load to the slope in the form of pile-up.The middle and lower rock layers of the surface create a curved deformation zone of the gently inclined rock layer.The secondary excavation disturbance of the slope further develops the two deformation zones.The displacement caused by the secondary excavation is not as remarkable as that of one excavation,but The secondary excavation loose zone range is greater than one excavation.(4)The design parameters such as the density,length,setting angle and prestress of the anchor and anchor cable are positively correlated with the slope stability,and there are optimal design values.If the optimal design value is exceeded,the bolt and anchor cable will be lowered support effect.(5)The axial force of the bolt support is convex.The stability of the secondary excavation surface is improved by the anchor cable-anchor and the anchor state is weakened.The anchor cable is anchored in the active reinforcement state.The axial force distribution of the section is curved and attenuated.It is attenuated by more than 90% in the range of 3~4m,and the anchor tail is basically unstressed.The anchored anchor cable in the passive reinforcement state is convexly distributed,and the axial force level is significant greater than the active reinforcement state anchor cable.(6)Based on the measured working load value of anchor bolt in first excavation slope,when the working stress of anchor bolt and anchor cable measured in the second excavation slope is close to the judgement load,the early warning of slope instability is given.The research results can be used for the secondary excavation of similar slopes in the highway reconstruction and expansion project construction provides theoretical reference and technical support.