Research On Control Technology Of Soft Rock Base Arch For Ballastless Track In High-speed Railway

The topography and geomorphology of mountainous areas in southwest China are complex.In the planning and construction of high-speed railway,tunnels and deep cuttings are common.Tunnels can shorten running distances and avoid large ramps.Deep cuttings can ease the longitudinal slope of lines and the control elevation of the crossing ridge for ridgecrossing lines.Therefore,tunnels and deep cuttings account for an important proportion of Railways in Southwest China.The regional geomechanical characteristics of red bed soft rock in southwest China area are complex,and the base diseases of high-speed railway occur frequently,especially base arch of tunnels and deep cuttings.This paper focuses on the control technology of soft rock base arch.Through cases analysis and numerical simulation,the control effect and variation law of soft rock base arch under different control schemes were studied,and the influence of rock conditions on the control effect were studied by changing rock parameters.The main results are as follows :(1)Thickening secondary lining,deepening inverted arch,applying prestressed anchor bolts and arranging pressure relief holes at the tunnel bottom can effectively control the base arch of tunnels.Increasing the thickness of secondary lining,the depth of inverted arch,the length of anchor bolts and the depth of pressure relief holes,or reducing the spacing between anchor bolts and pressure relief holes can improve the deformation control effect of the upper arch at the tunnel bottom.When the thickness of secondary lining,the depth of inverted arch,the length of anchor bolts and the depth of pressure relief holes increase to a certain extent,the sensitivity on base arch of tunnels to their change will be reduced.According to the numerical simulation results,the influence of the four base control technology on the base arch control rate from large to small is: Deepening inverted arch,thickening secondary lining,applying prestressed anchor bolts at the tunnel bottom,and arranging pressure relief holes at the tunnel bottom.(2)The change of rock conditions can significantly affect the control effect on the base arch of tunnels.When the lateral pressure coefficient increased,thickening secondary lining,deepening inverted arch,applying prestressed anchor bolts and arranging pressure relief holes at the tunnel bottom can maintain a good control effect.The increase of soft rock thickness had a great influence on the control effect of thickening secondary lining and arranging pressure relief holes,and the influence on the control effect of deepening inverted arch and applying prestressed anchor bolts were relatively small.(3)Pile-plate structure can effectively reduce the base arch displacement of deep cuttings.Increasing pile diameter and pile length of pile-plate structure can improve the control effect of pile-plate structure.However,with the increase of pile diameter and pile length to a certain extent,the sensitivity of base displacement to their changes decreased.(4)The timeliness of pile-plate structure is related to rock creep.After strengthening the base of the deep cutting by pile-plate structure,the base arch displacement was obviously controlled within one year,and the control rate was high.With the increase of creep time,the control effect of pile-plate structure on the base was weakened,but it can still effectively control the base arch deformation.