| When the varying cross-section tunnel with large span crossing the steep thin bedded phyllite rock with high geo-stress,influenced by the high initial geo-stress,weak steep thin bedded phyllite surrounding rock and complex type of tunnel structures,the large deformation is extremely easy to occur during the construction process.Therefore,the study of deformation law and deformation control measures of varying cross-section tunnel with large span and high geo-stress has definitely important engineering value and significance.The paper is based on the transition section between the single hole double line and double hole single line in Yangjiaping tunnel of Cheng-Lan railway as a project background.The deformation mechanism and deformation law of the tunnel were studied by theoretical analysis and numerical simulation and the deformation control measures for this project is proposed.The main research contents and results are as follows:(1)According to the deformation spatiotemporal effect of tunnel during construction,the theoretical closed-form solution of construction deformation of tunnel in steep thin bedded soft rock with high geo-stress was derived.The results revealed that,the deformation of tunnel in steep thin bedded soft rock with high geo-stress is a dynamic changing process over time and space.The deformation increases with time,duration of which is long and the convergence speed of which is slow.(2)The research,which was developed from geological conditions of surrounding rock,the deformation characteristics of soft rock and the effect construction,revealed the deformation mechanism of construction of the tunnel in steep thin bedded soft rock with high geo-stress.The results revealed that,the deformations of construction of the tunnel in steep thin bedded soft rock with high geo-stress were controlled by structure character of surrounding rock,geo-stress level,disturbance of construction,bearing capacity of support structure and lithology,etc.(3)The 3D-numerical models of the typical cross-section segment,large span segment and varying cross-section segment of tunnel in steep thin bedded soft rock with high geo-stress were established respectively and the deformation laws of which were studied.The results revealed that,the deformation of the tunnel in steep thin bedded soft rock with high geo-stress present obvious spatiotemporal effect,the deformation increases with time observably,the convergence speed of which is slow and the deformation of which is large.The influence range of construction disturbance is large and the deformation of surrounding rock present integral inward extrusion effect.Subject to the horizontal stress,the horizontal convergence deformation is larger than vertical.The deformation is obviously influenced by excavation span,the deformation increases with the increase of excavation span.The deformation of tunnel in varying cross-section segment was obviously influenced by the advance direction of construction and the more optimal scheme is excavate from small span segment to large span segment.The convergent value of deformation in tunnel construction change obviously after changing the cross-section.(4)The control measures were proposed based on the construction deformation laws of the tunnel in steep thin bedded soft rock with high geo-stress.The study revealed that,while the step excavation method is adopted as a construction method,support immediately after excavation to shorten the closing time of primary support or to close piecemeal.Construct the advance support activly.To strengthen the support structure by set the heavy type of steel frame with short longitudinal space and thickening the shotcrete.According to the actual situation,to improve the layout of bolt and add the long bolt at the side wall.Timely implementation of second lining can effectively control the deformation of the tunnel in steep thin bedded soft rock with high geo-stress. |
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