| China’s underground engineering construction has entered a period of rapid development。The pace of tunnel construction continues to advance。In order to realize "safety plus,cost minus" in tunnel construction,higher requirements are put forward for the fine construction of tunnel construction.Deformation allowance plays an important role in tunnel construction:The setting of deformation allowance amount can make the surrounding rock of the tunnel produce deformation within the allowable range after excavation and support to release energy and reduce the pressure on surrounding rock and support structure.If the value is too large or too small,it will cause adverse effects,so it needs to be optimized based on the field deformation monitoring data.At present,the optimization research on the deformation allowance of tunnel mostly relies on the point-based analysis of deformation monitoring data.It is difficult to obtain the overall change of the tunnel section,so it is urgent to introduce 3D laser scanning technology to carry out the overall study of the whole section.In this paper,literature investigation,experimental verification,field monitoring,numerical analysis and back analysis are used.The optimization method of deformation allowance based on 3D laser scanning holographic deformation monitoring is studied.The research results and conclusions are as follows:(1)This paper inquired the relevant papers about the amount of deformation allowance.Grasps the current tunnel construction for the surrounding rock deformation monitoring method and the deformation allowance determination method,and summarizes the shortcomings.On this basis,the ideas and methods of this paper are put forward.(2)The "congenital deficiency" and "acquired loss" of traditional monitoring and measurement techniques are compared and analyzed with examples.This paper expounds the great advantages of 3D laser scanning technology in data accuracy,data authenticity,data integrity and feedback efficiency in monitoring the overall deformation of tunnel.The average error and medium error of the measured data based on the field test are less than 1mm,which meets the accuracy requirement.The feasibility of applying 3D laser scanning holographic deformation monitoring technology to tunnel deformation monitoring is verified.(3)The deformation allowance was optimized based on data-driven,Based on a railway tunnel,it is found that the maximum deformation of the test section is 7.5cm,which is less than the designed deformation allowance of 15 cm.According to the characteristics of nonuniform deformation and the quality guarantee rate,an optimization method of setting the deformation allowance amount in step shape is put forward.Finally,it is determined that the deformation allowance in the vaults of the test section is set at 7 cm,and the deformation allowance in the other areas is set at 5 cm.(4)Compared with the traditional optimization method of deformation allowance,the optimization efficiency of the proposed method is improved by 43% and the cost is reduced by 775 yuan per meter.(5)Displacement loading back analysis was carried out by using 3D laser holographic deformation monitoring data.Convert the results of displacement into internal forces to master the dynamics of surrounding rock and the internal force of supporting structure.The tunnel structure of the test section deforms towards the clearance side,which is consistent with the loading mode of shotcrete with larger axial force and smaller bending moment.The whole ring is mainly under compression,the deformation and force mode accord with the deformation pressure characteristics,and the structure is in the state of small eccentric compression.The deformation pressure action mode is consistent with the rigid loading action mode,which confirms the scientific nature of displacement loading. |
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