| The technical conditions of highway tunnel,an important infrastructure on highway operation lines,directly affect the traffic safety of highway.Tunnels constructed by new Austrian tunneling method tend to have quality defects,such as insufficient thickness of secondary lining and missing steel bar.According to the existing industrial evaluation standards,the defect section generally needs to be reworked.But in fact,according to the design theory of load-structure method,surrounding rock pressure is designed to be the maximum loosening pressure that may be born.However,in practical engineering,due to advance support and bolt action,the surrounding rock is not necessarily loosened,so the actual pressure born by secondary lining is relatively small.In this paper,stress release method is adopted to test the stress of second lining concrete,calculate in reverse the load born by the secondary lining structure,and compare it with the bearing capacity of actual second lining structure,which is used as an evaluation basis for secondary lining structure in the quality defect section.Finally,reinforce compensation treatment on the quality defect section is carried out based on engineering practice.The research of this paper has great engineering value.The main work and achievements of this paper are as follows:(1)Stress release simulation on the eccentric compression concrete member was carried out by using ANSYS finite element software,and when depth of the square slot opened reaches 44mm,concrete stress at the measure point can be completely released;the depth of complete stress release required by cutting two translots is the same with that required by cutting square ring slot by edges;the larger the spacing of the translot opened is,the greater the depth of stress complete release will be,and the slot spacing of 100mm is reasonable spacing;the depth of stress complete release is independent of the size of the upper imposed load.(2)The experimental study of 5 concrete members was carried out,and the result was compared with that of finite element analysis,with focus on the strain of thedepth of stress complete release.The experiment studied the slotting sequence,slotting method,loads at all levels and slotting stress release without load.It was concluded that the residual strain caused by disturbance is an absolute value,with the average value of about-40με;the experimental error excluding disturbance is about±10με,which meets the accuracy requirement of the experiment.45mm can be taken as the depth of stress complete release in slotting method.(3)With MIDAS finite element software,the surface strain regularity of secondary lining under different load effects and in four working conditions with the combination of standard two-lanes and three-lanes and Grade IV and Grade V surrounding rocks was analyzed.6 key strain test points were selected,namely,apex of arch,left and right arch waists,left and right side walls and arch bottom.Based on the ANSYS software platform,through establishing the inverse relations between surface strains and load,back analysis program was developed to carry out back analysis on the load of secondary lining structure of tunnels in standard two-lanes and three-lanes.The feasibility of this method was verified by the design of calculation cases in this paper,and the method has a strong generalization performance.Based on the study of stress release of compression-flexure members,a more effective method for safety evaluation of secondary lining structure was proposed.(4)On-site test on the secondary lining structure of some tunnel was carried out,the main conclusions was that the minimum thickness of the secondary lining structure differs by 9.8cm from that of the original design;two reinforcement methods of surrounding rock grouting and sticky steel board were adopted to treat the defect tunnel;the pre-reinforcement thickness of surrounding rock grouting is recommended to be 4m,and the reinforcement thickness of sticky steel board to be 2cm. |
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