Study On The Characteristics Of Grouting Marerial For Secondary Lining Viod Of Tunnel And Its Similarity Model Test

With the continuous development of high-speed railway,the number of railway tunnels is increasing day by day,a considerable proportion of tunnels have different degrees of disease problems,among which the phenomenon of cavity behind the secondary lining is the main cause of tunnel disease.The void behind the secondary lining of the tunnel will change the overall stress situation of the structure and endanger the traffic safety.In order to solve the problem of poor integrity of transmission structure caused by the traditional grouting technology,tiezong vigorously promoted the synchronous grouting construction technology of lining arch crown with formwork,but did not provide the corresponding grouting materials and proportion matching with the technology.Therefore,this paper develops a new cementbased grouting material which is matched with the mold grouting technology and meets the requirements of the technical specifications through experiments.Based on the similarity theory,through the structural model test,the paper studies the overall mechanical change characteristics of the tunnel structure during the process of injecting the new developed material into the cavity by the mold grouting technology of the arch crown of the tunnel lining.The main work and research results are as follows:(1)Single variable method was used to study the influence rules of fluidity,strength,apparent density and expansion rate of cement-based materials by fly ash,ore powder,silica fume,metakaolin and sand ratio.(2)Based on the benchmark mix ratio design test,three-factor three-level orthogonal test was adopted to analyze the influence of water ratio,sulphoaluminate cement content and silica fume content as the changing factors on the basic mechanical indicators of materials,and the early shrinkage rate and expansion rate of materials were measured to determine the optimal construction mix ratio.(3)Determine the vertical free expansion and constrained self-contraction of the optimal mixture material,and determine its volume stability;In addition,specimens of different ages were selected for X-ray diffraction analysis,scanning electron microscope analysis and energy spectrum analysis,and the structural characteristics of the material were analyzed from the microscopic level to explain its macroscopic performance.(4)Through the similar model test,the paper simulates the phenomenon of void in different positions behind the secondary lining of reinforced concrete tunnel.The new developed material is injected into the cavity by the grouting technology of the arch crown of the tunnel lining.In this process,the mechanical change characteristics of the whole structure of the tunnel are simulated.The test and analysis results show that: when preparing cement-based grouting materials,silica fume is the most suitable mineral admixture,with a cement-sand ratio of 58:42(1.38),a water-cement ratio of 0.19,a content of 13% sulphoaluminate cement,and a content of 7%silica fume,the cement-based grouting materials have the characteristics of high early strength,slight expansion and good fluidity.The cement-based grouting material under this ratio has a certain expansibility at the initial stage of hardening,which can compensate for the shrinkage of the material itself and maintain the bulk stability of the material.During the grouting with mold,the bending moment increases the fastest in the cavity,while the bending moment at other positions far away from the cavity does not change significantly with the increase of the grouting pressure,and the second lining bending moment increases more than the initial supporting bending moment.The axial force increased the fastest in the void,while the axial force at other locations far away from the void did not change significantly with the increase of grouting pressure.In the vault,the increase of the initial supported axial force was greater than that of the secondary liner,and the increase of the secondary liner axial force was greater than that of the primary supported axial force at the right arch shoulder.