Study On The Critical Safety Thickness Of Tunnel Anti-burst Slab In Front Of Water-rich Fault Zone

Water-rich fault zone is the one of main sources of geological disaster in tunnel construction,which is easy to cause water/mud burst in the construction process,resulting in serious casualties and economic losses.When the tunnel construction is close to the water-rich fault zone,the safety of tunnel construction can be guaranteed if the critical safety thickness of anti-burst slab in front can be determined timely and accurately,and the effective reinforcement measures can be taken timely when the tunnel construction reaches.Although there have been many research achievements at home and abroad,there are still some imperfections in the research on the critical safety thickness of anti-burst slab,such that the predicted formula is incomplete in influence factors,complicated and lack of engineering practicability.Therefore,by taking Tianhe Mountain Tunnel of Hexing Railway as the background,using the methods of information research,numerical simulation,engineering example,formulas comparision and application,the critical safety thickness of tunnel anti-burst slab in front of water-rich fault zone is studied in this paper.As follows:1.By comprehensively analyzing the water/mud burst mechanism of tunnel with water-rich fault zone?disaster models,occurrence conditions and influence factors?,the influence factors of the critical safety thickness of anti-burst slab are summarized.2.By comprehensively analyzing the development of groundwater seepage,surrounding rock deformation,and plastic zone distribution in the process of tunnel construction closing to water-rich fault zone using the fluid-solid coupling function of FLAC^3D,understanding the evolution process of water/mud burst disaster,and combining with relevant data,a critical criterion for the wate/mud bursting considering comprehensively the three aspects is proposed.3.By using the fluid-solid coupling function of FLAC^3D,and according to the proposed critical criterion,the influence of each factor on the critical safe thickness of anti-burst slab is studied,and a convenient and practical predicted formula for critical safe thickness of anti-burst slab under the comprehensive influence of various factors is proposed.4.By studying four engineering examples,it is shown that the predictied formula is highly reliable in specific rock formations?sandstone,slate,shale and mud rock?.5.Applying the predicted formula to Tianhe Mountain Tunnel and comparing it with three reference formulas further tests its convenience,practicality,good applicability and reliability.6.By using the predicted formula,the range of the critical safety thickness of tunnel anti-burst slab in front of water-rich fault zone under the common rock grades used in engineering is obtained between 0 and 1.5D.