The Occurrence Mechanism Of Geological Disaster Of Enriched Water Tunnel In High Altitude Glacier Accumulation And Its Control Techniques

Due to many limitations from topography,hydrogeology,climate and geological disasters,construction of long-large tunnels in high altitude cold regions,especially in glacier accumulation,is very difficult.A viable and worthy construction method has not been summed up yet.Based on the construction of Galongla tunnel,this study conducted an extensive research comprising laboratory experiments,theoretical analysis and numerical simulation,to analyze the mechanism,rules and features of sudden geological disasters and studied disaster prevention technology in high altitude glacier accumulation enriched water tunnel,contributed for the future plateau tunnel construction.The main work and conclusions are as follows:1)Through on-site monitoring and measurement,it was concluded in this work that the gushing water of Galongla tunnel usually begins in the early of dry season,and is less affected by the snow and ice melt;the water has a relatively high pressure and there is no signs of failure;there is a lag phenomenon in the development of gushing in poor geological conditions.Based on image processing technology,the tunnel entrance seepage characteristics were studied and the influence of non-uniformity surrounding rock to seepage was analyzed,and the relationship between the equivalent fracture width and the water inflow was derived.These findings have important theoretical and engineering significance.2)On the basis of field trials and using numerical simulation techniques,this study further analyzed the Grouting effect in high altitude cold regions tunnel body glacial deposits.It is concluded that:(1)from the water shut-off effect,the thicker the layer of grouting,the smaller the pressure on the lining produced by groundwater,and the slower the flow velocity within the lining,and the smaller the water flow through the tunnel section.Comprehensive technical and economic considerations indicate that the grouting layer thickness should be reasonably controlled at 3m.(2)from the stress-displacement analysis,Grouting lining surrounding rock layers has a great effect on improving the stress distribution and controlling the deformation:when D<3m,grouting thickness has a greater impact on the surrounding rock deformation;when D?3m,the tunnel deformation tends to be stable,with a horizontal convergence of around 1.8cm,vault settlement of about 1.2cm,and the dome end drum about 1.4cm.(3)by studying the change of plastic zone of surrounding rock,it was shown that the grouting layer can significantly reduce the plastic zone,maintaining the stability of surrounding rock:when D?3.5m,there is no plastic zone appearing in surrounding rock except a very small plastic zone in the lining.Therefore,from an economic,security and other aspects point of view,high altitude glacial deposits rich body of water tunnel proposal grouting layer thickness should be controlled at 3.5m.3)The avalanche of high-altitude glacier accumulation body tunnels has the following characteristics:the vast majority of avalanches occur in the slope of 22�?55�,among which those in the range of 28 �?46 � account for almost 90 percent,and most of them are land surface slope avalanche and the avalanche fails mainly by accumulation roll;Avalanche with slope less than 28 � is usually the plate-like avalanche in snow period.For these Avalanches with slope greater than 46�,the failure is most likely in overall which is caused by gravity;The occurrence of Avalanche concentrates in between January 20 to April 20,mostly dominated by(slope)surface avalanches;The frequency of trench avalanches significantly increases in March;in April,due to elevated temperatures,the cohesion of snow layers reduces and the strength reduces as well,some weak zones form a super weak area(crack)partially producing the stress concentration,and in the new snow gravity loads or other loads the continuous shear crack propagation becomes a plate avalanche;Vegetation usually under-develops in entry area of the tunnel,and the avalanche has a large throw-distance,moving fast,and the air pressure generated by the avalanche has a great destructive force.In exit area of the tunnel,the avalanche body moves relatively slowly due to the influence of pine needles,but the accumulation effect is strong and squeezing effect is obvious,and the second avalanche usually follows the previous sliding track with an obvious higher speed.Grassland helps form the avalanche,while forest vegetation can inhibit it.4)Build a hazard assessment and warning system for avalanche in the construction of tunnels:from collection of avalanche information,the disaster factors are extracted,and the avalanche hazard factors are divided into category ? and ?;by use of AHP,all levels of avalanche disaster factors are given the weight coefficients,and the occurrence patterns and incidence conditions are summarized;the critical conditions of occurrence are clarified,and the occurrence threshold is determined;the corresponding avalanche hazard assessment model is constructed.Dangerous levels and Treatment Measures avalanche disasters were finally graded.5)Based on the internal heat transfer process,seepage paths and rock stress moraine body analysis,the basic equation of glacial deposits of hydrothermal body tunnel structure interaction problems for the study of glacial frost resistance of the pile foundation tunnel.And under different conditions of depth and rock type,temperature and freezing tunnel ring range analyzed.Accordingly,the effects of different insulation materials and insulation thickness on thawing circle.The main conclusions are:With the increase of the thermal conductivity of insulation materials,frost depth also increases linearly,the thermal conductivity of insulation materials for each additional 0.001,country rock deep freeze to a corresponding increase of 12%;insulation thickness and depth of the tunnel thaw circle also an inverse relationship,when insulation thickness for each additional 1cm,thaw depth phase will be reduced by about 10%from the engineering point of view,the insulation thickness is designed to 5cm can achieve better insulation effect.6)Numerical simulations are carried out for braced excavation method in the construction of high-altitude glacial deposits rich body of water tunnel,and it is concluded in this study that:the three-step excavation construction method yields the smallest plastic zones;initial support is not fully plastic,giving a very good supporting effect,and the slope does not produce plastic zone,hence it is the preferred construction method;when using the three-step stepped construction method,the initial support major regional tensile stress control is temporary support and initial support intersects the site.There,before removing temporary support,it should increase the monitoring and measurement efforts to ensure the basic stability of surrounding rock convergence Treatment and after making a good way to stress,which may be removed temporary support;its focus is mainly controlled compressive stress in the initial support of the arch waist position,to strengthen the parts of the support and make the appropriate monitoring and measurement;Because Galongla tunnel site traffic can pass only small vehicles,a large pipe roof cannot be used,it is recommended hole glacial deposits strongly weathered broken body with a small range of multi-row duct grouting reinforced support,improve and strengthen the hole resistance to deformation monitoring grasp the rock stress measurements of displacement trends,strong support to 20m range can be adjusted on the basis of post-monitoring and measuring the results.7)On the basis of optimized low watering mix shotcrete lots,concrete coring freezing spray and shear tests are conducted,concluding that:freeze-thaw cycles have an impact on the interface shear strength,the average shear strength before freezing for 3.29MPa,the average shear strength after freezing and thawing is 1.84MPa;Although the average shear strength before freezing the sample compared to that after freezing and thawing reduced by about 44%,but on the whole,there are still 1.84MPa of jet shear strength of concrete and rock at the interface;as compared with ordinary shotcrete,the shear strength increased by 68%,which proves that tunnel syndrome Galongla low watering mix shotcrete concrete sections can significantly improve the initial cold plateaus rich water tunnel support concrete shear strength.This provides a certain research value and significance in solving construction problems for cold region water-rich tunnels.8)The key technologies for drainage of high-altitude water-rich tunnels are summarized.The frost insulation for ring drainage system,the grew Drainage Technology for anti-sloping tunnel sections and the key points of construction of Reflux drain hole for cold regions tunnel are elaborated.These will be useful references for future constructions of water-rich plateau tunnel drainage systems.