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The Reseach on Karst Waterburst Mechanism and Prevetion Measures in Zhongba Tunnel

Author: JiaRuTao
Tutor: DengHui
School: Chengdu University of Technology
Course: Geological Engineering
Keywords: Karst tunnel Waterburst mechanism Ahead geological forecasting Prevention
CLC: U457.2
Type: Master's thesis
Year: 2013
Downloads: 45
Quote: 0
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The rapid advance of china western development, more and more complex karst tunnels are being builded.In the construction process of this kind of tunnels,whose geological conditions are relatively complex and whose hole are long and deep, we often encounter a series of geological hazards problems,which of waterburst and nudburst is the most common and harmfullest, As soon as calamity occurs,it destroys machinery,floods the tunnel and interrupts the normal construction if the calamity is not serious;sometimes the calamity causes great casualties and huge economical losses,even forces the works to be suspended or to change its alignment if the calamity is serious.Therefore, to improve the long karst tunnel construction level,the formation mechanism, disaster prediction and prevention of waterburst and nudburst have become one of the major and widespread concern subjects.In this article, Zhongba karst tunnel was chosed for research. Based on the collection of previous research data, we survey the characteristics of karst and hydrogeological conditions detailedly, analyse the types of karst aqueous medium, water-bearing formation spatial distribution as well as the karst groundwater system’s complement, runoff and discharge conditions, draw the mechanism of waterburst. Construction Mechanics state was numerical simulated by using the FLAC3D software on the thickness of the rock of the water-filled cave and tunnel face security, We study the ahead geological prediction system of this tunnel and put forward waterburst prevention principles and measures. By summarizing, the conclusions are as follows:(1) When the tunnel excavated to mileage DK55+221, working face encountered waterburst. The water comes from the underground river which is be in the upper part of the tunnel roof. The main waterburst points lie in NW steep dip dissolution fissure which develops on the top left side of the tunnel, The fracture occurrences as N10°W/65°NE, maximum open is approximately10cm, The extending direction cuts through the top underground river channel to form a water guide channel,which to formate water channel. The dark river be on the top of the tunnel influxed lower excretion face which caused waterburst disaster.(2) Tunnel construction mechanical behavior were studied by using three-dimensional numerical simulation.Tunnel excavate along the positive y-axis,Full-face and14steps excavation can be used, each step excavate3m before step4, each step excavate lm in step5and Step6, each step excavate0.5m in7to14steps; By analyzing the calculated results can be drawn:①Rock Classification and the cave water pressure will affect the thickness of the tunnel face rock security, The lower level of surround rock, the thicker of rock security, the higher of cave water pressure, the greater thickness of the bedrock security;②Rock safe thickness is more sensitivity higher than surround rock from the surround rock conditions at the same level under the heading face rock the safe thickness cave water pressure curve.when the water pressure is1MPa, level V surround rock’s safe thickness increase than the class IV surround rock’s approximately0.5m, the increment up to3m when the water pressure is4MPa. Therefore, should pay more attention to the cave which is high water pressure water-filled in practical work, should pay attention to safety.(3) Through geological survey, infrared detection water, ground penetrating radar, drilling and other advanced geological prediction methods application results analysis in zhongba tunnel, Summed up the response characteristics, the advantages and disadvantages of the various forecasting methods adverse geological, combined with the complexity of the karst tunnel, by the comprehensive advanced geological prediction of ZhongBa tunnel exploratory study, preliminary set up the comprehensive advanced geological forecast system of the tunnel, to improve the accuracy of advanced geological prediction.(4) Using advanced drilling detect tunnel cavity ahead:Karst cavity is exposed at a distance of about5.3m in the current working face DK55+221, The size of the cavity in the forward direction of the tunnel is10to23m, which presents the characteristics of the two big middle small, and the irregular shape distribution. The part of the cavity space is filled with muddy soil, and presented the large under small funnel-shaped scale of7to20m, the rest of the spatial occurrence water.Nearly1100m3of mud has bursted on March15,2013, to make the karst cavity filling has been released. The level of underground water is higher than the bottom of the karst cavity, and there is abundant water supplement, the water source has well connection with the underground river which is be at the top of the ahead tunnel, The water quantity and water pressure of karst cavity body is likely to increase further, So, the large-scale waterburst is still likely to generate again in the process of construction.

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