Study On Geo-Hazards In Tunneling Of Deep-Buried Long Tunnels At Qinling-Dabashan Orogen Of The Three Gorges Reservoir Water Diversion Project

On the basis of field geological research, indoor examination analysis and simulativecalculation, using multidisciplinary theory like engineering geology, rock body mechanics and soon, this dissertation, combining with practical project, studies the geological hazards in tunnelingof deep-long tunnels at QingLing-DaBaShan mountain of the water diversion project from thethree gorges reservoir to the yellow river on the base of collecting and analyzing predecessor'sstudying. In the assistance with the teachers and schoolfellows of the project team, it givesemphasis to four points as follows: (1) area stability and active rift at QingLing-DaBaShanmountain of the water diversion project from the three gorges reservoir to the yellow river;(2)Three-dimensional finite element analog simulation of area tectonic stress field and QingLingextra long tunnels wall rock stree field's distributional characteristics; (3) Geological conditionand problems at QingLing-DaBaShan mountain of the water diversion project from the threegorges reservoir to the yellow river; (4) Rock blasting, water bursting and large deformation studyon the tunnels at QingLing-DaBaShan mountain of the water diversion project from the threegorges reservoir to the yellow river. By more than two years' study, we have obtained someprogress and conclusion as follows:1. Using engineering geomechanics' basal theory and concrete project as example, comparativelysystemic and all-round method of deep-long tunnels' main geological hazards prediction studieshave been put forward preliminarily, which is suit to the feasible study phase like bad condition,complicated geology and few data and so on. Geological hazards prediction with obvious phasecharacter and its prediction studies' basal method has also been put forward.2. Area present stree field analysis shows:â‘ present area stree field is mainly in the NNEdirection extrusion, and intersects at small angle with water inlet tunnel of SN direction. which ispropitious to the tunnels' stability.â‘¡the present maximal compressive principal stress valueincreases along with the deepness increasing. In the range of 100 meter of the earth's surface, thevalue is under 16MPa; in the range of 100-500 meter, the value is not more than 30MPa, which isclose to the measured data.3. It is complex of the geological conditions at QingLing-DaBaShan mountain of the waterdiversion project from the three gorges reservoir to the yellow river such as more transversefailure, body distortion being broken and more local weak interbed. The main geological hazardsexiting in the tunnel excavation are rock blasting, large deformation and water bursting. Especiallyinâ‘ the rock blasting hazards in the course of excavation being extrusive in the buried depth600-1700 meter of extra deep tunnels at QingLing-DaBaShan mountain;â‘¡the problem offracture belt and carst's water bursting being comparatively serious in south of DaBaShan atQingLing-DaBaShan mountain of the water diversion project. 4. On the basis of systemically analyzing eight influencing factors of rock burst occurrence, Theratio of rock uniaxial compressive strengh Rc to maximal principal stressσ₁, as the targetdistinguishing rockburst occurrence at Qinling extra long tunnel of the water diversion projectfrom the three gorges reservoir to the yellow river, is put forward. The plat of rockburstoccurrence and intensity class at Qinling extra long tunnel are predicted emphatically.Meanwhile, the threatening rockburst segment at Qinling-Bashan full line of the diversion workare predicted. The result shows:â‘ Strong rockburst occurs at few of plats in DaBashan regionfrom southern Han river. None but small scale rockburst is likely to occur at parts of thick layerdolostone.â‘¡Strong rockburst occurs around phenix mountain tunnel from northern Han river andconcentrates on 3-5 km inside scope of deep-buried tunnel.â‘¢The potentiality that strong rockburst occurs at deep-buried tunnel round Qinling mountain dominant peak is quite high, and thelength of strong rockburst occurrence distributes about 50km along Qinling extra long tunnel.among the rest,it need especial attention to the 20km distribution range of extra long tunnel belowthe qinling mountain dominant peak. The potentianlity that strong rockburst occurs at the majorityof the rest plat is very low.5. The plats where water gushing occurs in Qinling-DaBashan segment of the water diversionproject from the three gorges reservoir to the yellow river are predicted and evaluated. The resultshows: Along the line, water gushing occurs in quite a few segment with tunnels on construction.Among the rest, the segment where industrial scale water gushing occurs mostly concentrates onthe fault zones and karst multiple-unit control plats.Especially to the Qianhe tunnel betweenLianghekou and Chaxikou from southern Bashan mountain and Hongjiashan tunnel betweenMaoba and Han river from northern Bashan mountainThey need to set much value on industrialscale karst water gushing hazard. Water gushing occurring in Qinling deep-buried tunnel mainlyconcentrates on fracture zones and joint congest zones. The scale of water gushing is mostlymoderate, but industrial scale water gushing process is likely to occur in local crippling fractureintersection situs.6. The principle types of weak rock in Qinling-DaBashan region from the south to northinclude:Jurassic mudstone in Sichuan basin; Silurian mudstone in DaBashan mountain region;Proterozoic schist in Qinling orogenic belt (mica schist, chlorite schist, talc schist) and cleavageslate, phyllite,slate and black batt of Palacozoic group; Cretaceous mudstone in Yuehe basin;Low-rise cement degree fault fracture zones and quarternary clay etc. They are all weakintermediate rocks which can easily became large deformation and geological hazards.Argillaceous rock in research region and its engineering geological acttributes were investigated inemphasis.