| Geo-hazards such as karstic water flooding and mud surging, surface subsidence and exhausting of surface water in the tunnel stie will be caused by tunnel construction under complicated characteristics of hydraulic geology. It brought great trouble to the construction and the normal life of the people near the tunnel site.Wuzhi moutain tunnel is 3911 meters long. Under complicated characteristics of hydraulic geology, there are huge-scale water gushging many times in its construction process. And it brings great difficulties to the tunnel construction. Since the beginning of construction in 2004, seven aquiferous zones have been disclosed. In July 2005, there are huge-scale water gushings in the outlet section of the tunnel at K30+911. And in August 2005, there are huge-scale water gushings in the inlet section of the tunnle at K29+542. And it also brought big trouble to tunnel construction. So it is very significant to study on characteristics of hydraulic geology of karst and gushing in Wuzhi mountain tunnel.Depending on a lot of basic investigations such as physical geography condition in the Wuzhi mountain tunnel site, stratum lithology, geologic conformation, characteristics of hydraulic geology of karst, we found out the characteristics of water gushing in the construction of Wuzhi mountain tunnel and analyzed the causes of water gushing.The results of the dissertation are as follows:⑴Faultage F1 and F2 were found by surface investigation.⑵The development karst topography in the tunnel site is: The main topography near ground are turions, funnels, erosion-dissolution depression, dissolution gouge, peak cluster and valley. And the main topography under ground are crack, silo, sinkholes and caverns.⑶There was gypsum breccia in Wuzhi mountain tunnel.⑷The recharge-runoff-drainage condition of groundwater there is: rainfall recharges groundwater. Drainaging area is at the two sides of Wuzhi mountain. And the main runoff area is at the north-east of watershed.⑸The changes of water gushing in tunnel construction are analyzed. And it shows that water gushing is greatly dynamic changing. Depending on the function of volume of water gushing, the distributing position of the main water gushing location was precisely determined. It offered evidences to the real calculation of water gushing in the tunnel.⑹The causes of water gushing of gypsum breccia in the outlet section were found out. There are limestone, dolomite and gypsum breccia in the outlet section K30+912～K29+566. And water gushing from up-down gypsum breccia was 73 percents of the whole tunnel water gushing.⑺The causes of"8.6"water gushing and subsidence were found out. Water gushing occurred in sandstone T1t with 100 meters width in broken district of faultage and under circulatory pressure system of hydraulic geology. Water gushing occurred and caused subsidence of rock mass because of water recharging in broken district and enhance of static hydro-pressure.⑻Analyzing the chemical elements of gushing water in tunnel, we determine the hydro-chemistry characteristics of groundwater in shallow burial zone and deep buried zone. And it also offeres evidences to the origination of water gushing in the tunnel. |
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