Geological Evaluation Of Wenxi-jiyuan Zhongtiaoshan Highway Tunnel Project

Wen-Yuan Highway (Wenxi-Jiyuan Highway in Shanxi Province), from DongTown, Wenxi county of Shanxi Province to Puzhang, Yuanqu county of ShanxiProvince,82.812km in total length, equipped with the four-lane highway technologystandards, whose designed vehicular load level is Highway-Ⅰ，has the total length of9.21km of tunnels,3grand bridges,84medium-and-large bridges and256culverts,and the proportion of bridges and culverts account for about32%of the total length.ZhongTiaoShan Highway Tunnel, located in Mayaotou, Wenxi County, is aseparated double-hole tunnel. Two portals have clearance of about20m. Tunnelconstruction clearance is: Width of9.75m, Clear height of5.0m. The buried depthof about50%of the section of tunnel is more than100m.The left-line tunnel is3310m long, while the right is3175m long. According to the classification of tunnel,it is a long tunnel.This engineering geological evaluation aims at analyzing the acquired data whitgeology, geophysical prospecting and drilling exploration method, and then, basedon the reliable data, provides a suitable solution or suggestion for the design of thesubsequent reference.Ground observation of the tunnel was completed mainly through1:2000planargeological annotation, high-density electrical method measurement, acoustic logging,drilling and prospecting method.Main conclusions:①The engineering geological conditions of tunnel iscomplex，and it has no regional structure or regional geological stability, so buildingthe tunnel is feasible.②The surrounding rock classification of the tunnel portal inWenxi and Jiyuan is levelⅤ, while the classification of barrel is almost Ⅴ,and thelocal district,Ⅳ.③There is bias in the portals of left-line and right-line tunnels inWenxi and right-line tunnel in Jiyuan, so anti-bias lining support should be adoptedwhen designing the tunnels.④Several groups of joint fissure are developed alongthe tunnel and in the blended granite-gneiss. They has created unstable ‘prismatic’blocks under the rock surface fabric, which could easily cause ‘Tracking’ damage, sothe unstable blocks should be removed and surrounding rock support should be madetimely when constructing.⑤Surface water or groundwater has no erosiveness toconcrete.Suggestion:①Set up open cut tunnel or excavate a cutting in YK27+885～YK27+892.②After the excavation of tunnel in Jiyuan, protection treatment shouldbe made timely in case of rock decay, which will affect the stability of surroundingrock.③Surface drainage system in the tunnel entrance should be implemented.④Considering that the tunnel is located in metamorphic rock area, wheregroundwater is rich, hydrogeological conditions is poor, the groundwater headpressure is big, underwater gushing and inrush will be serious in some section whenthe tunnel excavation is begun, we should make strict construction and excavationplan and drainage measure.