大坂山公路隧道工程地质特征
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摘要
大坂山公路隧道位于青海省西宁市—甘肃省张掖市公路(即227国道),自南向北穿越大坂山主峰。隧道轴线长约1.538km,轴线走向29°,系国内海拔最高的公路隧道。由于隧道址区所处的特殊地形地质背景条件,必须查明一些特殊的隧道工程地质问题。经工程地质勘探查明了:一、大坂山址区不存在多年冻土,仅发育季节冻土,对隧道工程危害不大;二、隧道围岩类型分为四类、11段,其中稳定性好的Ⅴ类围岩占隧道全长51％,Ⅳ类围岩占15％,Ⅲ类围岩占2％,稳定性差的Ⅱ类围岩占32％;三、隧道址区地壳稳定程度属次不稳定级,为6.5级地震潜在震源区,在五十年地震活动强度超越概率0.1的条件下,相应地震烈度值为7.8度;四、隧道址区位于分水岭地带,水文地质条件简单,大气降水和地表水不易补给地下水,预测隧道总涌水量仅668m~3/d。
The Dabanshan highway-tunnel is situated at the middle part of the Xining-Zhangye highway and passed through the main peak of the Dabanshan mountain along N-Sdirection. As a highway-tunnel with the highest elevation in China, its axis is 1.538 Km inlength and 29°in strike. There are some special enineering geological problems to resolve be-cause of special topographic and geologic background of the tunnel site. Through engineeringgeological exploration, following aspects have been ascertained: (1) There was no per-mafrost but only seasonally frozen soil in the Dabanshan region and, therefore, no obviousdanger to tunnel engineering; (2) The country tocks of tunnel maybe classified into 4 kindsand 11 parts,Among which the fifth part with better stability acount for 51% of the tunnellength,the forth part 15%, the third part 2%,the second part with less stability 32%; (3)The stable degree of crust in the tunnel site was secondary unstable, where would be a po-tential focus of 6.5 earthquake With sucha circumstance of strengh of seismic activity wasmore than probability 0.1 in 50 years, seismic intensity was 7.8. (4) The tunnel is locatedat the water parting zone where the hydrogeological condition is simple, atmorspheric waterand surface water were difficult to rechage groundwater, the predictive dischage into tunnelwas only 668 m~3/d.
The Dabanshan highway-tunnel is situated at the middle part of the Xining-Zhangye highway and passed through the main peak of the Dabanshan mountain along N-Sdirection. As a highway-tunnel with the highest elevation in China, its axis is 1.538 Km inlength and 29°in strike. There are some special enineering geological problems to resolve be-cause of special topographic and geologic background of the tunnel site. Through engineeringgeological exploration, following aspects have been ascertained: (1) There was no per-mafrost but only seasonally frozen soil in the Dabanshan region and, therefore, no obviousdanger to tunnel engineering; (2) The country tocks of tunnel maybe classified into 4 kindsand 11 parts,Among which the fifth part with better stability acount for 51% of the tunnellength,the forth part 15%, the third part 2%,the second part with less stability 32%; (3)The stable degree of crust in the tunnel site was secondary unstable, where would be a po-tential focus of 6.5 earthquake With sucha circumstance of strengh of seismic activity wasmore than probability 0.1 in 50 years, seismic intensity was 7.8. (4) The tunnel is locatedat the water parting zone where the hydrogeological condition is simple, atmorspheric waterand surface water were difficult to rechage groundwater, the predictive dischage into tunnelwas only 668 m~3/d.
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