Water bursts during tunnel construction endanger construction,and it is therefore necessary to reserve a waterproof dike with the required thickness to avoid water bursts and to take reinforcement of the dike and treatment of the structure liable to trigger a water burst.Using the water burst at K5+398 of the Mingyueshan tunnel of the Shanghai-Chengdu expressway as an example,and considering the type of tunnel section and the upright mudstone of the dike,the waterproof dike at the work face is simplified as a round thin plate.A formula for the calculation of a minimum safety thickness for the critical waterproof dike is deduced by analyzing the force applied on the water-proof dike,and the minimum safety thickness for the water burst section at K5+398 of the Mingyueshan tunnel is cal-culated.The numerical simulation analysis demonstrates the critical thickness of waterproof dike at K5+398 of the Mingyueshan tunnel is 1.4-1.55 m,and the calculated water inflow and water burst basically agree with the actual condition.%隧道施工突水灾害严重威胁着隧道施工的安全.隧道施工掌子面前方存在突水致灾构造时,留足一定厚度的隔水岩盘——最小安全隔水岩盘,对确保突水致灾构造中水不至突出以及加固隔水岩盘和处理突水致灾构造至关重要.文章以沪蓉高速公路垫邻段明月山隧道K5+398处突水事件为例,基于隧道断面形式和隔水岩层为近直立泥岩层实际情况,将掌子面隔水岩墙简化为圆形薄板,以弹性力学薄板理论为基础,通过隔水岩墙受力分析,推导出临界隔水岩墙(盘)厚度——最小安全隔水岩盘厚度计算公式,并计算得出明月山隧道K5+398处突水位置最小安全隔水岩盘厚度.通过数值模拟分析验证,明月山隧道K5+398处掌子面隔水岩墙临界厚度为1.4～1.55 m,与实际涌突水情况总体吻合.
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