In order to analyze the mechanical behavior of the new type of lining structure combined with thickened floor and large ditch on tunnel bottom in water-rich karst area,commercial infinite element software is used to analyze and calculate the excavation conditions of the central water ditch.The results show that:(1)When the primary support is set above arch foot,and the tunnel floor is not closed,meanwhile the distance between central ditch and lower bench is 15 m,the tunnel concrete reaches limit condition,and the tunnel convergence and settlement are all within allowance, but the tunnel foundation uplifting amount and plastic zone are relatively large during excavation of Grade Ⅳa and Va surrounding rocks.(2)The excavation length of central ditch every circulation affects the deformation,foundation heave and plastic zone distribution little;while the delay of tunnel closure is the main cause for the deformation,foundation heave and plastic zone distribution.(3)The maximum distance between central ditch and lower bench should be 15 m, and the excavation length of central ditch every circulation should be 5 m both in Ⅳa and Ⅴa Linings.(4)The horizontal deformation of arch foot restricted by temporary support or anchor rope +grouting reinforcement of tunnel bottom should be carried out in Ⅴa lining section.%为研究岩溶富水区加厚底板+隧底大水沟的新型衬砌结构在开挖过程中的力学行为,利用大型商业有限元软件对中心水沟的开挖工况进行分析计算.结果表明:1)拱脚以上设置初期支护但底板不封闭时,中心管沟距离掌子面下台阶15 m情况下,Ⅳa型衬砌段和Ⅴa型衬砌段开挖过程中隧道混凝土接近正常使用极限状态,隧道收敛及沉降值均在规范允许范围内,但隧道基底隆起量及塑性区较大;2)中心管沟每循环开挖长度对隧道变形、基底隆起量及塑性区分布影响较小,隧道封闭时间滞后是主要影响因素;3)中心水沟与掌子面下台阶距离最大取15 m,2种衬砌段中心水沟每循环开挖长度取5 m;4)Ⅴa型衬砌段采用临时支撑约束拱脚水平变形或者对隧底地基进行锚索+注浆加固.
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