三峡地下电站27号机组厂房蜗壳外围混凝土结构上下游侧及左侧与基岩相连，其变形会受到基岩的约束作用，受力情况特殊，需进行蜗壳埋设方式研究。采用三维接触非线性有限元法对27号机组段蜗壳流道及其外围混凝土结构和围岩进行分析，为蜗壳埋设方式的选择和配筋设计提供科学依据。研究表明:直埋方案拉应力最大，所需配筋也最多，不经济；垫层方案除局部区域外，拉应力普遍较小，不能充分发挥钢衬钢筋混凝土结构的联合承载作用；组合方案的应力介于直埋方案与垫层方案之间，但下机架基础相对上抬位移接近控制标准。

The peripheral concrete structure of the spiral case of turbine unit No.27 in the Three Gorges underground power station  connects with bedrock in the upstream, downstream and left side. Concrete deformation is constrained by the bedrock, and the force situation is unusual. In order to provide scientific basis for the selection of embedding manner of the spiral case and the reinforcement of the concrete structure, we carried out 3-D nonlinear finite element analysis on the flow channel, peripheral concrete, and surrounding bedrock of the turbine unit. Results show that the scheme of spiral case embedded directly is not economical because of  high tensile stress and high reinforcement ratio; the scheme of spiral case embedded with cushion layers has the advantage of low tensile stress but could not well perform the function of joint-bearing; whereas for the  scheme combining the above two, the tensile stress fall between those of the above two schemes, but the relative rising displacement of the lower rack base approaches to the control standard. In view of this, measures should be taken to reduce the relative rising displacement of the lower rack base to prevent from penetrating cracks.