中文摘要：

对于坝后式水电站，厂坝分缝处钢管预留环缝焊接时机和分缝下游侧是否设置止推环均对垫层蜗壳以及水轮发电机组支撑结构的受力和变形存在影响。本文建立了坝-厂房三维有限元模型，通过数值模拟手段研究了上述影响。结果表明，对于坝后式水电站，在坝体变位作用下引水钢管对蜗壳进口作用一个数值可观、指向下游的推力，因此在分析垫层管过缝对厂房结构的影响时，在蜗壳进口施加轴向约束的简化处理不能合理反映实际情况。不同焊接时机条件下设置止推环对垫层蜗壳的受力、座环的抗剪等都是有利的，尤其在上游水位较低时焊接预留环缝，止推环的作用效果更加明显，在可能的条件下建议设置止推环。与此同时，为确保水轮发电机组的安全稳定运行，建议以座环和机墩的对角不均匀上抬变形为主要考虑因素，尽可能在上游水位较低时焊接钢管预留环缝。

英文摘要：

For a hydropower station at the dam toe, two factors have an influence on the spiral case with cushion layer and generator unit pedestal. They are the welding time to circumferential seam reserved for connecting penstock in dam and powerhouse parting and the optional anti-thrust ring at the downstream side of the joint. Based on a dam-powerhouse three-dimensional finite element model, the above-mentioned factors were investigated through numerical simulation. Firstly, if the penstock surrounded by cushion layer is adopted to cross the joint between dam and powerhouse, the diversion penstock acts a considerable thrust force on the spiral case in downstream direction due to the deformation of dam body. Therefore, ap-plying axial restraint on spiral case inlet is inadequate to reflect the real situation. Secondly, under differ-ent welding time,the anti-thrust ring all benefits the structural performance of spiral case and the shear-re-sisting of stay ring. If the girth welding is performed at a low water level of upstream reservoir, the above function is more obvious and the anti-thrust ring is recommended if allowed. Thirdly, in order to ensure safe and stable operation of the hydroelectric generator units, the non-uniform deformation of stay ring and generator pedestal should be considered as the mainly contributing factors, and the girth welding is recom-mended to be performed when the upstream reservoir water level is low.