流固耦合的多元结构深厚覆盖层透水地基的力学特性

深厚覆盖层多元结构坝基在渗流过程中各土层力学差异明显，分析时关注的具体问题也不尽相同，需要深入研究。基于比奥固结理论，考虑土体的非线性流变以及土体固结变形过程中孔隙度、渗透系数、弹性模量及泊松比的变化；借助ADINA流固耦合模块来模拟西藏达嘎水电站坝基渗流场与应力场耦合过程，分析各层力学特性及相互作用。研究表明，透水性较强的表层土体是渗流主要通道，也是渗流进出区和沉降变形体现区，应在上游采取措施提高其压缩模量，下游区域增设反滤层和排水设施；坝基中的粉细砂层是坝基沉降的主要原因，对坝基沉降起主导作用，同时应注意其液化特性对坝基的不利影响；坝基中的承压含水土层对下游上部结构产生向上顶托力，若位置较深，则破坏性较小；坝基深部土层对整个坝基的渗流破坏影响较小，但对沉降和渗流量的影响不可忽视；表层砂卵砾石层和粉细砂层的渗透系数相差较小时，土层间不会发生接触冲刷。此外，还发现坝基孔隙水压力在快速衰减阶段被消散，期间土体固结较快。垂直防渗墙能有效降低渗透坡降和渗流量，将坝基沉降变形控制在防渗墙上游区域，但上游坝基变形对防渗墙产生较大的水平推力，应加大防渗墙尺寸或者采用辅助渗控措施。

Mechanical properties of multiple-structure thick overburden pervious foundation based on fluid-solid coupling

The mechanical properties of each soil layer in multiple-structure thick overburden pervious foundation diverge significantly and specific questions that draw attention are quite different from each other. Based on the principle of Biot consolidation theory,the study takes soil non-liner rheological and the change of porosity, permeability coefficient, elastic modulus and poisson ratio at the consolidation deformation process of soil into account. The coupling process of seepage and stress fields of Daga hydropower station dam foundation is simulated by fluid-structure interaction module of ADINA to analyze mechanical properties and interaction of each layer. The research shows that the looser permeable soil on surface is the main seepage channel, also the inlet and outlet area of seepage and settlement deformation reflects area. Measures should be taken to improve the compression modulus in upstream and install the anti-filter layer and drainage facilities in downstream area. Fine sand layer in dam foundation is the main reason for dam foundation settlement, which plays a very leading role in the dam foundation settlement. Meanwhile, attention should be payed to the liquefaction properties of adverse impact on the dam foundation. Artesian aquifer in dam foundation produces up-holding force on the downstream side of the upper structure, and the destruction is small if the location is deep. Deep soil layer have a less effect on the seepage failure of dam foundation, but the effect can not be dismissed on settlement and seepage flow. Since in the permeability coefficient of sand gravel stratum and fine sand layer exists a modest distinction, the soil layer does not generate the contact erosion. In addition, the pore water pressure is dissipated at a rapidly-declining phase, and the dam foundation shows a stabletendency at rapid consolidation stage. Vertical cutoff wall can effectively decrease seepage gradient and seepage discharge, and the settlement deformation of dam foundation is controlled in upstream region of cuttoff wall. But the deformation of upstream dam foundation produces a large horizontal thrust to the cutoff wall, so the size of cutoff wall should be increased or the auxiliary seepage control measures shall be adoptedcorrespondly.