深厚覆盖层中弱透水层特性对渗流场的影响

中国西部地区的深厚覆盖层坝基中常存在弱透水层,对坝基渗流场有一定影响。基于非饱和土渗流理论,借助有限元软件Seep/w建立数值模型,得出渗流量和出逸坡降,并结合2个实际工程分析弱透水层深度、厚度、连续性对渗流场的影响。结果表明,采用悬挂式防渗墙或无防渗墙时,深度越小的弱透水层控渗效果越佳;深度越大的弱透水层与防渗墙形成的半封闭式联合防渗体系,越能有效控制渗流量和抑制出逸坡降。渗流量和出逸坡降都随着弱透水层厚度的增大而降低;弱透水层厚度及连续性对采用半封闭式防渗墙控渗时的渗流场影响最大,悬挂式防渗墙次之,全封闭式防渗墙最小。渗流量和出逸坡降随上游、底端开口长度的增加而增大;渗流量随下游开口长度的增加而增大,但出逸坡降随下游开口长度的增加呈先增大后减小的趋势。弱透水层的连续性对渗流场影响较小。采用半封闭式防渗墙时,渗流量和出逸坡降从高到低排序为底端开口、上游开口、下游开口。采用全封闭式防渗墙时,防渗墙承担主要的控渗任务,弱透水层的深度、厚度、连续性对渗流场的影响极小。

Effect of Characteristics of Deep Buried Aquitard on Seepage Field

Aquitard often appears in thick overburden dam base in Western China, which has a certain effect on seepage field of dam foundation. On the basis of seepage theory of unsaturated soil, the numerical model was established by software Seep/w. The seepage discharge and exit gradient were obtained and the effect of aquitard characteristics on seepage field was studied. The simulated results were compared with those of practical engineering projects. It shows that the shallower the buried depth of the aquitard , the better the seepage control effect for suspended cut-off wall or cut-off wall engineering. But for deep buried aquitard, the semi-closed seepage prevention system composed of aquitard and cut-off wall can also perform a good seepage control effect. Seepage discharge and exit gradient decrease with the buried depth of the aquitard. The thickness and continuity of the aquitard have the biggest impact on seepage field with a semi-closed cut-off wall, followed by suspended cut-off wall and totally enclosed cut-off wall in sequence. Seepage discharge and exit gradient increase with the bottom or the upstream gap between aquitard and cut-off wall. Seepage discharge increases with the downstream open length between aquitard and cut-off wall. The aquitard continuity has less influence on seepage field. Seepage discharge and exit gradient decrease orderly in the cases of bottom opening, upstream opending and downstream opening when semi-closed cut-off wall was adopted. Cut-off wall plays an important role in seepage control when totally enclosed cut-off wall was adopted, the influence of depth, thickness and continuity of aquitard on seepage field can be ignored.