深厚覆盖层中局部强透水层对渗流的影响研究

中国西部地区的深厚覆盖层坝基中常存在局部强透水层,其孔隙比大和渗透性强等特点对坝基渗流存在不利影响,是渗流控制中的薄弱环节。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,得出渗流量和坝踵处渗透坡降、出逸坡降,分析强透水层深度、厚度、连续性对渗流场的影响。结果表明:当强透水层深度大于防渗墙时,渗流量和坝踵处渗透坡降随强透水层深度的增大而减小;反之,渗流量则随着强透水层深度的增加而增大,坝踵处渗透坡降先降低后增大。渗流量、坝踵处渗透坡降、出逸坡降皆随着强透水层厚度的增加而增大。渗流量和出逸坡降随着强透水层上游开口长度的增加而增大;坝踵处渗透坡降以上游开口长度50 m为分界线,先增大后降低。渗流量和坝踵处渗透坡降以下游开口长度40 m为分界线,先增大后降低;出逸坡降随强透水层下游开口长度的增加而增大。当防渗墙深度小于55 m时,渗流参数随强透水层底端开口长度的增加而显著增大;当防渗墙深度为60～100 m时,渗流参数仅有较小幅度增大;当采用全封闭式防渗墙时,渗流参数随着底端开口长度的增大反而降低。

Study on effects of local strong permeable stratum characteristics in deep overburden on seepage field

Local strong permeable stratum often appear in thick overburden dam base in China''s west regions. The large pore ratio and permeability coefficient adverse effect on seepage of dam foundation, and it is a problem in seepage control. This paper obtained seepage discharge and exit gradient, seepage gradient at dam heel based on seepage theory of unsaturated soil and using numerical model by Seep/w. The effects of depth, thickness, and continuity of strong permeable stratum characteristics on seepage field were studied. The results showed that seepage discharge and seepage gradient at dam heel decreased with the increased of the depth of the strong permeable stratum, when the depth of strong permeable stratum is greater than cut off wall. Instead, seepage discharge augmented as the depth of strong permeable stratum increased, seepage gradient at dam heel decreased firstly and then increased. Seepage discharge and exit gradient, seepage gradient at dam heel augmented as the thickness of strong permeable stratum increased. Seepage discharge and exit gradient augmented as open length of strong permeable stratum at upstream increased. When open length of strong permeable stratum at upstream is 50 m, which is boundary for seepage gradient at dam heel, it increased firstly and then decreased. The seepage discharge and seepage gradient at dam heel are divided by the 40 m opening length downstream, which increases first and then decreases.The escape gradient increases with the increase of opening length downstream of strong permeable layer. When the depth of cut off wall is less than 55 m, seepage parameters augmented as open length of strong permeable stratum at bottom increased. When the depth of cut off wall is between 60 and 100 m, seepage parameters increased slightly. When totally enclosed cut-off wall was adopted, seepage parameters decreased as open length of strong permeable stratum at bottom increased.