多元结构坝基双排防渗墙控渗效果试验研究

Experimental study on seepage control using double cut-off walls on multiple-structure dam foundation

双排防渗墙已广泛应用于西南地区强弱互层深厚覆盖层地基,但双排防渗墙的间距及布置形式如何选择,控渗效果如何等都值得深入研究。基于非饱和土体渗流理论,以强弱互层深厚覆盖层坝基为研究对象,针对双排防渗墙进行试验研究,得出渗流量和出逸坡降,探讨各布置形式下双排防渗墙的控渗效果。研究表明:"前长后短"、"前短后长"、"前后同长"3种布置形式下总渗流量和出逸坡降都随着间距的增加而降低,"前长后短"、"前后同长"布置形式降低明显。坝体渗流量以间距L=13.2、16.5cm为分界线,先增大后降低;坝基渗流量以间距L=13.5、17.5cm为分界线,先降低后增大。双排防渗墙中深度较大的防渗墙消减的水头更大,两防渗墙深度一致时,前后防渗墙分别消减水头37.5%、50%。当前后防渗墙的深度之和一定时,双排防渗墙采用"前短后长"的布置形式相比采用"前长后短"的布置形式,能更有效降低渗流量和抑制出逸坡降,建议优先采用。

Double cut-off walls have been widely used in deep overburden foundation with alternating interloyered soils in Southwest China.However,how to determine the spacing and the layout of double cut-off walls,and the effect of seepage control need to be further investigated.In this paper,based on the unsaturated seepage theory,taking the deep overburden dam foundation with alternating interlayered soils as an example,double cut-off walls are experimentaly studied.The seepage discharge and exit gradient were obtained,and seepage control effect of cut-off walls under different layouts was discussed.Results show that the total seepage discharge and the exit gradient decrease with the distance.The seepage discharge of dam body is divided by the spacing of 13.2 and 16.5 cm,which increases at first and then decreases.Seepage discharge of dam foundation is divided by the spacing of 13.5 and 17.5 cm,which decreases at first and then increases.The wall with deeper penetration depth reduces the head of water more.The front and back walls reduce 37.5 percent and 50 percent,respectively,when the depth of two cut-off walls are same.It is found that given the same total penetration depth of two cut-off walls,the arrangement form with short in front and long in back decreases seepage discharge and controls exit gradient more effectively,which is therefore recommended for priority.