深厚覆盖层中弱透水层厚度及连续性对渗流场的影响

中国西北地区的深厚覆盖层坝基中常存在厚度不均和不连续的弱透水层，弱透水层的厚度、不连续形式及开口大小对坝基渗流场有一定的影响，其规律需要深入研究。基于非饱和土渗流理论，借助Seep/w进行渗流求解，探讨中间位置处弱透水层的厚度及连续性对单宽渗流量和出逸坡降的影响规律，并结合工程实例进行对比分析。研究表明：单宽渗流量和出逸坡降都随着中间位置处弱透水层厚度的增加而降低；弱透水层厚度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。开口在上游的弱透水层与防渗墙形成的半封闭式联合防渗体系的控渗效果最好，开口在下游的弱透水层次之，防渗墙上下游都存在开口时效果最差。单宽渗流量和出逸坡降随弱透水层上游开口长度的增加而增大，但开口长度对渗流场影响不显著，其原因在于各防渗体系下上游弱透水层仅起到微弱的隔水作用。建议防渗墙和下游弱透水层形成半封闭式联合防渗体系，避免防渗墙上下游弱透水层均存在缺口的不利情况。基于监测值和模拟值得出的误差满足规范要求，表明采用的计算方法和得出的结论皆可靠。

Influence of thickness and continuity of aquitard in deep overburden on seepage field

Aquitard with uneven thickness and discontinuities commonly occurs in thick-overburden dam base in Northwest China. The seepage field in dam foundation is affected by the thickness, discontinuity form and opening size of the aquitard, which is needed to be studied in depth. In this paper, based on the seepage theory of unsaturated soil and seepage solution in Seep/w, we aim to obtain the influence of thickness and continuity of a aquitard in the middle position on the discharge per unit width and exit gradient, and compare with engineering practices. Results show that discharge per unit width and exit gradient decrease as the aquitard thickness increases. The influence of aquitard thickness on seepage field decreases in order of semi-closed cut-off wall, suspended cut-off wall and totally enclosed cut-off wall. The semi-closed joint anti-seepage system formed by aquitard and cut-off wall at the upstream is of the best control effect, followed by aquitard that opens at the downstream, case in which opens at both the upstream and downstream is the worst. The discharge per unit width and exit gradient increase with the opening length of aquitard. But at the upstream seepage system, since the weak layer only plays a weak role in water separation, therefore the opening length has little influence on seepage field. It is suggested that a semi closed joint anti-seepage system formed by cut-off wall and downstream aquitard is a doable measure, which can avoid the adverse condition that opens of aquitard both at the upstream and downstream. It is found that, compared with the monitoring result, the simulating error meets the codes. Therefore, the calculation method and conclusions of this paper are reliable.