李家峡大坝6号坝段坝基扬压力异常成因综合分析

针对李家峡大坝6号坝段坝基扬压力产生异常的现象,建立了该坝及坝基的三维渗流有限元模型。详细介绍了模型中防渗帷幕及坝基、坝体排水孔模拟的方法,并且利用人工神经网络反演了岩体的渗透系数张量,对坝基进行了渗流有限元分析,分析不同防渗、排水以及基岩地质条件下的坝基渗流场,评估了各种因素对坝基渗流场的影响,结合坝基钻孔取芯、水质分析等试验成果,分析了扬压力异常的物理成因。研究结果表明,引起扬压力异常的原因是防渗帷幕局部存在缺陷,且帷幕前浅部岩层存在强透水带。建议对右岸6号坝段坝基进行灌浆处理,以阻断渗漏通道,提高防渗帷幕的阻水效果,并加强对渗水的抽排工作,以有效地降低扬压力。

Analysis of uplift pressure anomaly of Lijiaxia Dam foundation

With regard to the uplift anomaly phenomenon occurred in the right abutment of Lijiaxia Dam in China,a three-dimensional finite element model for seepage of the dam and its foundation was established.The methods of modeling the seepage prevention curtains were introduced.The drainage holes were modeled as so-called drainage sub-structures.Then an approach of back analysis for seepage parameters based on artificial neural network was proposed.The back analysis was conducted and the permeability tensors of the rock masses were obtained.The three-dimensional finite element analysis of seepage flow through the dam and its foundation was performed.Using the analytic results the influence of various factors such as seepage prevention measures,drainage and geologic conditions in the seepage field was evaluated,and then the cause of uplift anomaly was investigated combined with the results of the drilling and water quality tests in the foundation.It was shown that anomaly phenomenon was due to the grout curtain defects and leakage channel exiting in the shallow foundation.