近水平层状坝基岩体渗透结构及其工程意义

Permeability structure of the horizontally-stratified dam foundation rock mass and its engineering significance

查明坝基岩体的渗透结构对于大坝工程防渗方案的制定具有重要意义。以黄河古贤水利枢纽工程近水平分布的红层坝基岩体为研究对象,使用“连续、高分辨率”压水试验数据处理与统计方法,分析了岩体透水率与高程、岩性及顺层剪切带的关系,阐明了坝基岩体的渗透结构,提出了工程防渗建议。研究发现,坝基岩体渗透结构表现出结构性和随机性双重特征。结构性表现为岩体透水率随高程的降低而减小;随机性表现为岩体透水率会因岩性和剪切构造等随机变化。对于河床及滩地坝基岩体,风化卸荷带底高程在450 m附近,1 Lu关键透水率指标界线的底高程位于340 m附近。对于岸坡坝基岩体,3 Lu关键透水率指标界线的底高程位于560~580 m。在坝基勘察深度范围内,350~360 m高程段连续分布具有一定厚度的软岩类岩体,剪切构造不发育且岩体透水微弱,可视为相对隔水层,对坝基防渗帷幕优化设计具有指示意义。文章提出的统计、分析方法具有一定普适性,可为类似工程所借鉴。

Identifying the permeability structure of the dam foundation rock mass is important for the formulation of seepage control schemes.For the horizontally-stratified red-bed rock mass of the Yellow River Guxian Dam foundation,this paper adopted a"continuous,high-resolution"water pressure test data processing method to analyze the relationships between rock mass permeability and elevation,lithology and shear zones,clarifiy the permeability structure of the dam foundation rock mass,and propose seepage control advice.The results indicate that the Guxian Dam foundation rock mass is characterized by a structural and random permeability behavior.The structure shows that the permeability decreases with elevation.The randomness shows that the permeability randomly fluctuates due to lithology and shear zones.For the river-bed dam foundation rock mass,the bottom elevation of the weathering and unloading zone is 450 m or so,and the 1Lu bottom boundary is at the elevation of approximately 340 m.For the rock mass of the dam abutment,the 3Lu bottom boundary is located at the elevation of 560~580 m.The section of 350~360 m elevation has a certain thickness of soft rock,a poor development of shear structure,and a low permeability.It can be regarded as a confining layer and a potential target for the optimization of seepage control schemes.In view of the universal applicability,the method proposed in this paper can be used for reference in similar projects.