Analysis Of Leakage Characteristics And Seepage Mechanism Of Lingao Reservoir

Some reservoirs built in the 1950s have entered the ranks of "disease-risk reservoirs",and these reservoirs that operate with diseases are at risk of dam failure while contributing to the social economy.Once it occurs,it will bring great threats to the safety of the lives and properties of downstream residents,and will also cause serious damage to the environment in the area around the reservoir area.Taking The Lingao Reservoir as an example,this paper analyzes and discusses the seepage characteristics of the Lingao Reservoir and the seepage structure characteristics of the dam body by field investigation,indoor geotechnical test,field in situ test and nuclear magnetic resonance technology,and proposes the conceptual model of seepage flow of The Lingao Reservoir and analyzes its mechanism of action.The main conclusions reached are as follows:(1)According to the field investigation and drilling results combined with the analysis of regional geological data,there is no large fault isotonic channel in the reservoir area of Lingao Reservoir and the reservoir shore strata belong to the medium permeable and weak permeable bottom layer,and it is judged that there is no permanent leakage problem in the reservoir area of Lingao Reservoir.There are two types of dam shoulder leakage methods of Lingao Reservoir:①When the water level of the reservoir is raised,the reservoir water bypasses the interception wall and seeps out of the seepage channel formed by the formation with high permeability at the bottom or the ancient landslide and the fissure,forming leakage around the dam.② Due to the quality problem of the dam body itself,the dam dam soil develops in large pores under the action of seepage,and is connected with its lower pebble layer to form a seepage channel,resulting in leakage around the dam.Two conceptual models of seepage failure are proposed,namely the base erosion failure model and the dam body erosion failure model.(2)Through the analysis of NMR T2 spectroscopy of damming soil,it is found that under the same dry density condition,with the increase of time,all types of pores increase.The dry density of damming soil was in the range of 1.70 g/cm~3 to 1.75 g/cm~3,and with the increase of time,the small pores increased with time,and the changes of other types of pores were not obvious;the dry density of damming soil was in the range of 1.60 g/cm~3 to 1.65 g/cm~3,and the pores of each type increased to varying degrees;the dry density of damming soil was in the range of 1.50 g/cm~3 to 1.55 g/cm~3,and the small pores and medium pores did not change much,and the large pores increased significantly.(3)By comparing the pore distribution map and the sample particle distribution map,it is found that when the dry density of the sample is greater than or equal to 1.65g/cm~3,the pore diameter of the sample is more than 57.01%is less than the diameter of the soil particles,indicating that the soil particles are rarely eroded;when the dry density of the sample is 1.50g/cm~3,only 35.19%of the pore diameter of the sample is less than the diameter of the soil particles,indicating that the soil particles with small particle size are eroded and migrate from the large pores,resulting in the decline of the structural characteristics of the specimen,the increase in the number of pores and the increase in diameter.By comparing the NMR permeability at different times under different dry densities,it is found that the NMR permeability increases exponentially with the decrease of dry density.(4)Through the comprehensive analysis of the leakage characteristics of Lingao Reservoir and the characteristics of structural changes of damming soil under seepage,it is obtained that the compaction quality of the dam body is one of the key factors in the safety control of seepage.If the dam body is unevenly compacted,it will be in the weak part of the dam body,due to the role of permeability,fine particles will be transported in the pores formed by coarse particles,forming an seepage channel,and the small pores will gradually become large pores,and eventually the dam will produce pipe surge damage...