Reconstruction project of groundwater balance experiment site of Zhengzhou：selection of test media and construction of test soil columns

The rebuilding of Zhengzhou Groundwater Balance Test Site is one of the rebuilding projects of the Groundwater Balance Test Site in the National Groundwater Monitoring Project sponsored by Geological Environment Monitoring Institute of China. The construction of the testing column in the reconstruction of the balance experiment site is a core issue mainly including two aspects: the selection of the testing medium and the filling of the testing cylinder. According to the geological and geomorphic characteristics of Henan Province, Henan Province is divided into five geomorphic units:the alluvial plain north of the Yellow River, the alluvial plain south of the Yellow River, the alluvial plain of the Huaihe River, the Nanyang Basin, and the loess hills of western Henan. Combining with field investigation, the relationship between lithology of five geomorphic units and superimposition of different strata is generalized, and the representative of lithology and structure is demonstrated through typical section exploration, so as to determine the sampling sites of various lithologies in five zones and lay a geological foundation for the construction of test soil pillars. The total length of the test cylinder is 90 meters, and the soil samples are loaded into the test cylinder according to the design requirements. For this reason, a small column simulation settlement test is formulated, and the settlement coefficient of filling soil sample according to the design requirements is obtained, which serves as the basis for calculating the thickness of testing soil sample filling test cylinder.After the loading of the test soil column is completed, the settlement observation is carried out to confirm that the settlement tends to be stable and does not affect the installation of the sensor for the test soil column, and the construction of the test column is completed.