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This paper was aimed to study phreatic evaporation in Huaibei Plain during freezing-thawing period. The data was collected from long-term experiments at Wudaogou Hydrological Experimental Station from 1990 to 2018. In the experiments, a total of 38 lysimeters were installed. About half of them were planted with winter wheat. The others were bare lands. The soils in lysimeters were typical local soils: undisturbed lime concretion black soil and yellow moist soil. Soil temperature and air temperature were measured. The phreatic evaporation was determined and its relationship with soil depth was fitted with non-linear regression equations. According to the air temperature, the freezing-thawing period in the Huaibei Plain was from December to the next February. During the period, the soil was characterized with freezing at night and thawing during the day. The freezing layer was thin. In bare land, the phreatic evaporation increased firstly with depth and then decreased. The maximum phreatic evaporation occurred in the depth range of 0.1-0.3 m in the both soils. When the depth was smaller than the 0.1 m, phreatic evaporation increased with depth while it decreased with the depth when the depth was higher than 0.3 m. The characteristics of phreatic evaporation in soil profile during the freezing-thawing period was different from that in the period. The change of phreatic evaporation in the wheat land was similar with that in the bare land. However, the phreatic evaporation in the wheat land was smaller than that in the bare land when the depth was smaller than 0.4 m in lime concretion black soil and smaller than 1.0 m in the yellow moist soil. It was because the capillary was probably cut off due to covering on soil surface caused by roots or stalk residues or tillage before sowing, which affected the transport of water along the capillary and caused small phreatic evaporation. There was a peak in the phreatic evaporation curves. Therefore, 3 forms of distribution functions were selected to fit the change of phreatic evaporation with depth. Meanwhile, popular phreatic evaporation equations were compared. The Gaussian function could yield the best simulation for the phreatic evaporation in the bare land with the determination coefficient higher than 0.9 and the root mean square error smaller than 0.1. During the freezing-thawing period, the maximum phreatic evaporation from the lime concretion black soil occurred at 0.08 m below ground surface but at 0.29 m in yellow moist soil below ground surface. For wheat lands, the quasi-Gauss function was the best for constructing phreatic evaporation simulation formula with the determination coefficient higher than 0.9. The maximums of phreatic evaporation from the lime concretion black soil and the yellow moist occurred on the soil surface and 0.23 m below the soil surface, respectively. The soil depth corresponding to maximum phreatic evaporation was smaller in the wheat land than bare land. [ABSTRACT FROM AUTHOR]

The buoyancy of the underground structure is generally calculated on the basis of Archimedes law. However, the influence of surrounding backfilling soil was not taken into account in previous work. This article takes an underground granary that has been constructed as a research object. In this study, the 2:8 lime soil backfilling condition was considered in the indoor scale model tests. The diameters of the underground granary model cylinders were taken as 400 (Model cylinder A), 500 (Model cylinder B) and 600 mm (Model cylinder C), respectively. The whole scale model test consisted of two parts, the pure water test and the 2:8 lime soil backfilling tests. The results of the pure water test indicated that the actual buoyancy calculated based on Archimedes law and the theoretical buoyancy under the self-weight of the model cylinder (including the constrain reaction force of the upper part of the model cylinder, which is also converted into its own weight) were basically consistent. The errors between the actual buoyancy and the theoretical buoyancy for the three models cylinder were 0.03%, 1%, 3%, respectively. In the 2:8 lime-soil backfilling test, the water was injected slowly, the displacement was monitored by the displacement meter and the reaction force at the upper surface was measured by the pressure sensor. The numerical variation of displacement and constraint force during the whole process of the model cylinder floating was analyzed. The displacement mutation value lags behind the constraint force mutation value. When the pressure sensor reading changed significantly but the displacement meter reading did not, the actual water level served as the warning water level of the model cylinder. When the pressure sensor and the displacement meter reading changed significantly together, the actual water level was used as the actual floats water level of the model cylinder. Taking the warning water level and the actual floating water level as the theoretical basis for calculation, obtained the theoretical resistance to buoyancy under the self-weight of the model cylinder and the actual resistance to buoyancy. When reaching the warning water level, the actual resistance to buoyancy of model cylinder A, B, C were 1.93, 2.43, 1.66 times respectively as the theoretical resistance to buoyancy. When reaching the actual floating water level , the actual resistance to buoyancy of model cylinder A, B, C were 2.15, 3.36, 2.96 times respectively as the theoretical resistance to buoyancy. When backfilling 2:8 lime soil around an underground granary, calculating the buoyancy using Archimedes' law is safe. Considering the safety reserve comprehensively, the 2:8 lime-soil backfilling condition of underground granary, when reaching the warning water level, the actual resistance to buoyancy is 1.5 times of the theoretical resistance to buoyancy,and when reaching the actual floating water level, the actual resistance to buoyancy is 2 times of the theoretical resistance to buoyancy. The research results are able to provide a reference for the anti-buoyancy design of underground granaries and other underground structures in the future. [ABSTRACT FROM AUTHOR]