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- ItemHeat transfer by seepage in sand: Influence of saturated hydraulic conductivity and porosity(University of Ljubljana, 2021-06-06) Ghafoori, Yaser; Maček, Matej; Vidmar, Andrej; Říha, Jaromír; Kryžanowski, AndrejHeat transfer within the soil is a complex process in the presence of seepage flow. In such conditions, the soil’s thermal behavior is influenced by the thermal and hydraulic properties of the medium as well as the initial conditions and boundary conditions to which the medium is subjected. This paper presents the experimental and numerical studies of heat transfer within the sand subjected to the seepage flow. It focuses on the influence of saturated hydraulic conductivity and the porosity of medium on the heat transfer process. The temperature distribution within the sand was monitored by the optical fiber Distributed Temperature Sensor (DTS). The experiment was performed on three types of silica-dominated sands with different saturated hydraulic conductivities and different Soil Water Characteristic Curve (SWCC). In addition to the experimental study, a coupled hydrothermal numerical model was designed in FEFLOW software and validated by comparing its results with the experimental measurements. To determine the influence of porosity and saturated hydraulic conductivity on heat transfer, we analyzed the numerical models for different values of porosity and saturated hydraulic conductivity. The numerical and experimental studies showed that the thermal velocity is higher in sand with higher saturated hydraulic conductivity and temperature declination occurs more quickly due to the heat convection process. Saturated sand with larger porosity has an overall higher heat capacity, wherefore the temperature declination started later in the measuring points but dropped down lower close to the temperature of the upstream water.
- ItemUnsteady Flow and River Bed Stratification Mutual Impact on Scour at the Abutments(University of Split, 2020-04-08) Gjunsburgs, Boriss; Pařílková, JanaThe floods of different probability, sequence, frequency, duration, and the riverbed with different grain sizes, numbers, sequences, and thickness of the layers are one of the reasons for the bridge`s abutments failure because of scour. Although the problem is very topical, the mutual impact of multiple floods and stratified riverbed conditions on scour at the bridge abutments has not been studied. The method for computing scour development in time at bridge abutments was elaborated and confirmed by tests results. The method enables the computer to perform modelling of the mutual impact of unsteady flow and bed layering of scour processes. Computer modelling was made to expand scenarios for tests data in flume for unsteady flow for two steps of hydrograph with different dischargers and for the bed layers with varying grain sizes, numbers, sequence, and thickness. This approach makes it possible to estimate in advance mutual impact, with different scenarios, floods and geological data on the depth of scour at vertical wall abutment, at the design stage or during the maintenance period of the bridge crossing.
- ItemComparison of Hydraulic Conductivity Values Obtained from Empirical Formulae and Laboratory Experiments(Mendel University in Brno, 2020-08-30) Hala, Mario; Petrula, Lubomír; Alhasan, ZakarayaHydraulic conductivity determination plays an essential role in the investigation of groundwater flow regime which can then influence many field problems such as pumping capabilities in the area, transport of contaminant or heat and soil internal erosion. Numerous equations based on dimensional analysis or experimental measurements have been published since the end of the 19th century for the determination of hydraulic conductivity. However, not all of these formulae are applicable for every material and all of them bring some uncertainty in the value of hydraulic conductivity. This paper contains a description of experimental research carried out concerning the determination of hydraulic conductivity for four types of sand with different grain size distribution curves and variable porosity. Obtained values of hydraulic conductivity ranged from 1×10-4 to 4×10-3 according to the sample porosity. The series of experiments consisted of 160 separate tests conducted in order to obtain relevant statistical sets. In this paper, the experimental data are discussed and compared with hydraulic conductivities obtained from 6 empirical formulae recommended in a previous study. The comparison showed that some empirical formulae provide a good agreement with the experimental data (the most precise were formulae published by Terzaghi and by Sauerbrey). However, some formulae showed high deviation from measured data (formula published by Zamarin).
- ItemModelling hazards impacting the flow regime in the Hranice Karst due to the proposed Skalicka Dam(EGU - European Geosciences Union, 2024-10-30) Špano, Miroslav; Říha, JaromírThis study examines the hydrogeological hazard associated with the construction of the proposed Skalička Dam in the vicinity of the Hranice Karst. Prompted by the catastrophic regional floods in 1997 and 2010, the design of the dam aims to mitigate floods along the Bečva River downstream of the reservoir. However, concerns have been raised regarding the potential disturbance of the natural groundwater regime in the Hranice Karst and the source of mineral waters for the Teplice spa. This is due in particular to the dam's location in an area with limestone outcrops potentially susceptible to surface-water infiltration. Previous studies have also highlighted the strong correlation between the water level in the Bečva River and the water level in karst formations such as the Hranice Abyss, Zbrašov Aragonite Caves, and other caves in the locality. To address these concerns, a nonlinear reservoir-pipe groundwater flow model was employed to simulate the behaviour of the Hranice Karst aquifer and specifically the effects of the dam reservoir's impoundment. The study concluded that the lateral variant of the dam would have a practically negligible impact on the karst water system, with the rise in water level being only a few centimetres. The through-flow variant was found to have a more significant potential impact on water levels and the outflow of mineral water to the spa, with a piezometric rise of about 1m and an increase in the karst water discharge to the Bečva River of more than 50%. Based on these results, recommendations for further investigations concerning the design of the dam and its eventual construction have been formulated to reduce geological uncertainties and to minimize the potential impact of the hydraulic scheme on the hydrogeology of the karstic system.
- ItemShape of the nappe during free overfall from a rectangular channel with zero bed slope(Institute of Hydrology of the Slovak Academy of Sciences, Institute of Hydrodynamics of the Academy of Sciences of the Czech Republic, 2013-09-02) Zachoval, Zbyněk; Böhm, Petr; Pařílková, Jana; Šafář, Robert; Šulc, JanThe paper deals with selected procedures used to calculate the shape of compact nappe during free overfall from a smooth horizontal channel with rectangular cross section. Calculated and measured water surface and velocity conditions in the end section, the level of water surface upstream in front of the end section and the shape of the compact part of an overfall nappe are described for a particular compared case.