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Historically, seepage failure has always been the primary cause of failures and accidents of earth dams after overtopping. However, research on the reliability of earth dams against seepage failure remains scarce. Meanwhile, the influence of the uncertainty of the soil–water characteristic curve (SWCC) on the reliability of dams against seepage failure is still unclear. In this study, the van Genuchten–Mualem model is used to describe SWCC, and its uncertainty is characterized by discretizing SWCC fitting parameters a and n into cross-correlation lognormal random fields. Based on the random finite element method, this paper systematically studies the influence of the heterogeneity, autocorrelation, and cross-correlation of hydraulic parameters Ks, a, and n on the reliability of a dam against seepage failure. Sensitivity analysis indicates that Ks and autocorrelation distance crucially affect the reliability of the dam against seepage failure. Additionally, this paper also emphasizes and proves that considering the correlation between the hydraulic conductivity field and the critical hydraulic gradient field has a significant impact on evaluating the reliability of earth dams against seepage failure. However, this subtle but important potential characteristic has not been paid attention to in previous studies. [ABSTRACT FROM AUTHOR]

The disasters caused by groundwater during underground cavern excavation, are inevitable and difficult to predict. In this study, transient seepage analysis was performed during the excavation of Qingyuan power station's underground caverns and drainage hole arrays. The drainage hole arrays around the caverns were simulated using a new method, and the groundwater surface during transient seepage analysis was confirmed with the hydraulic conductivity adjustment method, by using ABAQUS user subroutines USDFLD and GETVRM. By simplifying the drainage hole into face geometry, the proposed drainage hole simulation method could reach the accuracy of the widely used substructure method with half nodes of the computational boundary, and reflect the influence of drainage hole diameter on seepage analysis results. Moreover, a sensibility analysis of the diameter and space of drainage hole arrays could be conducted using one simulation model with the proposed finite element mesh type. Transient seepage analysis showed the evolutions of the groundwater level, flow rate and maximum hydraulic gradient of drainage holes and underground caverns, during the construction of Qingyuan power station. Such results could provide a reference for the creation of design and construction schemes. The previous excavation of the drainage hole arrays could control the seepage field, and reduce the flow rate and maximum hydraulic gradient of the underground caverns. This study may provide valuable reference to the design and construction of similar projects. [ABSTRACT FROM AUTHOR]

Finite element method (FEM) is usually used in dam and large underground cavern engineering to evaluate complex anti-seepage and drainage systems. In general, the substructure method is used to simulate the drainage hole array, but it becomes cumbersome when the number of drainage holes is large and the model is more complicated. In this study, the drainage holes were simplified and simulated as a line. The calculation results of the proposed method were then compared with those of the substructure simulation method and the well flow formula. This method has approximate accuracy, and it is easier to model with fewer nodes and elements compared with the substructure method. Based on the data of Heihe Reservoir, a three-dimensional equivalent continuum seepage FEM, reflecting the topography and geology of the dam area, was established, along with engineering layout and anti-seepage drainage system. The seepage field of nine different anti-seepage and drainage facilities were studied. The effects of drainage hole spacing and impervious curtain on seepage field were investigated. When the drainage holes were working normally and the drainage hole spacing was 2 m, the phreatic line in the dam body was the lowest and the drainage effect was the best. The analysis results showed that the failure of drainage holes on the left and right banks significantly influenced the seepage discharge of dam body and impervious curtain. According to the distribution of seepage field, a reasonable spacing of drainage holes is selected, and reasonable suggestions are put forward for anti-seepage and drainage in different parts. [ABSTRACT FROM AUTHOR]

There are many practical problems in the rapid development of the concrete face rockfill dam, which mainly focus on a large number of cracks and extrusion breakages in the face slab caused by temperature-induced stress, shrinkage stress, deformation of dam and other reasons, which eventually lead to leakage, threatening the safety of the dam. To solve this problem, the three-dimensional finite element analysis method is combined with the block equivalent continuum method to calculate the three-dimensional seepage field of the dam area, in order to study the seepage characteristics of numerous and unevenly distributed cracks in the concrete face rockfill dam; then, the corresponding head distribution and seepage characteristics, including the phreatic line, the hydraulic gradient and the seepage discharge, were obtained. The findings of this paper validate the accuracy and reliability of the block equivalent continuum method. It not only meets the requirements of simulation accuracy, but also can obtain the characteristics of the local seepage field near the crack. At the same time, it greatly simplifies the finite element model and significantly improves the efficiency of seepage calculation. This method provides a reference for the seepage analysis of similar projects. [ABSTRACT FROM AUTHOR]

Concrete face rockfill dams are widely used in hydropower engineering because of their many advantages. As important structures, if the performance of the concrete face slab and the impervious curtain is weakened, leakages and even serious dam failures can occur. Based on an equivalent quasi-continuum medium model, three-dimensional finite-element numerical simulations of the seepage behaviour of Miaojiaba dam, China, are performed. The seepage field and seepage characteristics, including the phreatic line, maximum hydraulic gradient and seepage discharge, are analysed quantitatively and systematically under various abnormal conditions. The results show that cracks in different areas of the face slab and different degrees of degradation in the impervious curtain influence the seepage field in different ways, with cracks in the lower face slab being the most serious. Ensuring that the face slab and impervious curtain are working as intended is very important for the integrity of the dam. Therefore, the design and construction quality of impervious structures should be strictly controlled. Under abnormal conditions, seepage control should be realised to ensure the safety and stability of concrete face rockfill dams. [ABSTRACT FROM AUTHOR]

The coupling effect of seepage and temperature fields in fractured rock mass is a hot topic in the area of water conservancy, nuclear waste disposal and geothermal resources development. A coupling mathematical model of the seepage, flow temperature and rock mass temperature fields in the fracture network of rock mass is established based on the seepage and temperature interaction. A calculation program is developed and applied to calculate the seepage and temperature fields of the dam foundation of a water conservancy project. The interaction mechanism of the seepage, flow temperature and rock mass temperature fields is analyzed in this paper. Results show that the seepage field largely influences the temperature field, which can provide several suggestions for the deep underground disposal of nuclear waste, geothermal resources development and fractured rock mass in dam foundations. Considering the coupling effect of the seepage, flow temperature and rock mass temperature fields by the fracture network method is necessary. [ABSTRACT FROM AUTHOR]

The Qingyuan Pumped Storage Power Station is located in Liaoning, China and has large-scale water conveyance and underground powerhouse systems. In order to analyze the evolution of the flow rate, external water pressure, and hydraulic gradient of water conveyance and powerhouse systems or around them, a 3D equivalent continuum seepage finite element simulation model was established based on existing theories and a new drainage hole arrays simulation method was proposed in this study. The proposed method had approximate accuracy and was easy to model with fewer nodes and elements in comparison with the substructure method for complex hole arrays of diameter 5 cm. On the basis of four different conditions, the results show that the dehiscence of concrete lining lead to the peak values of the water conveyance flow rate, the water inflow of the powerhouse, and the water discharge of drainage hole arrays. The lapse of drainage hole arrays at a 50% rate resulted in the peak values of the external water pressure around the terminal of the diversion system and the hydraulic gradient around the upstream of drainage hole arrays. Besides, the hydraulic gradient around the downstream drainage hole arrays reached the peak value when the lower reservoir water level rose. [ABSTRACT FROM AUTHOR]

Landfilled municipal solid waste has evident heterogeneity, and clogging of the drainage layer can easily happen during operation of the landfill. These two factors significantly influence the distribution of leachate in a landfill. Herein, the distribution of waste permeability in the spatial and temporal domains was analyzed. Then, changes to the drainage-layer permeability in the temporal domain were fitted to these data. A simple model of multilayer waste slope was established combining the finite element software and a user subroutine. Herewith, changes of permeability in the waste and drainage layers were simulated, such that the heterogeneity of waste and the process of clogging of the drainage layer could be simulated. Then, the leachate distributions and transport conditions of nine schemes for landfill were analyzed. The results indicated that the distribution curve of waste-saturated permeability follows a logarithmic relation in the vertical direction, and the distribution curve of fresh-waste-saturated permeability follows a polynomial relation in time. After each landfill is worked for a few years, the drainage layer always encounters clogging problems of some kind and its permeability decreases by one to five orders of magnitude. Through numerical models, the simulation results of the permeability distribution in the spatial and temporal domains were found satisfactory. When the permeability distributions were layered in the buried depth, pore pressures and leachate levels are smaller than the logarithmic distributions. During the process of degradation, the pore pressures and leachate levels are increased slightly under the consideration of the polynomial distribution of waste permeability in time. With clogging of the permeability of the drainage layer, the pore pressures and leachate levels of landfill were found to be increasing gradually. To obtain results closer to that of actual situations, corresponding models should be established and analyzed based on a range of permeability, waste degradation rate, and degree of clogging. [ABSTRACT FROM AUTHOR]

The continuous migration and loss of small particles in fractured rock mass with water flow is the main cause of water inrush in fault zones. In this study, a fluid–solid coupling model for fault zone was established to study the complex coupling between the groundwater seepage and migration of broken rock mass, and reveal the mechanism of erosion-induced water inrush. The rock skeleton and broken rock mass in the fault zone were modelled by large skeleton particles and small filling particles, respectively, in 3D particle flow software while the fluid flow through the fault was modelled by the built-in computational fluid dynamics module. The numerical results show that: (1) with the increase of water pressure, the loss of filling particles increases continuously, and the whole seepage process can be divided into three stages: slow seepage, abrupt seepage and steady seepage, (2) the mass loss, porosity and permeability first increase slowly, then increase rapidly, and finally tend to be stable, (3) higher fine particle content are more likely to cause structural instability due to mass loss, thus increases the risk of water inrush and mud outburst. [ABSTRACT FROM AUTHOR]

Interfacial seepage on soil-structure interface is common in water-related engineering, such as dam, culvert, water tunnel, foundation pit, etc. As a weak part in the project, seepage failure on soil-structure interface has caused many project accidents. However, there are few studies on the seepage mechanism analysis of soil-structure interface. In this paper, a series of numerical tests of interfacial seepage are carried out using CFD-DEM coupling method. The seepage mechanism and characteristics of different soil layers in the seepage device are analyzed and a formula for calculating the critical hydraulic gradient of the interface is discussed. The main conclusions are as follows: (1) The seepage flow on soil-structure interface will go through three stages: stability stage, transition stage and particle erosion stage; (2) The porosity and flow velocity of soil on the interface are greater than those in the far-field soil at the beginning of seepage flow; (3) The particle erosion on the soil-structure interface occurs earlier and the erosion degree is more serious than that of the far-field soil; (4) The critical hydraulic gradient of the interface rises nonlinearly with the increase of the degree of soil compaction; (5) The formula for calculating the critical hydraulic gradient of the interface could predict the numerical test results well. [ABSTRACT FROM AUTHOR]

Seepage problems exist in water conservancy projects, groundwater research, and geological research, and hydraulic conductivity is an important factor that affects the seepage field. This study investigates the heterogeneity of hydraulic conductivity. Kriging methods are used to simulate the spatial distribution of hydraulic conductivity, and the application of resistivity and grain size is used to obtain hydraulic conductivity. The results agree with the experimental pumping test results, which prove that the distribution of hydraulic conductivity can be obtained economically and efficiently and in a complex and wide area. [ABSTRACT FROM AUTHOR]

To study the seepage characteristics of tailing sand, an indoor sand column test was performed with three kinds of tailing sand obtained from Henan and Shaanxi provinces, China. River sand, quartz sand, and glass beads were also employed for comparison. Using the nuclear magnetic resonance, the researchers studied pore size distribution and permeability under different hydraulic gradients. The chemical composition and particle morphology were analyzed by energy-dispersive spectrometry and X-ray diffraction. The results were as follows. (1) The three kinds of tailings sand are small in diameter, mainly in the range from 0.15 to 0.5 mm. Their diameter distribution is more concentrated than river sand. The surface of tailing sand is rough. As for chemical composition, tailing sand contains many kinds of metal elements. (2) With hydraulic gradient increasing, the micropores in the tailings samples become fewer, the larger pores grow in number, and the peak of the pore size distribution changes to the left; blocking is more obvious. (3) The small pores gradually decrease during the test. Under the influence of groundwater pressure, the smaller gravel could migrate and block tiny pores. The structure of particle arrangement becomes denser. Therefore, it would prevent the seepage liquid from passing through the medium. The permeability coefficient K decreases. [ABSTRACT FROM AUTHOR]

Xu, Z.; Wang, X., and Chai, J., 2020. Piping particle movement using a seepage test based on NMR technology. In: Hu, C. and Cai, M. (eds.), Geo-informatics and Oceanography. Journal of Coastal Research, Special Issue No. 105, pp. 12–17. Coconut Creek (Florida), ISSN 0749-0208. As a kind of seepage failure mode occurred in hydraulic earth structures (dikes, levies, or dams), piping could cause dam-break in earth-rock dams. Additionally, although many investigators have applied many experiments to study the mechanism of piping, the initiation and development mechanism of piping is still poorly understood. In this study, a vertical piping test was conducted on stained noncohesive soil by an experimental device to measure a serial of parameters (the critical hydraulic gradient, porosity, upper particle size of lost particles, and accumulated sediment) in the development of piping phases. The particle migration pattern and change of porosity were then observed by the nuclear magnetic resonance (NMR) technology. The results show that the phases of piping are controlled by the content of movable particles and the particle size distribution curve. Three migration types of particles can be distinguished by NMR results and stained noncohesive soil during the piping phase. On basis of the empirical formula between hydraulic gradient and flow rate, if it shows a liner that means the soil is still well graded during the piping; if it divides into two separate lines that means the soil is unstable in the range covered by the second line. Additionally, the critical hydraulic gradient is located around the lines' connection points. [ABSTRACT FROM AUTHOR]

The purpose of establishing a tailings dam is to safely store tailings to protect the natural environment from damage. Accidents at tailings dams are frequent, however, with serious consequences of not only threats to life and property but also the pollution of the environment. Many tailings dam accidents are caused by seepage failure. In this paper, the object of the case study is the Lixi tailings dam. Three- and two-dimensional finite element models are established. The seepage field of the project under different working conditions is simulated and the position of the phreatic line is obtained. The safety factors under different working conditions are obtained by combining the seepage field with the stable surface. Finally, the influence of different dry and upstream slope ratio on seepage and stability of tailings dam is obtained. The results show that the longer the length of the dry beach, the lower the phreatic line and the greater the safety factor. The higher the upstream slope ratio, the lower the phreatic line and the greater the safety factor. [ABSTRACT FROM AUTHOR]